Thoughts on the Carroll-Craig Debate

Recently, Sean Carroll (cosmologist and atheist, whom I have met a couple times at physics events) and St. William Lane Craig (philosopher and Christian apologist) had a debate about this topic:

"God and Cosmology: The Existence of God in Light of Contemporary Cosmology."

(Warning: when the debate transcript says something like 10500, it really means $10^{500}$.  Apparently whoever (or whatever) transcribed it doesn't understand scientific notation.)

Several readers have asked me to comment on this debate, and I plan to write more than one post doing so.

Let me just say first that I am not particularly interested in the question of who "won" this debate (between two people whom I both respect).  The existence of God does not, of course, depend on any particular person's ability to effectively argue for (or against) him.  I'd rather just make some opportunistic comments based on what the participants said.  What limited comments I have about the debate as a debate I will try to confine to this post.

William Lane Craig is a skilled debater who has done his best to keep abreast of Modern Cosmology.  This is commendable, but it was inevitable that his depth of knowledge in Cosmology was not as great as Carroll, who works on this subject professionally.  And often it showed.  That is why Craig had to rely mainly on a lot of quotes from famous physicists such as Alex Vilenkin—and sometimes this backfired, as in the case of Alan Guth, who apparently believes that the universe is eternal.

Since the topic was limited to Cosmology, Craig was unable to bring in any other types of evidence for the existence of God, besides those related to the Cosmological or Fine-Tuning Arguments.  In other debates, Craig has focused more on the evidence for miracles (such as the Resurrection of Jesus), which personally for me is much stronger evidence for the existence of God than anything coming from Cosmology.  For me, if Modern Cosmology is sufficient to get people to even wonder, "Is there maybe somebody who did that?" that's enough to start with—so long as it makes them curious enough to start exploring other lines of evidence, based on History or personal experience.

In other words, it's not necessary for Cosmology by itself to get people to a belief in God.   What matters is the cumulative case from Cosmology plus everything else.  If there are puzzling things such as fine-tuning which might be explained by God, and might have a different explanation (e.g. the multiverse), to me the most natural response seems to be to keep an open mind about all possible explanations.  But that would imply, that at least the existence of God is not absurdly unlikely (so far as Cosmology is concerned).  And if a person gets that far, then when they examine historical evidence or religious experiences, at least they won't do so with a giant presupposition in favor of Naturalism that requires them to explain away practically anything.

Assuming they are rationally consistent, that is.  Most people, if you try to argue for some proposition X that they don't want to believe in, will ask only whether the argument is so compelling as to force them to believe in it.  If not—if they can think of any possible way to defeat or evade the argument—they will act as though the argument has no force at all.  They are like the fearsome Barghest of legend, a monstrous black dog which can only be killed with a single blow.  If you do not strike hard enough to kill, then all of the damage is transferred from it to you.  (At least, that's how it works in Pendragon, the Arthurian Roleplaying System.)  With such people, if they can find any clever loophole in your argument—even if it involves totally speculative new physics—the next day they will say that the argument was refuted and provides no evidence for X at all.  This makes it impossible to make a cumulative case argument.

Anyways, I thought Craig did a pretty good job of sticking to the restricted topic of Cosmology.  Carroll somewhat less so, when he said:

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.

[As an aside, there's something a bit funny here.  Carroll thinks that God should have provided us with some scientific information in the Bible.  The most useful scientific fact he can think of is the importance of good hygiene.  And it is a fact that the most famously boring book of the Bible, the book of Leviticus, is chalk full of hygiene rules about cleanliness (embedded among other religious rituals).  Fairly decent rules too, given the 2nd millennium BC context.  No germ theory of disease, I admit.  But highly practical nonetheless.  Now, I'm not a religious fundamentalist who thinks that the Bible is a Science textbook.  Nor am I an antireligious fundamentalist who thinks it ought to have been a Science textbook.  But I do think it is ironic that the particular thing Carroll demands is, in some sense, present in the least-loved book of the Bible!  Carroll continues:]

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.

[Huh?  Theism is the belief that God exists.  It does not commit one to any particular view about the soul's relationship to the body.  The fact that our personalities are encoded in our brains is logically independent to the question of whether God exists.  Particular religious traditions might have particular views about the soul, but that's not what we're talking about here.]

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.

This, however, strayed from the parameters of the debate topic.  Whatever the merits of the Argument from Evil, it cannot be said that Evil is a discovery of Science.   It has nothing to do with Cosmology.  It is not a discovery of contemporary physics that there is random suffering, and that the universe isn't fair.  (What would a scientific theory of "Justice" even look like?)  Granted, the Argument from Evil is relevant to the cumulative case concerning God's existence (some of my own thoughts about that are here.)  But then Craig would also be entitled to throw in historical data about Jesus and anything else that might be relevant to the inquiry.

Naturally Craig called him on it:

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.  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.

Craig, being a skilled debater, makes sure to frame the debate question to be one which is comparatively easy to show.  According to Craig's framing, he only needs to show that Theism is more plausible given e.g. our current understanding of the Big Bang Model, compared to if we didn't know these facts.  This is a fairly modest ambition.  It certainly seems more likely now that the universe has a beginning than it would have seemed to a materialist living 500 years ago.  So if the beginning of the universe is a relevant datum for the existence of God, then cosmology provides some positive evidence.   (On the other hand, if it isn't relevant, why are we even discussing whether there was a beginning?)

At times, Carroll even seems to assume that if Craig doesn't believe in Theism for scientific reasons, his views can't be based on evidence at all:

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 was unable to track this quote down, but having some knowledge of Craig's views in other contexts, I highly doubt that Craig was referring to some inarticulate leap of faith not grounded in any good evidence at all.  I imagine—especially since he referred to Christianity—that he was thinking about some type of historical evidence that has to do with, say, Jesus or something.  Maybe something related to the fact that he did lots of miracles, and rose from the dead, and was seen by many eyewitnesses, who themselves did several miracles, leaving a band of committed followers to this day, who sometimes do miracles in his name, including naturalistically inexplicable healings with solid medical documentation—have I made my point yet?]

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.

These subjective warm fuzzy feelings are nice and all, but it is scientism to think that they are the only thing left after we remove stuff like Cosmology.  For example, History is also an evidence-driven field, and it has plenty of data supporting things like miracles.  Carroll made a joke about taking into account new evidence if the roof were to fall on his head, but perhaps if Carroll does some historical investigation, there might be more subtle ways for God to make a point.

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.

I always find it interesting, that when you poke a person who makes grand claims about the philosophical implications of Science, sooner or later they end up telling one of these historical just-so stories about how things used to be completely different before Science came along.

You know the drill.  Once upon a time, people used to use God to explain everything, and then one or two things got explained by Science, and then some more things got explained by Science, and now there are only two or three gaps in our knowledge, which stubborn religious people cling to in order to justify Theism, but we all know (by linear interpolation, I guess) that Science will eventually explain these things too, which is just as good as if it already had done so.  (This is closely related to the infamous "God-of-the-Gaps"™ strawman, about which I will have more to say later.)

In order to tell this story properly, Carroll needs to insist that he would have been a pious religious person 500 years ago.  But I'm not at all sure this is true.  He didn't really present any arguments for Theism based on the Science of 500 years ago, let alone one which is refuted by our present day understanding.  All he did was say why he doesn't believe in Craig's arguments (which, whether you believe them or not, are based on Modern Science, and couldn't even have been made 100 years ago, let alone 500).   All that stuff about random suffering, and multiple religions, and weird stuff in the Bible, and that the universe is really big while Earth is really small, and that tiredness and drugs and physiological secretions influence the mind, was just as evident to smart people 500 years ago as it is now.

No matter how much lecturing you hear about how Science works because we can always correct our theories with new data, they seldom bother to check these supposedly historical narratives with any actual data.  When you do, you usually find the story is far more complicated.

In the paragraph quoted above, the only actual Scientific revolution mentioned is that due to Darwin.  The rest is left suspiciously vague (for example, I'm not sure from the description what exactly is supposed to have happened 200 years ago, that made Theism "no longer the best theory").

In fact, for the most part it's pretty unclear what the implications of scientific theories are for or against Theism.  Take for example Maxwell's equations.  One could try to argue that: 1) lots of stuff is described by equations, 2) Maxwell's equations mean that one more thing is described by equations, 3) therefore probably everything is described by equations, 4) God is not an equation, therefore 5) God does not exist, but this seems like a rather weak argument from induction, not something that "undermines theism pretty devastatingly".  It's not like anyone in the 1500's was saying that magnetism couldn't be understood except as a special miracle of God, and then Maxwell showed they were all wrong.

There's a reason, therefore, why people fixate on Darwin.  Darwin's theory of Evolution really did remove one possible argument for the existence of God: namely that an act of special creation was necessary to explain the existence of each individual species, and its close adaptation to its environment.

Of course, the removal of a particular argument for God's existence isn't the same as disproving Theism.   In particular, this argument for the existence of God was not by any means the historically most important one.  In fact, you only really see people shortly before Darwin (like Paley) making this argument.   In medieval times, people used to think that life-forms like flies would spontaneously generate in rotting meat.  Obviously, they wouldn't have thought much of Paley's view that each species needed to be created individually by God.  It was only with the increase of scientific understanding that this "gap" in our understanding was noticed.  Thus, to say that filling this gap refutes the ideas of the medievals (who didn't even know there was a gap here to be filled) is absurd.

What history actually shows, is not a monotonic replacement of Theology by Science, but a complicated back-and-forth process where new Science produces some new arguments for Theism (Paley, fine-tuning), discredits others (Paley, the need for a Prime Mover rotating the outer heavenly sphere), and so on.  But that's too complicated to reduce to a tidy, one-sided historical meta-narrative, so lots of people just make up a story about Science and Religion being enemies, and stuff everything into that mold.

All of this was just picking around the edges.  In the next post, I will talk more about the so-called God-of-the-Gaps™-fallacy, which both Carroll and Craig pay their obligatory disrespects to.  Then I'll try to get to the actual substantive questions about whether the universe had a beginning, according to Modern Science.  And whether that has any theological implications.  And fine-tuning.  And about Carroll's arguments that Theism is ill-defined and false.   Things that relate to the actual substance of the Carroll-Craig debate.  That sounds like a plan.

I am a postdoctoral researcher studying quantum gravity and black hole thermodynamics at UC Santa Barbara. Before that, I studied the Great Books program at St. John's college Santa Fe, and got my Ph.D. in physics from U Maryland.
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9 Responses to Thoughts on the Carroll-Craig Debate

1. Jack Spell says:

Well done, Sir.

2. T.Yhip says:

Thank you St Aron (Wall) for this follow up commentary. You and the likes of St William (Craig) do a great service to theism by logical and reasonable discourse. Coming from respectable physicists as you are, the theistic arguments carry weight and credibility. I look forward to your Plan outlined in the closing paragraph, particularly (a) does the second law of thermodynamics support a finite time in the past? (b) does quantum physics provide a good argument against materialism, and (c) Boltzmann Brains.

3. Kevin V says:

Yes, keep up the great service of analyzing the Craig-Carroll debate (particularly the scientific issues) for those of us who aren't Reformed Epistemologists 7 days a week.

4. Aron Wall says:

5. Jack Spell says:

St. Aron,

If it's not too much trouble, I was wondering if you might do me the honor of giving my letter to Dr. Carroll a critique. The reason that I ask is because, after posting it to his blog, several folks took notice and one in particular asked if he could publish it on his own website. Since I do my best to spread the Truth, I want to avoid the spread of any and all false claims. Thus, if you would be so kind as to lend your expertise in these matters I would owe you a debt of gratitude. I understand that in all likelihood you have a lot on your plate; so if it takes you awhile (or if you cannot find the time at all) I'll understand. Thanks and God bless.

Dr. Carroll,

I want to thank you again for all of the thought-provoking material you produced over the two days of the conference. I say “again” because I was fortunate enough to have the opportunity to thank you in person on Saturday after the conference had concluded. You might remember me--I was the really conspicuously good-looking guy who, during the Q & A on Friday and Saturday, asked you about (1) an eternal set of necessary and sufficient mechanical conditions producing a universe containing a first moment of time, and (2) the specifics of Alan Guth’s affirmation of the probable eternality of the universe, respectively. Alright, alright, I may have exaggerated the part about my good-looks a little, but in all seriousness you might possibly remember the questions. Nevertheless, it was a real privilege to shake your hand and I thoroughly enjoyed hearing your take on these interesting issues. Having familiarized myself with some of your published work, I’m well aware that you are skilled writer. But having never seen you lecture or debate, I had no idea that you would prove to be such a wonderful public speaker and formidable debater. I look forward to more of it in the future.

While I’m sure that you have entirely too much on your plate to respond to every reply on your blog, nevertheless I would owe you a great debt of gratitude if you’re able to somehow find the time to respond to this one; that is, provided it’s substantive enough to warrant a response.

In light of a recent post, you seemed to have cleared up what led to a persistent confusion for some during the debate: namely, your maintaining that a universe with a “first moment of time” isn’t necessarily one that “begins to exist.” It seems to me that you are able to consistently hold to this view because you ascribe to a tenseless or, B-Theory, of time. That is what I suspected. So if I understand you correctly, are you saying that a universe with a first moment of time doesn’t “begin to exist” because, on the B-Theory, the entire universe exists *timelessly* for all eternity as a static, 4-dimensional block? If so, is it not perfectly legitimate to inquire as to what determines that this particular statically-existing universe obtains, rather than some other one or none at all? Also, would you agree that the A-Theory of time is the much more common sense view?

Moreover, there appears to be a few points in your post-debate reflections that might be cause for reflection. First, regarding your denial of both the premises in the Kalam Cosmological Argument (KCA), you said,

“My attitude toward the above two premises is that (2) is completely uncertain, while the “obvious” one (1) is flat-out false. Or not even false, as I put it, because the notion of a “cause” isn’t part of an appropriate vocabulary to use for discussing fundamental physics.”

As Dr. Craig (WLC) has repeatedly emphasized, he does not claim anything near “certainty” for the truth of these premises. Rather, he merely defends the notion that they are more plausibly true than their negations; the greater the degree to which they are more plausibly true than not, the stronger the argument becomes. So while I agree that we don’t have certainty with respect to the truth of premise (2), I do believe that we have good reason to believe that it is much more plausibly true than not; which is what a good argument entails.

With respect to the notion of a “cause,” I would have to disagree with your thinking that this isn’t the appropriate vocabulary to use here. The univocal meaning employed in the KCA is “that which produces the effect.” Thus, if we were to ask, “What is the ’cause’ of virtual particles?”, we would be asking, “What ‘produces’ virtual particles?”, with the answer to which — quantum fluctuations in the vacuum — being completely legitimate. Similarly we could ask, “What is the ’cause’ of the binding of like-charged nucleons in the atomic nucleus?”, and someone could answer, “The strong force is what produces that effect.” So it seems to me that a clear definition of terms makes appropriate the use of a “cause” in this context.

With that being said, when you say that, “The Hartle-Hawking ‘no-boundary proposal’ for the wave function of the universe, for example, is completely self-contained, not requiring any external cause,” in what sense do you mean, “self-contained?” It was pointed out in [http://arxiv.org/abs/astro-ph/9712344] that,

“The problem with this model is that it ignores the 'zero-point-energy'. . . . Thus, when the 'zero-point-energy' is considered, we see that the initial state is not a point but a tiny oscillating (0 ≤ a ≤ a1) Big Bang universe, that oscillates between Big Bangs and Big Crunches (though the singularities at the Big Bangs and Big Crunches might be smeared by quantum effects). This is the initial classical state from which the tunneling occurs. It is metastable, so this oscillating universe could not have existed forever: after a finite half-life, it is likely to decay.”

Therefore it seems to me that on this model the universe has only existed for a finite duration of time. So we could still validly inquire as to what produced it (or, given the truth of the more radical B-Theory of time, what determined that *this* universe tenselessly exists rather than some other?). Moreover, why think that this model shouldn’t be treated as nonrealist in character? How does changing from a Lorentzian metric signature to a Euclidean metric imply an ontological commitment? Given the fact that the Wick rotation performed takes the real time variable “T” and replaces it with the imaginary quantity “I × T”, Hartle and Hawking are said to employ “imaginary time” in their model. How does one intelligibly give a realistic interpretation to any value of “imaginary time?”

You later go on to state the following:

“The second premise of the Kalam argument is that the universe began to exist. Which may even be true! But we certainly don’t know, or even have strong reasons to think one way or the other. Craig thinks we do have a strong reason, the Borde-Guth-Vilenkin theorem. So I explained what every physicist who has thought about the issue understands: that the real world is governed by quantum mechanics, and the BGV theorem assumes a classical spacetime, so it says nothing definitive about what actually happens in the universe; it is only a guideline to when our classical description breaks down.”

It goes without saying that I would never claim to be any kind of subject matter expert on cosmology, especially when in comparison with your current level of expertise. However, in my novice opinion, I think it’s fair to say that last statement downplays the significance of BVG and, as far as I can tell, is false. While I agree that we can’t infer anything “definitive,” I think we can, however, make some significant inferences: given the fact that we have substantial evidence that our universe (classical spacetime) satisfies the only condition of BVG — Hav > 0 — all the way back until 10^-43 seconds, then according to [http://arxiv.org/abs/gr-qc/0110012],

“Whatever the possibilities for the boundary, it is clear that unless the averaged expansion condition can somehow be avoided for all past-directed geodesics, inflation alone is not sufficient to provide a complete description of the Universe, and some new physics is necessary in order to determine the correct conditions at the boundary. This is the chief result of our paper. The result depends on just one assumption: the Hubble parameter H has a positive value when averaged over the affine parameter of a past-directed null or noncomoving timelike geodesic.

“The class of cosmologies satisfying this assumption is
not limited to inflating universes.”

Vilenkin reiterates the point:

“A remarkable thing about this theorem is its sweeping generality. We made no assumptions about the material content of the universe. We did not even assume that gravity is described by Einstein’s equations. So, if Einstein’s gravity requires some modification, our conclusion will still hold. The only assumption that we made was that the expansion rate of the universe never gets below some nonzero value, no matter how small. This assumption should certainly be satisfied in the inflating false vacuum. The conclusion is that past-eternal inflation without a beginning is impossible.” [Vilenkin, Many Worlds in One, p. 175]

Thus, we have very good reason to think that unless the Planck epoch can avoid Hav > 0, our universe cannot be past-eternal. One possible way for this to happen is via an 'emergent universe' scenario. In discussing a model of this type, you mentioned a paper by Anthony Aguirre and John Kehayias; one that WLC cited in the debate:

“They examined the 'emergent universe' scenario of George Ellis and Roy Maartens, in which the universe is in a quasi-static pre-Big-Bang state infinitely far into the past. Aguirre and Kehayias showed that such behavior is unstable; you can’t last in a quasi-static state for half of eternity and then start evolving. Personally, I didn’t think this was worth talking about; I completely agree that it’s unstable, I never promoted or defended that particular model, and I just didn’t see the relevance. But he kept bringing it up. Only after the debate did it dawn on me that he takes the specific behavior of that model as representative of any model that has a quantum-gravity regime (the easiest way out of the 'beginning' supposedly predicted by the BGV theorem). That’s completely false. Most models with a quantum-gravity phase are nothing like the emergent universe; typically the quantum part of the evolution is temporary, and is surrounded on both sides by classical spacetime. But that’s so false that I didn’t even pick up that WLC was presuming it, so I never responded. Bad debater.”

According to that paper [http://arxiv.org/abs/1306.3232],

“We stress that we have analyzed only one version of the Emergent Universe, with a simplified model. Nonetheless, we believe that the effect that this analysis points to may be rather generic. For example, consider alternative theories of gravity. The Emergent Universe has been studied extensively in theories such as Hoˇrava-Lifshitz, f(R), Loop Quantum Gravity, and others (see, for instance, [8–11], respectively). There have also been several studies of the stability of the Einstein static universe in alternative theories (see [12], for example). However, in our framework we have, in a sense, decoupled gravity – it enters only when assessing the affect of the spreading wave-functional. Even in alternative theories in which the Einstein static universe is more stable than in standard General Relativity, we anticipate that once the wavefunctional has spread enough, the geometry must follow, and the spacetime becomes classically ill-defined as well as containing portions corresponding to singularities. Therefore, this seems like a generic (and perhaps expected, given our construction of the scenario) problem with such an eternal and precisely tuned inflationary scheme. . . .”

“. . . Models in which the field dynamics and material content are very different would require separate analysis, but may lead to a similar basic conclusion. For example, Graham et al. [14] construct static and oscillating universes with a specific non-perfect-fluid energy component that are stable against small perturbations. However, Mithani & Vilenkin [15] have shown that this model is unstable to decay via tunneling.

“Although we have analyzed only one version of the Emergent Universe, we would argue that our analysis is pointing to a more general problem: 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.”

Unless I’m missing something, this paper seems to strongly support WLC’s contention: quantum instability seems to prevent *any* emergent scenario — regardless of if whether it’s an unstable state (ESS) or a metastable state (LQG) — from being past-eternal. Moreover, this notion appears to be reinforced here [http://arxiv.org/abs/arXiv:1305.3836] as well:

“A number of authors emphasized that the beginning of inflation does not have to be the beginning of the universe. The ‘emergent universe’ scenario [11–15] assumes that the universe approaches a static or oscillating regime in the asymptotic past. In this case, the average expansion rate is Hav = 0, so the condition (1) is violated. The problem with this scenario is that static or oscillating universes are generally unstable with respect to quantum collapse and therefore could not have survived for an infinite time before the onset of inflation [16–18].”

I’m just not following you here; what would lead you to say that this belief of WLC is “completely false?”

With respect to the Aguirre-Gratton model (which posits a different scenario), you said,

“In contrast, I wanted to talk about a model developed by Anthony Aguirre and Stephen Gratton. They have a very simple and physically transparent model that (unlike my theory with Chen) imposes a low-entropy boundary condition at a mid-universe 'bounce.' It’s a straightforward example of a perfectly well-defined theory that is clearly eternal, one that doesn’t have a beginning, and does so without invoking any hand-waving about quantum gravity. I challenged Craig to explain why this wasn’t a sensible example of an eternal universe, one that was in perfect accord with the BGV theorem, but he didn’t respond. It wasn’t until the talks on the following day that Craig’s teammate James Sinclair admitted that it seemed like a perfectly good model to him.”

Vilenkin also addressed this model in the last paper I mentioned, and noted:

“Even though the spacetime has no boundary in the AG model, it does include a hyper-surface on which the low-entropy (vacuum) boundary condition must be enforced by some mechanism. This surface of minimum entropy plays the role of the beginning of the universe in this scenario. . . .”

“. . . Suppose the vacuum that fills this de Sitter space is a metastable (false) vacuum and that it can decay to one or more lower-energy vacua through bubble nucleation. Suppose further that we impose a boundary condition that the entire universe is in a false vacuum state in the asymptotic past, τ → −∞. Then bubbles nucleating at τ → −∞ will fill the space, the energy in the bubble walls will thermalize, and the universe will contract to a big crunch and will never get to the bounce and to the expanding phase.”

Even if one ignores the questionable reversal of the arrow of time, this model, according to Vilenkin, still cannot plausibly be past-eternal.

Nevertheless, this post is beyond lengthy already so I’ll stop here, despite my remaining questions. As I said, thanks again for such a civil, competitive debate and I appreciate your taking the time to entertain my questions.

6. Aron Wall says:

Dear Jack,

My critique is that your proposed letter is much too long to politely post on Dr. Carroll's blog. ;-)

But since you seem to already have done so, I'm not sure that piece of advice will help very much. I'm flattered that you should turn to me for help with scientifically critiquing your letter---I'm not offended that you asked me---but unfortunately this would require me to essentially rehash the debate an entire additional time, as viewed through the lens of your letter. It is hard enough work critiquing the debate once...

Since in your letter you made clear that you are not a professional cosmologist, I think you can reasonably expect that people will take the letter in the spirit in which it was intended, and won't assume that you are claiming any sort of infallibility for your opinions. But you could always ask the people posting it on their websites to add a disclaimer, if you think that is necessary.

[Just to clarify the situation for any visitors, on this blog I do not use the title "saint" when addressing someone in the second person, and I certainly don't require other commenters to refer to me (or anyone else, for that matter) in that way!]

7. Jack Spell says:

Dear Aron,

Thank you for your response. I apologize for the length of the letter; I just felt it was a necessary evil in order to properly combat (what I perceived to be) false claims propagated by Dr. Carroll's post-debate reflections.

As I previously stated, I fully understand if you cannot give it a proper critique; doing so would certainly exaust a considerable amount of your free time.

My primary concern (which I should have tried to state more clearly) was whether or not the papers that I cited were relevant and appropriate as refutations for Prof. Carroll's claims; that is all that I was hoping for your thoughts on. Nevertheless, again, I understand your position and thank you again for the response.

8. T.Yhip says:

Aron,

St. Paul wrote in (Rom. 1:16,17):”For I am not ashamed of the gospel of Christ, for it is the power of God to salvation for everyone who believes, for the Jew first and also for the Greek. For in it the righteousness of God is revealed from faith to faith; as it is written, 'The just shall live by faith'.”

It is reassuring to know there are respectable physicists and mathematicians like you and others (Stephen Barr, John Lennox, John Polkinghorne, just to name a few) who are not ashamed to be Christians, and who confidently profess their faith through their writings and speeches in a rigorous defence of theism and Christianity.

Keep up the good work.

9. LaplaceDemon says:

I think when you like at the argument map, Craig had the better argumention
http://remingtonscove.wordpress.com/2014/02/22/w-l-craig-v-sean-carroll-god-cosmology/comment-page-1/

There was a lot of stuff like "Craig saying this , but there are models that avoid this problem". And Craig would respond that "there are other problems with such models and Carroll has to come to grips with the problem" that I didn't know how to evaluate , because I only have a layman's knowledge of cosmology.