Transcript

“God and Cosmology: The Existence of God in Light of Contemporary Cosmology”

William Lane Craig vs. Sean Carroll

New Orleans Baptist Theological Seminary, New Orleans, LA, –

NOTE: Despite repeated requests Dr. Carroll has not yet furnished his PowerPoint slides or proofread his portion of the debate.

Dr. Stewart, Moderator

We are glad to see all of you here this evening, and all of those who are watching online as well. . . . Let me introduce our speakers, as if you don’t know who they are already!

William Lane Craig is a Research Professor of Philosophy at Talbot School of Theology in La Mirada, California, and a Professor of Philosophy at Houston Baptist University. He earned a doctorate in philosophy at the University of Birmingham, England, before taking a doctorate in theology from the University of Munich, Germany, where he was, for two years, a Fellow of the Alexander von Humboldt Foundation. Prior to his appointment at Talbot he spent seven years at the Higher Institute of Philosophy of the Katholike Universiteit Leuven, Belgium. His research interests include the interface of philosophy of religion and philosophy of space and time. He has authored or edited over 30 books including The Kalam Cosmological Argument; Theism, Atheism, and Big Bang Cosmology; and Time and the Metaphysics of Relativity. He has published over 150 articles in peer reviewed professional journals, such as The Journal of Philosophy, British Journal for the Philosophy of Science, International Studies in the Philosophy of Science, Philosophia Naturalis, and Astrophysics and Space Science. He has appeared as a guest on television shows such as 20/20, CNN Newsroom, Fox News, and Closer to the Truth.

Sean Carroll is a physicist and Senior Research Associate in the Department of Physics at the California Institute of Technology. He received his PhD in astronomy and astrophysics from Harvard University. His research focus is on theoretical physics and cosmology, especially the origin and constituents of the universe. He has contributed to models of interactions between dark matter, dark energy, and ordinary matter, alternative theories of gravity, and the arrow of time. Carroll is the author of From Eternity to Here: The Quest for the Ultimate Theory of Time, Spacetime and Geometry: An Introduction to General Relativity, and The Particle at the End of the Universe. He has been awarded fellowships by the Sloan Foundation, Packard Foundation, and the American Physical Society, and won the 2013 Royal Society Winton Prize for Science Books. He has appeared on TV shows such as the Colbert Report, Through the Wormhole with Morgan Freeman, and Closer to Truth.

Welcome our guests as they come to speak to us!

William Lane Craig – Opening Speech

Good evening! It is an honor to be taking part in a forum featuring such distinguished scientists and philosophers. Thank you very much!

Introductory Remarks

In his recent book, Where the Conflict Really Lies, Alvin Plantinga distinguished three ways in which scientific theories and theism might be related: apparent conflict, genuine conflict, and concord.[1] I take it as obvious that there does not exist even apparent conflict between contemporary cosmogonic theories and theism. Contemporary cosmology would therefore seem to be an area of obvious concord between science and theism.

But tonight I want to defend an even stronger claim, namely, that the evidence of contemporary cosmology actually renders God’s existence considerably more probable than it would have been without it:

Pr (Theism | Contemporary Cosmology & Background Information)
>> Pr (Theism | Background Information)

This is not to make some sort of naïve claim that contemporary cosmology proves the existence of God. There is no God-of-the-gaps reasoning here. Rather I’m saying that contemporary cosmology provides significant evidence in support of premises in philosophical arguments for conclusions having theological significance.

For example, the key premise in the ancient kalam cosmological argument that

2. The universe began to exist.

is a religiously neutral statement which can be found in virtually any contemporary textbook on astronomy and astrophysics. It is obviously susceptible to scientific confirmation or disconfirmation on the basis of the evidence.[2]

So, to repeat, one is not employing the evidence of contemporary cosmology to prove the proposition that God exists but to support theologically neutral premises in philosophical arguments for conclusions that have theistic significance.

In tonight's discussion I’ll focus on two such arguments: the kalam cosmological argument from the origin of the universe and the teleological argument from the fine-tuning of the universe.

The Kalam Cosmological Argument

Consider first the kalam cosmological argument:

1. If the universe began to exist, then there is a transcendent cause which brought the universe into existence.

2. The universe began to exist.

3. Therefore, there is a transcendent cause which brought the universe into existence.

By “the universe,” I mean that reality which is studied by contemporary cosmology, that is to say, all of contiguous physical reality, which currently takes the form of space-time and its contents.

I take it that (1) is obviously true.[3] Rather the truly controversial premiss is (2). Traditional supporters presented philosophical arguments in support of (2),[4] which, for me, constitute its primary warrant. But they’re not the subject of tonight’s debate. Rather what’s emerged during the 20th century is remarkable empirical confirmation of the second premiss from the evidence of astrophysical cosmogony. Two independent but closely interrelated lines of physical evidence support premiss (2): evidence from the expansion of the universe and evidence from the second law of thermodynamics.

In saying that the cosmogonic evidence confirms (2), I am not saying that we are certain that (2) is true. Too many people mistakenly equate knowledge with certainty. When they say that we do not know that the universe began to exist, what they really mean is that we are not certain that the universe began to exist. But, of course, certainty is not the relevant standard here. The question is whether (2) is more plausible in light of the evidence than its contradictory. As Professor Carroll reminds us,

Science isn't in the business of proving things. Rather, science judges the merits of competing models in terms of their simplicity, clarity, comprehensiveness, and fit to the data. Unsuccessful theories are never disproven, as we can always concoct elaborate schemes to save the phenomena; they just fade away as better theories gain acceptance.[5]

Science cannot force you to accept the beginning of the universe; you can always concoct elaborate schemes to explain away the evidence. But those schemes will not fare well in displaying the aforementioned scientific virtues.

Even many who have expressed scepticism about premiss (2) admit that it is more plausibly true than not. For example, in my recent dialogue with Lawrence Krauss, he volunteered, “I’d bet our universe had a beginning, but I am not certain of it. . . . based on the physics that I know, I’d say it is a more likely possibility.”[6] This is to admit precisely what cosmologists like Alexander Vilenkin have contended all along: that the evidence makes it more likely than not that the universe began to exist.[7]

Evidence from the Expansion of the Universe

Consider, first, the evidence from the expansion of the universe. The standard (Friedman-LeMaître Robertson-Walker) big bang cosmogonic model implies that the universe is not infinite in the past but had an absolute beginning a finite time ago. Although advances in astrophysical cosmology have forced various revisions in the standard model, nothing has called into question its fundamental prediction of the finitude of the past and the beginning of the universe. Indeed, as James Sinclair has shown, the history of 20th century cosmogony has seen a parade of failed theories trying to avert the absolute beginning predicted by the standard model.[8] Meanwhile, a series of remarkable singularity theorems has increasingly tightened the loop around empirically tenable cosmogonic models by showing that under more and more generalized conditions, a beginning is inevitable. In 2003 Arvind Borde, Alan Guth, and Alexander Vilenkin were able to show that any universe which is, on average, in a state of cosmic expansion throughout its history cannot be infinite in the past but must have a beginning.[9] In 2012 Vilenkin showed that cosmogonic models which do not fall under this condition, including Professor Carroll’s own model, fail on other grounds to avert the beginning of the universe. Vilenkin concluded, “None of these scenarios can actually be past-eternal.”[10] “All the evidence we have says that the universe had a beginning.”[11]

The Borde-Guth-Vilenkin theorem proves that classical space-time, under a single, very general condition, cannot be extended to past infinity but must reach a boundary at some time in the finite past. Now either there was something on the other side of that boundary or not. If not, then that boundary is the beginning of the universe. If there was something on the other side, then it will be a non-classical region described by the yet to be discovered theory of quantum gravity. In that case, Vilenkin says, it will be the beginning of the universe.[12]

Think about it. If there is such a non-classical region, then it is not past eternal in the classical sense. But neither can it exist literally timelessly, akin to the way in which philosophers consider abstract objects to be timeless or theologians take God to be timeless. For this region is in a state of constant flux, which, given the Indiscernibility of Identicals, is sufficient for time.[13] So even if time as defined in classical physics does not exist at such an era, some sort of time would.[14]

But if the quantum gravity era is temporal, it cannot be extended infinitely in time, for such a quantum state is not stable and so would either produce the universe from eternity past or not at all. As Anthony Aguirre and John Kehayias argue,

It is very difficult to devise a system – especially a quantum one – that does nothing ‘forever,’ then evolves. A truly stationary or periodic quantum state, which would last forever, would never evolve, whereas one with any instability will not endure for an indefinite time.[15]

Hence, the quantum gravity era would itself have to have had a beginning in order to explain why it transitioned just some 13 billion years ago into classical time and space. Hence, whether at the boundary or at the quantum gravity regime, the universe probably began to exist.

Evidence from Thermodynamics

Consider now the evidence from thermodynamics. According to the second law of thermodynamics entropy in a closed system almost never decreases. Given the naturalistic assumption that the universe is a closed system, the second law implies that, given enough time, the universe will come to a state of thermodynamic heat death, whether cold or hot. Given that the universe will expand forever, it may never reach a state of equilibrium, but it will grow increasingly cold, dark, dilute, and dead. But then the obvious question arises: why, if the universe has existed forever, is it not now in a cold, dark, dilute, and lifeless state? P. C. W. Davies gives the obvious answer: “The universe can’t have existed forever. We know there must have been an absolute beginning a finite time ago.”[16] The universe’s energy, says Davies, was simply “put in” at the creation as an initial condition.[17]

By contrast Professor Carroll’s solution to the problem confronts serious obstacles. He imagines that the overall condition of the universe is a state of thermal equilibrium (a sort of de Sitter space), but that random fluctuations spawn baby universes, which pinch off to become wholly independent space-times. We find ourselves in one such baby universe in a state of disequilibrium.

Let me raise two concerns about this model. First, not only are the production mechanisms of such baby universes admittedly conjectural, but such a scenario violates the so-called unitarity of quantum theory by allowing irretrievable information loss from the mother universe to the babies. Stephen Hawking, apologizing to science-fiction fans everywhere, came to admit, “There is no baby universe branching off, as I once thought. The information remains firmly in our universe.”[18]

Second, Professor Carroll’s solution provides no convincing answer to the Boltzmann Brain problem. Since the mother universe is a de Sitter space in which thermal fluctuations occur and since baby universes grow into de Sitter spaces themselves, there’s no explanation in the model why there exists a genuine low entropy universe around us rather than the mere appearance of such a world, an illusion of isolated brains which have fluctuated into existence out of the quantum vacuum. These and other problems make Professor Carroll’s model less plausible than the standard solution that the universe began to exist with an initial low entropy condition.

Skeptics might hope that quantum cosmology might serve to avert the implications of the second law of thermodynamics. But now a new singularity theorem formulated by Aron Wall seems to close the door on that possibility. Wall shows that, given the validity of the generalized second law of thermodynamics in quantum cosmology, the universe must have begun to exist, unless, as in Professor Carroll’s model, one postulates a reversal of the arrow of time at some point in the past, which, he rightly observes, involves a thermodynamic beginning in time which “would seem to raise the same sorts of philosophical questions that any other sort of beginning in time would.”[19] Wall reports that his results require only certain basic concepts, so that “it is reasonable to believe that the results will hold in a complete theory of quantum gravity.”[20]

Summary

Thus, we have good evidence both from the expansion of the universe and from the second law of thermodynamics that the universe is not past eternal but had a temporal beginning. So the second premise of the kalam cosmological argument receives significant confirmation from the evidence of contemporary cosmology. We have, then, a good argument for a transcendent cause of the universe.

The Teleological Argument

Turn now to the teleological argument from the fine-tuning of the universe. Scientists have been stunned by the discovery that the existence of intelligent, interactive life depends upon a complex and delicate balance of fundamental constants and quantities, like the gravitational constant and the amount of entropy in the early universe, which are fine-tuned to a degree that is literally incomprehensible.

Now there are three possibilities debated in the literature for explaining the presence of this remarkable fine-tuning: physical necessity, chance, or design. The question then is: Which of these three alternatives is the most plausible? On the basis of the evidence we may argue:

1. The fine-tuning of the universe is due to either physical necessity, chance, or design.

2. It is not due to physical necessity or chance.

3. Therefore, it is due to design.

Physical Necessity?

Consider the first alternative, physical necessity.

This alternative seems extraordinarily implausible because the constants and quantities are independent of the laws of nature. The laws of nature are consistent with a wide range of values for these constants and quantities. For example, the most promising candidate for a Theory of Everything (T.O.E.) to date, super-string theory or M-Theory, allows a “cosmic landscape” of around 10500 different universes governed by the present laws of nature, so that it does nothing to render the observed values of the constants and quantities physically necessary.

Chance?

So what about the second alternative, that the fine-tuning is due to chance? The problem with this alternative is that the odds against the universe’s being life-permitting are so incomprehensibly great that they cannot be reasonably faced. In order to rescue the alternative of chance, its proponents have therefore been forced to adopt the hypothesis that there exists a sort of World Ensemble or multiverse of randomly ordered universes of which our universe is but a part. Now comes the key move: since observers can exist only in finely tuned worlds, of course we observe our universe to be fine-tuned!

So this explanation of fine-tuning relies on (i) the existence of a specific type of World Ensemble and (ii) an observer self-selection effect. Now this explanation, wholly apart from objections to (i), faces a very formidable objection to (ii), namely, the Boltzmann Brain problem. In order to be observable the entire universe need not be fine-tuned for our existence. Indeed, it is vastly more probable that a random fluctuation of mass-energy would yield a universe dominated by Boltzmann Brain observers than one dominated by ordinary observers like ourselves. In other words, the observer self-selection effect is explanatorily vacuous. As Robin Collins has noted, what needs to be explained is not just intelligent life, but embodied, interactive, intelligent agents like ourselves.[21] Appeal to an observer self-selection effect accomplishes nothing because there’s no reason whatever to think that most observable worlds or the most probable observable worlds are worlds in which that kind of observer exists. Indeed, the opposite appears to be true: most observable worlds will be Boltzmann Brain worlds.

Since we presumably are not Boltzmann Brains, that fact strongly disconfirms a naturalistic World Ensemble or multiverse hypothesis.

Design?

It seems, then, that the fine-tuning is not plausibly due to physical necessity or chance. Therefore, we ought to prefer the hypothesis of design unless the design hypothesis can be shown to be just as implausible as its rivals. I’ll leave it up to Professor Carroll present any such objections.

Summary and Conclusion

In summary, it seems to me that the evidence of contemporary cosmology provides significant support for key premises in two philosophical arguments for conclusions having theological significance.

Thus, the existence of a Creator and Designer of the universe seems to be significantly more probable in light of contemporary cosmology than it would have been without it.[22]


[1] Alvin Plantinga, Where the Conflict Really Lies: Science, Religion, and Naturalism. (Oxford University Press, 2011). Plantinga further distinguishes between superficial conflict and deep conflict.

[2] Similarly the key premise in the teleological argument based on the fine-tuning of the universe that
2. The fine-tuning is not due to physical necessity or chance.
is logically equivalent to a conjunction, both of those conjuncts have been argued by scientists on theologically neutral grounds. As stated, (2) is a disjunction, but its logical form is equivalent to (¬p & ¬q).

[3] (1) does not presuppose a particular analysis of the causal relation. It requires simply that the universe did not come into being uncaused. For the universe to come into being without a cause of any sort would be to come into existence from nothing, which is worse than magic. Although some scientists have irresponsibly claimed that physics can explain the origin of the universe from “nothing,” what one inevitably discovers is that they are using the word “nothing” to refer to a physical system which undergoes a change of state. See David Albert, “On the Origin of Everything: ‘A Universe From Nothing,’ by Lawrence M. Krauss,” New York Times Sunday Book Review (March 23, 2012).

[4] For example, there were arguments based upon the impossibility of the existence of an actually infinite number of things. Here one argued that
 

1. An actually infinite number of things cannot exist.

2. A beginningless regress of temporal events implies the existence of an actually infinite number of things.

3. Therefore, a beginningless regress of temporal events cannot exist.

In support of the first premiss, one typically pointed to the metaphysically absurd situations which could result from an actually infinite number of things. David Hilbert’s famous hotel comes to mind. It is widely thought that premiss 1 has been defeated by Cantorian set theory. But as Hilbert realized, this claim is mistaken. As Kasner and Newman put it, “the infinite certainly does not exist in the same sense that we say, ‘There are fish in the sea.’ . . . ‘Existence’ in the mathematical sense is wholly different from the existence of objects in the physical world” (Edward Kasner and James Newman, Mathematics and the Imagination [New York: Simon & Schuster, 1940], p. 61). The mathematical existence of the actual infinite amounts to nothing more than the logical consistency of the axioms and theorems of set theory, which holds no implications for what is metaphysically possible. There is no example of an actually infinite number of anything in reality, and, as noted by Solomon Feferman, science can dispense with the notion of the actual infinite without impairment: “Infinitary concepts are not essential to the mathematization of science, all appearances to the contrary. And this puts into question the view that higher mathematics is somehow embodied in the world, rather than that it is the conceptual edifice raised by mankind in order to make sense of the world” (In Light of Logic [Oxford: Oxford University Press, 1998], p. 19; cf. p. 30).

Or again, there were arguments based upon the impossibility of forming an actual infinite by successive addition. Here one argued that

1. An actually infinite collection of things cannot be formed by successive addition.

2. The regress of temporal events is a collection formed by successive addition.

3. Therefore, the regress of temporal events cannot be actually infinite.

This argument is based upon a view of time which entails the objectivity of tense and temporal becoming. Although most physicists, accustomed as they are to a geometric presentation of space-time theories, tend uncritically toward a tenseless theory of time, philosophers of time are about evenly divided as to the objectivity of tense and temporal coming. Given the objectivity of temporal becoming, I think it is extraordinarily difficult to see how an actually infinite series of past events could have been completed successively.

[5] Sean Carroll, “Does the Universe Need God?” in The Blackwell Companion to Science and Christianity, ed. J. B. Stump and Alan G. Padgett (Oxford: Wiley-Blackwell, 2012), p. 196.

[6] William Lane Craig and Lawrence Krauss, “Life, the Universe, and Nothing (I): Has Science Buried God?” Brisbane, Australia (August 7, 2013), http://www.reasonablefaith.org/media/craig-vs-krauss-brisbane-australia (accessed February 23, 2014).

[7] In answer to the question “Did the universe have a beginning?” Vilenkin concludes “it seems that the answer to this question is probably yes” (Audrey Mithani and Alexander Vilenkin, “Did the universe have a beginning?” arXiv:1204.4658v1 [hep-th] 20 Apr 2012, p. 5). See http://arxiv.org/abs/1204.4658 (accessed March 19, 2014).

[8] William Lane Craig and James Sinclair, “The Kalam Cosmological Argument,” in The Blackwell Companion to Natural Theology, ed. Wm. L. Craig and J. P. Moreland (Oxford: Wiley-Blackwell, 2009), pp. 101-201; idem, “On Non-Singular Spacetimes and the Beginning of the Universe,” in Scientific Approaches to the Philosophy of Religion, ed. Yujin Nagasawa, Palgrave Frontiers in Philosophy of Religion (London: Macmillan, 2012), pp. 95-142.

[9] A. Borde, A. Guth, A. Vilenkin, “Inflationary Spacetimes Are Incomplete in Past Directions,” Physical Review Letters 90 (2003): 151301, http://arxiv.org/abs/gr-qc/0110012 (accessed February 23, 2014).

[10] Mithani and Vilenkin, “Did the universe have a beginning?” p. 1; cf. p. 5. For application to the Carroll-Chen model, see http://www.youtube.com/watch?v=NXCQelhKJ7A (accessed February 23, 2014), where Vilenkin concludes, “there are no models at this time that provide a satisfactory model for a universe without a beginning.” See further Alexander Vilenkin, “Arrows of time and the beginning of the universe,” arXiv:1305.3836v2 [hep-th] 29 May 2013.

[11] A.Vilenkin, cited in “Why physicists can't avoid a creation event,” by Lisa Grossman, New Scientist (January 11, 2012).

[12] “If indeed all past-directed geodesics encounter a quantum spacetime region where the notions of time and causality no longer apply, I would characterize such a region as the beginning of the universe” (A. Vilenkin to William Lane Craig, personal correspondence, December 8, 2013).

[13] Moreover, it is supposed to have existed before the classical era, and the classical era is supposed to have emerged from it, which seems to posit a temporal relation between the quantum gravity era and the classical era. This feature of quantum cosmogony is very problematic, since diachronic emergence of time is obviously incoherent (J. Butterfield and C. J. Isham, “On the Emergence of Time in Quantum Gravity,” in The Arguments of Time, ed. J. Butterfield [Oxford University Press, 1999], pp. 111-68; Vincent Lam and Michael Esfeld, “A dilemma for the emergence of spacetime in canonical quantum gravity,” Studies in History and Philosophy of Modern Physics 44 [2013]: 286–293; Reiner Hedrich, “Hat die Raumzeit Quanteneigenschaften? – Emergenztheoretische Ansätze in der Quantengravitation,” in Philosophie der Physik, ed. M. Esfeld [Berlin: Suhrkamp, forthcoming], pp. 287-305). But how can one make sense of a synchronic emergence of time as a supervenient reality in the context of cosmogony? The authors cited do not tell us. The best sense I can make of it is to say that the Euclidian description is a lower-level description of classical spacetime prior to the Planck time. (One recalls Hawking's remark that when we go back to the real time in which we live, there still would be singularities.) So the same reality is being described at two levels. That implies that if the classical spacetime has a beginning, then so does the quantum gravity regime. For they are descriptions of the same reality. In the one a singularity is part of the description; in the other it is not. So what is prior to the Planck time is not the quantum gravity era as such; rather what is prior is the classical period of which the quantum gravity description is the more fundamental description. If this is correct, then, given the beginning of the classically described universe, it is impossible for the universe as quantum gravitationally described to be without a beginning. For they just are the same universe at different levels of description.

[14] Christopher Isham observes that although quantum cosmogonies “differ in their details they all agree on the idea that space and time emerge in some way from a purely quantum-mechanical region which can be described in some respects as if it were a classical, imaginary-time four-space” (C. J. Isham, “Quantum Theories of the Creation of the Universe,” in Quantum Cosmology and the Laws of Nature, second ed., ed. Robert J. Russell et al. [Vatican City State: Vatican Observatory, 1996], p. 75). But see the previous note.

[15] Anthony Aguirre and John Kehayias, “Quantum Instability of the Emergent Universe,” arXiv:1306.3232v2 [hep-th] 19 Nov 2013. They are specifically addressing the Ellis-Maarten model, but their point is generalizable.

[16] Paul Davies, “The Big Questions: In the Beginning,” ABC Science Online, interview with Phillip Adams, http://www.abc.net.au/science/bigquestions/s460625.htm (accessed February 23, 2014).

[17] P. C. W. Davies, The Physics of Time Asymmetry (London: Surrey University Press, 1974), p. 104.

[18] S. W. Hawking, “Information Loss in Black Holes,” http://arXiv.org/abs/hep-th/0507171v2 (15 September 2005): 4. N.B. that just as Hawking came to accept information conservation regarding black holes, Carroll himself opts for information conservation in an expanding universe (Sean Carroll, From Eternity to Here: The Quest for the Ultimate Theory of Time [New York: Penguin, 2010], p. 294). Cf. his blog “The Eternally Existing, Self-Reproducing, Frequently Puzzling Inflationary Universe,” posted on October 21, 2011 (http://www.preposterousuniverse.com/blog/2011/10/21/). [links accessed February 23, 2014]

[19] Aron C. Wall, “The Generalized Second Law implies a Quantum Singularity Theorem,” arXiv: 1010.5513v3 [gr-qc] 24 Jan 2013, p. 38. See http://arxiv.org/abs/1010.5513v3 (accessed March 19, 2014).

[20] Ibid., p. 4.

[21] I’ve had the privilege of reading portions of Robin’s forthcoming book The Well-Tempered Universe, which will be the definitive work on fine-tuning for many years to come.

[22] I’m grateful to James Sinclair, Robin Collins, Aron Wall, and Christopher Weaver for comments on the first draft of this speech and discussion of the many points within.

Sean Carroll – Opening Speech

Well thank you very much, it’s a great pleasure to be here. The Greer-Heard Forum has been very wonderful. I thank Dr. Craig for participating. For everyone here I appreciate your attendance, and I need to add a word of appreciation to this beautiful chapel that we’re holding the event in. I just hope that somewhere in the middle of my talking the roof does not fall on my head. But if it does that would be evidence and I would update my beliefs accordingly.

I also want to start with a confession that my goal here is not to win a debate. The discussion we are having tonight does not reflect a debate that is ongoing in the professional cosmology community. If you go to cosmology conferences there’s a lot of talk about the origin and nature of the universe; there is no talk about what role God might have played in bringing the universe about. It is not an idea that is taken seriously. My goal is to explain why we think that. You may or may not agree with me at the end but you should be able to understand why we cosmologists have that view. And it comes down to a conflict between two major fundamental pictures of the world—what philosophers would call ontologies: naturalism and theism. Naturalism says that all that exists is one world, the natural world, obeying laws of nature, which science can help us discover. Theism says that in addition to the natural world there is something else, at the very least, God. Perhaps there are other things as well. I want to argue that naturalism is far and away the winner when it comes to cosmological explanation. And it comes down to three points. First, naturalism works—it accounts for the data we see. Second, the evidence is against theism. Third, theism is not well defined. I’m going to be emphasizing this third point because if you ask a theist about the definition they will give you some very rigorous sounding definition of what they mean by God. The most perfect being, the ground for all existence, and so forth. There are thousands of such definitions, which is an issue, but the real problem is not with the definition, it’s when you connect the notion of God to the world we observe. That’s where apparently an infinite amount of flexibility comes in and I’m going to be inveighing against using that in cosmology.

So, I think I can make these points basically by following Dr. Craig’s organization starting with the kalam cosmological argument, and unlike what he said I should be doing I want to challenge the first of the premises: If the universe began to exist it has a transcendent cause. The problem with this premise is that it is false. There’s almost no explanation or justification given for this premise in Dr. Craig’s presentation. But there’s a bigger problem with it, which is that it is not even false. The real problem is that these are not the right vocabulary words to be using when we discuss fundamental physics and cosmology. This kind of Aristotelian analysis of causation was cutting edge stuff 2,500 years ago. Today we know better. Our metaphysics must follow our physics. That’s what the word metaphysics means. And in modern physics, you open a quantum field theory textbook or a general relativity textbook, you will not find the words “transcendent cause” anywhere. What you find are differential equations. This reflects the fact that the way physics is known to work these days is in terms of patterns, unbreakable rules, laws of nature. Given the world at one point in time we will tell you what happens next. There is no need for any extra metaphysical baggage, like transcendent causes, on top of that. It’s precisely the wrong way to think about how the fundamental reality works. The question you should be asking is, “What is the best model of the universe that science can come up with?” By a model I mean a formal mathematical system that purports to match on to what we observe. So if you want to know whether something is possible in cosmology or physics you ask, “Can I build a model?” Can I build a model where the universe had a beginning but did not have a cause? The answer is yes. It’s been done. Thirty years ago, very famously, Stephen Hawking and Jim Hartle presented the no-boundary quantum cosmology model. The point about this model is not that it’s the right model, I don’t think that we’re anywhere near the right model yet. The point is that it’s completely self-contained. It is an entire history of the universe that does not rely on anything outside. It just is like that. The demand for more than a complete and consistent model that fits the data is a relic of a pre-scientific view of the world. My claim is that if you had a perfect cosmological model that accounted for the data you would go home and declare yourself having been victorious.

You might also ask, “Could the universe be eternal?” (since Dr. Craig talked about this) without having a beginning at all. Again, the answer is: yes, just build a model. This is my favorite model. It’s actually not even a model that I think is right; once again, it’s a model I helped create. But it’s about the search for models, not about saying any one model is the right idea. We hope that some day we get there but we don’t claim that we are there yet. So whether or not the universe can be eternal does not come down to a conversation about abstract principles. It comes down to a conversation about building models and seeing which one provides the best account for what we see the universe to be doing.

So I’d like to talk about the Borde-Guth-Vilenkin theorem since Dr. Craig emphasizes it. The rough translation is that in some universes, not all, the space-time description that we have as a classical space-time breaks down at some point in the past. Where Dr. Craig says that the Borde-Guth-Vilenkin theorem implies the universe had a beginning, that is false. That is not what it says. What it says is that our ability to describe the universe classically, that is to say, not including the effects of quantum mechanics, gives out. That may be because there’s a beginning or it may be because the universe is eternal, either because the assumptions of the theorem were violated or because quantum mechanics becomes important. If you need to invoke a theorem, because that’s what you like to do rather than building models, I would suggest the quantum eternity theorem. If you have a universe that obeys the conventional rules of quantum mechanics, has a non-zero energy, and the individual laws of physics are themselves not changing with time, that universe is necessarily eternal. The time parameter in Schrödinger’s equation, telling you how the universe evolves, goes from minus infinity to infinity. Now this might not be the definitive answer to the real world because you could always violate the assumptions of the theorem but because it takes quantum mechanics seriously it’s a much more likely starting point for analyzing the history of the universe. But again, I will keep reiterating that what matters are the models, not the abstract principles.

Dr. Craig brings up an argument about the Second Law of Thermodynamics and I’ve written a whole book, you can buy it on Amazon right now from your iPhones, about the second law and its relationship to cosmology. It is certainly a true issue that we don’t know why the early universe had a low entropy and entropy has ever been increasing. That’s a good challenge for cosmology. To imagine the cosmologist cannot answer that question without somehow invoking God is a classic god-of-the-gaps move. I know that Dr. Craig says that is not what he’s doing but then he does it. We don’t know why the early universe had a low entropy but that is not an argument that we can’t figure it out. There is more than one possibility. Maybe there is a principle, like Stephen Hawking would say, that puts the early universe in a low entropy state. Or maybe there is no high entropy state. In my model of an eternal universe the reason why our universe is always changing is because the universe always can change. There is no equilibrium for it to fall into. Dr. Craig brings up a quote – he brings up various things that I think really muddle the cosmological picture here. He says that my model is not working very well because it violates unitarity—the conservation of information—and that is straightforwardly false. In my model unitarity is the whole point. There’s a quantum mechanical wave function that describes the evolution of the universe from one piece into multiple pieces and that evolution is perfectly unitarity. He quotes Stephen Hawking backsliding his statement about baby universes but that was in the context of black holes. That had nothing to do with cosmology. That quote was taken completely out of context. Finally, he makes a big deal about Boltzmann Brains. I’m going to talk about that a little bit later. Most importantly, he talks about the fact that if the universe is eternal and you have a Second Law of Thermodynamics then there must have been a moment in the middle when the entropy was lowest, and he calls this a thermodynamic beginning and he quotes another paper. That’s fine except it’s an equivocation on the word beginning. A thermodynamic beginning is not a beginning—it happens in the middle. It’s a moment in the history of the universe from which entropy is higher in one direction of time and the other direction of time. There is no room in such a conception for God to have brought the universe into existence at any one moment.

If you really believe that the beginning of the universe is an important piece of evidence for God, an eternal universe with a low entropy state in the middle is not helping your case. What you should be doing is trying to build models, like I said. So the question is, “Are there realistic models of eternal cosmologies?” Well, I spent half an hour on the Internet and I was able to come up with about seventeen different plausible looking models of eternal cosmologies. I do not claim that any of these are the right answer. We’re nowhere near the right answer yet but you can come up with objections to every one of these models. You cannot say that they are not eternal. There’s a theorem, Borde-Guth-Vilenkin, that has assumptions so if you violate those assumptions you can violate the theorem. Meanwhile, theism, I would argue, is not a serious cosmological model. That’s because cosmology is a mature subject. We care about more things than just creating the universe. We care about specific details. At the cosmology conferences we’re discussing these questions that you see before you. I’m not going to list all of them but a real cosmological model wants to predict. What is the amount of density perturbation in the universe? And so forth. Theism does not even try to do this because ultimately theism is not well defined.

So let’s go to the second argument, the teleological argument from fine-tuning. I’m very happy to admit right off the bat – this is the best argument that the theists have when it comes to cosmology. That’s because it plays by the rules. You have phenomena, you have parameters of particle physics and cosmology, and then you have two different models: theism and naturalism. And you want to compare which model is the best fit for the data. I applaud that general approach. Given that, it is still a terrible argument. It is not at all convincing. I will give you five quick reasons why theism does not offer a solution to the purported fine-tuning problem.

First, I am by no means convinced that there is a fine-tuning problem and, again, Dr. Craig offered no evidence for it. It is certainly true that if you change the parameters of nature our local conditions that we observe around us would change by a lot. I grant that quickly. I do not grant therefore life could not exist. I will start granting that once someone tells me the conditions under which life can exist. What is the definition of life, for example? If it’s just information processing, thinking or something like that, there’s a huge panoply of possibilities. They sound very “science fiction-y” but then again you’re the one who is changing the parameters of the universe. The results are going to sound like they come from a science fiction novel. Sadly, we just don’t know whether life could exist if the conditions of our universe were very different because we only see the universe that we see.

Secondly, God doesn’t need to fine-tune anything. We talk about the parameters of physics and cosmology: the mass of the election, the strength of gravity. And we say if they weren’t the numbers that they were then life itself could not exist. That really underestimates God by a lot, which is surprising from theists, I think. In theism, life is not purely physical. It’s not purely a collection of atoms doing things like it is in naturalism. I would think that no matter what the atoms were doing God could still create life. God doesn’t care what the mass of the electron is. He can do what he wants. The only framework in which you can honestly say that the physical parameters of the universe must take on certain values in order for life to exist is naturalism.

The third point is that the fine-tunings you think are there might go away once you understand the universe better. They might only be apparent. There’s a famous example theists like to give, or even cosmologists who haven’t thought about it enough, that the expansion rate of the early universe is tuned to within 1 part in 1060. That’s the naïve estimate, back of the envelope, pencil and paper you would do. But in this case you can do better. You can go into the equations of general relativity and there is a correct rigorous derivation of the probability. If you ask the same question using the correct equations you find that the probability is 1. All set of measure zeroof early universe cosmologies have the right expansion rate to live for a long time and allow life to exist. I can’t say that all parameters fit into that paradigm but until we know the answer we can’t claim that they’re definitely finely-tuned.

Number four, there’s an obvious and easy naturalistic explanation in the form of the cosmological multiverse. People like to worry about the multiverse. It sounds extravagant. I claim the multiverse is amazingly simple. It is not a theory, it is a prediction of physical theories that are themselves quite elegant, small, and self-contained that create universes after universes. There’s no reason, no right that we have, to expect that the whole entire universe look like the conditions we have right now. But more importantly, if you take the multiverse as your starting point you can make predictions. We live in an ensemble and we should be able to predict the likelihoods that conditions around us take different forms. So in cosmology papers dealing with the multiverse you see graphs like this [slide image] that try to predict the density of dark matter given other conditions in the multiverse. You do not see graphs like this in the theological papers trying to give God credit for explaining the fine-tuning because theism is not well defined.

Now Dr. Craig makes a lot about the Boltzmann Brain problem. The problem that in the multiverse we could just be random fluctuations rather than growing in the aftermath of a hot big bang. This is a significant misunderstanding of how the multiverse works. The multiverse doesn’t say that everything that can possibly happen happens with equal probability. It says that there’s a definite history of the multiverse and you can make predictions. Different multiverse models will have different ratios of ordinary observers to random observers. That’s a good thing. That helps us distinguish between viable models of the multiverse and non-viable models, and there are plenty of viable models where the Boltzmann Brain, or random fluctuations, do not dominate. Furthermore, just as a little preview of coming attractions, I’m trying to write a paper (when I’m not debating about God and cosmology; I’m a physicist). I’m currently working on a paper that says, actually, Boltzmann Brains (random fluctuations) occur much, much less frequently than we previously believed. It comes down to a better understanding of quantum fluctuations. There’s a caricature of theism that says theism is an excuse to stop thinking. You say, “Oh, there’s a problem, I don’t need to solve it because God will solve it for me.” That’s clearly false because many theists think very carefully and very rigorously about many problems. But sometimes there’s an element of truth to it. This is an example. You’re faced with the Boltzmann Brain problem and you go, “I get out of that by saying that God created a single universe.” That might have stopped you from thinking about the physics in a deeper way and discovering interesting facts like this.

Fifth, and most importantly, theism fails as an explanation. Even if you think the universe is finely-tuned and you don’t think that naturalism can solve it, theism certainly does not solve it. If you thought it did, if you played the game honestly, what you would say is, “Here is the universe that I expect to exist under theism. I will compare it to the data and see if it fits.” What kind of universe would we expect? I’ve claimed that over and over again the universe we would expect matches the predictions of naturalism not theism. So the amount of tuning, if you thought that the physical parameters of our universe were tuned in order to allow life to exist, you would expect enough tuning but not too much. Under naturalism, a physical mechanism could far over-tune by an incredibly large amount that has nothing to do with the existence of life and that is exactly what we observe. For example, the entropy of the early universe is much, much, much, much lower than it needs to be to allow for life. You would expect under theism that the particles and parameters of particle physics would be enough to allow life to exist and have some structure that was designed for some reason whereas under naturalism you’d expect them to be kind of random and a mess. Guess what? They are kind of random and a mess. You would expect, under theism, for life to play a special role in the universe. Under naturalism, you would expect life to be very insignificant. I hope I don’t need to tell you that life is very insignificant as far as the universe is concerned.

Here is a photograph [slide image] from the Hubble Space Telescope of a few hundred out of the hundreds of billions of galaxies in our observable universe. The theistic explanation for cosmological fine-tuning asks you to look at this picture and say, “I know why it is like that. It’s because I was going to be here or we were going to be here.” But there is nothing in our experience of the universe that justifies the kind of flattering story we like to tell about ourselves. In fact, I would argue that the failure of theism to explain the fine-tuning of the universe is paradigmatic. It helps understand the other ways in which theism fails to be a better theory than naturalism. What you should be doing over and over again is comparing the predictions or expectations under theism to under naturalism and you find that over and over again naturalism wins. I’m going to zoom through these. It’s not the individual arguments that are important, it’s the cumulative effect.

If theism were really true there’s no reason for God to be hard to find. He should be perfectly obvious whereas in naturalism you might expect people to believe in God but the evidence to be thin on the ground. Under theism you’d expect that religious beliefs should be universal. There’s no reason for God to give special messages to this or that primitive tribe thousands of years ago. Why not give it to anyone? Whereas under naturalism you’d expect different religious beliefs inconsistent with each other to grow up under different local conditions. Under theism you’d expect religious doctrines to last a long time in a stable way. Under naturalism you’d expect them to adapt to social conditions. Under theism you’d expect the moral teachings of religion to be transcendent, progressive, sexism is wrong, slavery is wrong. Under naturalism you’d expect they reflect, once again, local mores, sometimes good rules, sometimes not so good. You’d expect the sacred texts, under theism, to give us interesting information. Tell us about the germ theory of disease. Tell us to wash our hands before we have dinner. Under naturalism you’d expect the sacred texts to be a mishmash—some really good parts, some poetic parts, and some boring parts and mythological parts. Under theism you’d expect biological forms to be designed, under naturalism they would derive from the twists and turns of evolutionary history. Under theism, minds should be independent of bodies. Under naturalism, your personality should change if you’re injured, tired, or you haven’t had your cup of coffee yet. Under theism, you’d expect that maybe you can explain the problem of evil – God wants us to have free will. But there shouldn’t be random suffering in the universe. Life should be essentially just. At the end of the day with theism you basically expect the universe to be perfect. Under naturalism, it should be kind of a mess—this is very strong empirical evidence.

Now, I know what you’re thinking. You’re thinking, “But I can explain all of that.” I know you can explain all of that—so can I. It’s not hard to come up with ex post facto justifications for why God would have done it that way. Why is it not hard? Because theism is not well defined. That’s what computer scientists call a bug, not a feature.

Immanuel Kant famously said, “There will never be an Isaac Newton for a blade of grass.” In other words, sure you can find some physical explanation for the motion of the planets but never for something as exquisitely organized and complex as a biological organism. Except, of course, that Charles Darwin then went and did exactly that. We can paraphrase Dr. Craig’s message as saying there will never be an Isaac Newton for the cosmos but everything we know about the history of science and the current state of physics says we should be much more optimistic than that. Thank you.

William Lane Craig – Rebuttal Speech

Thank you, Dr. Carroll, for that vigorous interaction!

Introductory Remarks

In my opening speech, I argued that God’s existence is significantly more probable given the evidence of contemporary cosmology than it would have been without it. This is due to the support which cosmology lends to key premises in the cosmological and teleological arguments.

Before we review those arguments, let me just say a word about Professor Carroll’s concluding remarks, which, I believe, are extraneous to tonight’s discussion.

He is very concerned to show that God’s existence is improbable relative to certain non-cosmological data. For example, the problem of evil, our insignificant size, and so forth. The very fact that these are non-cosmological data shows that they are not relevant in tonight’s debate. I have addressed things like the problem of evil extensively, for example, in Philosophical Foundations for a Christian Worldview.[23] So the debate tonight is not over the probability of theism versus naturalism. That would require us to assess all sorts of non-cosmological data. Rather, the question is: is God’s existence more probable given the data of contemporary cosmology than it would have been without it? And I think it certainly is.

Let’s look at those two arguments that I defended.

The Kalam Cosmological Argument

Consider, first, the evidence for the beginning of the universe from the expansion of the universe and thermodynamics.

The Causal Premise

To my surprise, Dr. Carroll challenges the first premise of this argument by saying it is based on outmoded Aristotelian concepts of causality. I protest – not at all! There is no analysis given of what it means to be a cause in this first premise. You can adopt your favorite theory of causation or take causation to be a conceptual primitive. All it requires is that the universe did not pop into being uncaused out of absolutely nothing. If that is the price of non-theism, then I think the non-theist is welcome to it. Dr. Carroll says on the Hartle-Hawking model the universe is uncaused. Not at all! The universe comes into being on such a model, and there is nothing in the theory that would explain why that universe exists rather than not. The model may be self-contained; but that is perfectly consistent with my argument. I am not arguing for some kind of interventionist deity, but rather, why does the universe exist? Why did it come into being at all?

Evidence from the Expansion of the Universe

With respect to the second premise, Dr. Carroll says there are all kinds of beginningless models of the universe. Well, it certainly is true that such models exist; but the problem is that none of them is successful.

 

Beginningless Models

Model average expansion history

Condition requiring a beginning

1

Expanding models

Singularity theorems

2

Asymptotically static models

Metastability

3

Cyclic models

Second Law of Thermodynamics

4

Contracting models

Acausal fine-tuning

As Jim Sinclair has shown in our article in the Blackwell Companion, all of the models that Dr. Carroll has mentioned have been shown to be either untenable or not to avert the beginning of the universe.[24] Alex Vilenkin says flatly, “there are no models at this time that give a satisfactory model for a universe without a beginning.”[25]

Consider in particular Dr. Carroll’s own model.

This model presupposes a reductionistic view of time according to which the direction of time is defined in terms of entropy increase. Now, in the model notice there are two arrows of time for the mother universe pointing in opposite directions. So on this view of time, we don’t really have an eternally existing mother universe here at all. Rather, you have two universes which share a common origin in the central surface. So what the model actually implies, rather than avoids, is a beginning of time and of the universe. Time has a beginning on this model, and therefore it involves all of the problems that are pertinent to the universe’s coming into being.

Be that as it may, I think it is safe to say that there is no credible classical model of a beginningless universe today.

Dr. Carroll does hold out hope that quantum cosmology might serve to restore the past eternality of the universe; but I would say that not only is there no evidence for such a hope, but I would agree with Vilenkin that if there is a quantum gravity regime prior to the Planck Time, then that just is the beginning of the universe. Dr. Carroll says you can have quantum descriptions of the universe that are eternal, and that is certainly true, but the question is: why would the universe transition to classical spacetime just 13 billion years ago? It could not have existed from infinity past in an unstable quantum state and then just 13 billion years ago transition to classical spacetime. It would have done it from eternity past, if at all.

So I think we’ve got good evidence from the expansion of the universe that the universe probably began to exist.

Evidence from Thermodynamics

What about the evidence from thermodynamics? First is the problem of information loss to baby universes on his theory. You will recall that is why Stephen Hawking rejected the baby universe hypothesis. Dr. Carroll responds, “My mechanisms for generating the baby universes don’t use Hawking’s mechanisms.” All right; but are they any more successful? I don’t think so. According to Chris Weaver in his article on the Carroll-Chen model,

The FGG [Farhi-Guth-Guven] nucleation [that Dr. Carroll uses] out of a de Sitter space-time is merely speculative and . . . Carroll’s discussion of it should be thought of as exploratory. . . . it is therefore safe to conclude that a central piece of the model is missing, and so the CC-M [Carroll-Chen model] is incomplete in that it does not have a clear recommended dynamical path from the background [space-time] to the birth of [universes] like ours.[26]

In fact, Weaver goes on to point out that for a universe described by the Borde-Guth-Vilenkin theorem (like ours), the Farhi-Guth-Guven mechanisms cannot produce such a universe. Therefore, these mechanisms fail.

I also, secondly, pointed out that there is a Boltzmann Brain problem with respect to Dr. Carroll’s model. It seems to me that he just didn’t respond to the point that I was making, namely, that since every baby universe grows into a de Sitter space, there will be vastly, vastly more of these Boltzmann Brains in the long run than there will be ordinary observers. So what Dr. Carroll would need to do is to justify some non-standard measure of probability that would make ordinary observers more probable than Boltzmann Brains. But he admits that he cannot do it.

We also then saw that quantum gravity will not avert this conclusion because of the Wall theorem, which should be valid for the quantum gravity era and requires a beginning of the universe.

Summary

So it seems to me we’ve got good evidence from the expansion of the universe and from thermodynamics that the universe is probably not past eternal but began to exist.

The Teleological Argument

What about that second argument based upon the fine-tuning of the universe?

Reality of Fine-Tuning

Here Dr. Carroll expresses scepticism that the fine-tuning is real. But a good many, if not most, of his colleagues would simply disagree with him here. Luke Barnes provides a list of just some of the scientists who have published works in defense of the reality of fine-tuning:

I can think of one more name that we should add to the list – namely, Sean Carroll! Listen to what he has to say about the low entropy condition of the early universe, which Robin Collins calls “potentially the most outstanding case of fine-tuning.”[27] Carroll writes, “If the universe we see is really all there is with the Big Bang as a low-entropy beginning, we seem to be stuck with an uncomfortable fine-tuning problem.”[28] So he tries to explain away this fine-tuning via the world ensemble, or multiverse, hypothesis.

Chance?

But then, as I argued in my opening speech, he confronts the Boltzmann Brain problem once again. Even if Dr. Carroll could show that ordinary observers predominate in life-permitting worlds, what about all of those worlds that are not life-permitting because the other constants and quantities are not finely-tuned? In such worlds – which vastly outnumber finely-tuned worlds – there will be no ordinary observers, and yet there will be untold numbers of Boltzmann Brains produced by thermal fluctuations. So the entire multiverse will be dominated by universes having vastly more Boltzmann Brains than ordinary observers like us.[29] Therefore, the data on the multiverse hypothesis is incomprehensibly improbable. The evidence is strongly disconfirmatory of the World Ensemble hypothesis.

Design?

Dr. Carroll says that theism does no better in accounting for the low entropy condition of the universe. For why, he asks, did God make the entropy of the universe so unnecessarily low in order to create us? Well, I have two responses to this. First, it is no part of the fine-tuning argument to assert that the purpose for which the universe was created is us! There may well be intelligent life created by God scattered throughout the universe. But, secondly, as Robin Collins has pointed out, even if a general low entropy condition is not necessary for our existence, it is necessary for the discoverability of the universe. God hasn’t given us an instruction manual about how the world works. But what he has done is make a world which is susceptible to rational exploration and discovery. And if God wanted to make a universe discoverable by embodied, conscious agents, he might well make it in such a low entropy condition. (You will hear more about that tomorrow when Robin gives his paper.)

So it seems to me that Dr. Carroll faces uniquely a Boltzmann Brain problem for a number of reasons – a problem that does not afflict theism.

Summary and Conclusion

So, in summary, this is not a debate between naturalism and theism. Otherwise, I would be offering ontological arguments, moral arguments, other sorts of arguments. For that debate, you need to listen to my debate with Dr. Rosenberg last year at Purdue University.[30] What this debate is about is: to what degree do the data of contemporary cosmology render God’s existence more probable than it would have been if we didn’t have that data? To my mind, it is almost undeniable that God’s existence is much more probable given the evidence that we have for the beginning of the universe and the fine-tuning of the universe. Therefore, contemporary cosmology is strongly confirmatory of theism.


[23] See Chapter 27, “The Problem of Evil” in J. P. Moreland and William Lane Craig, Philosophical Foundations for a Christian Worldview (Downers Grove, Ill.: InterVarsity Press, 2003), pp. 536-53.

[24] William Lane Craig and James Sinclair, “The Kalam Cosmological Argument,” in The Blackwell Companion to Natural Theology, ed. Wm. L. Craig and J. P. Moreland (Oxford: Wiley-Blackwell, 2009), pp. 101-201.

[25] Alexander Vilenkin, “Did the universe have a beginning?” http://www.youtube.com/watch?v=NXCQelhKJ7A

[26] Christopher Gregory Weaver, “On the Carroll-Chen Model,” September 17, 2013, arXiv:1309.4976 [physics.hist-ph], p. 11. See http://arxiv.org/abs/1309.4976 (accessed March 20, 2014).

[27] Robin Collins, The Well-Tempered Universe, pre-print.

[28] Sean Carroll, From Eternity to Here, p. 365. Cf. “If our universe began at the Big Bang, it is burdened with a finely-tuned boundary condition for which we have no good explanation” (Ibid., p. 5).

[29] Thanks to Robin Collins for bringing my attention to this point!

 

Sean Carroll – Rebuttal Speech

Great. Well, thanks again. I think that we can just go right back to my three major points, and I think that, halfway through our forum, I believe these three major points more strongly than ever. Now, I know that Dr. Craig would disagree but I’ll try to establish that his disagreements with number one are based on misunderstandings of the science. His disagreements with number two, the evidences against theism, is largely based on using number three—the fact that theism is not well defined.

So let’s go to the kalam cosmological argument. There’s a deep philosophical difference between us. I claim that a consistent, complete model that fits the data accounts for what we see in the world is a success. There’s no right that we have to demand more than that, and I believe that Dr. Craig’s response was, “Yes there is.” I don’t think this counts as a very good response. It’s a very difficult thing because the universe is different than our everyday experience. That doesn’t sound like a surprising statement but we really need to take it to heart. To look at a modern cosmological model and say, “Yes, but what was the cause?” is like looking at someone taking pictures with an iPhone and saying, “But where does the film go?” It’s not that the answer is difficult or inscrutable; it’s completely the wrong question to be asking. In fact it’s a little technical, most of my second talk here, but I think it’s worth getting it right. Why should we expect that there are causes or explanations or a reason why in the universe in which we live? It’s because the physical world inside of which we’re embedded has two important features. There are unbreakable patterns, laws of physics—things don’t just happen, they obey the laws—and there is an arrow of time stretching from the past to the future. The entropy was lower in the past and increases towards the future. Therefore, when you find some event or state of affairs B today, we can very often trace it back in time to one or a couple of possible predecessor events that we therefore call the cause of that, which leads to B according to the laws of physics. But crucially, both of these features of the universe that allow us to speak the language of causes and effects are completely absent when we talk about the universe as a whole. We don’t think that our universe is part of a bigger ensemble that obeys laws. Even if it’s part of the multiverse, the multiverse is not part of a bigger ensemble that obeys laws. Therefore, nothing gives us the right to demand some kind of external cause.

The idea that our intuitions about cause and effect that we get from the everyday experience of the world in this room should somehow be extended without modification to the fundamental nature of reality is fairly absurd. On a more specific level we talked about my model. Again, I’m not trying to defend my model; I’m the first one to say that it has problems. None of the problems that it has are the ones that Dr. Craig raised. He says that it’s not really eternal, which it is hard to express the extent to which I think this is grasping at straws. The axis for time goes from the top to the bottom and it goes forever. The only sense in which this universe is not eternal is that there is a moment in the middle where the entropy is lowest. I made the point in my opening speech that that has nothing to do with the kind of beginning you would need to give God room to work and as far I can recall Dr. Craig didn’t address that argument.

He does say that it is speculative, the idea of baby universes coming into existence. I’m the first to agree. It’s completely speculative. He quotes a paper that says the mechanism by which baby universe are created is speculative, it might not be right. Again, it’s completely true. He claims to use it to say that unitarity is violated even though the quote he read didn’t even mention unitarity and wasn’t about unitarity. That is not a sensible objection.

I will repeat – the quantum eternity theorem, a sensible analysis of the history of the universe, might be with the rules of quantum mechanics. He claims that someone else said there might be a singularity in quantum gravity but he gives us no understanding, he simply repeats his previous analysis. So, I want to draw attention not to my model but to the model of Anthony Aguirre and Steven Gratton because this is perfectly well defined. This is a bouncing cosmology that is infinite in time, it goes from minus infinity to infinity, it has classical description everywhere. There is no possible sense in which this universe comes into existence at some moment in time. I would really like Dr. Craig to explain to us why this universe is not okay.

Now there’s a theorem by Alan Guth, Arvind Borde, and Alex Vilenkin that says the universe had a beginning. I’ve explained to you why that’s not true but in case you do not trust me I happen to have Alan Guth right here. One of the authors of the Borde-Guth-Vilenkin Theorem, Alan what do you say? He says, “I don’t know whether the universe had a beginning. I suspect the universe didn’t have a beginning. It’s very likely eternal but nobody knows.” Now how in the world can the author of the Borde-Guth-Vilenkin theorem say the universe is probably eternal? For the reasons I’ve already told you. The theorem is only about classical descriptions of the universe not about the universe itself.

So, going to the teleological argument. It is true – Dr. Craig brings up the point that people disagree with me, it is true. I attempted to give an argument and not merely an opinion poll. If we’re allowed to take opinion polls I will poll my fellow cosmologists on whether God had anything to do with creating the universe and I will win by a landslide. I suspect that Dr. Craig thinks the majority of the opinions of cosmologists is important for some issues but not for others. The entropy of the early universe is exactly backwards when it comes to being an argument for fine-tuning according to theology. Dr. Craig quotes me in a “gotcha-moment” saying, “Look, the early universe was finely-tuned with a low entropy.” That is absolutely true. The point that I raised was not that there is not fine-tuning, it’s that there’s no evidence the fine-tuning is for life to exist. Indeed, the maximum possible entropy of the part of the universe we observe is this huge number, 10122. The entropy that you would need is a little bit lower than that if you wanted life to exist. But it’s almost the same. It’s 0.999 etc. times the maximum entropy, whereas the actual entropy of the early universe is enormously smaller than that. There’s absolutely no reason why the universe would look like this if the fine-tunings were put there in order for life to exist. I’m not saying there’s not fine-tunings; I’m saying they’re not there for life.

Turning to the multiverse, again it is a completely speculative thing, but it is a completely natural thing and I don’t really see any argument against that. The multiverse, the idea that outside the universe we see there could be very different regions with very different physical parameters, is no more radical then the idea that there are different planets with different atmospheres. To a frog on a lily pad that lily pad is its universe. To us in the universe we see a hundred billion galaxies is enough but it’s very, very easy to come up with physical models that have much more out there. The main argument Dr. Craig has against this is the Boltzmann Brain argument. Again, I gave you why that’s not a good argument and it seems to have been ignored in Dr. Craig’s last speech; namely that the multiverse does not predict that everything happens. It predicts certain things happen with certain frequencies. So what you do as a working cosmologist is check that your universe is not dominated by Boltzmann Brains. Are there multiverse models that pass that test? Yes, there are. It is easily avoided. Then he brings up this weird argument, he says, “There could be the regions where ordinary observers could not exist because the parameters are not right but Boltzmann Brains could exist.” But the whole point is that Boltzmann Brains are forms of life. Boltzmann Brains can only exist where life is possible. So what one does in cosmology is look at the multiverse regions where life is possible and counts the number of Boltzmann Brains versus the number of ordinary observers—there are models that pass the test.

Now, I think that this is, again, a philosophical point here because when I talked about the list of ways in which our expectations for theism come out completely wrong when you compare them to the world, Dr. Craig said, “Well, that’s not the point, we’re not arguing about morality” and things like that. But again that misses the point of my argument. I was not actually putting forward these as strong predictions of theism. I was making the point that there are no strong predictions of theism. It’s not that there should be no evil in the world if God exists, it’s that you can always wriggle out of the prediction that there should be no evil in the world if God exists. That’s why it’s not a good theory of the world generally, that’s why it’s not a good cosmological model, particularly. Now, Dr. Craig said that we shouldn’t expect to know things about the world simply because we say that God finely-tuned it. “Just because under theism,” he says, “God made the parameters of the universe such to allow life to exist doesn’t mean we can have any other expectation for predicting what those parameters are.” This reflects something that he said on his website earlier. In a similar context he said, “Suppose God is more like the cosmic artist who wants to splash his canvas with the extravagance of design and who enjoys creating this fabulous cosmos designed with fantastic detail for observers.” So, what this attitude is saying is that – well, my point is that – this is not some sort of sophisticated apologetic strategy. This is an admission of defeat. This is saying we should never expect theism to explain why the universe is one way rather than some other way. You know God—God is an artist. You know artists; they’re kind of quirky and unpredictable. We can’t expect to know what they’re going to do ahead of time. Anything you might possibly observe about the universe, according to this view, I can explain as saying, “That is what God would have done.”

In naturalism, on the other hand, you need to play by the rules. When we say in cosmology or physics that a certain parameter is finely-tuned, it’s not just the parameter looks funny to us, it’s that we have a prior set of expectations for what values the parameters should take on and the parameter doesn’t fit those expectations. So we look for physical models that explain it, and that drive to understand things better helps us understand physics better, helps us understand the real world better. So, unlike God who is an artist and can’t be predicted, nature is not an artist. Nature plays by the rules. Nature makes predictions. Nature provides explanations. Thank you.

William Lane Craig – Closing Speech

Perhaps you feel like you have been drinking from a fire hose this evening! But let me in my final speech try to draw together some threads of the debate and see if we can draw some conclusions.

Introductory Remarks

I hope that it has been obvious tonight that I am not offering God as a theory to compete with scientific theories about the universe. Rather, I am saying that those self-contained, secular theories provide evidence for theologically neutral premises in philosophical arguments leading to a conclusion that has theistic significance—premises like “The universe began to exist” or “The fine-tuning is not due to physical necessity or to chance.” If those premises are supported, then it follows deductively that there is a Creator and Designer of the universe. Dr. Carroll’s complaints about theism’s not making predictions would be important only if I were offering some sort of theistic theory of the world. But I am not doing so. I am simply appealing to the cosmological evidence in support of these theologically neutral premises that go to deductively imply the existence of a Creator and Designer.

Let’s look again at those arguments that I defended.

The Kalam Cosmological Argument

The Causal Premise

First, the kalam cosmological argument. Dr. Carroll challenges the first premise, that if the universe came into existence, there is a transcendent cause that brought the universe into being. Honestly, I am quite astonished that he would think that the universe can literally pop into being out of nothing. Let me just give three arguments for why there must be a cause.

First of all, it seems to me a metaphysical first principle that being doesn’t come from non-being. Things don’t just pop into existence from literally nothing. Nothingness has no properties, no potentialities. It is not anything. So it seems to me inconceivable metaphysically to think the universe can come into being from nothing.

Secondly, if the universe could come into being from nothing, then why is it that only universes can pop into being out of nothing? Why not bicycles and Beethoven and root beer? What makes nothingness so discriminatory? If universes could pop into being out of nothing, then anything and everything should pop into being out of nothing. Since it doesn’t, that suggests that things that come into being have causes.

Finally, all the empirical evidence we have supports the truth of the causal principle. When Dr. Carroll says, “The universe is different than our experience,” this is really committing what Alexander Pruss calls the taxi-cab fallacy, that is to say, you go with the causal principle until you reach your desired goal and then you think you can just dismiss it like a hack because you don’t want there to be a cause of your entity – the universe. But if the universe came into existence, if the universe is not eternal, then surely it would need to have a cause. In fact, to deny this is unscientific because the whole project of contemporary cosmogony is to try to find what is the cause of the universe! So on his principle, it would be a science-stopper and would destroy his very field of expertise.

Evidence from the Expansion of the Universe

With respect to the second premise that the universe did begin to exist, he denies that he actually has an origin of time going in two opposite directions.

But this is a different diagram of his model.[31] Notice that on this diagram, you have a non-reductionistic arrow of time that goes from past to future. This is not an arrow of time that is determined by entropy increase, as he had in the other diagram. This is a non-reductionistic view of time, that Professor Maudlin and I accept, where the direction of entropy increase doesn’t define the direction of time. On this model, the universe contracts down from eternity past from infinity to a relatively low entropy point and then begins to expand again. That kind of model is physically impossible. It contradicts the second law of thermodynamics. That is why you have got to have the arrows pointing in both directions, if you want to hope for this model to be realistic. But if you have a double-headed arrow of time in both directions, then you have a beginning of time and of the universe. So I want to co-opt Dr. Carroll’s model for myself! On his model of the universe, the universe began to exist, along with time.

I also pointed out that on the Borde-Guth-Vilenkin theorem, there are no classical models that succeed in showing the universe to be beginningless. He rightly points out this is just classical space-time. But then I never heard a response to my claim that if there is a quantum gravity era prior to the Planck time, then it would have to be itself finite because otherwise it becomes inexplicable why classical spacetime only came into being 13 billion years ago rather than from eternity past.

So I think we have got good evidence for the beginning of the universe from the expansion of the universe.

Evidence from Thermodynamics

As for thermodynamics, here I argued that in order to explain why we are in a low entropy state, the standard answer is that the universe began relatively recently with its low entropy condition at the beginning. By contrast, his model, I charged, violates the unitarity of quantum physics. He says, “No, because I am not using the same mechanisms as Hawking.” But then I pointed out that the mechanisms that he appeals to are both conjectural and actually incompatible with a universe described by the Borde-Guth-Vilenkin theorem, as Christopher Weaver points out in his critique of the model.

Secondly, the Boltzmann Brain problem. I don’t think that Dr. Carroll has really come to grips with this, quite honestly. There are at least two reasons why Boltzmann Brains would dominate. First, because on his multiverse model, in the long run every baby universe becomes a de Sitter space and will become dominated with Boltzmann Brains. Secondly, in all of the other worlds that are not fine-tuned, there just aren’t any ordinary observers; but there will be thermal fluctuations that will produce Boltzmann Brains. So he is the one who has to justify some non-standard measure of probability in order to explain why ordinary observers like us should exist rather than Boltzmann Brains.

Then I appealed to the Wall theorem to show that even on a quantum gravity theory you are not going to avoid the beginning of the universe. Dr. Carroll may have responded to this, but if he did, it went by so quick I didn’t hear it. So it seems to me we’ve still got the Wall theorem showing that even with a quantum gravity era there has to be a beginning.

The Teleological Argument

Design?

As to the teleological argument from fine-tuning, he seems to have rested his entire case here on the fact that entropy would be way, way unnecessarily too small on theism. But I gave two responses to that. First, there may be life throughout the universe, not just us. Secondly, as Robin has pointed out, the low entropy condition is suitable for the discoverability of the universe. By contrast, on his view, it is incomprehensibly improbable that we should exist, given the equilibrium or the heat death state at which the universe would more probably exist.

Summary and Conclusion

So, in sum, in seems to me that on balance that we have got good evidence that the universe began to exist and that, therefore, there must be a Creator that brought it into being. Moreover, this is a personal Designer of the universe in view of the fine-tuning of the universe for intelligent, interactive agents like ourselves.


[31] The different diagram in Fig. 17 is from Sean Carroll, From Eternity to Here: The Quest for the Ultimate Theory of Time (New York: Plume, 2010), p. 363, Fig. 87.

Sean Carroll – Closing Speech

All right, congratulations to everyone for having made it this far. I will confess a bit of frustration in this final talk because I think almost everything that Dr. Craig had said in his last talk he had already said, and I tried to give my best response to it. They weren’t always matched. So, I’m going to take advantage of that to do something bizarre and unpredictable, which I’ll get to in a second.

First, I want to notice some of the things he did say. He said he was astonished that I refused to accept the fact that things need causes to happen. To which I could only quote David Lewis, “I do not know how to refute an incredulous stare.” I tried to give the reason why the causation analysis that we use for objects within the universe does not apply to the universe but that more or less whizzed on by. Dr. Craig gets a lot of mileage out of the presumed nuttiness of things just popping into existence. “Why don’t bicycles just pop into existence?” Again, I tried to explain what makes the universe different but more importantly the phrase “popping into existence” is not the right one to use when you’re talking about the universe. It sounds as if it’s something that happens in time but that’s not the right way to do it because there’s no before the beginning, if there’s a beginning. The correct thing to say is there was a first moment of time. When you say it that way it doesn’t’ sound so implausible. The question is, is there a model in which that’s true? Do the equations of the model hang together? Does the model fit the data? And we have plausibly positive answers to all of those.

He spends a lot of time on my own model, more time than I would have spent on it. He is upset that I did not include an arrow at the bottom in my axis when I drew the graph previously. I don’t care about that to be very honest. The double arrows here are just to express the fact that there’s no intrinsic arrow of time. The arrow of time that we experience is because of the behavior of matter in the universe—the entropy increasing. And he says that’s in violation of the Second Law of Thermodynamics. Yes, it is an explanation of the Second Law of Thermodynamics. This is the reason why we in our little part of the universe observe the second law. He mentions once again Boltzmann Brains and he says that there should be more Boltzmann Brains than ordinary observers. I again explain why that’s not true because it’s a model dependent statement. In this particular model it turns out to be easier to make a universe than to make a brain. That’s a selling point of the model.

So, with that under our belts, I want to actually just completely go off the topic and talk about issues beyond naturalism and theism. We’re having a discussion here about God and cosmology but let’s pull back the curtain a little bit. There are very few people in the modern world who become religious, to come to believe in God, because it provides the best cosmology or because it provides the best physics or biology, or psychology, or anything like that. And that includes Dr. Craig. There’s a famous quote by him that says, “The real reason, the primary reason, for believing in Christianity isn’t cosmological arguments.” I’m not mentioning this as a criticism; it is simply an observation of fact. There are other reasons to be a theist other than cosmology, and I think that is true. I think that makes sense. Most people who become religious do so for other reasons—because it gives them a sense of community, a sense of connection with the transcendent, it provides meaning or fellowship in their lives. The problem is that the basis of religion in the modern Western world is theism, belief in the existence of God. I’ve tried to make the case that science undermines theism pretty devastatingly. Five hundred years ago it would have made perfect sense to be a theist. I would have been a theist five hundred years ago. By two hundred years ago science had progressed to the point where it was no longer the best theory. By a hundred years ago after Darwin it was a rout. And by these days with modern cosmology there’s no longer any reason to take that as your fundamental worldview.

So what do you do if you identify as a member of a religious tradition in this situation. I think there are three options. One is to deny the science, to think that the world is six thousand years old. Happily, nobody up here on this stage today takes that attitude. That was a previous debate from a couple weeks ago. But there is a second attitude which is to accept the science but deny the implications—to say that none of the progress of modern science has in any way altered the fundamental view of reality that we put together two thousand years ago. I think that there’s two reasons why that’s not a good idea. Number one, I think it’s wrong, as I tried to explain throughout the debate, but number two, I think it’s a strategic mistake. I think that if one believes in theism that must be central to one’s view of the world for many, many other reasons, and because theism has been undermined by science it takes theists and it marginalizes them as part of the wider intellectual conversation. Humanity is at a crossroads. It’s at a very important time in the history of the world. We need to have deep discussions about who we are and where we’re going, and people who cling to the belief in God after science has undermined it are increasingly not going to be part of that discussion.

We talked about cosmologists and physicists, here’s what philosophers believe. There’s a recent survey that asked philosophers thirty big questions. And you know philosophers don’t agree on anything, but here are the three questions they had the greatest amount of consensus on: external reality exists, science tells us something about that external reality, and God does not exist. Now, again, get three philosophers in a room and they don’t even agree that there are three philosophers in the room. So, the fact that there’s only 73% is a still very impressive, and this includes professional philosophers of religion.

So I claim that there is a third option. Here’s the point where I start giving people advice who did not ask me for any advice. So, I ask your indulgence here. The third option, as I see it, for the person who is religious is to say, “Look, we admit we were wrong. We were wrong hundreds of years ago when we based our belief system on the idea that God was in charge of it all. Of course we were wrong, it was two thousand years ago! We didn’t have microscopes or telescopes. What right do we have to think that we would have gotten the fundamental nature of reality right but,” this person could hypothetically say, “religion is much more than theism. It’s not just the belief in God. There is the fellowship we feel for our fellow human beings.” For centuries, religious traditions were the place where human beings did their most careful, sustained, and rigorous contemplation about what it means to be human, about what it means to experience joy or suffering, to feel camaraderie with your fellow man, to be charitable, and so forth—to have meaning and purpose in your lives. So, maybe this person could say there is something to be learned even for naturalists from the outcome of all that contemplation. Maybe there is wisdom in Scriptures and the Sermon on the Mount, in the art and the music and the lives of the saints, or for that matter, the Bhagavata Gita or the Daodejing. I don’t know whether there is wisdom there, I’m asking for guidance. At the end of the day we’re all human beings trying to figure out our way in this confusing world.

The point is that naturalism replaces theism but it doesn’t replace religion. It doesn’t necessarily provide answers to the hard questions of meaning and fulfillment and purpose. I think that it can. I find naturalism, personally, to be an inspirational and profound view of the world. Ironically, the part I find most inspirational is the fact that some day I will die. Everyone in this room will someday be dead and there will not be an afterlife, a continuance, a judgment. The lives we lead now are not dress rehearsals. They are the only performance we have; therefore, what matters is what is here—the people we know and love, the lives we can change, the good we can do for the world. That is all there is, so of course that is what matters. Another way of putting it is naturalism has addressed the easy questions, the basic physical features of how the world works, but there are hard questions of meaning and purpose and fulfillment yet to be answered. What I like to say is we have picked the low-hanging fruit off of the tree of knowledge but there’s a lot of succulent goodies up there on the higher branches, and we’ll get there faster if we all climb together. Thank you.

Question and Answer Session

MODERATOR: Let’s give them both another hand. [applause] This was just amazing. The one thing I am amazed by is that there are great disagreements about time but both of them stayed on time. [laughter] Thanks, guys! Come on up to the podium. Let me explain how this is going to work. I need to get my notes here. My wife gets very nervous when it's just my stream of consciousness working. [laughter]

We have a microphone in each aisle for questions. The aisle over here on Sean's side is for questions for Sean Carroll. The aisle over here by Bill's side is for questions for Bill Craig. And we're going to alternate from one to the other, and we'll have an even number of questions—alright? When a question is asked to Sean, Sean will have two minutes to answer. If Bill wants to respond he'll have up to one minute. And vice versa—when a question is asked to Bill he has up to two minutes to answer, and Sean has up to one minute.

Let me give some instructions to those who are asking questions. Number one: state your question in a hurry, like twenty seconds, okay? Number two: make sure that it's a real question. [laughter] The way to make sure that you're asking real questions is ask yourself a question. Ask yourself this question: was I paid to come here? [laughter] Exactly! If you were not paid to come here then you are welcome to ask a question but you are not invited to lecture. So make sure it's a real question. Second, ask yourself this question: will everyone benefit from hearing this question? Is it a question that's going to shed light, to get at more truth? Or is it more akin to some interesting thoughts you had one night after your third highball? You've heard it said, there is no such thing as a stupid question. That's not true. [laughter] That's a stupid saying. And my last instruction would be: you only get one question. When you ask your question, step away from the microphone. No follow-ups, unless Sean or Bill asks you. If they don't understand what you're saying and they ask you a question, you can clarify it. So we can get more questions in and everyone will be happier. So come to the microphones now, and we will begin.

One other thing: here at the Greer-Heard forum we follow Robert's Rules. My name is Robert, I make the rules. [laughter]

Question 1: Hey, Dr. Carroll, how are you doing? Thank you for being here tonight, sir. In your polemic tonight on theism you said something like, “Look, if you have a fully explainable model, why do you keep looking for something else to add?” Okay? Now, my question is something like this: if you took as a metaphor for the universe, say, that we have a complete and entire physical explanation for the existence of the jet engine – you know, we can talk about internal combustion, all the things that go into making it and so forth – but does that complete knowledge mean that Frank Whittle didn't exist? Does a fully accurate mathematical model make this so? My question is this, exactly: isn't this a category mistake to assume that it does; namely, that law and mechanism does away with personal agency?

Dr. Carroll: Great. This is being recorded, I don't need to repeat the question—right? So his question got on to the tape? Okay. Yeah, so, it's a very good question and I think the answer is the universe is different than things inside the universe. As I tried to explain, there is a reason why there are reasons why. There are reasons why in our everyday life it is perfectly correct to speak a language of causation and explanation and invention and creation, and when you look carefully what those reasons are, they don't apply to the universe. The universe isn't part of a bigger structure in which there are patterns, evolution laws, arrows of time, expectations for what should happen. So a jet engine and a universe are just not very analogous to each other.

Dr. Craig: It seems to me that that's just fantastic, to think that the universe could just come into being from non-being; that it just pops into existence. And, as I said, if one says that that is possible, then you're confronted with the difficulty: why only universes? It seems to me then that everything and anything would come into being from nothing because there's nothing about nothing that could make it discriminate between universes and anything else. So it seems to me that this is a difference without a difference. I would say that the condition that applies to the universe that makes the causal principle relevant would be its beginning to exist. If a horse begins to exist, there's got to be a cause for that. If a building begins to exist, there's got to be a cause for that. Similarly if the universe begins to exist, there needs to be a cause for that. And in that respect the conditions for the causal principle do apply. Sorry, I'm out of time!

Question 2: Dr. Craig, what would you say to a Thomist, a follower of Thomas Aquinas, who says, “I have good arguments for God such as Aquinas' Five Ways that are based on indubitable metaphysical principles. It would be imprudent to advance a theistic argument that rests even partly on modern science since science can change and if some theistic argument loses face as science changes so does theism.?” Dr. Craig, what about this charge of imprudence from the Thomist.

Dr. Craig: Yes, I would say that Thomas Aquinas' own metaphysical principles are highly dubious and in doubt, and that therefore I have little confidence that his arguments are, as he claimed, demonstrations. Aquinas was familiar with the kalam cosmological argument. This is a very ancient argument, and he was aware of the Muslim medieval thinkers who championed it. And Aquinas said if the universe did began to exist, then clearly there had to be a cause of the beginning and of motion. But he thought you couldn’t prove with demonstrative certainty that the universe did begin to exist. (Of course, they had none of the modern empirical evidence.) But I am persuaded, and I think Aquinas would agree, that the philosophical arguments for the beginning were good probability arguments, even if they weren't mathematical demonstrations. So I think Aquinas simply raised the bar too high for what constitutes a good argument for God's existence. We don't need to have certainty or mathematical demonstrability. All we need to do is offer arguments that are logically valid, have true premises, and the premises are more plausibly true than not. And if that's right, then that's a good argument for the conclusion. And I think we've got such arguments today, and we shouldn't be preoccupied with Aquinas' concern for metaphysical or mathematical demonstration.

Dr. Carroll: One of the architects of the Big Bang model was George Lemaître, who's a Belgian physicist, mathematical physicist, MIT and Harvard graduate, and also a Jesuit priest. And later in life, in the 1950s, he was serving on a papal commission because the Pope at the time wanted to put forward a statement that said, “Look! The Big Bang! Excellent evidence for the existence of God.” And Lemaître stopped him from doing that. He said, “No, you can't get your peanut butter of theology mixed up with the chocolate of science. It does not actually taste great together because, who knows, someday some smartass will come up with a theory of the universe that is eternal and there isn't a Big Bang anymore.” Dr. Craig and I are on the same side. We think that Lemaître was wrong to make that kind of statement. We both believe that if you're going to be an intellectually honest theist you need to accord with the best data from the universe. And as we both agree, science isn't in the job of proving things with metaphysical certitude. It says that models get better and better at fitting the data. I think that works just as well for theism as it does for naturalism.

Question 3: Dr. Carroll, thanks for being here tonight. My question: at the end of your first speech you mentioned how, in a nutshell, the theist weasels his way out of predictions that we would make based on the evidence. My question is, though: coming at it, that seems to be assuming that naturalism is some sort of default position and that theism is just adding one step on. My question would be that: do you not find that naturalism is a sort of a bent, an angle, that you're coming at in that you allow nothing in that realm? Because, I mean granted I know that's what naturalism is, but that you're so shut off from the beginning that nothing could ever, ever, ever meet the evidence. Like Lawrence Krauss says, even if it was written in the sky, he would maybe consider it.

Dr. Carroll: That's right, yeah, I think this is a good point. Personally I think that there would be no problem for me to be persuaded out of naturalism. Alright, the roof is not falling on me. [laughter]. But I think it's a matter of what is the model that best fits the data. Again, five hundred years ago I would have been a committed theist because that was the best we could have done at the time. So I think that it is not an assumption. Some people try to sometimes say that science or naturalists start from an assumption of naturalism so they just simply won't consider alternatives. I'm very happy to consider alternatives. I think that if there were some phenomena in the world which really looked exactly like some religious tradition was saying should happen and was miraculous, was seemingly violating the laws of physics, what would scientists do in that situation? They would not say, “Oh, we're not allowed to think about this because we agreed yesterday at faculty tea that the world was a natural world.” I think they would try to come up with the best explanation. If the best explanation is not naturalism, then I would buy that. I will say that naturalism seems to me to be a priori simpler than theism because naturalism is the natural world, theism has the natural world and something else that I think is ill-defined. But I didn't actually use that. I think in a proper quantitative Bayesian probability analysis my prior for naturalism is higher than my prior for theism, but overwhelming evidence will always take care of that. I just don't think it's there.

Dr. Craig: Both the naturalist and the theist can be stubbornly committed to their worldviews and not allow contrary evidence to overthrow it. Naturalists are just as adept as theists at explaining away evidence that they find inconvenient—I mean, even to the extent of asserting that the universe popped into being out of nothing! So that's a charge that, I think, goes both ways. It would be possible to falsify theism, for example, by showing a contradiction in the concept of God, as some have sought to do – that there could not be, for example, an omniscient person or a timeless person or something of that sort. So that would be a means of falsifying theism if one could go that route.

Question 4: Dr. Craig, I'd like to understand whether the kalam argument (because I am struggling with this) . . . You're stating that the universe has a beginning, and then you evoke cause and effect, but cause and effect is a temporal concept. So if there is no time?

Dr. Craig: Is a what?

Question 4: It is a temporal concept; it makes sense if time exists. But before the universe there's no time, and considering that, why would you need a cause when the concept of cause and effect does not make really any sense?

Dr. Craig: Now, when you say that cause and effect are temporal concepts, what do you mean by that?

Question 4: Well, that you have a cause has always precedes the effect.

Dr. Craig: Ah, that's what I thought you might think! Yeah, I don't think that's at all true. Don't you think that causes and effects can be simultaneous?

Question 4: If they are then God and universe came into being at the same time, then why would you need God to explain the birth of the universe because they're born at the same time?

Dr. Craig: Okay, so you are willing to grant that causes and their effects can be simultaneous—right?

Question 4: Sure.

Dr. Craig: Okay, yes, I think that that's evident. So, what I would say is that God's creation of the universe is simultaneous with the universe’s coming into being. And what could be more obvious than that, when you think about it? When else could it come into being than at the moment when God created it? So my own studied view of God's relationship to time – which is a terribly interesting subject – is that God is timeless without creation and he is in time from the moment of creation on. The exercise of causal power by which God brings the universe into being marks God's entrance, as it were, into time in virtue of his causal relationship with the effect that he brings about. So I don't think causes do need to precede their effects temporally; they can be simultaneous with them. And in the case of creation I would say the universe comes into being at t=0, and that is the same moment at which God causes the universe to come into being.

Dr. Carroll: I'm pretty sure nobody cares about my opinion of God's atemporality, [laughter] so I will use this as an excuse to reiterate my objection to the language of coming into existence or popping into existence. That is not what the universe does even in models where the universe has a beginning, a first moment. Because the verb popping, the verb to pop, has a temporal connotation, is the word I'm looking for. It sounds as if you waited a while, and then, pop, there was the universe. But that's exactly wrong. The correct statement is that there are models that are complete and consistent in which there is a first moment of time. That is not the same as to say there was some process by which the universe popped into being. That's yet another difference between the universe and things inside the universe.

Question 5: Dr. Carroll, you said in prior talks that in the laws of physics that we observe today there's no room for free will. I'd like to know – granted that I consider you to be a rational, critical thinker – how do you reconcile critical thinking if at the same time you believe we don't have the free will to choose between true and false premises and valid and invalid logic. If those choices are made for you how is anything anybody says not immediately irrational?

Dr. Carroll: I know I'm in trouble when someone says “I consider you to be a rational thinker” before they ask me the question. [laughter] I'm not exactly sure what you read. I think if you read carefully, I believe in free will. I'm pro-free will. I think of free will as an emergent concept in a universe which at the fundamental level is completely mechanistic. I think there are laws of physics that do not involve what we call a libertarian approach to free will. I do not think that human beings supersede the laws of physics. I think that human beings are collections of elementary particles interacting according to the laws of physics. And if I were to, say, write down every single particle in my body and I had a Leplace's demon level of computation ability, I could predict what I would do. But I don't have any of that. I don't have the information, the micro-state of my quantum mechanical wave function, and therefore the vocabulary I use to describe myself is as human being making choices according to rational principles. And I think that it is absolutely legitimate in that framework to say free will is real. The most I ever wrote on free will was a short blog post called “Free will is as Real as Baseball.” Baseball is nowhere to be found in the fundamental laws of physics. It is a description at a collective level of things that happen in the macroscopic world. That doesn't mean that baseball doesn't exist, it just means that it's not there in the fundamental laws. I think that free will is exactly the same way. I think there is nothing wrong with using the language of people making choices, people being correct or incorrect.

Dr. Craig: Well, it seems to me that on your view, free will is ultimately illusory because everything we do is determined by what goes on on the fundamental level. And therefore, even though I have the illusion of free will, if I could really understand it, I would see that, in fact, I am determined to do everything that I do—including believing in determinism, which makes my choice to believe in determinism, it seems to me, irrational—or arational, I should say. I'm simply determined to believe in determinism. So I don't think it's helpful to talk about free will as an emergent reality when at a fundamental level you're affirming determinism. Then it's freedom only in name and not in reality, and in that case I think the questioner is right—it's very difficult to see how anything I do is rational. It's just like a tree growing a branch. It's all determined by mindless forces.

Question 6: Dr. Craig, it's an honor to speak with you tonight. I was going to ask Dr. Carroll something, but the line was so long, and I like short lines. So I came over here. [laughter] I'm not an atheist.

Dr. Craig: You could say, “If you were Dr. Carroll, what would you . . .” [laughter]

Question 6: There you go! I'm not an atheist, an agnostic, or a classical theist. I feel like there's a middle camp between the two of you that's ignored, and I'm more along the lines of a panentheist and along the lines of Spinoza and Einstein, and I think that that whole discussion gets lost here tonight. But the real question I want to get to and the important one, I think, is what Roger Penrose talks about with the necessity of conscious observation and the neglect of the Copenhagen interpretation of quantum mechanics among practicing physicists who seem to ignore the necessity of conscious observation creating quantum decoherence. And I wanted to find out what you thought about Roger Penrose and his ideas. Thank you.

Dr. Craig: Well, there are at least ten different physical interpretations of the equations of quantum mechanics, and they're all empirically equivalent, they're mathematically consistent, and no one knows which, if any, of them is the correct physical interpretation. I'm inclined to agree with philosophers of science who think of the traditional Copenhagen Interpretation as really just quite unintelligible. And I'm therefore more inclined to some sort of deterministic theory of quantum mechanics, like David Bohm's quantum mechanics. [laughter] Now I know that Sean Carroll holds to Everett's Many Worlds Interpretation; but that, again, seems to me to be just fantastic and has difficulty making sense out of the probabilities in quantum theory. But basically I don't think we need to decide. No one knows for sure what is the correct physical interpretation. It works, and that's what the practicing scientist is concerned with. But it remains a matter of deep debate as to how to understand it.

Dr. Carroll: Well, I'm glad we found another very important area of agreement between Dr. Craig and myself. The Copenhagen interpretation is basically nonsense. No thoughtful person still holds to it, and yet we teach it to all of our undergraduates—that's kind of a scandal. [laughter] And no one knows what the right answer is; I would also agree with that. I do hold to the Many Worlds interpretation. I think that you see it's kind of a consistent split that we have because people, when faced with the statement of the Many Worlds interpretation, it bothers them at an emotional level. I mean, where do you put all of those worlds? How do you fit them into the universe? But when you look at the level of the equations, it is the simplest possible interpretation of quantum mechanics. There are important questions that are still raised about it. I'm also writing papers about that. I think these are important issues to be addressed. But I judge simplicity by the number of ideas and concepts, not by the number of universes.

Question 7: Well, thank you for taking my question. Assume we had a model of the universe that corresponds to reality concerning all material things. Is it still logically possible to affirm the existence of a God?

Dr. Carroll: Yes. [laughter]

Dr. Craig: I didn't hear the final words – is it still possible, what?

Dr. Carroll: Yeah, maybe say the whole thing over again.

Question 7: Yeah, one more time; I'm sorry. Assume we had a model of the universe that corresponds to reality concerning all material things. Is it still logically possible to affirm the existence of a God.

Dr. Carroll: Good. So, yes.

Dr. Craig: Sure.

Dr. Carroll: You can. It's logically possible to assert a whole bunch of things. I mean, it's logically possible to assert that Isaac Newton had the right theory of gravity and Einstein didn't. It's logically possible to assert the steady state theory. You can probably find . . . I get emails from people who believe this. They're not very logical people, admittedly. But the way that science goes about deciding on theories is not on the basis of logic alone. You want your theories to be logical—I think that's the minimum requirement. But there are many, many logical theories. One of them is that we're all living in a computer simulation, there's a mad scientist out there. One of them is that none of you exist and I'm a brain in a vat. These are all logical possibilities. And about a similar level of plausibility in my mind is there's the logical possibility that we live in a world that always obeys the laws of physics and yet God created it and is hiding from us. So it is absolutely logically possible—I don't give it a lot of credence.

Dr. Craig: Yeah, logical possibility is simply too easy. And therefore, I think, you probably meant something, perhaps, different than just mere logical possibility. What we're talking about is, maybe, metaphysical possibility, or plausibility? Those are the real issues that, I think, are important because it would be pretty surprising if you could show that something like this would be logically impossible.

Question 8: Dr. Craig, you've been very skeptical about the idea of universes just popping into existence. Does cosmology have anything to say about where God might have come from? Or are we allowed to think that he could have popped into existence?

Dr. Craig: No, obviously cosmology would not have anything to say about where God came from because God is a non-physical, transcendent entity beyond the universe. That's why I used the word transcendent in that argument – this is something beyond the universe. The universe is defined as all contiguous physical reality. But I do want to take this opportunity to highlight for you a very significant difference between Sean and myself that is a philosophical difference that has tremendous impact upon this whole debate. And that has to do with this idea of “popping into existence.” If I'm not mistaken, Dr. Carroll holds to what is called a tenseless theory of time. That is to say, past, present, and future events are all equally real. Temporal becoming is merely a subjective illusion of human consciousness. There is nothing privileged about the present, ontologically speaking. I hold to quite a different view of time. I think that temporal becoming is a real and objective feature of the universe. The future doesn't in any sense exist; things really do come into being and go out of being. And that's why I use the language of popping into existence. Not because I illicitly presuppose time prior to the origin of the universe, but because I believe in a tensed theory of time which affirms the objectivity of temporal becoming. And on that view the beginning of the universe does not just tenselessly exist. The universe comes into being, and surely that requires a cause. Now this is not just an unfounded metaphysical assumption on my part. I've written two books on this in which I defend the tensed theory of time, giving arguments for it and answering objections against it, and then I attack the tenseless theory of time, giving arguments against it and answering arguments for it.[32] But this is a huge metaphysical assumption that underlies this debate and divides us.

Dr. Carroll: So I will confess, I don't know. This is not answering your question but it's a confession that as a scientist there is this enormous temptation that I am constantly resisting when I am in dialogue between science and theology which is that as theologians talk about the relationship between God and time, or God's status as necessary or anything like that, there's a big part of me that wants to say, “Why are you working so hard to extract yourself from these dilemmas when you can just say God doesn't exist?” It just sounds crazy. And then I realize I'm a cosmologist. And the same people could say the same thing about everything that I say. There's plenty of things that I say that sound crazy. So all I'm saying is that these are difficult, interesting questions, and it's very, very hard on the basis of thinking alone to get the right answers. That's why scientists have this huge advantage – we collect data.

Question 9: Dr. Carroll, you asserted that theism is unreasonable at least in part because the term God is poorly defined. So at the end of your first talk you said, “The solution to the problem that, from a theist's point of view, the world is not as we would predict, is easily solvable because of the flexibility of the terminology of God. So the theist can simply form any of hundreds of models of God that explain why the world is the way it is while maintaining the creative agency of God. And that's unreasonable.” But when you want to show the plausibility of an eternal universe you build a model and you showed seventeen of those and you said that all of them could work, but you don't think that any of them are right. They could be right but you don't think they're right. And that is reasonable. And I'm just wondering if you could clear up for me how that's consistent.

Dr. Carroll: Sure, that's fine. I think there is a difference in principle between the theist trying to use the idea of God to explain all these different aspects of the universe and the scientist developing many, many mutually inconsistent models and not know which one is right until they're developed. I think that with every one of these scientific models there is an expectation, indeed a demand, that when we understand the model perfectly it will make absolutely unambiguous “unwiggle-out-able-of” predictions about what the universe is like. I think this is not in principle possible in theism. I think – and different theists probably have different expectations about this – but I think that theists would not claim that once we understand God perfectly we can predict the mass of the Higgs Boson. But a physicist would claim that once we have the correct theory of everything we will be able to predict the mass of the Higgs Boson, and I think that's an absolutely crucial distinction.

Dr. Craig: I love this question because in the same way that the scientist develops models of the universe in order to understand it, the theologian does the same thing with respect to God – different models of God, understanding what he's like. And for Christians, the biblical data concerning God is underdeterminative. There's a great deal of latitude in developing your model or concept of God. For example, one of the classic questions is, “Is God timeless or is he infinite throughout all time?” And theologians develop different models of God and time, and then these models are tested. They're not tested by predictability; but they're tested by their coherence and by how well, for example, they would explain how an eternal being could create the universe, or how he could know, for example, tensed facts. I've written a great deal on this, and so you're quite right in saying it's analogous or parallel.

Question 10: Yeah, Dr Craig, you use the Borde-Guth-Vilenkin theory to justify an absolute beginning of the universe, and I was curious how you would address the point that was brought up about Guth probably holding that the universe in fact was eternal.

Dr. Craig: I haven’t spoken to him about it. I have spoken with Vilenkin. I think that they would agree that the theorem under this single stated condition shows that classical space-time did have to have a beginning, and Guth doesn't dispute that. He says that. Now when he holds up a little sign saying “I think the universe is probably eternal,” that's probably just reflecting a sort of personal preference or skepticism that maybe we'll find a quantum theory or something that will be a non-classical model that will restore the eternality of the universe. That could be his predisposition or his hope or hunch or something of that sort. But in terms of scientific evidence, there's no evidence at all that the universe is beginningless. As Vilenkin said, all of the evidence is on one side of the scale, that the universe began to exist, and there are no models of a beginningless universe that are successful. So I don't know exactly what he meant by that. But I think we do know that the implications of the theorem are that any model that falls under its single condition will have a beginning to classical space-time. And also I would say that models that don't fall under that condition usually always have other problems, as well. And then I argued that this quantum gravity regime, if there was such a thing that preceded the classical space-time regime, that marked the beginning of the universe, if the universe didn't begin at the classical space-time boundary.

Dr. Carroll: So I don't think it's the right thing to say that the Borde-Guth-Vilenkin theorem says that the classical universe had a beginning. The part of the universe that we can describe using classical space-time had a beginning just like this room had a beginning. But that says nothing at all about the universe as a whole. Alan Guth does not believe the universe is eternal because it's a hunch or personal preference. It's because he's a scientist and he's trying to develop models that fit the data. We have puzzles in cosmology. Given his knowledge of the models, he believes the best way forward, the most promising way forward, are the models in which the universe is eternal. He knows that there is a theorem saying if you obey the rules of quantum mechanics under the assumptions I gave the universe must be eternal. He knows the early universe had a low entropy and the best possible explanation we currently have for dynamically explaining that involves an eternal cosmology. This is exactly how scientists work all the time.

Question 11: Dr. Carroll, someone actually got to this question earlier, so just kind of a repeat and maybe you have some further comment on it. But suppose there was, you know, a naturalistic model for the universe and everything. What would your rebuttal be for someone who said there is yet a God that still works outside that model? Those might kind of be unfalsifiable but I'd still like a comment on that.

Dr. Carroll: Sure, I think that, again, it is absolutely conceivable. Let's go all the way to the extreme. I completely can conceive of a universe that was brought into existence by God who was omnipotent and so forth and for whatever reason God has chosen to be completely invisible and the universe runs by purely naturalistic principles. In that case I'm not saying that it is logically possible or even that it is illegitimate to conceive of that possibility. I just say it gets you nothing. By all of the conventional standards of scientific or even philosophical explanation, if I have two possible models that fit what we observe about the universe and one of them has less stuff, less ideas, it is more self-contained, is more rigid and well-defined than the other one, I'm going to prefer that one. I'm never going to say I completely rule the other one out. And this is not a completely hypothetical circumstance. Cosmology, quantum mechanics, quantum field theory, particle physics are full of many, many models that are in principle compatible with the data, but only if you take some parameters and push them out to where they shouldn't be, make them very, very small, make them very, very invisible. We put limits on our theories. We do not rule them out entirely. But when the limits, the constraints, becomes so strong the theories become uninteresting. We have a better way of moving forward. To me that's the situation with naturalism vs. theism.

Dr. Craig: The arguments that I've offered tonight are consistent with the universe’s being self-contained in the way that Dr. Carroll described. So that needn't be an issue of debate between us. But I don't see any reason to think that the universe is self-contained. I don't see any reason at all to think that the transcendent God doesn't act miraculously in the world. And there's simply no way that Dr. Carroll, as a scientist, could know that God never acts miraculously in the universe. So that the idea that the universe is causally closed or self-contained is really a naturalistic article of faith. It's a metaphysical presupposition, not an inference drawn on the basis of science.

Question 12: Dr. Craig, I really have enjoyed listening to both of you today. My question is . . .

Dr. Craig: Can you speak directly into the mic, please?

Question 12: Can you hear me now? [laughter]

Dr. Craig: Yes!

Question 12: Oftentimes when particularly believers or theists are talking about religion inside the arena of religion they are very, very comfortable, they know what they're talking about, but when they leave that arena and they go into places and talk about cosmology or they talk about medicine, it seems like that they are trying to make their religious beliefs fit into that sphere. So my question is this, and given that you said a few seconds ago God is not of this world or bigger than this world, why would he find it important to have a discussion about medicine, or find it important to have a discussion about the stars? Why would that be significant or relevant to him? Because, I mean, he is omnipotent.

Dr. Craig: As a systematic theologian, I am committed to having what I call a synoptic worldview, that is to say, a worldview that takes into account all of the data of human experience, not only what we learn from revealed truth in theology, but also from science, from history, from psychology, and the humanities. As a Christian I want to have a world and life view that makes sense of reality. And so I think that's why the Christian is vitally interested in these subjects and why I as a philosopher and theologian am terribly interested in these scientific theories about the origin of the universe, about the fundamental nature of physical reality, about the origin and evolution of biological complexity. I want to have a worldview that makes sense of the data of science. And I think that's one of the great things about the Christian worldview, that it does form a coherent worldview that answers our deepest questions and yet is consistent with what we learn from other sources of knowledge. So that's why I am committed to the project of developing this sort of synoptic world and life view.

Dr. Carroll: I hesitate when it comes to my job to tell believers what to think. And then I do it. So I'm not a believer but if I were a believer, if I were a theist, to me I would think that the fact of my theism would be absolutely central to everything I believed about the world in all of its aspects. I think that there's a modern tendency to try to shield religious belief and practice from the encroachment of scientific knowledge by saying, well, my religion has to do with my practice and my values but nothing to do with the physical world, the biological world, the scientific world. I think that that is actually a much less intellectually honest point of view than one like Dr. Craig's that engages with the full picture.

Question 13: Dr. Carroll, I'm going to try to phrase this without using terms I know you don't like—make this a how question instead of a why question. If our universe, our observable universe, had a first moment in time, and naturalism is true then it would seem that we need to explain that with some sort of eternal existing set of conditions, and they would have to be necessary and sufficient to produce the effect, which is our universe coming into being or having a first moment in time. So the difficulty seems to be that if we have an eternally existing set of causal conditions that are sufficient to produce the effect, why isn't the effect coeternal with the cause? It seems like that's very problematic, and it seems like the easiest explanation or the most plausible explanation to how the universe with a first moment in time could come about is to say that agent causation is where we need to look; that it was a personal agent endowed with freedom of the will who can spontaneously exercise causal powers to bring about a new effect. So if that's not true how is naturalism to provide an explanation for that case?

Dr. Carroll: Yeah, I think this is a good question in the sense that this is the kind of issue that tugs at our ability to make sense of these large cosmic questions given our everyday experience with reality. But I will give you a frustrating answer to it by denying your premise. I do not think that if the universe has a first moment in time that means there is any sort of eternal or preexisting conditions or rules or laws or anything like that. It simply means that our best and maybe the correct description of the cosmos is one that had a first moment in time. The question is, can that be self-contained in the sense that I'm using it, which is that if I write down the equations and the conditions and so forth that describe the universe with an earliest moment, am I done? Are there questions that I might have about that universe that cannot be answered by that formalism? And I think there is no obstacle whatsoever to coming up with such models. And so I would simply un-ask the question. I would say, no, there aren’t preexisting or eternal rules. There is the universe and the universe has a first moment and the universe obeys rules during those moments when the universe exists. During those moments when the universe does not exist, there are no moments, there is no time, there are no rules.

Dr. Craig: This question is very closely related to the argument that I gave against the quantum gravity regime's being past eternal. Namely, if the causal conditions that are present there are sufficient for the effect, then the effect would always have been there. But if they're not sufficient, then it becomes incomprehensible why the effect appeared just 13.7 billion years ago. And therefore it seems to me, I argued, that this regime would itself have to have a beginning and come into existence. The contrast with this is, when you have a libertarian agent with free will, he can exist from eternity and then freely decide to produce an effect in time without any antecedent determining conditions. And so in that sense theism provides, I think, an explanatorily superior account of the origin of the universe because it's got the explanatory power that is vested in an agent with libertarian free will.

Question 14: Yes, I'm really afraid I'm going to ask that stupid question, so please excuse me. But I don't really understand how you come up with the probability – or improbability, as you have been saying – of the universe, if it's a universe, when a universe has only begun once? How do you come up with that? Don't you have to have more scores to calculate such a probability?

Dr. Craig: Yeah, now, which argument is this relevant to, in your mind?

Question 14: Before you said there is a universe, and then you have been repeating a lot that it's highly improbable that it just popped out of nothing.

Dr. Craig: Oh, like the finely-tuned universe—okay. I don't think this is a good objection to fine-tuning because what we can do is simply conceptualize a multitude of universes by varying these constants and quantities and seeing what would result. So, for example, the physicist John Barrow gives the following illustration: he says, put a red dot on a piece of paper and let that be our universe. Now, alter slightly one of the constants or quantities. That will make a new universe. If it's life-permitting, make it a red dot. If it's life-prohibiting, make it a blue dot. Now, do it again, and do it again, and do it again, until your sheet of paper is filled with dots. And what you will come up with is a sea of blue with only a couple pin-points of red. It is in that sense that one can say that these finely-tuned universes are enormously improbable. You don't need the universes to actually exist in order to say they're improbable. All you need to do is have this, so to speak, logical space of possible universes described by these different quantities and constants in order to say that finely-tuned worlds are extremely rare.

Dr. Carroll: I think this is a great question because we do have this tendency to speak informally of probabilities and likelihoods and so forth. And even professional cosmologists do this when we talk about the early universe – “That seems improbable, unlikely, unnatural” is the usual term that we use. And sometimes we're just totally wrong about that. As so the example that Dr. Craig just gave about the blue dots and the red dots sadly almost never applies in cosmology because it assumes there is a discrete set of dots that we can color blue or red. Usually in cosmology there is a continuous spectrum of possibilities, and in that case it's much harder to even imagine assigning probabilities consistently. The example I gave, which was then sort of not talked about later, was the expansion rate of the early universe. There was a naïve argument that says it's very improbable. When you look more carefully you realize it's extremely probable. So there's not a definitive answer as to what the correct answer is, but I'm agreeing with your implication that we should be very, very careful when using words like that.