Falsification of eternal inflation

[offroff]

Almost all planets in a multiverse with eternal inflation will be much younger than our earth.

Almost all conscious creatures in such a multiverse will live on young planets with an exceptionally quick evolution (related to the theoretical expected evolution speed).

But we live on an old planet with an evolution that most biologists don't think is exceptionally quick.

I think the observation of our situation and this reasoning is a falsification of eternal inflation.

Why do people believe in eternal inflation anyway?

 

[skydivephil]

If you would like to understand the case for eternal inflation. Guth states it here:
http://arxiv.org/abs/hep-th/0702178

 

[offroff]

I've read that.

Eternal inflation predicts that almost all conscious creatures live on planets with close to maximal evolution speed. That would mean that our Earth is extremely atypical, it doesn't make sense.

 

[skydivephil]

I don't think cacluating probabilites in the multiverse is as clear as youve suggested.

 

[offroff]

I think it's clear and easy. If it's not I wish someone can explain why.

 

[edgepflow]

I have worked through some of the math of choatic eternal inflation. It has its merits but there is quite a bit of hand waving and in the end I was not convinced I did a scientific calculation.

I would ask: is eternal inflation really needed to explain any observations?

 

[Chalnoth]

Almost all planets in a multiverse with eternal inflation will be much younger than our earth.

Almost all conscious creatures in such a multiverse will live on young planets with an exceptionally quick evolution (related to the theoretical expected evolution speed).

But we live on an old planet with an evolution that most biologists don't think is exceptionally quick.

I think the observation of our situation and this reasoning is a falsification of eternal inflation.

Why do people believe in eternal inflation anyway?

Probabilities don't work that way. Basically, imagine the following: you have a hundred boxes. You live among the first ten of those boxes. Now, we have two competing theories: theory one suggests that boxes 1-20 are filled, while theory two suggests that only boxes 1-10 are filled.

It turns out that our existence in boxes 1-10 provides no evidence whatsoever one way or the other as to which of these theories is more accurate.

 

[offroff]

Chalnoth,
I think you missed my argument, I'm afraid I didn't explain it very well.

Let's say we have a theory that says that one box is filled with blue color, and 99 boxes are filled with red color.
Another theory says that 99 boxes are filled with blue color and one box is filled with red color.

That's more like my argument. I think if we open a box with blue color we know which theory is the more probable.

Eternal inflation predicts that we find ourselves in a world with a very fast evolution. That's not what we see and from my point of view it makes eternal inflation an impossible theory.

Eternal inflation predicts red but we find blue. I'd be very happy if someone can understand my argument.

 

[Chalnoth]

Chalnoth,
I think you missed my argument, I'm afraid I didn't explain it very well.

Let's say we have a theory that says that one box is filled with blue color, and 99 boxes are filled with red color.
Another theory says that 99 boxes are filled with blue color and one box is filled with red color.

That's more like my argument. I think if we open a box with blue color we know which theory is the more probable.

No, it doesn't work, because eternal inflation predicts that there are many more boxes. The point of my analogy is that you can't compute probabilities using simple ratios when the total number isn't conserved.

 

[offroff]

Chalnoth,
You have no reason to be certain that this line of reasoning doesn't work, but you are right that I didn't define the problem very well.

Anyway, now I read Guths paper, it's a great one, and realize that this problem is very much about the youngness paradox. Guth believe that his reasoing about the youngness paradox is fine, but he admits:
"Although the problem of defining probabilities in eternally inflating universe has
not been solved"

So this is an open question I guess.

Then I would like to state the following: If the youngess paradox is true, then eternal inflation is false, because we have no reason to believe we are that special from a biological perspective.

What do you think of that statement?

 

[Chalnoth]

Chalnoth,
You have no reason to be certain that this line of reasoning doesn't work, but you are right that I didn't define the problem very well.

Anyway, now I read Guths paper, it's a great one, and realize that this problem is very much about the youngness paradox. Guth believe that his reasoing about the youngness paradox is fine, but he admits:
"Although the problem of defining probabilities in eternally inflating universe has
not been solved"

So this is an open question I guess.

Then I would like to state the following: If the youngess paradox is true, then eternal inflation is false, because we have no reason to believe we are that special from a biological perspective.

What do you think of that statement?

The youngness paradox is silly because inflation makes no statements about longevity. Sure, it produces a lot of young universes. But every single one of those will become an old universe in time (provided it doesn't recollapse, of course, but inflation tends to prevent that much of the time). The fact that many new, younger universes are always being created has nothing whatsoever to do with the fact that a universe will, in fact, become older.

 

[mitchell porter]

Eternal inflation predicts that almost all conscious creatures live on planets with close to maximal evolution speed.

Explain how it predicts that.

 

[Chalnoth]

Explain how it predicts that.

The prediction comes about as follows:
Eternal inflation continues causing part of the universe to expand at a dizzying pace forever into the future. Every second, an ever-increasing number of regions begin reheating. Because the number of new regions increases into the future, an equal-time slicing at any point of the universe will be overwhelmingly dominated by newly-reheated regions. I forget the exact numbers, but it's something like there is roughly 10^90 times more volume in regions that are just one second younger (this is because inflation causes the universe to grow by about 10^90 in volume every second). By this estimate, you would have around 10^(2,840,123,340) times as much volume in regions of the universe one year younger than our own (yes, that's a 1 with nearly 3 billion zeros following it).

The probability estimate, in other words, depends critically upon this idea of taking an equal-time slicing of the universe. Which I claim is nonsensical: whatever is going on outside our region of our visible universe cannot have any impact on anything that is going on here.

 

[mitchell porter]

It's a problem in specifying asymptotic frequencies in infinite sets. If you write down the natural numbers (in base 10) according to a certain pattern, you will always have more numbers starting with the digit 1 than with any other digit. So you could "prove" that, asymptotically, most numbers start with the digit 1. But it's just an artefact of a particular ordering. There must be a sensible mathematical or logical approach to such problems, but I don't know what it is.

 

[Chronos]

I was under the impression eternal inflation implies the 'multiverse' is undefinably ancient. Under that premise, it appears the universe in which we reside has an indefinite lineage of prior universes - hence we are among the younger of all universes having ever existed.

 

[Chalnoth]

I was under the impression eternal inflation implies the 'multiverse' is undefinably ancient.

No, that's not true. Eternal inflation is future-eternal. It still runs into the same problems as normal inflation in that it requires a beginning.

 

[offroff]

Mitchell porter,
I think if we are dealing with infinite sets I guess you're right it's hard to do the calculations (I didn't try ).

However, personally I don't grasp the concept of actual infinites in the real world. Am I supposed to believe in that? Eternal inflation has a beginning and I don't see how it reach infinity somewhere.

I guess my assumption is that we don't deal with an infinite set.

Chalnoth,
You're right that what's going on outside our region doesn't impact us. But we don't know what's going on there, we just have a theory and a theory must make predictions. It appears that we know that at any time the number of young universes are so many more than the old ones, it simply looks like we can use that knowledge.

Maybe it's nonsensical, and if you're thinkning of infinites like Mitchell, then I guess our different intuitions have to do with that.

(Maybe your philosophy of time is eternalism but I go with presentism)

 

[Chalnoth]

(Maybe your philosophy of time is eternalism but I go with presentism)

Presentism is incompatibility with relativity, which demonstrates that there is no such thing as a global "now".

 

[Farahday]

Presentism is incompatibility with relativity, which demonstrates that there is no such thing as a global "now".

In effect, you are correct, but in reality you are not. Given the two basic phenomena of existence and change whenever a change occurs, the situation of the entire universe is instantly altered.

Object a and object b are distance x from each other. All the objects around object a - and all the objects at any distance from a - are defined as being adjacent to an object that is x distance from object b.

If object a moves closer to object b - all the objects surrounding a are immediately defined as being located beside an object that is now y distance from b.

The situation was altered immediately, but reaction to it may not propagate for a while.

It takes time for change to occur, but a situation can change instantly in real time.

 

[offroff]

Chalnoth,
I guess a naive form a presentism looks stupid but I'm under the impression that the question of time is very open.

Since I don't believe in actual infinites in the real world I also can't believe in eternalism.

 

[Calrid]

The universe is eternal at least from our perspective it's also finitely old.

I agree this doesn't sound like a scientific principle, but then how could it be, we are the only life we know about that has reached sentience in x number of years. Although I'd dispute many people have tbh.

It's like the probability calculation that predicts the number of life forms in the universe, it could be 1 trillion life bearing planets or 0 except ours, no matter how unlikely that is it is possible. Ultimately though no supposition is going to be scientific no matter how philosophically robust the logic is. It is of course just an idea, chose to believe in its likelihood of success on that basis.

Since I don't believe in actual infinites in the real world I also can't believe in eternalism.

Be careful about expressing that opinion, every time I have threads have been locked for daring to claim that even in maths infinities are allusions, or a representation of a mythical property that denotes apparently logical proof in more poetic terms. Probably get this thread locked if someone replies to this so I wouldn't.

I don't think the concept of infinity makes any sense outside of asymptotic limit concerns personally, I think it is a mere conceit, in maths per se it is an aesthetic use of artistic license, that ultimately has no purpose.

I'm with the pre cantor philosophers on this one and in my experience the post Cantor philosophers. You cannot define what is beyond God, any more than you can define a mathematical God.

Sure as a set theory based on a non sequitur taken at face value it works. The maths is undeniable if we accept 1+1=2 then it must be true by the mere axiom itself, the philosophy however is not at all easy to justify sensibly.

I never argued that set theory is false by axiom, only that it is false without it and by using any real axiom that makes any sense intuitively, deductively or otherwise. I therefore question the utility of semantic wibble that distinguishes itself nowhere except in the dark cupboards where maths texts books are held in captivity.

 

[Chalnoth]

In effect, you are correct, but in reality you are not. Given the two basic phenomena of existence and change whenever a change occurs, the situation of the entire universe is instantly altered.

That's just false. There is no instantaneous communication of information, period. Changes propagate at or slower than the speed of light, period.

Object a and object b are distance x from each other. All the objects around object a - and all the objects at any distance from a - are defined as being adjacent to an object that is x distance from object b.

If object a moves closer to object b - all the objects surrounding a are immediately defined as being located beside an object that is now y distance from b.

The situation was altered immediately, but reaction to it may not propagate for a while.

It takes time for change to occur, but a situation can change instantly in real time.

I don't understand what this contortion is supposed to demonstrate. In any event it remains a fact that the definition of "now" is arbitrary, which means that there can't be any physical thing as a global "now", which means presentism is impossible.

 

[Chalnoth]

Chalnoth,
I guess a naive form a presentism looks stupid but I'm under the impression that the question of time is very open.

Since I don't believe in actual infinites in the real world I also can't believe in eternalism.

Eternalism doesn't require actual infinities. It just states that all points in time are equally real. Which is the view that we are forced into by relativity.

The name "eternalism" is somewhat misleading in that it seems to imply an eternal universe, but there is no reason to assume this.

 

[Farahday]

That's just false. There is no instantaneous communication of information, period. Changes propagate at or slower than the speed of light, period.

A change of condition propagates from element to element from the source. A change of situation is instantaneous. If a is adjacent to b and b is adjacent to c and suddenly a is replaced by d, then c is adjacent to an element (b) now adjacent to d instead of a. Once the replacement is made, it takes no time for the change of situation to occur.

BTW: Relativity dictates light speed limits apply to elements that have the property of mass, but what about elements that don't?

I don't understand what this contortion is supposed to demonstrate. In any event it remains a fact that the definition of "now" is arbitrary, which means that there can't be any physical thing as a global "now", which means presentism is impossible.

 

[Chalnoth]

A change of condition propagates from element to element from the source. A change of situation is instantaneous.

I have no idea what you mean by this distinction between "change of condition" vs. "change of situation", but it is irrelevant: within relativity, it is fundamentally impossible for any information, no matter the type, to propagate at faster than the speed of light.

BTW: Relativity dictates light speed limits apply to elements that have the property of mass, but what about elements that don't?

If it has no mass, then it always travels at the speed of light.

 

[Farahday]

I have no idea what you mean by this distinction between "change of condition" vs. "change of situation", but it is irrelevant: within relativity, it is fundamentally impossible for any information, no matter the type, to propagate at faster than the speed of light.

Propagation is a chain-REACTION. It is a response to a stimulus. It requires time to occur.
A change in situation is not a reaction - it is a change in the definition of reality as a whole.

If it has no mass, then it always travels at the speed of light.

Space has no measureable mass. Does it, too, travel at C?

 

[Chalnoth]

Propagation is a chain-REACTION. It is a response to a stimulus. It requires time to occur.
A change in situation is not a reaction - it is a change in the definition of reality as a whole.

Then your "change of situation" is either impossible or irrelevant.

Space has no measureable mass. Does it, too, travel at C?

Space isn't an entity in the same way that a particle is an entity. However, it seems likely that space-time is made up of the action of large numbers of individual gravitons that would, themselves, travel at the speed of light (just as an electromagnetic field is made up of many photons that individually travel at the speed of light).

It's worth mentioning, also, that gravitational waves travel at the speed of light.

 

[skydivephil]

No, that's not true. Eternal inflation is future-eternal. It still runs into the same problems as normal inflation in that it requires a beginning.

Aguirre claims he has found a way round that:
http://arxiv.org/abs/hep-th/0702178

If you read pg 16 of Guths's 2007 eternal inflaiton review you see he refers to it here

http://arxiv.org/abs/hep-th/0702178

 

[Chalnoth]

Aguirre claims he has found a way round that:
http://arxiv.org/abs/hep-th/0702178

Yeah, well, I doubt it. Making inflation past-eternal requires infinite fine tuning. However, you have the wrong link, as that's Guth's 2007 inflation review.

 

[skydivephil]

Yeah, well, I doubt it. Making inflation past-eternal requires infinite fine tuning. However, you have the wrong link, as that's Guth's 2007 inflation review.

sorry meant to paste this one:
http://arxiv.org/abs/astro-ph/0111191

 

[Chalnoth]

sorry meant to paste this one:
http://arxiv.org/abs/astro-ph/0111191

Thanks.

I don't buy it, though. They basically propose that you can get around the problem by simply ignoring it. You only get the geometry of deSitter space-time that they mention if your space-time is perfectly empty.

 

[dm4b]

I noticed an article in Scientific American recently that seemed to claim eternal inflation is losing support - possibly even by Guth himself.

Haven't had a chance to read it yet, though.

Anybody know more about this development?

 

[Chalnoth]

I noticed an article in Scientific American recently that seemed to claim eternal inflation is losing support - possibly even by Guth himself.

Haven't had a chance to read it yet, though.

Anybody know more about this development?

Well, it was only ever a speculative model to begin with. As far as I'm concerned, it's a potentially interesting but largely irrelevant possibility. A universe with eternal inflation sure would be strange, but I don't think it would directly impact much of anything we know about the universe.

So, in my view, it just comes down to the data: if we can sufficiently nail down the parameters of inflation to say whether or not our observable past was capable of eternal inflation, then we may be able to say whether or not there was eternal inflation. To determine this, we need to know two things:

1. The energy scale of inflation.
2. The size of perturbations during inflation.

If we can detect the gravitational wave signal from inflation with sufficient accuracy, then we will be able to determine these. This may be possible through observing the B-mode polarization in the CMB (which has not yet been done, though if we're really lucky, Planck will provide a first detection).

 

[offroff]

dm4b,
Do you mean http://www.nature.com/scientificamerican/journal/v304/n4/full/scientificamerican0411-36.html"?

 

[offroff]

Steinhardt makes a good point:

Now you should be disturbed. What does it mean to say that inflation makes certain predictions—that, for example, the universe is uniform or has scale-invariant fluctuations—if anything that can happen will happen an infinite number of times? And if the theory does not make testable predictions, how can cosmologists claim that the theory agrees with observations, as they routinely do?

I thought the theory can make testable predictions but maybe I was wrong. That's a serious problem

However, even if we're dealing with infinite sets I think we should be able to find a way to deal with probabilities. I mean; in some worlds we would see very very strange patterns and eternal inflation predicts that. It still doesn't make sense to let eternal inflation be the explanation for any problem (even if it might be true).