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Questions on the Arrow of Time

Dr. Craig tackles some fascinating questions on the nature of time, including a question from a young student on what God was doing before He created the universe!


Transcript Questions on the Arrow of Time

KEVIN HARRIS: Glad you are here for Reasonable Faith with Dr. William Lane Craig. Dr. Craig, we have some questions. Some of these questions that we’ve been dealing with on our podcast are in the popular culture. The movie Interstellar really deals with the A-Theory of Time versus the B-Theory of Time which we've talked about a lot. At any rate, we’ve got some questions here today that deal in those areas. This first question begins,

I’d like to thank you, Dr. Craig, for making an intellectually rigorous case for the Christian faith. It is a genuine pleasure to read your work. In particular, I found your work on the kalam cosmological argument fascinating. I am especially pleased with your efforts to engage with physicists in this area, being that I study physics and as a result of this you have helped spark an interest in philosophy in me as well. Anyway, my question concerns, unsurprisingly, the kalam cosmological argument. It can be succinctly put as “What sort of beginning is necessary in order for the kalam cosmological argument to work?” As you’ve explained many times before the kalam is rooted in an A-Theory of Time, or at least on a theory of time in which temporal becoming is objective.


Let me pause here and say this question gets a little technical, but Dr. Craig will break it down here in just a moment. He says,

As you’ve explained many times before the kalam is rooted in an A-Theory of Time, or at least on a theory of time in which temporal becoming is objective. The reason for this is that on such a theory “beginning to exist” is equivalent to “coming into being out of nothing.” We have a strong metaphysical intuition that this is metaphysically absurd. I think this makes sense. To sum up, my questions are: what sort of beginnings are equivalent to coming into being out of nothing? Are all beginnings equivalent in this way or only some? To give a particular example, do models of time with arrow of time reversal have a beginning with this equivalence? Finally, what physical arrow of time should we identify with the metaphysical arrow postulated by the A-Theory of Time?


DR. CRAIG: There is a lot to unpack there, Kevin. Let’s take the first question. What sort of beginning is equivalent to “coming into being out of nothing?” What I’m talking about when I say “come into being out of nothing” is something that comes into being without a cause of any sort. Aristotle distinguished various kinds of causes. For example, efficient causes which produce the being of the effect. Or material causes which is the stuff (the matter) out of which something is made. For example, Michelangelo is the efficient cause of the statue David, but the block of marble that he sculpted is the material cause for the David. When I speak of something’s coming into being from nothing, I mean something that comes into being utterly uncaused. It has no material or efficient cause or any other sort of cause at all. I think that already answers the second question: “are all beginnings equivalent in this way or only some?” Obviously, they are not all equivalent. Many things that come into being have causes. In particular, they have material causes. For example, when a person comes into existence at the moment of conception, the material causes would be the stuff out of which the egg and the sperm are made, and the sperm and the egg would be efficient causes that produce this new individual. When a carpenter makes a chair, the chair comes into being as a result of the causal activity of the carpenter. He is the efficient cause of the chair. The wood which he assembles into the chair is the material cause of the chair.

Obviously, not all beginnings are beginnings from nothing. In fact, actually I argue there is nothing that comes into being out of nothing. This is metaphysically absurd. There must be at least an efficient cause even when there is lacking a material cause.[1] This is the point that it is metaphysically absurd to say that something comes into being without a cause of any sort. But in our experience, normally the things that begin to exist that we have interaction with have both efficient causes and material causes.

Now, “to give a particular example,” Andrew writes, “do models with arrow of time reversal have a beginning with this equivalence?” What is he talking about here? He is talking about a model of the universe like the one defended by Sean Carroll in the debate we had at New Orleans Baptist Seminary last year on the evidence of cosmology for the existence of God.[2] Carroll proposes a model in which the so-called arrow of time is running in one direction toward our future (what we call the later-than direction) but if you go back far enough into the past he says the arrow of time reverses and starts to go in the other direction. If you take that literally and seriously as a piece of serious metaphysics then this would not be an example of an eternal universe because that mirror universe on the other side of the time reversal point is in no sense our past. That is a different universe with a different arrow of time. It is in no sense an earlier stage of our universe. So if you take that kind of model with metaphysical seriousness it would postulate a beginning of two universes without any sort of physical, material cause for such a thing because one of those universes is in no sense the cause of the other. They are unrelated temporally. The one is not in the future of the other, and the other is not in the past of the one – they are two different universes that share a common origin point. The question would be: what caused those universes to come into existence?

In fact, I don’t take those models featuring a time reversal metaphysically seriously.

KEVIN HARRIS: Where did that come from? Who came up with that?

DR. CRAIG: Where it comes from is identifying the arrow of time with the direction in which entropy is increasing. It is treating time as though it were something that is physically determinable. So the direction in which entropy is increasing (that is, thermodynamic disorder) is the future.

KEVIN HARRIS: Would it look like this? I have two pens end-to-end and . . .

DR. CRAIG: The points are in opposite directions.

KEVIN HARRIS: Yeah, and they mirror each other in a sense. We are interested in that area where they reverse.

DR. CRAIG: Right. And I would say that you have exactly what you have – you have two pens there if you take this as a metaphysically serious model of reality. But that assumes that the arrow of time is to be identified with the arrow of entropy increase because on this side of that mirror surface entropy is increasing toward our future but on the other side of that boundary entropy is increasing in the other direction. That is why the claim is that this is a reversal of the arrow of time. Entropy increases in both directions away from that common boundary. So the claim is time reverses.

I think that is metaphysically absurd. Entropy increase is not to be identified with the direction of time. It is merely a physical measure of time. But time is a metaphysical reality that can exist quite independently of any clocks or physical measures of it. I think this is very easy to see. Just imagine God existing alone without creation and he is counting down to the moment of creation. 3 . . . 2 . . . 1 . . . Let there be light! Clearly, the succession of mental events in God’s mind counting down is sufficient to create a temporal series wholly in the absence of any physical universe or natural laws of any sort. So at the very most, the direction of entropy increase can serve as a measure of time but it is not time itself.[3]

In these so-called “time-reverse models” what you’ve really got going on, I think, is a universe in which entropy is decreasing from eternity past for infinite time until it gets to this neck in the hourglass and then entropy begins to increase on the other side of that. That is thermodynamically impossible. It contradicts the second law of thermodynamics to think that you could have a universe which (in defiance of the second law of thermodynamics) is, for infinite past time, declining in entropy until this point where entropy begins to increase again. I would say, in answer to his question, that this is not an example of a true reversal of time. It is merely a reversal of entropy increase, and as such it is physically impossible. These models are physically ruled out.

Finally, he says “What physical arrow of time should we identify with the metaphysical arrow postulated by the A-Theory of Time?” If there is this metaphysical time that is beyond physics, then what physical arrow ought we identify with it? What I’ve argued in my work is that the cosmic time that measures the duration of the universe from its beginning is a plausible measure of God’s metaphysical time. The cosmic time that measures the duration of the universe is observer-independent, it is not relativistic in the sense of being bound to any particular reference frames, it is the same for any observer in the universe, and this is the proper time of the existence of the universe. It is how long the universe has existed from the moment of its creation. As such, I think the universe serves as a sort of clock for God. In fact, quite literally the universe is God’s clock. It provides the closest physical measure of God’s metaphysical time. It is how much time has elapsed since the moment at which God created the universe. I think it is the physical time that is most plausibly to be identified as the measure of God’s time.

KEVIN HARRIS: One more question today, Bill. I think this is great. It says, “Dear Dr. Craig, my thirteen year old daughter asked me, ‘What was God doing before he created the universe?’ I did not and don’t know how to answer that.”

A lot of people can relate. Somebody will ask me that from time to time, and I still don’t know quite where to start. Sometimes it is kind of hard to know where to start on that. Eventually I will get it out, but it just takes me about thirty minutes. [laughter]

DR. CRAIG: I imagine this is hard to help a child grasp based upon the difficulty I found adults grasping this. But I think he should tell her that time began at the moment of creation. Between us, we don’t know that that is true. God could have been creating angelic realms prior to his creation of the universe. Or he could have been counting down to creation in the way I imagined. But since we have no reason to think that God was doing anything of that sort prior to creation, for simplicity's sake it is easiest to just say time began at the moment of creation. So there really isn’t any moment before creation. That is purely a product of your imagination. God existing alone without the universe was enjoying the fullness of the love relationships between the three persons of the Trinity – the Father, the Son, and the Holy Spirit – in a changeless, perfect state of happiness and interpersonal transparency between the three persons of the Trinity. That would be the way I would answer the question.[4]