Falsification of eternal inflation

[Calrid]

My entire point here is that there isn't evidence for a unique universe, or for a multiverse. And we shouldn't just think that a multiverse requires evidence when a unique universe does not merely because people have thought our universe unique for longer.

And when we look at the actual merits of the two ideas, the multiverse wins hands down. Now, obviously, without strong evidence we can't say with any tremendous degree of confidence that a multiverse is true. But we can say it is more likely.

Note, also, that the same arguments that lead one to the conclusion that some sort of multiverse is likely also leads one to the conclusion that any specific multiverse proposal is unlikely.

Correct neither has any more validity because of age or any other quality you can imagine they are both equally valid and since they are mutually exclusive either one must be true or the other, which is about all we can say atm.

No it does not win hands down. You have again just proceeded straight to the conclusion without making an argument.

I'm not sure what you are saying any more tbh.

The fact still remains that neither a multiple universe or eternal multiple universe hypothesis distinguishes itself in any form, philosophically or otherwise. If you don't believe me you probably should try stepping out of your comfort zone and reading "theories" other than those who recommend multiverses. There is nothing wrong with any of them on philosophical grounds, apart from the fact none of them are scientific yet. You might say its easier to test for bounces than multiverses but again ease of testing does not = likelihood of correctness.

 

[Fra]

My entire point here is that there isn't evidence for a unique universe, or for a multiverse.

I do not see where the idea of uniquness comes from? I don't recognise mylself here.

My point is also exactly this: The action of any observer, depends only upong the evidence at hand. Which happens to be incomplete uncertain evidence of the observable universe she lives in. And this "picture" is constantly evolving.

There is no assumption of uniquenss here, on the contrary, the lack of definitivess is exactly what the single universe evolves. Evolves doesn't just mean classical cosmologial expansion, I mean that the laws of physics a re constatly challages and renegotiated as previously inferred symmetries are broken, and new symmetries are inferred.

My point is exactly that:

The rational action of any obsever, depends only upon the evidence at hand. But this evidence and action are evolving as things evolve. And there is not external description of this evolution, only inside views. Ie. a rational observer has not incentive to focus on anything by the evidence at hand, relating to the universe he lives in.

There is no uniqueness about this?

/Fredrik

 

[Fra]

The evidence at hand; is what FORMS the picture of the universe the observer lives in.

Ie. the "observable universe" as inferred from any inside observer is just due to the actual evidence it has. The only decision problem existing in this picture, is what action to take. The generalized locality principle then suggest that it's irrational to think that information that is not at hand would influence this decision.

This doesn't imply the assumption that there the future can't reveal things that will come to challage the current state. It just means that it's rational to place your bets according to your eviedence and nothing else. So it's like a game, without absolute rules. The rules are a matter of negotiation and evolution in an undecidable way from the point of view of the single player.

/Fredrik

 

[Calrid]

I do not see where the idea of uniquness comes from? I don't recognise mylself here.

My point is also exactly this: The action of any observer, depends only upong the evidence at hand. Which happens to be incomplete uncertain evidence of the observable universe she lives in. And this "picture" is constantly evolving.

There is no assumption of uniquenss here, on the contrary, the lack of definitivess is exactly what the single universe evolves. Evolves doesn't just mean classical cosmologial expansion, I mean that the laws of physics a re constatly challages and renegotiated as previously inferred symmetries are broken, and new symmetries are inferred.

My point is exactly that:

The rational action of any obsever, depends only upon the evidence at hand. But this evidence and action are evolving as things evolve. And there is not external description of this evolution, only inside views. Ie. a rational observer has not incentive to focus on anything by the evidence at hand, relating to the universe he lives in.

There is no uniqueness about this?

/Fredrik

Well he was talking to me. I see no issue with saying that both uniqueness and multiverse theories are pretty much on a par as hypotheses go, although I'd agree that the God did it hypothesis seems unlikely given it requires a divine and infinite being, but I cannot argue likelihoods all that strongly or with any conviction, because frankly nothing is preferred by what I think or anyone thinks. or any observer alien or human thinks which would be a stronger anthropic principle. And true your argument needs neither probably because it isn't some sort of religion driven argument it is completely secular as far as I can tell.

 

[Fra]

Well he was talking to me.

Ah Ok. I guess part of the confusion was due to me jumping into the middle of dicussion.

/Fredrik

 

[Chalnoth]

The fact still remains that neither a multiple universe or eternal multiple universe hypothesis distinguishes itself in any form, philosophically or otherwise.

Again, the number of assumptions is different. A singular universe (one big bang event, where the low-energy laws of physics are the same everywhere) requires additional assumptions. It is therefore highly unlikely.

 

[Calrid]

Again, the number of assumptions is different. A singular universe (one big bang event, where the low-energy laws of physics are the same everywhere) requires additional assumptions. It is therefore highly unlikely.

Why though?

If MWI contains less assumptions does it make it more likely to be true. Also does MWI really contain less assumptions or is it just another way of describing Copenhagen? The same can be said of both theories that really the only difference is how the universes are arranged, they are actually on paper identical with the same number of assumptions, the same number of potential variables; the issue of assumptions is semantic and has little to do with science. Also I don't think that the laws have to be the same everywhere in one universe at all, that is an added assumption that is entirely superfluous. Plus of course with every new universe then the laws are different because of the quantum starting conditions, depending on which theory you are talking about. Given enough monkeys and enough type writers and enough time, and given monkeys of infinite diversity that all type infinitely fast is a semantic way of saying the same thing.

Again you will have to explain this default thing to me again because I don't think you have even attempted to explain why x no of alternative universes are actually any different from x no of eternal universes. I've seen philosophical papers on both and to be honest they appear to be different ways of saying the same thing just like physics interpretations are.

You're not making a case here your just proceeding from a conclusion to a conclusion it's definitely a tautology.

The assumption issue to me all seems to be in how you want to apply language and nothing to do with science. Neither maths nor language underlie reality the reverse is true.

 

[Chalnoth]

Why though?

Why what? Why are fewer assumptions more likely to lead to the truth? Or why does a unique universe require more assumptions (same low-energy physical laws everywhere, one singular big bang event)?

Well, I've already given arguments to both. So instead I'll just give an example for the second: the standard model of particle physics. The standard model of particle physics contains within it spontaneous symmetry breaking. This well-tested theory unambiguously predicts that far enough away, the low-energy laws of physics will be different. To get a unique universe, you have to add assumptions to the theory: you need some new physical process to transform the spontaneous symmetry breaking into explicit symmetry breaking.

If MWI contains less assumptions does it make it more likely to be true.

Yes.

Also does MWI really contain less assumptions or is it just another way of describing Copenhagen?

It's not another way of describing the Copenhagen interpretation, because it actually describes what happens at the boundary of collapse, while the Copenhagen interpretation does not. Despite the use of the word "interpretation", the two are not the same theory, because MWI drops the assumption of collapse. Its predictions about the boundary of collapse have also been experimentally verified:
http://prl.aps.org/abstract/PRL/v77/i24/p4887_1

So here the intuition about fewer assumptions has worked fantastically.

 

[Calrid]

Why what? Why are fewer assumptions more likely to lead to the truth? Or why does a unique universe require more assumptions (same low-energy physical laws everywhere, one singular big bang event)?

Why indeed, do fewer assumptions always lead to truth or is that just your bias talking? Clearly many theories have far more assumptions than others and clearly are much better. The theory of the four elements and the theory of atoms for example.

Well, I've already given arguments to both. So instead I'll just give an example for the second: the standard model of particle physics. The standard model of particle physics contains within it spontaneous symmetry breaking. This well-tested theory unambiguously predicts that far enough away, the low-energy laws of physics will be different. To get a unique universe, you have to add assumptions to the theory: you need some new physical process to transform the spontaneous symmetry breaking into explicit symmetry breaking.

I disagree and so does Smolin et al.

Symmetry breaking can occur in both theories given time in one and given multiple universes in the other. This has yet to be established as a reason to favour one over the other. If it has I will be all ears.

It's not another way of describing the Copenhagen interpretation, because it actually describes what happens at the boundary of collapse, while the Copenhagen interpretation does not. Despite the use of the word "interpretation", the two are not the same theory, because MWI drops the assumption of collapse. Its predictions about the boundary of collapse have also been experimentally verified:
http://prl.aps.org/abstract/PRL/v77/i24/p4887_1

So here the intuition about fewer assumptions has worked fantastically.

So intuition working in one case dictates reality? That's not a very solid basis for an axiom is it. There are no black swans just because one person has never seen any? In this case we have. Clearly some people believe that all the posits remain consistent between the two ideas. If you think that one interpretation is favoured you are clearly not in the same ball park as the rest of science. If that were the case then these interpretations would not still be growing at a pace.

MWI describes what happens if the wave function is real, it has only moved the goal posts to a different area. We know nothing at all about the wavefunctions mapping onto the reality. Hence MWI is merely just the same way of stating the same thing, neither is more likely to be true. Tell me is the wave function real ie a pictorial representation of the wave or is it a purely inductive statement based on unknowable variables?

"If a tree falls in the woods and no one is around to hear it does it make a sound?"

Intuition is no substitute for science and evidence. Conjecture is no substitute for the facts of where we stand atm nor is philosophical blather about occams razor. If philosophy cannot distinguish two competing hypotheses then it must remain ignostic. Evidence will out.

http://www.world-science.net/exclusives/060330_multiversefrm.htm

<<quoted article deleted - go to the link above>>

The debate is still very much alive and kicking. Choosing a side seems premature to me.

I might buy it too, but arm waving is seldom convincing in science.

I can't read your paper by the way sadly. So I cannot comment on it. I doubt it has resolved this speculative issue though. Atm one can always question the interpretation of results.

 

[Chalnoth]

Why indeed, do fewer assumptions always lead to truth or is that just your bias talking? Clearly many theories have far more assumptions than others and clearly are much better. The theory of the four elements and the theory of atoms for example.

I never said that fewer assumptions always lead to the truth. What I said was that fewer assumptions usually lead to the truth. And it's obviously only a valid statement as long as the theories in question aren't already falsified.

And that's a terrible, terrible example anyway because not only was the old theory of four elements falsified long ago, it wasn't all that well-defined in the first place.

I disagree and so does Smolin et al.

And yet, you haven't been able to come up with a single coherent argument to support a unique universe, regardless of the fact that a unique universe requires more justification.

MWI describes what happens if the wave function is real, it has only moved the goal posts to a different area. We know nothing at all about the wavefunctions mapping onto the reality. Hence MWI is merely just the same way of stating the same thing, neither is more likely to be true. Tell me is the wave function real ie a pictorial representation of the wave or is it a purely inductive statement based on unknowable variables?

No, they are materially different theories. Wave function collapse is never absolute in MWI, whereas Copenhagen Interpretation assumes that under unspecified conditions, the wave function collapses. The problem with testing the Copenhagen Interpretation is precisely the fact that the theory is ill-defined: this means that any time what you're testing looks like MWI, you can just shift the boundary of collapse in CI to save CI from being falsified. Collapse in CI, in other words, is just a "god of the gaps". MWI, on the other hand, is exactly specified and can, in principle, be falsified (whereas the wavefunction collapse postulate of CI cannot be falsified).

The debate is still very much alive and kicking. Choosing a side seems premature to me.

It's reasonable to have some debate. What is unreasonable is people insisting that their ideas hold special status such that any other ideas must have evidence to be considered reasonable, without any justification for making such a claim.

The paper, by the way, basically shows two things:
1. The boundary of collapse is gradual, as predicted by MWI.
2. The wavefunction collapse occurs even though no measurement of the wavefunction is performed (an interaction is turned on, the results of which are not recorded).

 

[Calrid]

I never said that fewer assumptions always lead to the truth. What I said was that fewer assumptions usually lead to the truth. And it's obviously only a valid statement as long as the theories in question aren't already falsified.

And that's a terrible, terrible example anyway because not only was the old theory of four elements falsified long ago, it wasn't all that well-defined in the first place.

Which is a qualitative claim that has nothing to do with science.

I don't think any example is going to satisfy you with such premises as you have so meh.

It's reasonable to have some debate. What is unreasonable is people insisting that their ideas hold special status such that any other ideas must have evidence to be considered reasonable, without any justification for making such a claim.

Ironically that is precisely what you are doing.

I'm not making any claims, quite the opposite, I am saying we cannot make any claims atm both are equally likely to be true.

No, they are materially different theories. Wave function collapse is never absolute in MWI, whereas Copenhagen Interpretation assumes that under unspecified conditions, the wave function collapses. The problem with testing the Copenhagen Interpretation is precisely the fact that the theory is ill-defined: this means that any time what you're testing looks like MWI, you can just shift the boundary of collapse in CI to save CI from being falsified. Collapse in CI, in other words, is just a "god of the gaps". MWI, on the other hand, is exactly specified and can, in principle, be falsified (whereas the wavefunction collapse postulate of CI cannot be falsified).

No they are not materially different, ie the wave function has been shown to exist in all possible states by experiment, they are conceptually different.

It's not a "god of the gaps" because CI makes no judgement about what exists in those gaps it can only say that what happens between emission and measurement is undefined, ie it is agnostic about an entity before measurement. The wave may exist as a definite entity but such a contention cannot be known. Hence we say that it's description is a figurative one not a pictorial one.

The paper, by the way, basically shows two things:
1. The boundary of collapse is gradual, as predicted by MWI.
2. The wavefunction collapse occurs even though no measurement of the wavefunction is performed (an interaction is turned on, the results of which are not recorded).

Have they shown that there really is gradual collapse? I Wouldn't know I can't read the paper. AFAIK anyway Copenhagen is agnostic on what measurably happens at collapse anyway as it has to be by definition.

Doesn't MWI contend that collapse doesn't happen anyway because the wave function is real and the wave function actually exists as a complete description of physical reality before measurement? Hence it is deterministic.

The results are not recorded and never can be. This isn't even philosophy it's pure arm waving.

It is kind of pointless discussing that paper since I can't read it, but I bet plenty of people have contended that its results do not prove CI is wrong, or I would of heard about it. I suspect your conclusions are arguable and a matter of interpretation.

 

[Chalnoth]

Ironically that is precisely what you are doing.



Your conclusions are arguable and a matter of interpretation.

Uh, what? No they aren't. That's what the experiment shows. There is a measurement of the resulting wavefunction, obviously. That is how the progressive decoherence is observed. It is the interaction in the middle that involves no measurement.

 

[Calrid]

Uh, what? No they aren't. That's what the experiment shows. There is a measurement of the resulting wavefunction, obviously. That is how the progressive decoherence is observed. It is the interaction in the middle that involves no measurement.

So we still don't know what exactly happens at measurement, but we'll claim we do anyway? it still sounds inductive to me?

Kind of a pointless contention anyway because I can't read what you are talking about. An interesting analogy to the wave but ultimately a pointless discussion.

 

[dm4b]

Well, the main issue here is that we don't know how to sensibly talk about a universe without a spacetime. But even if you want to consider a universe starting literally out of nothing, the default expectation would be for it to start in a generic state, not in a very special one. And a generic state is, by definition, a high-entropy state. So even with a universe beginning out of nothing, you run into the exact same entropy considerations.

Looks like I missed a few pages of activity on this thread!

The human mind has the tendency to feel that what it cannot imagine, is not there. Just because spacetime could have been "created" at the moment of the Big Bang, does not mean the Universe was created out of nothing.

And, if we understand so little about how the Universe could have come about in this way, as to say it was created out of nothing, we surely can't say what the default expectation would be. Also, is entropy going to exist outside time/space? I would think a more highly ordered state would be just as likely, which might make a lower entropy beginning to the Universe more likely.

So, I disagree, I don't think we necessarily would have the exact same entropy considerations.

But, you're right, we do lack the ability at this point and time to talk sensibly (in physics terms anyhow) about a reality (NOT our Universe, which wouldn't be around anyhow) without space and time. But, then again, I'm not so sure reality is restricted by what we humans can talk about, let alone imagine.

I am reminded of an Alan Watts saying when I see some of the challenges in physics today: "A persistently insolvable problem should always be considered to perhaps be a question being asked the wrong way".

 

[Calrid]

And, if we understand so little about how the Universe could have come about in this way, as to say it was created out of nothing, we surely can't say what the default expectation would be.

I think it's rather arrogant to assume we have as yet any concrete answers.

Also, is entropy going to exist outside time/space? I would think a more highly ordered state would be just as likely, which might make a lower entropy beginning to the Universe more likely.

Entropy is such a contentious term, it only really makes sense in very specific situations we can measure with any consistency, when it comes to commenting on overarching reality it is such an ill defined term. Hell I don't recall the name, but one scientist went mad trying to pin it down to a system specifically.

For a start define ordered? Isn't that a human conceit? What is more ordered about a human being and the chemicals that make up his structure in whatever state they happen to be in. Or a diffuse mostly hydrogen gas cloud and a star? Think about it?

But, then again, I'm not so sure reality is restricted by what we humans can talk about, let alone imagine.

Quite we tend to be very anthropocentric. As I said before I'm not sure reality gives a toss about our speculations on it, or the conditions we try to force on it because of our biases.

I think Bohr had it right we might not have the language or maths to describe reality, that I hope will not always be the case.

I am reminded of an Alan Watts saying when I see some of the challenges in physics today: "A persistently insolvable problem should always be considered to perhaps be a question being asked the wrong way".

Nice way of putting it, I'm sure Bohr would of approved.

 

[George Jones]

It's not another way of describing the Copenhagen interpretation, because it actually describes what happens at the boundary of collapse, while the Copenhagen interpretation does not. Despite the use of the word "interpretation", the two are not the same theory, because MWI drops the assumption of collapse. Its predictions about the boundary of collapse have also been experimentally verified:
http://prl.aps.org/abstract/PRL/v77/i24/p4887_1

I have access to the paper but I have not read (or even downloaded) it. From its abstract:

The decoherence phenomenon transforming this superposition into a statistical mixture was observed while it unfolded

This seems to agree with my limited understanding. Decoherence takes a quantum state to a statistical mixture of classical states, and each classical possibility is a branch for the MWI.

A statistical mixture of classical states is represent by a diagonal density matrix, but the decomposition of a given diagonal density matrix into a classical mixture of states is highly non-unique! Which decomposition is used for the branching?

 

[Calrid]

Gah I so wish I could read it.

The Devil is in the details.

Be damned if I'm spending money on something if it doesn't conclusively disprove CI though. I doubt it does though, I suspect it just throws up more questions. If it does then surely science missed out on the moment where once and for all CI was disproved, I have as yet seen no breaking news.

 

[George Jones]

Gah I so wish I could read it.

Don't you have access to the paper (hardcopy or ecopy or both) through your school?

I'm a "mature" student studying maths & physics p/t AAMOI.

 

[marcus]

Hi George and Cairid,
Cairid did you know of the concept *Kairos* in Christian theology?
"In the New Testament kairos means "the appointed time in the purpose of God", the time when God acts (e.g. Mark 1.15, the kairos is fulfilled). It differs from the more usual word for time which is chronos (kronos)."
http://en.wikipedia.org/wiki/Kairos#In_Christian_theology

Your handle could be interpreted "of or pertaining to the Hour" (of fulfillment or of some significant event.)

I have no particular interest in theology, I just happened to notice the nice analogy between "the collapse of the wave function" and the Greek concept of *kairos*, the moment of fulfillment. Just an odd association that came to mind.

 

[Chalnoth]

Looks like I missed a few pages of activity on this thread!

The human mind has the tendency to feel that what it cannot imagine, is not there. Just because spacetime could have been "created" at the moment of the Big Bang, does not mean the Universe was created out of nothing.

And, if we understand so little about how the Universe could have come about in this way, as to say it was created out of nothing, we surely can't say what the default expectation would be. Also, is entropy going to exist outside time/space? I would think a more highly ordered state would be just as likely, which might make a lower entropy beginning to the Universe more likely.

So, I disagree, I don't think we necessarily would have the exact same entropy considerations.

Oh, we absolutely would. And here's why: entropy is proportional to the logarithm of the number of states that replicate the same overall properties of the system. So the number of configurations that look like a low-entropy state are vastly, vastly outnumbered by the number of states that look like a high-entropy state. The argument for a universe out of nothing starting in a generic state, then, has nothing to do with the physics of what came before. It's just simple counting.

In order to get a low-entropy start of the universe, you'd have to have some sort of physical process that makes the much smaller number of low-entropy states more likely, despite their very small number.

 

[Chalnoth]

Gah I so wish I could read it.

The Devil is in the details.

Be damned if I'm spending money on something if it doesn't conclusively disprove CI though. I doubt it does though, I suspect it just throws up more questions. If it does then surely science missed out on the moment where once and for all CI was disproved, I have as yet seen no breaking news.

A quick Google search found a free version:
http://www.atomwave.org/rmparticle/ao%20refs/aifm%20refs%20sorted%20by%20topic/decoherence%20refs/BHD96.pdf

But by the way, it doesn't falsify the Copenhagen Interpretation per se, because the Copenhagen Interpretation is, in regard to its treatment of wavefunction collapse, unfalsifiable, due to the fact that the conditions of collapse are completely unspecified. So in this regard, CI is "not even wrong". MWI, on the other hand, could have been falsified but wasn't.

 

[dm4b]

In order to get a low-entropy start of the universe, you'd have to have some sort of physical process that makes the much smaller number of low-entropy states more likely, despite their very small number.

Well, and that is sort of the key point I was trying to make.

Since we have no idea what physics would be required to "create" time itself, I don't think we can make any definitive claims. It may very well be that the "mechanism" that brought about the Universe (and spacetime), only allows the very Universe that we happen to have.

Also, once again, this in no way implies that the Universe came out of "nothing" either.

 

[Chalnoth]

Well, and that is sort of the key point I was trying to make.

Since we have no idea what physics would be required to "create" time itself, I don't think we can make any definitive claims. It may very well be that the "mechanism" that brought about the Universe (and spacetime), only allows the very Universe that we happen to have.

Also, once again, this in no way implies that the Universe came out of "nothing" either.

My point is that even if we don't know how to sensibly talk about what came before, we can sensibly talk about the beginning itself.

In any event, whatever the physical process that started off our region of space-time, that physical process has to somehow produce low-entropy states with higher frequency than would be implied by their entropy. One idea that I rather like is this one:
http://arxiv.org/abs/hep-th/0410270

It proposes that if we take seriously the idea of a small positive cosmological constant, then the asymptotic future of a universe is one that is very large and very empty, with extremely high entropy. But, it also has a very large volume, which means a low entropy density. So if only a tiny fraction of this volume undergoes a quantum fluctuation to become a new region of space-time, then that will actually not be a terribly large change in entropy, so it is not so strongly disfavored.

 

[dm4b]

So if only a tiny fraction of this volume undergoes a quantum fluctuation to become a new region of space-time

That does sound like an interesting proposal, within the framework of eternal inflation.

I'm not real up on the details of eternal inflation, so just wondering:

(1) How exactly does the new region of spacetime get "created" under eternal inflation? What's the mechanism for bringing about a new "Universe"? What math is used to describe this mechanism?

(2) How is this new region "connected" to our region of spacetime (assuming it spawned off our region of spacetime because of the above mentioned quantum fluctuation)?

(3) Does the theory allow any communication, or transit, between our spacetime and the newly created region of spacetime?

Thanks in advance for any info you can provide on these.

dm4b

 

[Chalnoth]

That does sound like an interesting proposal, within the framework of eternal inflation.

This isn't the same sort of idea as normal eternal inflation. It is similar in that it is future eternal, with new regions undergoing inflation all the time. But the difference is that they look at fluctuations in the late universe that can produce new inflating regions, instead of considering inflation itself to continue eternally all the time.

(1) How exactly does the new region of spacetime get "created" under eternal inflation? What's the mechanism for bringing about a new "Universe"? What math is used to describe this mechanism?

A universe dominated by a small cosmological constant has a temperature, albeit a very small one. This temperature will lead to fluctuations in all sorts of matter fields including, very occasionally, the inflaton field.

(2) How is this new region "connected" to our region of spacetime (assuming it spawned off our region of spacetime because of the above mentioned quantum fluctuation)?

It actually becomes disconnected almost instantly after formation. The new universe, from the outside, looks like a microscopic black hole that pops into existence then immediately decays away into nothing. From the inside, though, and entire new universe can form: the new universe sort of "pinches off" and becomes its own region of space-time.

(3) Does the theory allow any communication, or transit, between our spacetime and the newly created region of spacetime?

Nope.

 

[marcus]

...
In order to get a low-entropy start of the universe, you'd have to have some sort of physical process that makes the much smaller number of low-entropy states more likely, despite their very small number.

The Loop bounce does that.
Since when quantized in loopy fashion, gravity becomes repellent at very high density.
Uniformized states became more likely for a brief interval around the bounce.

Ashtekar's most recent review paper: http://arxiv.org/abs/1005.5491

BTW I see that the 2004 Carroll-Chen paper you cite has accumulated 33 citations:
http://arxiv.org/cits/hep-th/0410270
That's better than I would have expected, pretty respectable under the circumstances.
However, a good many of the cites look to be of the polite mention-in-passing variety. I don't see the Carroll-Chen idea catching on, being developed by other researchers, picked up by phenomenologists and so forth.

 

[Chalnoth]

The Loop bounce does that.
Since when quantized in loopy fashion, gravity becomes repellent at very high density.
Uniformized states became more likely for a brief interval around the bounce.

Ashtekar's most recent review paper: http://arxiv.org/abs/1005.5491

I remain extraordinarily skeptical of the bounce approach. The symmetry around the bounce would seem to require extreme fine tuning at the bounce, despite claims to the contrary. After all, if the picture is genuinely generic, then this approach predicts that if we reverse our time coordinate, then the finite past of our universe looks like a collapsing universe, which, according to LQC, predicts an inflationary expansion into the past behind the bounce (with the subsequent increase in entropy that this brings along with it).

So it seems like the idea has a contradiction built-in: if it's genuinely generic, then it predicts there will be an increase in entropy into the past, but that increase in entropy into the past requires massive fine tuning.

BTW I see that the 2004 Carroll-Chen paper you cite has accumulated 33 citations:
http://arxiv.org/cits/hep-th/0410270
That's better than I would have expected, pretty respectable under the circumstances.
However, a good many of the cites look to be of the polite mention-in-passing variety. I don't see the Carroll-Chen idea catching on, being developed by other researchers, picked up by phenomenologists and so forth.

I don't see how this is relevant.

 

[skydivephil]

With regards to inflation being eternal into the future but the not the past I have a question.
If we label the present T and future eternal inflation is true then there is a real point eternally into the future,lets call that point Te. IF Te is real then oberveers at Te will consider point T an eternity into their past. So for them the past is eternally far away. How could we know that we are not them? Can someone illucidate?

 

[dm4b]

(1) How exactly does the new region of spacetime get "created" under eternal inflation? What's the mechanism for bringing about a new "Universe"? What math is used to describe this mechanism?

A universe dominated by a small cosmological constant has a temperature, albeit a very small one. This temperature will lead to fluctuations in all sorts of matter fields including, very occasionally, the inflaton field.

Thanks for the info Chalnoth. I'm still confused on one question, which is quoted above.

As I understand it, inflation did not start at t=0 in our Universe. If so, inflation did not create the Universe. Is that correct?

If it is correct, I don't see what the mechanism is to actually create another region of spacetime, which spawns off our Universe. So, why does a quantum fluctuaton in our spacetime, bring about an entirely separate region of spacetime? What is the mechanism for this? What math desribes that mechanism and process? What physics is used to describe the creation of spacetime?

Your second response seems to be starting to answer this. But, I'm still not understanding the physics of how one region of spacetime can get "pinched off" our Universe?


In addition, it also seems like eternal inflation is a chicken/egg type question. If it does indeed claim that new Universes are created, or spawned off from, inflation fields created by quantum fluctuations in existing Universes, well, what started it all? Where did the first Universe come from? It doesn't go eternally into the past, which means there is a t=0, right? Well, what kicked it all off?

 

[Chalnoth]

Thanks for the info Chalnoth. I'm still confused on one question, which is quoted above.

As I understand it, inflation did not start at t=0 in our Universe. If so, inflation did not create the Universe. Is that correct?

Well, that depends upon what you mean by "t=0". If you mean the time of the singularity if you naively extrapolate a Lambda-CDM model back in time, yes, it is correct that inflation started before then. That time t=0 would have just been a particular time late in inflation, just before reheating, not any special time. The start of inflation would have come earlier. We don't know exactly when so it's not so easy to label a specific time t=0 that would have been the beginning of inflation.

Inflation is still responsible for the generation of the observable universe.