William Lane Craig's Science of Cosmology

Basically Carroll-Chen assumes that prior to the big Bang with started our expanding universe there was a universe contracting from infinity this would avoid something called the BVG theorem that basically states that a universe, which on average is expanding cannot be infinite in the past. Carroll-Chen by having a infinitely contracting state the universe is never ‘on average’ expanding. The problem with any contracting space-time is that it requires absolute fine-turning or the whole thing folds up into a non-blackhole singularity. Craig pointed this out in the debate that this was fatal to Carroll-Chen but this was not the serious mistake that Carroll made in his own paper. Carroll-chen has to assume that the minimum of entropy was reached at the bounce Craig pointed out that Carroll offered no mechanisms or arguments as to why this is the case. Carroll claimed that a technical result in his paper did deal with this issue but Craig pointed out that Carroll was WRONG; the expanding universe would start with maximum entropy . I think this is what Patrick meant when he claimed that Craig does not understand the physics or entropy. The problem is that Craig was spot on and Carroll completely wrong. I feel in some ways that I am wasting my time Carroll has abandoned Carroll-Chen as unworkable validating the criticisms of Craig and many others. see here https://www.reasonablefaith.org/writings/question-answer/honesty-transparency-full-disclosure-and-the-borde-guth-vilenkin-theorem/although this is more about Krauss editing an e-mail from Vilenkin on the BVG, Vilenkin makes exactly the same points that Craig made.


And I think you are right, in that I vaguely remember @Patrick referencing something like this.

Where is that adjudicated by a third party with credentials? Or where does Carroll concede this point?

Is that here?

@Patrick I’m familiar with Lambda-CDM, and with the cosmic background radiation, and with inflation. I’m not following the logic though. How does determine if there are or are not multiverses? And what does this have to do with the Kalam argument?

That is what I said - the standard big bang modal of the universe has been validated to new unprecedented level of detail. IT SAYS NOTHING about the origin of the universe. What I find interesting is that you claim that Craig does not understand cosmology, he has always championed the standard Big bang model. Carroll has been pushing multiple universes for years now, Stephen Hawking M-theory, Lawrence Krauss quantum fluctuations from nothing (well something). Craig has criticized these models as internally incoherent, philosophically illiterate and as bad metaphysics for years now. BIG win for Craig I think. By the way the BVG theorem still holds. M theory, multiple universes have not been discredited as they are not really physics but mathematical metaphysics divorced from reality. Sadly I think they will continue.

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“And what does this have to do with the Kalam argument?” Absolutely nothing. But what I find fascinating is that Patrick has vilified Craig for not understanding cosmology dispite the fact that Craig has defended the standard big bang cosmology for nearly 40 years against multiple universes, String theory, Quantum fluctuations, rho-braine cosmology etc… Carroll asserts multiple universes, Hawking M-theory, Krauss quantum fluctuations. By Patrick’s own post Craig (who does not understand cosmology) has been right all along and Carroll, Hawking, Krauss all wrong.

Slow down a bit and carefully document that string of claims. You are not in a debate with @Patrick. Drop the indignance. I want a good account of the story, with documentation so I can sort out what really happened. If you give a good and honest account, @Patrick will either grow silent, or thank you for correcting his mistake.


@theman8469 you seem surprisingly knowledgeable about this. Do you have physics training? Can you tell us a bit about yourself? I’m really looking forward to seeing this thread develop.

@Patrick, the link @theman8469 offered to WLC’s newsletter is enlightening.

It seems that Krauss has not been upfront about the science. You and I both have a shared commitment to honesty. I am curious what you think about this. Reading this, what do you make of this?

Were his redactions honest or misleading?

It all starts by Krauss forwarding a heavily redacted email from Vilenkin to Krauss, which seems to support many of the points that you @Patrick have made.

During your recent dialogue in Sydney Professor Krauss presented personal E-mail correspondence with cosmologist Alexander Vilenkin concerning the application of the Borde-Guth-Vilenkin theorem to the beginning of the universe. According to Vilenkin’s E-mail, in the case of a quantum theory of gravity “all bets are off.”

Craig, however, got his hands on the unredacted version of the email, and showed it to everyone here.

To my delight Vilenkin furnished the unabridged version of his letter to Krauss.1 I have put Krauss’ deletions in boldface:

Hi Lawrence,

Any theorem is only as good as its assumptions. The BGV theorem says that if the universe is on average expanding along a given worldline, this worldline cannot be infinite to the past.

A possible loophole is that there might be an epoch of contraction prior to the expansion. Models of this sort have been discussed by Aguirre & Gratton and by Carroll & Chen. They had to assume though that the minimum of entropy was reached at the bounce and offered no mechanism to enforce this condition. It seems to me that it is essentially equivalent to a beginning.

On the other hand, Jaume Garriga and I are now exploring a picture of the multiverse where the BGV theorem may not apply. In bubbles of negative vacuum energy, expansion is followed by cocntraction, and it is usually assumed that this ends in a big crunch singularity. However, it is conceivable (and many people think likely) that singularities will be resolved in the theory of quantum gravity, so the internal collapse of the bubbles will be followed by an expansion. In this scenario, a typical worldline will go through a succession of expanding and contracting regions, and it is not at all clear that the BGV assumption (expansion on average) will be satisfied.

I suspect that the theorem can be extended to this case, maybe with some additional assumptions. But of course there is no such thing as absolute certainty in science, especially in matters like the creation of the universe. Note for example that the BGV theorem uses a classical picture of spacetime. In the regime where gravity becomes essentially quantum, we may not even know the right questions to ask.


It appears as if Krauss edited the letter to make it say the opposite of what it meant. For example, he excluded this line, which is exactly WLC’s point that the best cosmology seems to indicate there was a beginning to the universet:

It seems to me that it is essentially equivalent to a beginning.

I don’t know enough of the story to know what is really going on. I trust William Lane Craig not to so boldly lie as to make up the full letter. I do not know Krauss’s state of mind when he edited that letter. For all I know, he might have genuinely thought he was being helpful.

In your view though, @Patrick, do you think those are fair edits? Were his redactions misleading?

I agree that the Carroll-Chen model is strongly disfavored by 2018 Planck Final Results. And yes Craig was spot on. Vilenkin pointed this out also in a letter to Scientific American. Many models are now strongly disfavored by Planck. The Guth-Linde slow roll inflation model is strongly favored now. It is a very simple idea that seems to explain in a single quantum field called the inflaton expands space so that universe can come out of the energy the empty space contains. The universe starts out with minimum entropy and entropy increases every since.

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Seems so. But in physics the proof is in the observational results. It seems like the simplest model of inflation is all that is necessary to explain the beginning of the universe we live in. The data is quite compelling. We don’t know what dark energy or dark matter is but the model, the math and the data all seem to fit. Amazing in just 54 years after Penzias and Wilson discovery down the street.

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We don’t trust the observational results if we don’t trust the scientist who reports them.

If Krauss was in error here, I hope he apologizes and retracts. That is how we identify who we can trust in the conversation. @Patrick, do you know if Krauss ever set the record straight and acknowledged his error here? Or, alternatively, demonstrated it was not actually an error?

I agree it is pretty amazing.

And yet so much mystery abounds…

The observation results were published with over 600 names on the papers. Are you saying that these 600 scientists are part of an elaborate hoax to distort the data in order to fit their pet theory?

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Of course not. I’m talking about the conversation on what those observations mean. I bet you that on that list of 600 at least, say, 10 are convinced the universe had a beginning. It might even be as high as 200. I bet they would be all confused about what this has to do with arguing against Craig’s position on Kalam.

The bigger issue is an issue of integrity in our leaders. As for me, I think honesty is a non-negotiable. We can make mistakes, but we do have to acknowledge them. Krause does not seem to have honestly reported a private correspondence. May he can fill in some details that clarifies he was not in error. If he wants in error, this is a really serious issue.

Krause is in the penalty box right now. Don’t think he is engaging the public much.

Our universe had a beginning 13.787 ± 0.020 billion years ago. I don’t think there is any controversy about this.

I don’t know what you mean about whether the universe we live in now had a beginning.

The Planck measurements have significantly constrained
the physics of inflation. The hypothesis of adiabatic Gaussian
scalar fluctuations with a power spectrum described by a simple
power law, which is the key prediction of the standard
single-field slow-roll inflationary models, has been tested to unprecedent
accuracy (PCI13; PCI15;Planck Collaboration XXIV
2014; Planck Collaboration XVII 2016). Planck has set tight
constraints on the amount of inflationary gravitational waves
by exploiting the shape of the CMB temperature spectrum
(PCI13). These results have inspired a resurgence of activity
in inflationary model building. For more details, see, for example,
the following review articles and references therein:
Linde (2015); Martin et al. (2014a); Guth et al. (2014); and
Burgess et al. (2013). Planck analysis and interpretation have
also sparked a debate on the likelihood of initial conditions for
some inflationary models (Ijjas et al. 2013; Ijjas & Steinhardt
2016; Linde 2017), which is primarily of theoretical interest
and is not addressed in this paper. In combination with more
sensitive B-mode ground-based polarization measurements, as
from BICEP-Keck Array (BKP), Planck has convincingly ruled
out the slow-roll inflationary model with a quadratic potential
(PCI15). In terms of physics beyond the simplest slow-roll inflationary
models, the pre-Planck hints of a running spectral index
(Hou et al. 2014) or of large non-Gaussianities (Bennett et al.
2012) have disappeared as a result of the Planck measurements.

if you mean universe as in the four dimensional manifold we find ourselves in then yes, there is no controversy. If you mean universe as in the whole of physical reality then there is uncertainty. I’m uncertain. Though I lean towards a beginning.

Hi , I think this was a way to regain face on the part of Krauss. Krauss did poorly in a debate with Craig and Krauss wrote an essay on the event at an atheist site scienceblogs. The essay was pretty bad but Krauss also wrote the following

“(2) There are no arguments that our universe need be unique and not derived from something pre-existing, or even eternal. Indeed, the Ekpyrotic Universe promoted by Turok and Steinhardt, which I don’t find compelling, argues for potentially eternal periods of expansion and contraction. Craig doesn’t understand the physics.”

Notice the usual rhetoric

“Craig doesn’t understand the physics”.

The problem is that I do understand the physics in this case, as does Craig and many other philosophers and physicists. Krauss was dead wrong. The Ekpyrotic Cyclic model is one of the most basic models to fall to the BVG theorem. What is shocking is that just about anyone in astrophysics knows this; although the lay person may not see the problem this stands out like a wolf in a chicken pen to the initiated. Very serious error on Krauss’ part and the post was very quickly taken down. See here https://www.reasonablefaith.org/writings/question-answer/lawrence-krauss-response-and-perspective/#_ednref1. As Craig states

“The Ekpyrotic Cyclic model is precisely one of those higher dimensional “brane” cosmogonies covered by the Borde-Guth-Vilenkin theorem. Therefore, it cannot be past eternal. (And I don’t understand the physics?)”

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Open mouth, insert cosmological foot. Try to remember whether you’ve done it before; there may be an important pattern.

“so that universe can come out of the energy the empty space contains”. The sad thing is that you are unaware that you have contradicted yourself.


That is sad. Too many of the those who’ve had power, have not used power well. This goes for Christians, Atheists, and everyone else. I hope we can find a different way.

Looking at his rebuttal, its not clear which way is up or down. I’m glad I’m not the one adjudicating these things.