The BGV Theorem

[grosso]

Wow , have you not been listening to any WLC's debates in the past few years?
here is an example, WLC versus Stephen LAw. Note the only piece of scientific evidence WLC brings up in this debate is the BGV theorem:

"his purely philosophical conclusion has been confirmed by remarkable discoveries in astronomy and astrophysics. We now have pretty strong evidence that the universe is not eternal in the past but had an absolute beginning a finite time ago. In 2003, Arvin Borde, Allan Guth, and Alexander Vilenkin were able to prove 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 past spacetime boundary. What makes their proof so powerful is that it holds regardless of the physical description of the early universe. Because we don’t yet have a quantum theory of gravity, we can’t yet provide a physical description of the first split second of the universe. But the Borde-Guth-Vilenkin theorem is independent of any physical description of that moment. Their theorem implies that the quantum vacuum state of the early universe—which some scientific popularizers have misleadingly and inaccurately referred to as “nothing”—cannot be eternal in the past but must have had an absolute beginning. Even if our universe is just a tiny part of a so-called “multiverse” composed of many universes, their theorem requires that the multiverse itself must have an absolute beginning.

Of course highly speculative scenarios, such as loop quantum gravity models, string models, even closed timelike curves, have been proposed to try to avoid this absolute beginning. Now these models are all fraught with problems; but the bottom line is that none of these theories, even if true, succeeds in restoring an eternal past. At most they just push the beginning back a step."


See? he didnt use any other scientific evidence , only the BGV theorem. He also totally mispoke when he said even if other models like loop or string cosmologies are true then they dont avoid the beginning (perhaps  as the BGV is independent of any physics? lol). These models may or may not be right, but if they are right they certainly dont contain any beginning event in them. Most of these models dont have singularities and do  have prior contraction thus violating the BGV.

in fact I would go as far to say WLC simply doesnt understand LQC. he says here:
"The third class of Quantum Gravity models, Loop Quantum Gravity theories, features versions of a cyclical universe, expanding and contracting. These models do not require an eternal past, and trying to extend them to past infinity is hard to square with the Second Law of Thermodynamics and seems to be ruled out by the accumulation of dark energy, which would in time bring an end to the cycling behavior."

Read more: http://www.reasonablefaith.org/contemporary-cosmology-and-the-beginning-of-the-universe#ixzz3aTzL3POL

However Craig has it totally wrong yet again. LWC does not predict a cyclic universe. it predicts that singularities are replaced by bounces. This means if dark energy is a cosmological constant then there is just a one time bounce, an mirror image of our expanding branch is matched by contracting phase of the universe on the other side of the bounce. Look a bit like this:
http://science.psu.edu/news-and-events/2011-news/Ashtekar8-2011

I don't think he is appealing solely to the BGV. He's also appealing to the fact that all the empirical evidence we have points to the fact that all our empirical evidence vis a vis our universe meets the BGV constraint of on-average cosmic expansion. In addition that the BGV applies regardless of the physical description of the early universe.

In addition, he seems to be saying that attempts to avoid the BGV are all highly speculative. I imagine that's because they introduce ad hoc assumptions, contrived especially to avoid a beginning, which is not supported by any empirical data.

So the BGV, in addition to an analysis of the models on hand (which tightens the noose further towards a beginning), and in addition to the empirical evidence observed within our universe (which underweights ad hoc speculative models designed to escape a beginning), together provide strong evidence.

This is obvious when you do a close reading of his claim.

The way you're approaching this is not the way credible academics do.

[redtilt1]

Wow , have you not been listening to any WLC's debates in the past few years?
here is an example, WLC versus Stephen LAw. Note the only piece of scientific evidence WLC brings up in this debate is the BGV theorem:

"his purely philosophical conclusion has been confirmed by remarkable discoveries in astronomy and astrophysics. We now have pretty strong evidence that the universe is not eternal in the past but had an absolute beginning a finite time ago. In 2003, Arvin Borde, Allan Guth, and Alexander Vilenkin were able to prove 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 past spacetime boundary. What makes their proof so powerful is that it holds regardless of the physical description of the early universe. Because we don’t yet have a quantum theory of gravity, we can’t yet provide a physical description of the first split second of the universe. But the Borde-Guth-Vilenkin theorem is independent of any physical description of that moment. Their theorem implies that the quantum vacuum state of the early universe—which some scientific popularizers have misleadingly and inaccurately referred to as “nothing”—cannot be eternal in the past but must have had an absolute beginning. Even if our universe is just a tiny part of a so-called “multiverse” composed of many universes, their theorem requires that the multiverse itself must have an absolute beginning.

Of course highly speculative scenarios, such as loop quantum gravity models, string models, even closed timelike curves, have been proposed to try to avoid this absolute beginning. Now these models are all fraught with problems; but the bottom line is that none of these theories, even if true, succeeds in restoring an eternal past. At most they just push the beginning back a step."


See? he didnt use any other scientific evidence , only the BGV theorem. He also totally mispoke when he said even if other models like loop or string cosmologies are true then they dont avoid the beginning (perhaps  as the BGV is independent of any physics? lol). These models may or may not be right, but if they are right they certainly dont contain any beginning event in them. Most of these models dont have singularities and do  have prior contraction thus violating the BGV.

in fact I would go as far to say WLC simply doesnt understand LQC. he says here:
"The third class of Quantum Gravity models, Loop Quantum Gravity theories, features versions of a cyclical universe, expanding and contracting. These models do not require an eternal past, and trying to extend them to past infinity is hard to square with the Second Law of Thermodynamics and seems to be ruled out by the accumulation of dark energy, which would in time bring an end to the cycling behavior."

Read more: http://www.reasonablefaith.org/contemporary-cosmology-and-the-beginning-of-the-universe#ixzz3aTzL3POL

However Craig has it totally wrong yet again. LWC does not predict a cyclic universe. it predicts that singularities are replaced by bounces. This means if dark energy is a cosmological constant then there is just a one time bounce, an mirror image of our expanding branch is matched by contracting phase of the universe on the other side of the bounce. Look a bit like this:
http://science.psu.edu/news-and-events/2011-news/Ashtekar8-2011

I don't think he is appealing solely to the BGV. He's also appealing to the fact that all the empirical evidence we have points to the fact that all our empirical evidence vis a vis our universe meets the BGV constraint of on-average cosmic expansion. In addition that the BGV applies regardless of the physical description of the early universe.

In addition, he seems to be saying that attempts to avoid the BGV are all highly speculative. I imagine that's because they introduce ad hoc assumptions, contrived especially to avoid a beginning, which is not supported by any empirical data.

So the BGV, in addition to an analysis of the models on hand (which tightens the noose further towards a beginning), and in addition to the empirical evidence observed within our universe (which underweights ad hoc speculative models designed to escape a beginning), together provide strong evidence.

This is obvious when you do a close reading of his claim.

The way you're approaching this is not the way credible academics do.

Can you show me where in that statement he used anything other tan the bGV as scientific evidence for a beginning?
i see nothing

[grosso]

In his written work, he refers to (at least) two papers by Vilenkin in defense of some of the abovementioned claim. I have the papers on my computer, but I think you'll find this on the website using the search function above.

So your criticism comes up empty.

Perhaps to keep it alive your next move will say "I meant empirical evidence" which tries to rule out theoretical work done by scientists. Or you might say "why didn't he say so explicitly" despite the fact that it was a debate with time constraints, and if challenged on it he would no doubt mention the citations. Or you might say you did a search and no article was cited even in his written work, in which case you could easily be proved wrong.

Is there another option?

[redtilt1]

In his written work, he refers to (at least) two papers by Vilenkin in defense of some of the abovementioned claim. I have the papers on my computer, but I think you'll find this on the website using the search function above.

So your criticism comes up empty.

Perhaps to keep it alive your next move will say "I meant empirical evidence" which tries to rule out theoretical work done by scientists. Or you might say "why didn't he say so explicitly" despite the fact that it was a debate with time constraints, and if challenged on it he would no doubt mention the citations. Or you might say you did a search and no article was cited even in his written work, in which case you could easily be proved wrong.

Is there another option?

The question was where in his debate with Stephen Law ( and I can give many other example if I need to) did he use any other scientific evidence tan the BGV theorem. You answer was in his written work, but that is not what the people who watch the debate are going to see. So if you watch the debate and are convinced by WLC argument you will have a false impression that the BGV i strong evidence for a beginning.
Moreover WLC said that even if true string and loop models dont avoid the conclusion of the beginning, this is simply wrong. So yet agin he misleads his audience.
Even is everything in his writtenwork is 100% accurate , tat still means the vast majority of people WLC is interacting with are being misled.

Now  the two papers of Vilenkin that I find on RF is (1)his BGV theorem, which you have already agreed is not strong evidence for a beginning and (2)his later paper with Mithani. In this paper the basically add one other model to the analysis that was already in the BGV paper, thats the model of George Ellis emergent universe. Since this model has very citations and is not exactly the dominant approach in quantum gravity research i hardly think its very convincing.
The appraoch that does seem to dominate the quantum gravity research is that of a non singular bounce and this Vilenkin has already admitted does violate his theorem and is not covered by his other paper with Mithani.

[grosso]

So if someone omits content from their presentation due to time constraints, but has the data openly available on their website an in their books, you'll accuse them of being misleading?

Also, you're confusing Vilenkin's BGV paper with the theorem itself. And your criticism of the Mithani paper is that it's "not exactly the dominant approach in quantum gravity research and has very few citations"- as if these things make the conclusions false?

Your criticism sounds more agenda-driven than scholarly, redtilt.

[Andrew Wells]

BGV integrate the Hubble parameter and show that it must be lower than some finite bound in the past. The other way of putting this is that the null geodesic (paths of massless particles) and time like geodesics (paths of particles with mass), must terminate at some point in the past. In principle General Relativity does not allow you to extend the geodesic beyond the singularity. So yes, if the conditions maintain then the Universe has a beginning.

However, Alan Guth has apparently changed his mind. He no longer believes the metric detailed in their original paper is an appropriate assumption. The condition of the BGV theorem is that the Universe has an above average expansion rate, but some cosmologists like to "quantise" the metric tensor in GR. Think of it this way: if Gravity is the curvature of space time and physicists want to "quantise" gravity, they must "quantise" space time. Meaning the classical metric is no longer a good descriptor. And space time is likely emergent (e.g., Hartle-Hawking) in that case it no longer makes sense to talk of 'expanding in the later than' direction because this is a statement which is derived from the metric. Therefore it's likely they BGV won't hold in quantum gravity.

[Tejretics]

From what I've read and heard, in light of the evidence, the universe had an absolute beginning. The Borde Guth Vilenkin Theorem seems to be another strong justification for the second premise. In the past, even Vilenkin himself has said to Dr. Craig, "I think you represented what I wrote about the BGV theorem in my papers and to you personally very accurately." Furthermore, at Stephen Hawking's birthday party, Vilenkin said, "All the evidence we have says that the universe had a beginning." And in his book, Vilenkin says, "With the proof now in place, cosmologists can no longer hide behind the possibility of a past-eternal universe." Therefore, I was devastated to hear Alan Guth, another author of the BGV theorem, say in the Craig-Carroll debate, that the universe is "very likely eternal." How can this be? How can two cosmologists who made the same theorem have such radically different views? Does the BGV theorem really imply a beginning? I've been trying to find the answers everywhere. Please help.

There are multiple varying interpretations of the BGV theorem. It's possible that Vilenkin interprets it differently from Guth. All interpretations don't entail an absolute beginning of the universe. The BGV theorem is compatible with Hawking's "no-boundary" proposal; it doesn't, therefore, necessitate a beginning. The BGV-theorem concludes that almost all inflationary model universes are past indeterminate. Which is to say, we have no idea what is going on, our models give no answer.