Big Bang CosmologyWilliam Lane Craig
This is the submitted version of "Big Bang Cosmology" to be published in final form in the Encyclopedia of Philosophy of Religion (link to Wiley.com to come). Used by permission.
In Aristotelian physics, prime matter, of which all physical substances are composed, is, like God Himself, eternal and uncreated. It underlies the eternal process of generation and corruption undergone by things in the sub-lunary realm. In its large-scale structure the universe has remained unchanged from all eternity.
Even with the demise of Aristotelian physics in the scientific revolution completed by Isaac Newton, the assumption of a static universe remained unchallenged. Although Newton himself believed that God had created the world, the universe described by his physics was to all appearances eternal. To be sure, there were already clues in pre-relativistic physics–like Olbers’s Paradox or the impending heat death of the universe–, that there was something wrong with the prevailing assumption of an eternal, static cosmos. But these niggling worries could not overturn what was everywhere taken for granted: that the universe as a whole has existed unchanged forever.
General Relativistic Cosmology
Tremors of the impending earthquake which would demolish the old cosmology were first felt in 1917, when Albert Einstein made a cosmological application of his newly discovered gravitational theory, the General Theory of Relativity (hereafter, GR). Einstein assumed that the universe is homogeneous and isotropic and that it exists in a steady state, with a constant mean mass density and a constant curvature of space. To his chagrin, however, he found that GR would not permit such a model of the universe unless he introduced into his gravitational field equations a certain “fudge factor” in order to counterbalance the gravitational effect of matter and so ensure a static universe. Einstein’s static universe was balanced on a razor’s edge, however, and the least perturbation–even the transport of matter from one part of the universe to another–would cause the universe either to implode or to expand. By taking this feature of Einstein’s model seriously, the Russian mathematician Alexander Friedman and the Belgian astronomer Georges Lemaître were able to formulate independently in the 1920s solutions to the field equations which predicted an expanding universe.
In 1929 the American astronomer Edwin Hubble’s measurements of the red-shift in the optical spectra of light from distant galaxies, which was taken to indicate a universal recessional motion of the light sources in the line of sight, provided a dramatic verification of the Friedman-Lemaître model. Incredibly, what Hubble had discovered was the isotropic expansion of the universe predicted by Friedman and Lemaître on the basis of Einstein’s GR. It was a veritable turning point in the history of science. “Of all the great predictions that science has ever made over the centuries,” exclaims John Wheeler, “was there ever one greater than this, to predict, and predict correctly, and predict against all expectation a phenomenon so fantastic as the expansion of the universe?”
The Standard Big Bang Model
According to the Friedman-Lemaître model, as time proceeds, the distances separating galactic masses become greater. It is important to understand that as a GR-based theory, the model does not describe the expansion of the material content of the universe into a pre-existing, empty, Newtonian space, but rather the expansion of space itself. The ideal particles of the cosmological fluid constituted by the matter and energy of the universe are conceived to be at rest with respect to space but to recede progressively from one another as space itself expands or stretches, just as buttons glued to the surface of a balloon would recede from one another as the balloon inflates. As the universe expands, it becomes less and less dense. This has the astonishing implication that as one reverses the expansion and extrapolates back in time, the universe becomes progressively denser until one arrives at a state of infinite density at some point in the finite past. This state represents a singularity at which space-time curvature, along with temperature, pressure, and density, becomes infinite. It therefore constitutes an edge or boundary to space-time itself. The term “Big Bang,” originally a derisive expression coined by Fred Hoyle to characterize the beginning of the universe predicted by the Friedman-Lemaître model, is thus potentially misleading, since the expansion cannot be visualized from the outside (there being no “outside,” just as there is no “before” with respect to the Big Bang).
The standard Big Bang model, as the Friedman-Lemaître model came to be called, thus describes a universe which is not eternal in the past, but which came into being a finite time ago. Moreover, the origin it posits is an absolute origin ex nihilo. For not only all matter and energy, but space and time themselves come into being at the initial cosmological singularity. As John Barrow and Frank Tipler emphasize, “At this singularity, space and time came into existence; literally nothing existed before the singularity, so, if the Universe originated at such a singularity, we would truly have a creation ex nihilo.” On the standard model the universe originates ex nihilo in the sense that at the initial singularity it is true that There is no earlier space-time point or it is false that Something existed prior to the singularity.
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. These beginningless models have been repeatedly shown either to be physically untenable or to imply the very beginning of the universe which they sought to avoid. 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. In 2012 Vilenkin showed that cosmogonic models which do not fall under this single condition fail on other grounds to avert the beginning of the universe. Vilenkin concluded, “There are no models at this time that provide a satisfactory model for a universe without a beginning.” Vilenkin has since strengthened that conclusion: “We have no viable models of an eternal universe. The BGV theorem gives reason to believe that such models simply cannot be constructed.”
The BGV theorem proves that classical spacetime, 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.
For consider: If there is such a non-classical region, then it is not past eternal in the classical sense. But neither does it seem to exist literally timelessly, akin to the way in which philosophers consider abstract objects to be timeless or theologians take God to be timeless. For 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. In any case, 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.
Hence, the quantum gravity era would itself have to have had a beginning in order to explain why it transitioned just some 14 billion years ago into classical time and space. Hence, whether at the boundary or at the quantum gravity regime, the universe began to exist.
Creation ex nihilo
Paul Davies raises the inevitable question:
What caused the big bang?’ . . . One might consider some supernatural force, some agency beyond space and time as being responsible for the big bang, or one might prefer to regard the big bang as an event without a cause. It seems to me that we don’t have too much choice. Either . . . something outside of the physical world . . . or . . . an event without a cause.
It might seem metaphysically absurd that the universe should come into being without a cause and therefore a supernatural agency is to be preferred. But some scientists have contended that quantum physics can explain the origin of the universe from nothing.
Unfortunately, some of these scientists have an outrageously naïve grasp of language. The word “nothing” is a term of universal negation. It means “not anything.” But because the word “nothing” is grammatically a pronoun, we can use it as the subject or direct object of a sentence. By taking “nothing,” not as a term of universal negation, but as a word referring to something, we can generate all sorts of funny situations. If you say, “I had nothing for lunch today,” the wiseacre replies, “Really? How did it taste?” The use of such words of negation like “nothing,” “nobody,” and “no one” as singular terms referring to something is a joke.
How astonishing, then, to find that some physicists, whose mother tongue is English, have used “nothing” precisely as a singular term of reference. Lawrence Krauss, for example, has told us with a straight face that:
“There are a variety of forms of nothing, [and] they all have physical definitions.”
“The laws of quantum mechanics tell us that nothing is unstable.”
“70% of the dominant stuff in the universe is nothing.”
“There’s nothing there, but it has energy.”
“Nothing weighs something.”
“Nothing is almost everything.”
All of these claims take the word “nothing” to be a singular term referring to something, for example, the quantum vacuum or quantum fields. These are physical realities and therefore clearly something. To call these realities nothing is at best misleading, guaranteed to confuse laypeople, and at worst a deliberate misrepresentation of science.
Coming into Being from Nothing
Vilenkin has a different proposal as to how the universe could come into being from literally nothing. He explains,
Modern physics can describe the emergence of the universe as a physical process that does not require a cause. Nothing can be created from nothing, says Lucretius, if only because the conservation of energy makes it impossible to create nothing [sic; something?] from nothing. . . .
There is a loophole in this reasoning. The energy of the gravitational field is negative; it is conceivable that this negative energy could compensate for the positive energy of matter, making the total energy of the cosmos equal to zero....
If all the conserved numbers of a closed universe are equal to zero, then there is nothing to prevent such a universe from being spontaneously created out of nothing. And according to quantum mechanics, any process which is not strictly forbidden by the conservation laws will happen with some probability. . . .
What causes the universe to pop out of nothing? No cause is needed.
Grant the supposition that the positive energy associated with matter is exactly counter-balanced by the negative energy associated with gravity, so that on balance the energy is zero. Vilenkin’s key move comes with the claim that in such a case “there is nothing to prevent such a universe from being spontaneously created out of nothing.” Now this claim is a triviality. Necessarily, if there is nothing, then there is nothing to prevent the universe from coming into being. By the same token, if there is nothing, then there is nothing to permit the universe to come into being. If there were anything to prevent or permit the universe’s coming into being, then there would be something, not nothing. If there is nothing, then there is nothing, period.
The absence of anything to prevent the universe’s coming into being does not imply the metaphysical possibility of the universe’s coming into being from nothing. To illustrate, if there were nothing, then there would be nothing to prevent God’s coming into being without a cause, but that does not entail that such a thing is metaphysically possible. It is metaphysically impossible for God to come into being without a cause, even if there were nothing to prevent it because nothing existed.
Vilenkin, however, infers that “no cause is needed” for the universe’s coming into being because the conservation laws would not prevent it and “according to quantum mechanics, any process which is not strictly forbidden by the conservation laws will happen.” Grant that if there were nothing, then both the conservation laws and quantum physical laws would still hold. Why think that, given the laws of quantum mechanics, anything not strictly forbidden by the conservation laws will happen? The conservation laws do not strictly forbid God’s sending everyone to heaven, but that hardly gives grounds for optimism. Neither do they strictly forbid His sending everyone to hell, in which case both outcomes will occur, which is logically impossible, as they are logically contrary universal generalizations. The point can be made non-theologically as well: the conservation laws do not strictly forbid something’s coming into existence, but neither do they forbid nothing’s coming into existence, but both cannot happen. It is logically absurd to think that because something is not forbidden by the conservation laws, it will therefore happen.
Finally, Vilenkin’s inference that because the positive and negative energy in the universe sum to zero, therefore no cause of the universe’s coming into being is needed is hard to take seriously. This is like saying that if one’s debts balance one’s assets, then one’s net worth is zero, and so there is no cause of one’s financial situation! Christopher Isham rightly points out that there still needs to be “ontic seeding” to create the positive and negative energy in the first place, even if on balance its sum is naught.
Given the metaphysical impossibility of the universe’s coming into being from nothing, belief in a supernatural Creator is eminently reasonable. At the very least we can say confidently that the person who believes in the doctrine of creatio ex nihilo will not find himself contradicted by the empirical evidence of Big Bang cosmology but on the contrary fully in accord with it.
John Wheeler, “Beyond the Hole,” in Some Strangeness in the Proportion, ed. Harry Woolf (Reading, Mass.: Addison-Wesley, 1980), 354.
John Barrow and Frank Tipler, The Anthropic Cosmological Principle (Oxford: Clarendon Press, 1986), 442.
 Principally the addition of an early inflationary era and an accelerating expansion.
 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), 101-201; idem, “On Non-Singular Spacetimes and the Beginning of the Universe,” in Scientific Approaches to the Philosophy of Religion, ed. Yujin Nagasawa (London: Macmillan, 2012), 95-142.
 Alexander Vilenkin, “Did the universe have a beginning?” http://www.youtube.com/watch?v=NXCQelhKJ7A. Cf. Audrey Mithani and Alexander Vilenkin, “Did the universe have a beginning?” arXiv:1204.4658v1 [hep-th] 20 Apr 2012, p. 1, where they state: “None of these scenarios can actually be past-eternal.”
 Alexander Vilenkin, “The Beginning of the Universe,” Inference: International Review of Science 1/4 (Oct. 23, 2015), http://inference-review.com/article/the-beginning-of-the-universe.
 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. Isham, “Quantum Theories of the Creation of the Universe,” in Quantum Cosmology and the Laws of Nature, second ed., ed. Robert Russell et al. [Vatican City State: Vatican Observatory, 1996], 75). This feature of quantum cosmogony is very problematic, since diachronic emergence of time is obviously incoherent. But how can one make sense of a synchronic emergence of time as a supervenient reality in the context of cosmogony? The most sensible thing to say seems to be that the Euclidian description is a lower-level description of classical spacetime prior to the Planck time. 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.
 Anthony Aguirre and John Kehayias, “Quantum Instability of the Emergent Universe,” arXiv:1306.3232v2 [hep-th] 19 Nov 2013.
 Paul Davies, “The Birth of the Cosmos,” in God, Cosmos, Nature and Creativity, ed. Jill Gready (Edinburgh: Scottish Academic Press, 1995), 8-9.
 All of these quotations are from Krauss’s videos posted on YouTube, including his Asimov Memorial “Nothing Debate” 1:20:25; American Atheists lecture 26:23; Richard Fidler interview; discussion with Richard Dawkins at Arizona State Origins Project 37min.; and Stockholm lecture 46:37.
 Vilenkin, “The Beginning of the Universe.”
 Christopher Isham, “Quantum Cosmology and the Origin of the Universe,” lecture presented at the conference “Cosmos and Creation,” Cambridge University, 14 July 1994.