Thursday, 11 April 2019

The BGV Theorem Does Not Mean What You Think Means


I’ve addressed the use and misuse of the Borde-Guth-Vilenkin (BGV) Theorem a number of times in the past (The Misquoting WLC, The Eternally Inflated (Multiverse and WLC) and Multiholes in WLC’s Physics Arguments).

The apologetic argument goes a bit like this:  Atheists are terrified by the idea the universe must have begun, because if the universe has not been in existence forever, something must have created it.  The BGV Theorem says that inflation must have had a beginning, so the universe has a beginning, therefore the universe has a creator.  Therefore god.  (Much leaping around fisting the air and yelling “OOH-ya” and “who da man”.)

To be brutally frank, Vilenkin (one of the authors of the theorem) seriously did not help when he wrote:

It is said that an argument is what convinces reasonable men and a proof is what it takes to convince even an unreasonable man. With the proof now in place, cosmologists can no longer hide behind the possibility of a past-eternal universe. There is no escape: they have to face the problem of a cosmic beginning.

Admittedly, he did write a couple of paragraphs later:

Theologians have often welcomed any evidence for the beginning of the universe, regarding it as evidence for the existence of God… So what do we make of a proof that the beginning is unavoidable? Is it a proof of the existence of God? This view would be far too simplistic. Anyone who attempts to understand the origin of the universe should be prepared to address its logical paradoxes. In this regard, the theorem that I proved with my colleagues does not give much of an advantage to the theologian over the scientist. As evidenced by Jinasena’s remarks earlier in this chapter, religion is not immune to the paradoxes of Creation.

But the damage had already been done, there was a paragraph begging to be cherry picked by apologists and they went to town.  (A search on “There is no escape: they have to face the problem of a cosmic beginning” brings up page after page of apologetic nonsense.

As an aside to very interesting video on a universe from ‘nothing’, Vilenkin makes a very clear comment to the effect that the BGV Theorem does not mean what people like WLC want it to mean.  In this part of the video, he very specifically says that the BGV Theorem does not conclude that the universe must have a beginning, it concludes only that expansion must have a beginning.

WLC will need to find a new argument for an absolute cosmic beginning.  Well, he should, but given his track record, it’s likely that he will just ignore inconvenient statements by the people whose arguments he misrepresents.