Falsification of eternal inflation

Chalnoth

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

Farahday

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.

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

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

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

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

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?

Chalnoth

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.

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

Farahday

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

Chalnoth

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

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

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

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

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

Chalnoth

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

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 this article?