First, Dr. Craig posted the e-mail from Vilenkin to Krauss, which Krauss used in his debate with Craig, with the parts Krauss omitted in bold:
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.
Now recall that Krauss excuses the selective editing of the e-mail in the debate by saying that it was “too technical” to include. Judge for yourself if the omitted lines are “too technical” or whether they were omitted in order to mislead people about the evidence for the beginning of the universe.
Dr. Craig comments:
Whoa! That puts a very different face on the matter, doesn’t it? Why didn’t Krauss read the sentence, “It seems to me that it is essentially equivalent to a beginning”? Because it was too technical? Is this the transparency, honesty, and forthrightness that Krauss extols? (By the way, Vilenkin’s criticism of these models is the same one that Vilenkin makes in his Cambridge paper: far from showing an eternal past, these models actually feature a universe with a common beginning point for two arrows of time.)
And why did Krauss delete Vilenkin’s caveat that the BGV theorem can, in his estimation, be extended to cover the case of an expanding and contracting model such as Garriga and Vilenkin are exploring? And why delete the remark that such a model is usually assumed to be incorrect? It’s evident that Vilenkin’s email was selectively edited to give it the spin Krauss wanted.
Some people told me that they thought that Dr. Craig needed to be a little less gracious with Krauss in the debate, but that comment takes Krauss on directly. Too bad most of the people who watch the debate will never know unless they see the original e-mail from Vilenkin that Craig posted.
Dr. Craig then wrote to Dr. Vilenkin about this misrepresentation and here is part of the reply:
The Aguirre-Gratton model can avoide singularities by postulating a small “initial” closed universe and then allowing it to evolve in both directions of time. I put “initial” in quotation marks, because Aguirre and Gratton do not think of it that way. But this model requires that a very special condition is enforced at some moment in the history of the universe. At that moment, the universe should be very small and have very low entropy. Aguirre and Gratton do not specify a physical mechanism that could enforce such a condition.
Carroll and Chen claim that the universe did not have to be small at that special moment. But in my recent paper I show that in this case singularities are unavoidable.
[...]I think you represented what I wrote about the BGV theorem in my papers and to you personally very accurately.
Now I don’t want anyone to get the idea that all atheists are like Krauss. I distinctly remember another atheist named Anthony Flew debating Dr. Craig and a questioner from the audience asked him why not prefer speculative cosmologies like the eternally oscillating model. Dr. Flew (unlike Dr. Krauss) was honest – he said that we have to accept the science we have today based on the evidence we have today. Dr. Krauss is not willing to accept the science we have today and the evidence we have today. That’s the difference. This is a failing of Dr. Krauss’ will and intellect. He simply cannot bring himself to accept what science has shown, if it impacts his autonomy in any way. He would rather mislead himself and others with speculations rather than face reality.
Watch the whole debate – see for yourself
I’ll re-state the relevant part of my Craig-Krauss debate summary below. The summary has the full video.
The segment from 52:18 to 57:12 about the Vilenkin e-mail on the BVG theorem is a must-see. Krauss is standing up and gesticulating while Craig is calmly trying to quote a paper by Vilenkin that shows that Krauss is misrepresenting Vilenkin. Krauss constantly interrupts him. After a while, when Craig exposes him as having misrepresented Vilenkin and gets him to admit that all current eternal models of the universe are probably wrong, he quietens down and can’t even look at Craig in the face.
- Craig: The e-mail says any universe that is expanding, on average, requires a beginning
- Craig: There are two models – Aguirre & Gratton and Carroll & Chen – where there is a period of contraction before the expansion
- Craig: The two models are the ones cited in the e-mail that Dr. Krauss showed
- Craig: In the very paper by Vilenkin that I cited, he says that both of those models don’t work
- Krauss: (agitated and interrupting) Vilenkin said that they have to make an assumption about entropy that they have no rationale for
- (as Craig starts to talk Krauss makes an exaggerated, disrespectful gesture and sits down in a huff)
- Craig: Yes, an unwarranted assumption means that they don’t have EVIDENCE for their theories being correct
- Krauss: (agitated and interrupting) “All the evidence suggests that the universe had a beginning but WE DON’T KNOW!!!!!!!” (raising his voice)
- Craig: I’m not saying that we know that the universe had a beginning with certainty
- Craig: I am saying that the beginning of the universe is more probably true than false based on the evidence we have
- Craig: And you agree with me about that – you think the universe had a beginning
- Krauss: (agitated and interrupting) (Unintelligible)
- Moderator: One at a time
- Craig: In your Vilenkin e-mail slide, at the end of the paragraph where the two models are mentioned that Vilenkin specifically shows…
- (I am guessing that Craig is going to ask why so much of what Vilenkin wrote has been cut out of the e-mail that Krauss showed)
- Krauss: (agitated and interrupting) Because it was technical…
- Moderator: Lawrence! Hang on a sec!
- Craig: He specifically shows that these models are not past eternal, and that they require a beginning just like the others…
- Krauss: (agitated and interrupting) We can do the math if you want
- Craig: Now wait. I couldn’t help notice that there on your slide there was a series of ellipsis points indicating missing text…
- Krauss: (agitated and interrupting) “Yeah, because it was technical!”
- Craig: “I wonder what you deleted from the original letter”
- Krauss: (agitated and interrupting) “I just told you!”
- Craig: “Now wait. Could it have been something like this: (reads a quote from Vilenkin) ‘You can evade the theorem by postulating that the universe was contracting prior to some time. This sounds as if there is nothing wrong with having contraction prior to expansion. But the problem is that a contracting universe is highly unstable. Small perturbations would cause it to develop all sorts of messy singularities, so it would never make it to the expanding phase.’
- Craig: “That’s Vilenkin.”
- Krauss: “In this paper, that’s absolutely right”
- Krauss: But it’s ok for theories to assume things that we know are wrong – they are still good theories – it’s unknown
- (Craig turns away and looks through his papers)
- Craig: “Isn’t it true that the only viable quantum gravity models on order today involve a beginning – have a finite past?”
- Krauss: “No”
- Craig: “Well, can you give us one then”
- Krauss: (talks about a variety of possible eternal models) “In my experience in science, all of them are probably wrong”
- Krauss: “You know most theories are wrong, which is why, you know, it’s hard”
- Craig: “Right”
Krauss accused Dr. Craig of misrepresenting science many times in his three Australia debates, but now we know the truth about who misrepresented science.
UPDATE: This whole episode made me think of a lecture by famous physicist Richard Feynman.
The first principle is that you must not fool yourself–and you are the easiest person to fool. So you have to be very careful about that. After you’ve not fooled yourself, it’s easy not to fool other scientists. You just have to be honest in a conventional way after that.
I would like to add something that’s not essential to the science, but something I kind of believe, which is that you should not fool the layman when you’re talking as a scientist. I am not trying to tell you what to do about cheating on your wife, or fooling your girlfriend, or something like that, when you’re not trying to be a scientist, but just trying to be an ordinary human being. We’ll leave those problems up to you and your rabbi. I’m talking about a specific, extra type of integrity that is not lying, but bending over backwards to show how you are maybe wrong, that you ought to have when acting as a scientist. And this is our responsibility as scientists, certainly to other scientists, and I think to laymen.
Now given what Krauss did in the debate, it seems to me that he is not in agreement with Feynman.
UPDATE: Dr. Craig reports that Dr. Krauss refused to let the organizers live-stream the three Australia debates, as well as refusing to let the Australian Broadcasting Corporation live-broadcast the three debates.