BGV theorem

[lee_merrill]

The concept of an absolute beginning is a philosophical/theological assumption.

And now the subject of a proof!

All the different theorems or hypothesis of origins involve our space time universe no matter what terminology you want to use.

And the BGV theorem applies to such universes, with the caveat that space-time may not apply at the very start.

Blessings,
Lee

[lee_merrill]

I think what Vilenken is saying here is that are an unlimited number of pocket universes in the course of inflation and therefore an unlimited number of beginnings.. In short, no one absolute beginning.

Yes, that appears to be what he is saying, so presumably one of the caveats to the BGV theorem is applied here.

Best wishes,
Lee

[lee_merrill]

So you didn't quote Vilenkin's exceptions, and rather than admit that and confess that you have ignored them, you want to change the subject.

No, I acknowledge caveats, Vilenkin's and Strauss's and whoever else may have an understanding of the theorem.

BGV is based on the eternal inflation model, which is an extension of Big Bang theory. BGV assumes the Big Bang happened and considers the beginning of the period of expansion.

No, it does not focus on the beginning, nor does it assume a beginning, It says any geodesic in space-time cannot be infinite in the past.

Now - why don't Vilenkin's apparent exceptions refute your assertion that a succession of universes must have a beginning?

My claim is that under the assumptions and conditions of the BGV theorem, any succession of universes must have a beginning. And those assumptions and conditions are pretty minimal.

Blessings,
Lee

[JimL]

So, an infinite regress of universes? But that is what the BGV theorem addresses.

If you take time into consideration, it's an infinite regress no matter which way you look at it. If our universe were the only universe, and if it were created only 13.8 billion years ago then that which created it existed for infinite increments of time prior to creating that universe, ergo an infinite regress in time. For something to exist, it would need time in order to exist in it, in order to endure. That's what existing means, to endure in time. Therefore no-thing exists prior to time, and from out of that no-thing, virtual particles do pop into and out of existence, and so just like those virtual particles, it is from out of that "timeless nothingness" that universes of time are born. Of course this is a a different understanding of what is meant by "nothingness." It's a nothingness, a vacuum, in which virtual particles are constantly popping into and out of existence.

[Roy]

And those assumptions and conditions are pretty minimal.

Really? What are those assumptions and conditions? I doubt you know.

[lee_merrill]

If you take time into consideration, it's an infinite regress no matter which way you look at it. If our universe were the only universe, and if it were created only 13.8 billion years ago then that which created it existed for infinite increments of time prior to creating that universe, ergo an infinite regress in time. For something to exist, it would need time in order to exist in it, in order to endure. That's what existing means, to endure in time.

Though time requires matter in order to exist, correct?

It's a nothingness, a vacuum, in which virtual particles are constantly popping into and out of existence.

Popcorn particles!

Blessings,
Lee

[lee_merrill]

Really? What are those assumptions and conditions?

As far as I understand, the BGV theorem assumes a space-time universe, and the condition is that the universe is on average, expanding.

Blessings,
Lee

[shunyadragon]

And now the subject of a proof!

Ahh . . . no. It has been repeatedly been brought to your attention there is not proof here.

And the BGV theorem applies to such universes, with the caveat that space-time may not apply at the very start.

Blessings,
Lee

The BGV theorem applies in this interpretation if universes begin as time space began as a singularity from preexisting energy. This is a caveat that very well may not be true. You are basically grasping at straws where this remains not the consensus of the scientists.

If universes can potentially be cyclic in one form or another there may not be a start for space-time.

I accept the BGV theorem as a very likely scenario for the beginning of all possible universes from preexisting energy, but beyond that things get too hypothetical without sufficient information for the nature of a possible multiverse scenario.

[JimL]

Though time requires matter in order to exist, correct?

Says who? And is there a point you are trying to make?

[shunyadragon]

Though time requires matter in order to exist, correct?

Sort of incomplete. Yes, the time space continuum began with the expansion of the singularity according most models of the temporal beginning of the universe and matter was the result as a part of our universe, and all possible universes.

. . . but that is not the only possible concept of time, In Quantum Mechanics at the Quantum level there are possibly discrete units of time measured in quanta that occur at Quantum level of Quantum Zero Point Energy and Quantum Gravity called Quantum Time. It would be true that the time-space continuum does not exist at the Quantum level as it does in the macro universe.

Some also propose that in reality time does not exist.

Stephen Hawking introduced the concept of imaginary time, which would be another subject.

Like Jim I would also ask; What is your point?

[Roy]

As far as I understand, the BGV theorem assumes a space-time universe, and the condition is that the universe is on average, expanding.

Your own source says that BGV theorem also assumes that there isn't a period of contraction prior to the expansion. It also doesn't apply if there are a series of expanding and contracting universes.

Your claim that BGV theorem shows that a succession of universes must have a beginning is contradicted by the your own source: "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."

You claim to acknowledge caveats, but in truth you don't acknowledge them unless you're forced to, and even then it's mostly pretence. This whole thread can be summed up as:

Some-one said this theory shows there's a beginning, but I haven't checked. I'll assume there aren't any other possibilities, but won't check that either, in case I'm wrong.

[Tassman]

Yes, that appears to be what he is saying, so presumably one of the caveats to the BGV theorem is applied here.

It's a very significant caveat: Vilenkin from 1983: By "nothing" I mean a state with no classical spacetime. "Nothing" is a realm of unrestrained quantum gravity, a pre-geometric state in which all of our basic notions of space, time, energy, entropy etc., lose their meaning. (Quantum Cosmology Alexander Vilenkin Tufts Institute of Cosmology).

[lee_merrill]

Ahh . . . no. It has been repeatedly been brought to your attention there is not proof here.

I meant there is a proof, a theorem in this area of discussion.

And the BGV theorem applies to such universes, with the caveat that space-time may not apply at the very start.

The BGV theorem applies in this interpretation if universes begin as time space began as a singularity from preexisting energy.

I'm not sure what you mean here.

If universes can potentially be cyclic in one form or another there may not be a start for space-time.

Yes, though the one universe we know of is expanding without limit.

I accept the BGV theorem as a very likely scenario for the beginning of all possible universes from preexisting energy, but beyond that things get too hypothetical without sufficient information for the nature of a possible multiverse scenario.

Well, again, the BGV theorem provides a restriction on possible universe scenarios, it is not in itself a scenario.

Blessings,
Lee

[lee_merrill]

Though time requires matter in order to exist, correct?

Says who? And is there a point you are trying to make?

Says Einstein! As far as I understand him, space-time binds together space and time.

And this is important for the BGV theorem, because it only applies when the universe is describable as space-time.

Blessings,
Lee

[lee_merrill]

Your own source says that BGV theorem also assumes that there isn't a period of contraction prior to the expansion.

No, the source says the BGV theorem's requirement of an on-average expanding universe may not be met. No additional requirement here.

It also doesn't apply if there are a series of expanding and contracting universes.

If they are not on-average expanding, correct.

Your claim that BGV theorem shows that a succession of universes must have a beginning is contradicted by the your own source: "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."

And again, if the BGV assumption of on-average expansion is not satisfied, then the theorem does not apply. But if the universes on-average do expand, then any worldline under consideration cannot be infinite in the past.

Blessings,
Lee