Replies

He doesn't need to explain it, because Borde-Guth-Vilenkin themselves not only don't claim any such thing, they actually wrote: "What can lie beyond the boundary? Several possibilities have been discussed, one being that the boundary of the inflating region corresponds to the beginning of the Universe in a quantum nucleation event." Vilenkin himself suggested one such possibility. http://mukto-mona.net/science/physics/a_vilinkin/universe_from_nothing.pdf There are others. There is the possibility, for example, that time is finite but has no boundary. Another possibility is that time has only recently become time-like (in the sense of Lorentz invariance) and at the boundary was actually a space-like dimension. The authors you cite actually don't talk in the absolute terms you're suggesting; and they certainly don't rule out a uniquely quantum beginning to the universe.

He does not need to......Well, I suppose you are right, but it does not change what the theory says. What you quoted was a paper Vilenkin published (not Borde/Guth) in 1982. In the October 1, 2001, they published "Inflation Is Not Past-Eternal" . http://arXiv:gr-qc/0110012v1.

A watershed, of a sort, came with this publication where Borde, Guth, Vilenkin formulated their theory estabishing that any universewhich has on average over its past history been in a state of cosmic expansion. Theorists intent on avoiding an absolute beginning of the universe could previously take refuge in the period of time known as Planck time, an era so poorly understood that one commentator has compared it with the regions of the maps of ancient cartographers marked "Here there be dragons!" But the Borde-Guth-Vilenkin theorem does not depend upon any particular physical description of the universe prior to Planck time, being based on a deceptively simple physical reasoning which will hold regardless of our uncertainty concerning that era. It sweeps away the most important attempts to avoid an absolute beginning of the universe. Vilenkin pulls no punches. "It is said that an argument is what convinces reasonable men and proof is what it takes to convince even an unreasonable man. Moreover, the Borde-Guth-Vilenkin theorem requires that the multiverse itself cannot be extended into the infinite past.

I guess Vilenkin learned a lot in 20 years, or from his collaboration with Borde and Guth. I addressed a quantum beginning earlier.

You are mistaken.

The quote is from a paper by Borde-Guth-Vilenkin in 2003, which weakens the conditions of the paper you cite from 2001. To wit, http://arxiv.org/PS_cache/gr-qc/pdf/0110/0110012v2.pdf. It is not from Vilenkin alone.

Even though this requires weaker conditions, and is therefore a stronger result, the authors of the paper IMPLY NO SUCH CONSEQUENCE AS YOU ERRONEOUSLY MAINTAIN.

You are also mistaken in this claim: [applies to] any universe which has on average over its past history been in a state of cosmic expansion

The authors do not claim this to be so. There are assumptions in their theory, and Vilenkin [post 2003] himself merely says, "almost all."

In particular:

"[If] someone asks me whether or not the theorem I proved with Borde and Guth implies that the universe had a beginning, I would say that the short answer is “yes”. If you are willing to get into subtleties, then the answer is “No, but…”

Theorists intent on avoiding an absolute beginning of the universe could previously take refuge in the period of time known as Planck time

They could but they didn't have to; because there are theories which have a bounded time dimension which still has no beginning or end.

But the Borde-Guth-Vilenkin theorem does not depend upon any particular physical description of the universe prior to Planck time, being based on a deceptively simple physical reasoning which will hold regardless of our uncertainty concerning that era

The reasoning is neither deceptive, nor is it simple. It is based on the paths of geodesics in differential geometry constrained by Lorentz invariance and is largely inaccessible to laymen, which may be one reason why it is so largely misunderstood by them.

It sweeps away the most important attempts to avoid an absolute beginning of the universe.

No, it doesn't, as the quote from the 2003 paper clearly shows.

You then proceed to quote -- not from a peer-reviewed paper at all, but from a popular book Vilenkin wrote in 2006, Many Worlds in One . The fact that Vilenkin wrote this book alone with the collaborators from whom he "learned so much," appears not to bother you very much:

"It is said that an argument is what convinces reasonable men and proof is what it takes to convince even an unreasonable man. Moreover, the Borde-Guth-Vilenkin theorem requires that the multiverse itself cannot be extended into the infinite past. "

This is not research, simply an opinion in a popularized book on Cosmology. Unfortunately for your thesis, though, on the very same page of the book you think makes such a strong statement, Vilenkin has this to say:

"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."

Which is anything but a ringing endorsement of your position. [Nor could it be, since Vilenkin himself has offered at least one speculation which supports a Creator-less origin.]

I addressed a quantum beginning earlier.

If by "addressed" you mean "said something completely wrong," then we are in agreement.