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 dont 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

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

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

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

Explain how it predicts that.

Chalnoth

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

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)