Falsification of eternal inflation [Archive]

Chalnoth

Mar18-11, 07:31 AM

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

Mar18-11, 07:32 AM

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

Chalnoth

Mar18-11, 07:42 AM

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

Mar18-11, 07:58 AM

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

Mar19-11, 11:59 AM

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

Mar19-11, 12:26 PM

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

Mar19-11, 12:56 PM

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 :redface:).

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

Mar19-11, 01:06 PM

(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

Mar19-11, 05:10 PM

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

Mar20-11, 02:53 AM

Calrid

Mar20-11, 03:06 AM

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. :wink:

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. :smile:

Chalnoth

Mar20-11, 04:43 AM

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

Mar20-11, 04:45 AM

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

Mar20-11, 12:40 PM

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

Mar20-11, 02:01 PM

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

Mar20-11, 04:49 PM

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

Mar20-11, 05:59 PM

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

Mar22-11, 04:05 AM

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

Mar22-11, 04:44 AM

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

Mar22-11, 05:40 AM

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

Mar22-11, 06:00 AM

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

Mar28-11, 05:58 PM

Chalnoth

Mar28-11, 07:27 PM

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

Mar29-11, 05:38 AM

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

offroff

Mar29-11, 06:10 AM

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 :biggrin:

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).

Chalnoth

Mar29-11, 06:32 AM

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 don't think that's a very good point. If it were, then quantum mechanics itself would make no predictions whatsoever. But it does: it makes probabilistic predictions. And when you have large numbers (the number of fluctuations in the early universe was very large), the statistics of those numbers becomes highly predictable, even if, in principle, anything can happen.

The primary issue that he does have a good point on is, to me, the measure problem. I am extremely skeptical of his discussion about the cyclical universe, however, as that seems to completely violate everything we know about thermodynamics.

Calrid

Mar30-11, 01:24 AM

Has anyone pointed out that inflation is obviously eternal since nothing exists outside of time and there has never AFAIK been a time when the Universe was not inflating.

I'd like to think bangs and crunches were true because there should be evidence in this universe of them. But most likely it's just heat death and the slow demise of time itself. Or maybe in the quantum dominated almost void it starts all over again! :smile:

offroff

Mar30-11, 02:47 AM

Chalnoth,
Yeah, we really need probabilistic predictions but one of the arguments in this thread was that we can't use that on an infinite set.

My initial argument was maybe flawed but in theory there must be a prediction how the typical evolution of life in the multiverse looks like. Do you agree?

Chalnoth

Mar30-11, 10:33 AM

Has anyone pointed out that inflation is obviously eternal since nothing exists outside of time and there has never AFAIK been a time when the Universe was not inflating.
It doesn't work that way, actually. Basically, if you look at the way inflation works back into the past, unless you would like to impose an infinite degree of fine tuning, you end up with a singularity in the finite past. It seems clear that this singularity is rather unphysical, and thus inflation began as a result of some physical process in the finite past.

Even eternal inflation falls for this difficulty, and thus eternal inflation is generally considered to only be eternal in the future, not the past. There is nothing fundamental about inflation that requires it to have the properties for it to be eternal.

Chalnoth

Mar30-11, 10:35 AM

Chalnoth,
Yeah, we really need probabilistic predictions but one of the arguments in this thread was that we can't use that on an infinite set.
I already mentioned that the problem is the measure problem, not the general property of quantum mechanics that "everything happens".

dm4b

Mar30-11, 11:12 AM

offroff, yes that was the article, thanks! Maybe, since I am slow at work today, I will take the time to read it now ;-)

dm4b

Mar30-11, 12:55 PM

Well, I just read that article. This paragraph stuck out for me:

"Its raison d'être is to fill a gap in the original big bang theory. The basic idea of the big bang is that the universe has been slowly expanding and cooling ever since it began some 13.7 billion years ago. This process of expansion and cooling explains many of the detailed features of the universe seen today, but with a catch: the universe had to start off with certain properties. For instance, it had to be extremely uniform, with only extremely tiny variations in the distribution of matter and energy. Also, the universe had to be geometrically flat, meaning that curves and warps in the fabric of space did not bend the paths of light rays and moving objects."

So, inflation was brought about so the Universe would not be dependent upon a set of highly unlikely initial conditions?

But, maybe the Universe really was born out of a set of highly unlikely initial conditions.

Sort of like buying a lottery ticket. Many folks think that with 180 million to 1 odds, it's a waste of time ... they say, "you can NEVER win". Well, every other month, or so, somebody does win. Those people usually wouldn't question whether or not they CAN win anymore .. because they just did.

Maybe questioning the fact that the Universe started off with unlikely properties, wasn't the best idea? Maybe, it really did. Well, we have to question, but perhaps it has brought us full circle, with a tour through a not-meant-to-be theory called Inflation? And, in doing so, we become faced with even worse scenarios along these lines - "bad" inflation being more likley than "good" inflation, and even no inflation being more likely than inflation, etc.

Anyhow, with all that said, I thought the original Big Bang theory had other gaps in it other than unlikely initial conditions? Is that correct?

Chalnoth

Mar30-11, 01:01 PM

So, inflation was brought about so the Universe would not be dependent upon a set of highly unlikely initial conditions?

But, maybe the Universe really was born out of a set of highly unlikely initial conditions.
Well, it was. Inflation doesn't solve this problem. In fact, it basically has to be this way, because entropy has been increasing ever since.

Sort of like buying a lottery ticket. Many folks think with 180 million to 1 odds, it's a waste of time ... they say, "you can NEVER win". Well, every other month, or so, somebody does win. Those people usually wouldn't question whether or not they CAN win anymore .. because they just did.
The thing is, if you take the naive view of this, just using entropy, you run into the Boltzmann Brain problem: small fluctuations out of entropy are much more likely than large fluctuations. So it's much easier to get, for example, a single galaxy using this view than a whole universe. It's even easier to just get a single solar system. Easier still to just get a mind that merely thinks it sees an external universe, then immediately winks out of existence (the Boltzmann Brain).

But we know that's obviously wrong, so there had to be some interesting physics that let you get enough real universes produced that the real observers outnumber the Boltzmann Brains.

dm4b

Mar30-11, 04:18 PM

Well, I've lost access to that article, so I can't comment on the first part. Sounds like maybe I've misunderstood something a bit though.

As far as the Boltzmann Brain - hadn't heard of it before. But, I just read this on wiki:

"our current level of organization, having many self-aware entities, is a result of a random fluctuation, it is much less likely than a level of organization which is only just able to create a single self-aware entity."

This logic seems over-stretched to me, because life, once started, appears to be a self-organizing "force". In some sense, it constantly fights against entropy. We're basically dying from the day we are born, but there are forces in the body that renew and heal us all the time, which keep us going.

In addition, a "single self aware entity", takes many millions of years of evolution to form. They don't just instantly pop out of nowhere from a random fluctuation. In addition, once the stage is set for one to evolve, it is set for many to evolve. That's just sorta how life seems to work. I doubt you will find a self aware entity anywhere in the Universe with a lonely history completely unique to itself.

So, the reasoning in the Boltzmann Brain problem makes sense to me right up to the part where it considers the "Brain", or until it considers life.

dm4b

Mar30-11, 04:31 PM

The thing is, if you take the naive view of this, just using entropy, you run into the Boltzmann Brain problem: small fluctuations out of entropy are much more likely than large fluctuations. So it's much easier to get, for example, a single galaxy using this view than a whole universe. It's even easier to just get a single solar system. Easier still to just get a mind that merely thinks it sees an external universe, then immediately winks out of existence (the Boltzmann Brain).

Now, that I think twice about it, the Boltzmann Brain doesn't make sense to me at all, lol.

Could a Universe exists that actually consisted of a single galaxy. Or, a single solar system?

How could a solar system exist, w/o prior generation of stars that put out, in their deaths, some of the heavier elements that planets are made of. Could a galaxy exist, as we know it, without other galaxies?

In addition, it seems to argue that the order from most complex to most simple is, our Universe, a galaxy, a solar system, a self aware entity.

I would argue the order should be Our Universe with self-aware entities, Our Universe without self-aware entities, a galaxy, a solar system.

I think the whole idea ignores all the interdependencies that are required for the existence of the "objects" it takes under consideration.

Anyhow, I guess this is getting off topic ...

Chalnoth

Mar30-11, 07:50 PM

Now, that I think twice about it, the Boltzmann Brain doesn't make sense to me at all, lol.
That's sort of the point. It's an "argumentum ad absurdum", aka and argument from contradiction. If you consider a universe to simply be a particularly large fluctuation out of equilibrium, then you inevitably arrive at the conclusion that individual brains popping in and out of existence, as rare as they are, are far more common than real observers. And that is nonsense: it contradicts the observation that we are real.

So if your theory predicts that Boltzmann Brains are more common than real observers, that theory is wrong. That was my point.

dm4b

Mar30-11, 09:37 PM

That's sort of the point. It's an "argumentum ad absurdum", aka and argument from contradiction. If you consider a universe to simply be a particularly large fluctuation out of equilibrium, then you inevitably arrive at the conclusion that individual brains popping in and out of existence, as rare as they are, are far more common than real observers. And that is nonsense: it contradicts the observation that we are real.

So if your theory predicts that Boltzmann Brains are more common than real observers, that theory is wrong. That was my point.

Well, I get that. I'm just not sure that our theories really predict that.

It seems to me it's assuming something is common, only because we are neglecting the fact that many other things are also required, and must come first, due to the interdependent nature.

If you look at it that way, perhaps the small fluctuations can't really bring about anything. It's only a large one, which can bring about everything we see that can, in reality, actually achieve anything. It's the whole show or nothing.

I don't know if this is the right way to think about things. It just seems like the other view is missing something too.

Calrid

Mar31-11, 02:38 AM

It doesn't work that way, actually. Basically, if you look at the way inflation works back into the past, unless you would like to impose an infinite degree of fine tuning, you end up with a singularity in the finite past. It seems clear that this singularity is rather unphysical, and thus inflation began as a result of some physical process in the finite past.

Even eternal inflation falls for this difficulty, and thus eternal inflation is generally considered to only be eternal in the future, not the past. There is nothing fundamental about inflation that requires it to have the properties for it to be eternal.

I'm not sure everyone would agree with that assertion or that its even justifiable.

Eternal means existing always, from our perspective the universe has always existed since outside of time makes no practical sense. It does not I think mean what you think it does. The universe has always been in a stage of inflation since t>0 or when time and hence space exists if you like. The so called singularity or point of origin at t=0 is undefined for obvious reasons. If we prove that there was a before t = 0 empirically this may change. At the moment such a contention is still speculative so any conjecture is rather philosophical atm.

offroff

Mar31-11, 03:59 AM

dm4b,
Boltzmann brains is not offtopic, my thoughts about ultraquick evolution is similar (my argument failed though). I think we need to be aware that there are a lot that needs to be explained. A cosmological theory that explains physics is not enough, it also needs to be in line with philosophy, psychology and biology as well. I think physicists should know that :)

Chalnoth

Mar31-11, 04:51 AM

Well, I get that. I'm just not sure that our theories really predict that.
Boltzmann Brains are a definite prediction of a naive thermal fluctuation model, where one tries to explain the low entropy in the early universe by just saying, "Well, thermal fluctuations out of equilibrium happen all the time, maybe the early universe was just a particularly big thermal fluctuation."

Most think that the small physical size of the inflationary epoch likely has something to do with this, and there are some reasonable explanations that solve the problem. Eternal inflation, by the way, isn't one of them.

Chalnoth

Mar31-11, 04:53 AM

I'm not sure everyone would agree with that assertion or that its even justifiable.

Eternal means existing always, from our perspective the universe has always existed since outside of time makes no practical sense. It does not I think mean what you think it does. The universe has always been in a stage of inflation since t>0 or when time and hence space exists if you like. The so called singularity or point of origin at t=0 is undefined for obvious reasons. If we prove that there was a before t = 0 empirically this may change. At the moment such a contention is still speculative so any conjecture is rather philosophical atm.
Uh, what? There is no reason whatsoever to believe that inflation at the start of our observable universe was the beginning of all time and space.

Calrid

Mar31-11, 05:07 AM

Uh, what? There is no reason whatsoever to believe that inflation at the start of our observable universe was the beginning of all time and space.

There's no reason to believe it wasn't either. That is the point. It's a philosophical issue really isn't it.

Since all we know or theorise on is the evolution of the Universe at t>0 or post whatever the singularity was, or in a phase of expansion then not only has inflation always happened but from our perspective it is also eternal as far as is known. Any meaningful proposition that has any observable evidence, can only be determined when time and space existed from inside our reality. Will that always be so I have no idea, maybe?

Chalnoth

Mar31-11, 05:09 AM

there's no reason to believe it wasn't either. That is the point.
Oh, there is certainly a very good reason. If a physical process can happen once, chances are it can happen many times. Claiming that the physical process that started our universe only happened once is special pleading, and exceedingly unlikely.

But the original point was just that from our perspective the universe is eternal, which is hard to argue with unless you have proof otherwise.
That has nothing to do with whether or not inflation itself is future-eternal.

Calrid

Mar31-11, 05:14 AM

Oh, there is certainly a very good reason. If a physical process can happen once, chances are it can happen many times. Claiming that the physical process that started our universe only happened once is special pleading, and exceedingly unlikely.

Do you have any evidence?

Special pleading it is not. What you are doing is begging the question.

I make a case that neither is distinguishable going on the evidence we have anyway. I provide an alternative merely to demonstrate this is still a purely philosophical issue.

That has nothing to do with whether or not inflation itself is future-eternal.

I never said it did, now did I? However it could be true. It could be that there is no evidence of previous Universes and never will be. This could be for one of two reasons, neither of which has anything more evidence based support. This is and has been the only universe (big bangs and collapses would also be in that category) or the evidence is just not available to us from inside the universe and hence the answer to the question is eternally moot.

Chalnoth

Mar31-11, 05:33 AM

Do you have any evidence?

Special pleading it is not. What you are doing is begging the question.
Um, no. This is just the way math works. It is far more difficult to have just one member of a class of objects than it is to have an entire class of objects. Basically, in order to have just one member of a class of objects, you need all of the axioms required to get the entire class of objects, plus some more to specify the single member.

That's why it's special pleading: you need to add additional restrictions to get just one.

I make a case that neither is distinguishable going on the evidence we have anyway. I provide an alternative merely to demonstrate this is still a purely philosophical issue.
This is why we have Occam's Razor. If a model requires additional assumptions, it's probably wrong. Specifying only a single universe requires additional assumptions, so it's probably wrong.

Calrid

Mar31-11, 05:38 AM

Um, no. This is just the way math works. It is far more difficult to have just one member of a class of objects than it is to have an entire class of objects. Basically, in order to have just one member of a class of objects, you need all of the axioms required to get the entire class of objects, plus some more to specify the single member.

That's why it's special pleading: you need to add additional restrictions to get just one.

So maths makes proof now how trite.

You need to have internal inflation and collapse with quantum "starting"/"ending" conditions which explain fluctuations in constant properties actually.

It requires nothing other than a philosophy atm to imagine these things. Maths does not and has never constituted a proof of anything on its own, nor does your theory that there are infinite universes or x universes distinguish itself from any eternal expansion and collapse theory. It is assuming the antecedent aka begging the question.

You are assuming that the "end" of space and time before collapse is dominated by classical phenomena and that the singularity behaves in a classical manner after collapse. I think its pretty certain that entropy is not a process that tends to produce reversible consequences anyway, again your assumptions are flawed. Both theories could produce an extraordinarily wide variety of starting conditions. Neither is distinguishable in science as yet.

This is why we have Occam's Razor. If a model requires additional assumptions, it's probably wrong. Specifying only a single universe requires additional assumptions, so it's probably wrong.

Ockam's razor is a tendency it is certainly not a scientific principle, or we'd still be sitting in caves debating which of the four elements made up wood.

Clearly quantum mechanics is far more complex than the pre quantum models, and general and special relativity are far more involved than Newtons ideas about time and space.

If you are going to use philosophical principles as proofs at least acknowledge this is still a philosophical question. And as yet there are no clear answers that are scientific.

Occam's razor is that the most parsimonious theory tends to be right more often. I don't believe yours is tbh.

Chalnoth

Mar31-11, 06:24 AM

Occam's razor is that the most parsimonious theory tends to be right more often.
And positing one single universe requires more assumptions than positing a class of universes. You not only have to posit the physical process, and everything that involves, in starting the universe off, but you also have to assume it only happens once. And because the assumption is specific to the thing being claimed, it is special pleading.

You don't get out of special pleading by saying, "Well, maybe I'm right after all!" Yes, maybe you're right. But most likely you're wrong, as you already admitted.

Calrid

Mar31-11, 06:33 AM

And positing one single universe requires more assumptions than positing a class of universes. You not only have to posit the physical process, and everything that involves, in starting the universe off, but you also have to assume it only happens once. And because the assumption is specific to the thing being claimed, it is special pleading.

You don't get out of special pleading by saying, "Well, maybe I'm right after all!" Yes, maybe you're right. But most likely you're wrong, as you already admitted.

I never said it only happens once quite the opposite the big bang could of happened an inconceivable amount of times, I just said that the Universe goes through endless bangs and collapses, which means there is only one Universe. Obviously it follows then it is eternal, it could be I'm wrong but using philosophically specious maxims wont prove that, evidence might. I am agnostic if anything.

Assuming that it must have multiple universes is in fact begging the question and still is since either hypothesis seems to be able to produce physically diverse universes, either over time or all at once. To distinguish the two you would have to prove that either of these assumptions was more likely true than the other at least and or that the other could not happen. To make it science you would need evidence.

It's not special pleading please stop saying that, it doesn't make sense as I am not making any claim of one theory being better than another for a reason I am assuming. It is a simpler version than yours I think (for whatever that is worth which is nothing pretty much) which makes your assumption that the only valid solution requires multiple Universes suspect. You have assumed that the only reasonable explanation involves multiple universes but this is not something that is true. I also suspect Lee Smolin would beg to differ since it is for the most part his "theory" du jour.

Like with most of these argument simpler tends to devolve into what you consider simple. Is it simpler to have only one universe with an indeterminate number of a bangs and crunches or multiple universes. I'd say just one universe with an entropic progression producing many varied parameters but its probably a matter of taste and how you weigh complexity.

There is nothing hypothetically limiting either "theory" from being true, likewise there is nothing that distinguishes them atm.

If I am using special pleading to say that the two "theories" are indistinguishable I have no idea where?

I don't get why you think I am claiming one wins over the other because of any assumption, quite the contrary both are legitimate hypothetically, neither distinguishes itself beyond that though.

Chalnoth

Mar31-11, 06:52 AM

I never said it only happens once, I just said that the Universe goes through endless bangs and collapses, which means there is only one Universe. That is eternal, it could be I'm wrong but using philosophically specious maxims wont prove that, evidence might. I am agnostic if anything.
It's still special pleading to assume only one universe, however. In any event, I find such a scenario obscenely unlikely, because it seems to violate entropy considerations.

And yes, I will keep saying special pleading, because it's the correct word to use. Special pleading is when you make up an assumption just to apply to the argument at hand. Without the assumption of a single universe, you get a proliferation of universes and have fewer assumptions.

Multiple universes isn't an additional assumption. It's the default: it's what you get when you fail to add the assumption of a single universe.

Calrid

Mar31-11, 06:57 AM

It's still special pleading to assume only one universe, however. In any event, I find such a scenario obscenely unlikely, because it seems to violate entropy considerations.

And yes, I will keep saying special pleading, because it's the correct word to use. Special pleading is when you make up an assumption just to apply to the argument at hand. Without the assumption of a single universe, you get a proliferation of universes and have fewer assumptions.

Ok then keep misapplying the term, to be special pleading I would have to be making a case that something is true or more likely, when I am making a case that neither can be distinguished as of yet. I am not making a case for either so special pleading is inapt.

Your idea that more universes makes it simpler than 1 universe is spurious also. One universe with multivariate constants if anything is simpler.

You assume there are multiple universes without telling us why one eternally expanding and collapsing universe cannot produce the same observable results, which of course I'm sure many scientists would contend with. Why is Smolin's theory of eternal collapse and inflation less likely than yours? What distinguishes the two?

Multiple universes isn't an additional assumption. It's the default: it's what you get when you fail to add the assumption of a single universe.

Huh default is not even a philosophical term it's just arm waving, what makes any of these positions the default exactly?

It's what you get when you fail to add the assumption of multiple universes.

Or more precisely when you can determine why one should be more likely than the other or the other false.

In any event, I find such a scenario obscenely unlikely, because it seems to violate entropy considerations.

Can you explain this further? What about entropy concerns forbids theories like this?

The Big Bounce is a theorized scientific model related to the formation of the known universe. It derives from the cyclic model or oscillatory universe interpretation of the Big Bang where the first cosmological event was the result of the collapse of a previous universe.[1]

Expansion and contraction

According to some oscillatory universe theorists, the Big Bang was simply the beginning of a period of expansion that followed a period of contraction. In this view, one could talk of a Big Crunch followed by a Big Bang, or more simply, a Big Bounce. This suggests that we might be living in the first of all universes, but are equally likely to be living in the 2 billionth universe (or any of an infinite other sequential universes).

The main idea behind the quantum theory of a Big Bounce is that, as density approaches infinity, the behavior of the quantum foam changes. All the so-called fundamental physical constants, including the speed of light in a vacuum, were not so constant during the Big Crunch, especially in the interval stretching 10−43 seconds before and after the point of inflection. (One unit of Planck time is about 10−43 seconds.)

If the fundamental physical constants were determined in a quantum-mechanical manner during the Big Crunch, then their apparently inexplicable values in this universe would not be so surprising, it being understood here that a universe is that which exists between a Big Bang and its Big Crunch.
[edit] Recent developments in the theory

Martin Bojowald, an assistant professor of physics at Pennsylvania State University, published a study in July 2007 detailing work somewhat related to loop quantum gravity that claimed to mathematically solve the time before the Big Bang, which would give new weight to the oscillatory universe and Big Bounce theories.[2]

One of the main problems with the Big Bang theory is that at the moment of the Big Bang, there is a singularity of zero volume and infinite energy. This is normally interpreted as the end of the physics as we know it; in this case, of the theory of general relativity. This is why one expects quantum effects to become important and avoid the singularity.

However, research in loop quantum cosmology purported to show that a previously existing universe collapsed, not to the point of singularity, but to a point before that where the quantum effects of gravity become so strongly repulsive that the universe rebounds back out, forming a new branch. Throughout this collapse and bounce, the evolution is unitary.

Bojowald also claims that some properties of the universe that collapsed to form ours can also be determined. Some properties of the prior universe are not determinable however due to some kind of uncertainty principle.

This work is still in its early stages and very speculative. Some extensions by further scientists have been published in Physical Review Letters.[3]

Peter Lynds has recently put forward a new cosmology model in which time is cyclic. In his theory our Universe will eventually stop expanding and then contract. Before becoming a singularity, as one would expect from Hawking's black hole theory, the Universe would bounce. Lynds claims that a singularity would violate the second law of thermodynamics and this stops the Universe from being bounded by singularities. The Big Crunch would be avoided with a new Big Bang. Lynds suggests the exact history of the Universe would be repeated in each cycle. Some critics argue that while the Universe may be cyclic, the histories would all be variants.

http://en.wikipedia.org/wiki/Big_Bounce

Just AAMOI.

dm4b

Mar31-11, 11:22 AM

It's still special pleading to assume only one universe, however. In any event, I find such a scenario obscenely unlikely, because it seems to violate entropy considerations.

I can't help but wonder if we need to think outside the box ( of spacetime ) on this one.

What I mean is that entropy really only functions within spacetime. How can entropy increase without time? How can you get a fluctuation without time?

If spacetime was created at t=0, applying thinking/logic that is linear in time is not going to fit the bill before that. How can we say a fluctuation gave rise to spacetime, since the fluctuation would have had to happen "before" time existed, in order to give rise to it.

Unless we are going to say time existed always, just to get out of that trap. But, that doesn't really seem all that pleasing either.

Chalnoth

Mar31-11, 12:47 PM

Ok then keep misapplying the term, to be special pleading I would have to be making a case that something is true or more likely, when I am making a case that neither can be distinguished as of yet. I am not making a case for either so special pleading is inapt.
Doesn't really matter. You're still making the case that the two ideas are roughly equivalent when they're not even close to being so.

Your idea that more universes makes it simpler than 1 universe is spurious also. One universe with multivariate constants if anything is simpler.
Not based upon any relevant definition of simplicity. Fully-define one universe, and you automatically get lots of others unless you explicitly exclude them. That explicit exclusion makes the one universe idea the more complex one.

Can you explain this further? What about entropy concerns forbids theories like this?
Because it's cyclical. At least in a simplistic view, you can't go from "entropy always increases" to a cyclical universe. In order for me to come close to believing this, they'd have to show that entropy increases continuously throughout the whole process. This would mean, among other things, that each "bounce" was different from the last.

Never mind that given the observed acceleration of our observable universe, this picture looks exceedingly unlikely to apply to our universe.

Chalnoth

Mar31-11, 02:53 PM

I can't help but wonder if we need to think outside the box ( of spacetime ) on this one.

What I mean is that entropy really only functions within spacetime. How can entropy increase without time? How can you get a fluctuation without time?
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.

Calrid

Apr1-11, 12:22 AM

Doesn't really matter. You're still making the case that the two ideas are roughly equivalent when they're not even close to being so.

Ok lets cut the bs. Can you justify this or not? If not then there's no point talking about it. Show me how one of these theories is more likely than the other?

How would you go about it without evidence anyway. All the well crafted philosophy in the world has never made anything true without evidence, it could be that there has only ever been one universe and God made it for all I know. As much as I don't believe that to be true I cannot prove it absolutely is not.

Not based upon any relevant definition of simplicity. Fully-define one universe, and you automatically get lots of others unless you explicitly exclude them. That explicit exclusion makes the one universe idea the more complex one.

Simplicity is a qualitative term and hence has no explicit use. I disagree less variables means a simpler system. Do you see what I mean. This contention has no more use to science than your bench mark idea had, which was bizarre by the way.

Because it's cyclical. At least in a simplistic view, you can't go from "entropy always increases" to a cyclical universe. In order for me to come close to believing this, they'd have to show that entropy increases continuously throughout the whole process. This would mean, among other things, that each "bounce" was different from the last.

Er that makes no sense, entropy is still increasing when it bounces, things don't get more organised when compacted they are all just as disorganised hence the multivariate starting conditions. Your arguments make no sense there is no philosophical contention to these theories let alone scientific ones.

Entropy is a philosophically contentious term in itself at least as it applies outside of heat concerns. More or less organised is extremely anthropocentric. What makes a neutron star more organised than a cloud of hydrogen anyway? Doesn't even make any philosophical sense from an unbiased point of view. In fact what makes a human being more organised than a vat full of the same chemicals exactly?

The universe is still technically the same size as t>1 as it is when it is t>100000 sextilion anyway just as it has the same amount of energy at the singularity as it does at heat death.

Even if entropy is reversed it is unlikely we will see the same patterns emerging in reverse anyway.

Never mind that given the observed acceleration of our observable universe, this picture looks exceedingly unlikely to apply to our universe.

Yet another religious statement you have failed to justify.

Clearly you have not studied the model enough to comment on it anyway. The op starts with the contention that the view eternal expansion is losing support. Whether it is or it isn't its interesting, even if it proves nothing.

Of course I haven't even started on other theories that don't rely on multiple universes, like big bangs becoming ever more likely after heat death and the approach of the end of "time" and thus there are infinite universes contained in the same universe not seperate. One universe that lives on the remains of another. There's another one you couldn't possibly begin to dismiss with such worthless philosophical nothing.

Philosophical wibble \neq science and it never will be, I hope. Although clearly String Theorists would like Nobel Prizes to be handed out for their philosophy. :tongue:

Max™

Apr1-11, 02:13 AM

Occam's razor is a tendency it is certainly not a scientific principle, or we'd still be sitting in caves debating which of the four elements made up wood.
Water and Earth, hafter converting Air using the Skyfire for an energy source to activate the catalysts, obviously.
Occam's razor is that the most parsimonious theory tends to be right more often. I don't believe yours is tbh.
No, the razor says nothing about accuracy, it says when given a choice between different explanations of a phenomenon, the one which requires the least assumptions while providing the same utility as an explanatory framework should be preferred.

Additionally it is more difficult to test a hypothesis which multiplies entities needlessly, so the subtle selection pressure of physically possible experiments would naturally favor the most simple models.

As for eternal inflation, I'm still a fan of the black hole -> selection ideas, though the CCC idea is neat enough that I still need to look at it sometime, I always liked Penrose.

Calrid

Apr1-11, 03:28 AM

Water and Earth, hafter converting Air using the Skyfire for an energy source to activate the catalysts, obviously.

Yes but what about the 5th element by which I mean not Mila Jovovich in skimpy clothes, but spirit.

No, the razor says nothing about accuracy, it says when given a choice between different explanations of a phenomenon, the one which requires the least assumptions while providing the same utility as an explanatory framework should be preferred.

Additionally it is more difficult to test a hypothesis which multiplies entities needlessly, so the subtle selection pressure of physically possible experiments would naturally favor the most simple models.

As for eternal inflation, I'm still a fan of the black hole -> selection ideas, though the CCC idea is neat enough that I still need to look at it sometime, I always liked Penrose.

Ok that's just semantics but fine. Occams razor is a means to select methods which will then more likely provide a better answer (whatever the hell that means) doesn't really change anything or differ from what I said or where my argument was going, if we look at the context of the argument, rather what he was saying was that a property means that a hypothesis has more likelihood of being correct. This is clearly not true I quite agree with you on this even if I didn't make that clear at first.

should be preferred because of what? it's likelihood to be what? Simpler or have some form of qualitative value beyond just the simple? We're talking about science here so the razor to have any meaning needs to be grounded in the scientific method first.

It seems to me just saying it should be preferred because it is easier to test is trite and not what it really should mean in this context, as if we have no pragmatism we end up disappearing up our own axiom. In this argument we are talking about things that are unable to be distinguished which already means Occams razor is moot. Ultimately a property real or imaginary is not sufficient to make an argument logical and it certainly isn't in science.

The fact is in this discussion he is actually trying to suggest that a philosophical assumption constitutes a scientific one or some probabilistic chanciness of being right, I disagree that Occams razor has a quantitative truthiness value unless there is already a theory. So in essence we probably agree but disagree on semantics. It could be that the GUT is made up of one law or trillions, nothing rests on philosophy, everything rests on evidence.

A hypothesis does not stand or fall on its ability to be tested or the ease in doing so, it stands or falls on being right.

Which is both the curse and salvation of string theory incidentally. :smile:

This is why we have Occam's Razor. If a model requires additional assumptions, it's probably wrong. Specifying only a single universe requires additional assumptions, so it's probably wrong.

Besides I was responding to this so you should probably take it up with him. :tongue:

He was the one suggesting simplicity suggests correctness, I was the one disagreeing. :wink:

Chalnoth

Apr1-11, 05:20 AM

Ok lets cut the bs. Can you justify this or not? If not then there's no point talking about it. Show me how one of these theories is more likely than the other?
What, do you want a derivation of Occam's Razor? Um, okay.

Let's imagine that we have a set of theories, and we divide them into three groups.

Group A are theories which describe all current evidence and have N assumptions.
Group B are theories which describe all current evidence and have N+1 assumptions.
Group C are theories which either don't describe all current evidence, or use some different number of assumptions.

Now, the additional assumption in group B gives members of this group more freedom: they can be far, far more different from one another than the members of group A. This indicates that the members of group A are more likely to be close to reality (because they are closer to one another) than the members of group B.

Of course, we can't say that the members of group A are likely in an absolute sense, because we don't know if N is the minimum number of assumptions possible, and future experiment may rule out the members of group A entirely. However, due to the much greater number of members of group B, any specific choice of a member of group B is still unlikely to be correct.

Calrid

Apr1-11, 05:25 AM

What, do you want a derivation of Occam's Razor? Um, okay.

Let's imagine that we have a set of theories, and we divide them into three groups.

Group A are theories which describe all current evidence and have N assumptions.
Group B are theories which describe all current evidence and have N+1 assumptions.
Group C are theories which either don't describe all current evidence, or use some different number of assumptions.

Now, the additional assumption in group B gives members of this group more freedom: they can be far, far more different from one another than the members of group A. This indicates that the members of group A are more likely to be close to reality (because they are closer to one another) than the members of group B.

Of course, we can't say that the members of group A are likely in an absolute sense, because we don't know if N is the minimum number of assumptions possible, and future experiment may rule out the members of group A entirely. However, due to the much greater number of members of group B, any specific choice of a member of group B is still unlikely to be correct.

I don't know why you are answering this point as I and other posters have pointed out Occams razor is worthless without a theory with which to compare yours and my two suggestions are hypothesis. So if you want to compare String theory say (with multiple Universes) and Bounce theory with just one then all you have is a matter of opinion. If you're trying to suggest which one you think is most likely to be true fine I agree to some extent that many universes is quite attractive, however its qualities do not denote its degree of verracity. I disagree with your assertions simply because they are opinions, but then discussions on hypotheticals are always a matter of opinion since facts are not present. I could quite easily argue FSM done it and that therefore the values are what they are because FSM is perfect, and you wouldn't be able to disprove that either, philosophically or scientifically for that matter.

You can't get around basic scientific axioms like the method by arguing about the philosophy of a subject, even if you are a String Theorist, or a Cruncher you still aint going to win no Nobel science prizes for a matter that has yet to be tested.

I'm not saying you are a String theorist btw although you might be, I am just using them as examples of "theories" that are often at odds in terms of the origins of the Universe.

I seem to use this phrase a lot lately but it is very apposite:

"Existence is not a predicate."

Emanuel Kant.

It was actually mooted to contend with the ontological argument, but it does just as well here. No scientific theory is based on a quality something has real or imagined, it is based on a quantity. Weighing hypothesis is a pointless exercise, because without any means to test them they are equally undistinguished. God does not exist because he is the greatest thing you can imagine any more than multiple universes is truthier because of some razor, both predicates are axioms without a basis.

In physics, maths is the engine, and evidence is the axle on which the wheels turn. You are going nowhere without either.

I disagree that multiple universes is simpler, you'd do better to dispute that, the fact is though that either way if you win that point nothing has been settled.

Here's an example of two valid areas where we can contend on the basis of occams razor although nothing will be settled absolutely:

MoND (Modified Newtonian Dynamics) and Dark matter are both theories that explain the discrepancies in cosmology with tentative evidence. Which one would you contend is the simplest or most parsimoniuous. Which one would you then suggest was most likely true? What made you come to that conclusion? Was it simplicity, the maths, or the evidence?

End of the day its a nice and practical means of applying science but the results of experiment trump pithy philosophical axioms. If gravity is really weaker at greater distance by a relation that isn't exactly the inverse of r^2 then it will mean that Dark matter is either wrong, or that it is an incomplete answer. Whether it was a simpler solution or not counts for nothing and in fact you could probably argue MoND is simpler but it is not really very easy to model mathematically so it displeases people on aesthetic grounds. Another quality that means nothing in science incidentally.

Incidentally both MoND and dark matter could be true, its an option most people don't usually consider.

And as I said you kind of destroy your own point anyway because we don't have any theories all we have is ideas atm.

Long story short as I'm boring myself now:

On your basis FSM wins because it is a simpler explanation which is kinda funny really.

FSM fits because it has only one assumption and that is god created everything just so hence reality.

Assuming that there are multiple universes is just as big an assumption (by which I mean it requires the same number of assumptions 1) as assuming there is one that endlessly recycles itself also so again that destroys your point they aren't even distinguished here.

I'd like to hear your default argument again that was triffic, completely ungrounded but very interesting..? :smile:

Chalnoth

Apr1-11, 05:27 AM

I don't know why you are answering this point as I and other posters have pointed out occams razor is worthless without a theory with which to compare.
We're comparing two theories:
Our universe exists.
Our universe exists + it's the only one.

The first one is more likely, because it doesn't have the additional assumption of uniqueness.

Calrid

Apr1-11, 06:02 AM

We're comparing two theories:
Our universe exists.
Our universe exists + it's the only one.

The first one is more likely, because it doesn't have the additional assumption of uniqueness.

No we aren't what evidence do you have there are multiple universes?

You show me yours and I'll show you mine.

These are two competing hypothesis. Unless something dramatic happened and either Smolin or Susskind found evidence of multiple universes, stroke collapses while I wasn't looking.

Are you trying to suggest we know how the the universe came into being and what's more we know what is beyond it? Interesting...

Our universe exists and there are countless universes.
Our universe exists and there is only one universe.

Now you are being deliberately disingenuous.

Neither is more likely as I and someone else already pointed out that's not what Occams razor says nor does it have anything to do with weighing up hypothetical concerns in science.

Again uniqueness? Another qualitative statement, you appear to like quality over quantity. I wouldn't advise a career in science if that is the case. Although it makes a good rule of thumb in day to day life. :tongue:

Chalnoth

Apr1-11, 06:52 AM

Calrid

Apr1-11, 08:12 AM

Well, obviously this discussion is going nowhere. You absolutely refuse to pay attention.

The point I have been making all along is that uniqueness is an assumption, where as proliferation is not. Once you have fully-defined something, you automatically get more of that sort of thing unless you explicitly exclude more than one. I wash my hands of further discussion, because you absolutely refuse to accept this very simple point.

No I am I just don't get how proliferation is not and you have done nothing to explain that.

I refuse to accept it because it is nonsense, you insist that more than one universe is the standard on no basis whatsoever.

Fine storm off but your philosophy here is just plain wrong. Maybe you should contact Smolin et al and explain in depth how they are just wrong if you feel this strongly. I think they will probably just ignore you though if you insist on axioms that are not robust and cannot be accepted as a matter of course.

Reality doesn't conform to linguistic form it is linguistic form that conforms to reality, if it doesn't this is not science it is sophistry.

Simply any trite phrase (that itself can be seen as difficult to precisely manage in definite terms) like this has no bearing on the evidence that will reveal itself and it never will. The accuracy of anything cannot be established by any of what you have said and no one has and hopefully ever will ever of claimed it can.

Let me put it even more simply: reality does not give a crap what you think or for opinions. :smile:

You might not like that but this is the philosophy of science, the rules are slightly different from the philosophy of general practice. Hence why science is a discreet area of thought from philosophy and religion.

Fra

Apr1-11, 11:48 AM

Hello, I just stumbled upon this thread, I didn't follow it at all, so forgive me for inserting a random comment.

The question is what do we mean by multiple universes?

If the objection is against a unique universe, then flexibility can exist also in the evolving universe where you have evolving laws, a little bit in line with Smolins thinking. So there is still no uniqueness as it's constantly evolving.

Just because you reject the notion of multiple, non observable universes, doesn't mean you assume uniqueness. I don't.

I think all necessary flexiblity can be accounted for by evolution of law within the universe we live in.

So we rephrase what calnoth said
"that uniqueness is an assumption, where as proliferation is not"

this is very close to this

"assuming fixed eternal laws is an assumption, but allowing for evolution is not"

Paradoxally this is pretty much the argument Smoling uses to REJECT the multiverse idea.

Ie. just because the universe evolves, and laws change, doesn't mean there is a whole ensemble of different universes. It could well be the same one that just evolves. The latter seems to contain less assumtpions that assuming some state space of possible universes that can't be described anyway. It's the existence of unobservable ensembles of different universes that smolin object to.

His argument is never that the one universe is unique, or having static laws.

There is a thine line between "proliferation" and "evolution", isn't it?

/Fredrik

Chalnoth

Apr1-11, 01:32 PM

Fra

Apr1-11, 02:57 PM

I don't see how that makes a difference. You'd just be adding the assumption that there is only one unbroken chain of universes, instead of adding the assumption that the birth of a universe happens only once. It's still an added assumption.

You seem to focus on the chain, rather than each step I think this is the point of disagreement.

There is no objective expectation of this chain. One can even say that the chain is broken or recreated at each instant of time in evolution.

As I see it, there is indeeed an "minimum assumption argument" motivating the evolutionary picture, in the very sense that evolution takes one step at a time, guided by the current expectations. But each step is constantly updated as feedback is arrived.

If we consider from the perspective of rational inference and learning (science).

I think it would be completely irrational, to expect that a systems actions at any instant of time or evolution, would depend on anything else than it's current expectation/state. This is to say that the minimally speculative action (way of placing ets) is the evolutionary one.

My issue with multiverse thinking is not that it's impossible that there are worlds beyond this where there is stuff that is causally isolated from me. OF course that's sort of posisble. But the question is in what sense is it rational to list possibilities, to which my rational action is invariant anway?

So I am definitely not BANNING or excluding possbilities, all I'm suggesting is that it's irrational to suggest that decision problems in this universe should have to account for completely imaginary possibilities. I find that irrational; and thus speculative in the sense of pondering about possibilities that make no difference.

So, I care only about the univers I live in and see, not because it's the only logical possibility, but because it's the only rational choice. (or so goes my reasoning)

/Fredrik

Chalnoth

Apr1-11, 04:58 PM

You seem to focus on the chain, rather than each step I think this is the point of disagreement.

There is no objective expectation of this chain. One can even say that the chain is broken or recreated at each instant of time in evolution.

As I see it, there is indeeed an "minimum assumption argument" motivating the evolutionary picture, in the very sense that evolution takes one step at a time, guided by the current expectations. But each step is constantly updated as feedback is arrived.

If we consider from the perspective of rational inference and learning (science).

I think it would be completely irrational, to expect that a systems actions at any instant of time or evolution, would depend on anything else than it's current expectation/state. This is to say that the minimally speculative action (way of placing ets) is the evolutionary one.

My issue with multiverse thinking is not that it's impossible that there are worlds beyond this where there is stuff that is causally isolated from me. OF course that's sort of posisble. But the question is in what sense is it rational to list possibilities, to which my rational action is invariant anway?

So I am definitely not BANNING or excluding possbilities, all I'm suggesting is that it's irrational to suggest that decision problems in this universe should have to account for completely imaginary possibilities. I find that irrational; and thus speculative in the sense of pondering about possibilities that make no difference.

So, I care only about the univers I live in and see, not because it's the only logical possibility, but because it's the only rational choice. (or so goes my reasoning)

/Fredrik
I really don't understand what you're trying to say here. But the idea of some sort of unbroken chain of universes is incompatible, for instance, with a universe which expands forever, because such a universe would never become a new universe, in this view. And that view is at odds with the minimal cosmological model for our observable universe.

Fra

Apr2-11, 02:36 AM

I really don't understand what you're trying to say here. But the idea of some sort of unbroken chain of universes is incompatible, for instance, with a universe which expands forever, because such a universe would never become a new universe, in this view. And that view is at odds with the minimal cosmological model for our observable universe.

I really don't understand your objection either. Maybe it's becaus I was the one jumping in the middle of this.

What I mean with an "evolving universe" in the sense of evolving law, is something much more weird than just expanding or inflating universe (like classical cosmology).

My view is rooted from an inference or measurement perspective, not classical cosmology. Each obsever merely has an observable window of something unkonwn. The idea that there is some gigantic system in where are these observers exists and evolve in a way that can be described from an inside observer does not make sense to me.

This is why, I suppose maybe it would make more sense to say that each observer constantly recreates the inferred IMAGE of the universe. Then these obsevers itneract and exert selective pressure on each other. There is no external or objective picture on this event chain. Rather each observer has it's own, incomplete and distorted picture of the event chain, and this is what determines the action of the observers in interaction with thet environment,

About the cosmological constant comment, it seems to me you are thinking of a classically expanding single universe. Then we'ere talking pass each other. My fault.

I am envisoning something different. I'm thinking an evolving relational model of observers that responds to other observers. This entire game has evolving rules. And the only descriptive contexts are inside observers, but none of them can make a complete (ie. classical deterministic description, not even probabilistic). This is why MAYBE it makes more sense to you do say that each inside observer deifnes one universe (one observer = one world). But that use of the world makes not sense to me as they obviously interact.

I assume that the the meaning of decomposing into universes is that they are not interacting?

So I replace the "multiple universes" that are interacting, with multiple observers that are interacting. And in this picture each observer encodes an inside view of the universe. And the laws of that universe is a matter of negotiation among constitutients. No needto spawn new universes in black holes to revise the laws(like smolins CNS). There are different options to explain the laws and paramters. (that said it's still en open question of course)

Edit: the advantage of this thinking, is that there is an idea that this can lead to prediuctions. In particular can it infer the action we usually hardcode (EH action, SM action) as a form of inferential "rational action" that simply follows from a priciple of minimum speculation.

I'm sorry we're drifting away now but in explaining this has everything to do with at least my argument.
See some loose thinking here http://www.physicsforums.com/showthread.php?t=239414

/Fredrik

Chronos

Apr2-11, 04:00 AM

Fra

Apr2-11, 04:07 AM

Calrid

Apr2-11, 04:14 AM

Chalnoth

Apr2-11, 05:41 AM

The mulitverse concept is scientifically unappealing absent observational evidence favoring the existence of other universes. Reliance on intrinsically unobservable universes to explain 'fine tuning', or any other properties of our universe, is tantamount to theology.
a) The logical consequences of the weak anthropic principle apply whether or not you have any sort of multiverse. The weak anthropic principle is only a selection effect, after all, and is undeniably true no matter what the overall universe looks like (it is a tautology, so it has to be true). It therefore has to be considered for any theory which is to talk about the origins of the physical laws we observe. To call the use of a logical tautology a strike against multiverse ideas is absurd in the extreme.
b) Multiverse ideas are strongly preferred from a wide number of directions, from particle physics, to inflation, to simple logic (as I mentioned earlier, if the physical process that started our region of space-time happened once, chances are it happened many times). The multiverse, therefore, should be the default, and people claiming that there is only one universe should have to explain why their assumption of uniqueness is accurate.

Calrid

Apr2-11, 06:00 AM

a) The logical consequences of the weak anthropic principle apply whether or not you have any sort of multiverse. The weak anthropic principle is only a selection effect, after all, and is undeniably true no matter what the overall universe looks like (it is a tautology, so it has to be true). It therefore has to be considered for any theory which is to talk about the origins of the physical laws we observe. To call the use of a logical tautology a strike against multiverse ideas is absurd in the extreme.
b) Multiverse ideas are strongly preferred from a wide number of directions, from particle physics, to inflation, to simple logic (as I mentioned earlier, if the physical process that started our region of space-time happened once, chances are it happened many times). The multiverse, therefore, should be the default, and people claiming that there is only one universe should have to explain why their assumption of uniqueness is accurate.

Again this is riddled with assumptions that are purely philosophical.

You still don't get what I mean by reality not giving a crap what you think. These trite little rules and principles are subservient to evidence. No amount of principle or speculation will change that. You have no evidence so no matter what principle your highly biased mind wants to invent you cannot prove God does not exist or even that he is more or less likely to exist because of an opinion.

I fear you study physics not philosophy which is probably why your ontology is so weak.

I study physics, I just happen to be interested in the philosophy of physics too.

Your argument has axioms which not everyone will accept because they have no predictive power in this question.

I still don't see how the weak anthropic principle even matters here. There are either more than one universe or just one. Nothing rests on your predicates or axioms, they are just speculative arm waving.

How about instead of getting annoyed you start with explaining something simple like why they are preferred in particle physics. Its all very well stating that but I don't understand why that is the case? Hence I cannot agree with your axiom of choice, that the Universe has multiple versions by default.

Chances are that the universe happens many times, I agree we just differ on the number of Universes it takes or rather to be precise I disagree either concern as yet distinguishes itself. But for sake of argument let me take the position of being in favour of one universe theories: in yours all universes could of been created at the same time. In mine they were endlessly recycling. rather worryingly so far according to your occams razor God is wining the argument with just 1 once because it's simpler and requires no further assumptions than God did it. I'm not religious so you can see why this concerns me. :tongue:

Chalnoth

Apr2-11, 06:56 AM

I study physics, I just happen to be interested in the philosophy of physics too.
Clearly not interested enough that you care to actually understand any of it.

How about instead of getting annoyed you start with explaining something simple like why they are preferred in particle physics.
Particle physics, as we know it today, depends on the concept of spontaneous symmetry breaking, which indicates that at least some parts of the way in which physics behaves at low energy depends critically upon the outcome of random events in the past history of our universe. The expectation is that far away, the outcomes of these random events will have been different, and therefore the low-energy laws of physics are likely to be different far away.

More speculative theories, such as supersymmetry, predict even more aspects of physical law depend on such spontaneous symmetry breaking events.

Calrid

Apr2-11, 06:59 AM

Clearly not interested enough that you care to actually understand any of it.

Particle physics, as we know it today, depends on the concept of spontaneous symmetry breaking, which indicates that at least some parts of the way in which physics behaves at low energy depends critically upon the outcome of random events in the past history of our universe. The expectation is that far away, the outcomes of these random events will have been different, and therefore the low-energy laws of physics are likely to be different far away.

More speculative theories, such as supersymmetry, predict even more aspects of physical law depend on such spontaneous symmetry breaking events.

That doesn't say why we need 1 universe or infinite or x universes. Does it, it doesn't relate to the weak anthropic principle at all. Smolins proposal caters for the observable evidence equally as well as the others that Susskind appears to prefer. Again the contentions with weak or strong anthropic principles only come about if we have just 1 universe ever. We don't so semantically they are identical. Eternal universes is on paper identical to infinite universes or multiple universes. They both contain the same potential number of universes we only differ on form. I still can't see how any of this makes any scientific impact without evidence. Actually why it makes any impact without evidence either particularly since this is where we stand now.

Clearly I am interested enough because unlike you I don't think this is an answered question in physics, where as you seem to be labouring under the delusion it is. That's not healthy, I can assure you it is not. The reason you do believe that can only because of biased teaching or biased assumptions on your part. you need to distinguish between the probabilities of both here. As far as I can see both have equal probability of being correct hence both are valid hypotheses.

Actually Smolin I think has some more whacky theories about black holes and universe creation so he appears to also have some universe within universe theories too, but I'm not savvy on these so I can't comment.

I'm not sure why you find the idea that there are still some great unanswered questions in physics disturbing or even controversial? It seems odd that you do?

I think what you need to do is relate the strong and weak anthropic principles to a particular theory then construct a reason why multiple universes is favoured over eternal but singular universes using each theory and giving points for and against for both using whatever symmetry parameters or particle elements you think are relevant. Good luck that is a PhD in itself. Probably more of philosophy of science than science but meh, it's all good.

CPT violations wont help you here either btw. I have already stated that entropy isn't reversable and yes also the weak force isn't if anything that helps both theories not just one. I don't see the issue there, I don't also see why distance matters or you use the term far away as if somehow that is relevant?

SuSy is of course hypothetical, but relating theory to hypotheticals or hypotheticals to hypotheticals still produce hypotheticals I'm afraid.

Purely inductive reasoning will tell us nothing about reality unless it has a soupçon of deductive reasoning or what we like to call evidence based theory.

Chalnoth

Apr2-11, 07:14 AM

That doesn't say why we need 1 universe or infinite universes. Does it, it doesn't relate to the weak anthropic principle at all.
You asked a question, I gave an answer.

But yes, it absolutely does relate to the weak anthropic principle, because any time we're talking about the variability of natural law, the weak anthropic principle has a part to play as a selection effect in determining how we interpret how the theory relates to observation. Now, it's usually very very difficult to carefully make use of the selection effect that is the weak anthropic principle, but it's still something that has to be done to interpret such ideas.

Again the contentions with weak or strong anthropic principles only come about if we have just 1 universe ever. We don't so semantically they are identical.
What? The strong anthropic principle states that the laws of the universe must be such that life is possible. It's an absolute statement about the nature of physical law with no justification whatsoever. The weak anthropic principle, on the other hand, is purely a tautology: observers can only observe a universe where they can possibly exist.

Clearly I am interested enough because unlike you I don't think this is an answered question in physics, where as you seem to be labouring under the illusion it is. That's not healthy I can assure you it is not.
Answered? I never said that. I said that the default assumption should be proliferation. There's a difference.

It is heartening, of course, that evidence from cosmology and high energy physics appears to provide tacit support for the idea of a prolific universe, an idea which can be arrived at through very simple logical argument: it is mathematically more difficult to define a single element of a set than the whole set.

You, on the other hand, seem to be laboring under the delusion that old, unevidenced ideas about the universe should be given preference just because they're old ideas. I'm saying that an idea should be judged based upon its merits, not the number of people who have believed it in the past. And before even looking at the evidence, the broad, general concept of a multiverse is far far more likely than a single universe (that is, the entire universe being a simple, causal extension of our observable region with no change in physical law from place to place). The questions that remain are exactly how prolific is the universe, how much does the character of physical law vary, and, perhaps most importantly, which specific multiverse proposals, if any, are accurate.

Calrid

Apr2-11, 07:30 AM

You asked a question, I gave an answer.

But yes, it absolutely does relate to the weak anthropic principle, because any time we're talking about the variability of natural law, the weak anthropic principle has a part to play as a selection effect in determining how we interpret how the theory relates to observation. Now, it's usually very very difficult to carefully make use of the selection effect that is the weak anthropic principle, but it's still something that has to be done to interpret such ideas.

What? The strong anthropic principle states that the laws of the universe must be such that life is possible. It's an absolute statement about the nature of physical law with no justification whatsoever. The weak anthropic principle, on the other hand, is purely a tautology: observers can only observe a universe where they can possibly exist.

Neither say anything about reality though do they, they just say that certain ideas like God done it seem more unlikely than there are an infinite number of possible universes eternal or outside of each other.

Actually weak or strong anthropic principles are both tautologies, just in different ways.

They both assume the antecedent. It's how they go about it that is interesting.

I find the idea that you think tautologies are logically consistent rather odd though. This kind of tells me that you're relying on conclusions that are based on conclusions. Which is bad philosophy.

This question is also up in the air too, because the axioms cannot find distinction. So it highlights why we are still at the philosophy stage.

Answered? I never said that. I said that the default assumption should be proliferation. There's a difference.

Why though?

You keep stating this but it is hedged with non sequiturs. Am I to take it it is true because you say so or can you relate your idea to reality in a deductive fashion that proves that one "theory" is preferred?

It is heartening, of course, that evidence from cosmology and high energy physics appears to provide tacit support for the idea of a prolific universe, an idea which can be arrived at through very simple logical argument: it is mathematically more difficult to define a single element of a set than the whole set.

Maths does not denote science, you have been infected by the verve of String Theorists. What denotes a theory is evidence not arm waving.

Set theory is riddled with its own inconsistencies, such that its difficult to really make a completely coherent set theory without applying axioms that are not reliant on proofs by definition. You will get no help there either. The philosophy of maths is a completely different subject than the philosophy of science. One which you would do well to avoid comparing.

You can take my word on this as well, nothing will get a thread closed faster than challenging mathematical axioms or using them to explain scientific ones.

I'm afraid maths underlies reality not the other way around or vise-a-versa will not be indulged in a thread in this area of the forum so I'd avoid it.

Hell it would probably get locked in philosophy since everything always does. :smile:

This forum has a rather odd fear of philosophy no matter how interesting it is. But meh it is a science forum. There are plenty of places for arm waving. It just seems string theory is indulged being purely philosophical and other philosophical concerns are not so I question the standards here?

I was rather annoyed that a thread that moved into an area like NDEs which was being discussed on a scientific basis was closed, IMO it should of been moved to Skepticism & Debunking, hopefully it will be..? Or at least we can continue the debate there. Anyway beside the point.

You, on the other hand, seem to be laboring under the delusion that old, unevidenced ideas about the universe should be given preference just because they're old ideas. I'm saying that an idea should be judged based upon its merits, not the number of people who have believed it in the past. And before even looking at the evidence, the broad, general concept of a multiverse is far far more likely than a single universe (that is, the entire universe being a simple, causal extension of our observable region with no change in physical law from place to place). The questions that remain are exactly how prolific is the universe, how much does the character of physical law vary, and, perhaps most importantly, which specific multiverse proposals, if any, are accurate.

Old? Bounce theory is at the cutting edge? it's newer than Susskinds ideas or others. Another qualitative assumption that old is worse than new as well. You seem to like that. That's a philosophical maxim, it could be that the Big Bang endlessly recycling at heat death, an older idea is better than the big bounce.

Again if any are accurate has not been established in any way beyond mathematical masturbation, that is not science.

This is still deeply entrenched in philosophical debate, just like interpretations are; would you like to tell me which of the quantum interpretations is more likely to be true also?

Fra

Apr2-11, 06:22 PM

Calrid

Apr2-11, 08:00 PM

I'll just note that the evolving law I refered to is not at all the same as the weak anthropic principle. The "observer" I'm talking about has nothing at all to do with biological or carbon based life. This is starting to sound like the misconception realists always make in QM, confusing observers with consciousness.

The antrophic principle has nothing to do with the evolution of law I'm envisioning.

The predictive value in the picture I suggested lies in the conjecture that all actions are rational. This means that the laws automatically negotiate the laws that sustain the observers. It does not mean that the laws of the universe are created first - by a constraint that it must support life. It rather mans that the form of life and the laws are related. The mechanism of evolution is small variation and selection by environement.

I think the environment and laws is NOT pre-tuned to support life at all as per antrophic arguments at all, the environment and the laws of the universe AND observers emerge together, because the environment consists of other obserers. And the laws of the universe are whatever the compoents negotiate. Those obsever that are inconsistent with the laws are never banned in any way - they are just unstable.

/Fredrik

Let me some up: reality doesn't give a damn what you think.

:smile:

I agree anthropic principle is a red herring in discussions like this, it always muddies what is a simple issue does something happen like this and if so how? Consciousness issues always seem to devolve into why questions which are by their nature doomed to end in philosophy and ..?

Start from the most easy to prove assertion, consciousness has evolved in the universe, but don't use that consciousness as a basis for your ideas it is likely to come with all sorts of biases. They caused the problem in the first place with all that damned God stuff.

There may be a gas cloud of ionic particles arranged "organically" with sentience in the universe that finds our ruminations rather quaint and old fashioned. :smile:

Chronos

Apr3-11, 12:54 AM

Chalnoth

Apr3-11, 01:22 AM

Perhaps you missed my point - where is the observational evidence? I like pink fairies as well as anyone, but, resist accepting them as reality without a picture of one in action.
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.

Calrid

Apr3-11, 01:44 AM

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

Apr3-11, 05:17 AM

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

Apr3-11, 05:23 AM

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

Apr3-11, 05:32 AM

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

Apr3-11, 05:45 AM

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

Apr3-11, 08:46 AM

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

Apr3-11, 10:11 AM

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

Apr3-11, 12:35 PM

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

Apr3-11, 12:40 PM

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

Apr4-11, 07:18 AM

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

Apr4-11, 09:23 AM

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

Apr4-11, 09:26 AM

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

Apr4-11, 09:55 AM

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

Apr4-11, 10:48 AM

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

Apr4-11, 10:51 AM

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. :smile:

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. :smile:

George Jones

Apr4-11, 11:29 AM

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

Apr4-11, 11:43 AM

George Jones

Apr4-11, 12:04 PM

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

Apr4-11, 01:03 PM

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

Apr4-11, 03:13 PM

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

Apr4-11, 03:16 PM

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

Apr4-11, 05:24 PM

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 sorta 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

Apr4-11, 05:55 PM

Well, and that is sorta 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

Apr4-11, 06:35 PM

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

Apr4-11, 09:59 PM

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

Apr4-11, 10:09 PM

...
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

Apr4-11, 11:36 PM

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

Apr5-11, 01:49 AM

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

Apr5-11, 11:05 AM

(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 seperate 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

Apr5-11, 04:29 PM

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.

marcus

Apr5-11, 08:29 PM

...
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.

I'm curious, Chalnoth. How do you define the entropy of the universe? The quantity which you think would be increasing as you go back in time through and beyond the bounce?

dm4b

Apr5-11, 09:01 PM

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.

hmmm, doesn't really sound like you answered my questions, but that's okay, I kinda figured there may not be an answer for those particular ones.

Sounds like eternal inflation leaves as many questions as answers, as far as a "where did the Universe come from" theory.

Chalnoth

Apr5-11, 09:15 PM

I'm curious, Chalnoth. How do you define the entropy of the universe? The quantity which you think would be increasing as you go back in time through and beyond the bounce?
I don't see how it matters in this case, because we define entropy as increasing into the future in our universe. If the bounce is generic, then that is enough to show that the theory predicts entropy increasing into the past before the bounce.

Chalnoth

Apr5-11, 09:17 PM

hmmm, doesn't really sound like you answered my questions, but that's okay, I kinda figured there may not be an answer for those particular ones.

Sounds like eternal inflation leaves as many questions as answers, as far as a "where did the Universe come from" theory.
Well, I felt I'd go with the first one, since the rest depended on that.

marcus

Apr5-11, 10:01 PM

I don't see how it matters in this case, because we define entropy as increasing into the future in our universe. If the bounce is generic, then that is enough to show that the theory predicts entropy increasing into the past before the bounce.

I don't understand, entropy has to be defined or there is no argument.
BTW I assume that by "generic" you mean what Loop cosmology people call "robust". That is it happens pretty much with any choice of parameters, does not require fine adjustment or special choices.

Indeed that has been found. The bounce is a robust feature.

However the theory does not predict that the pre-bounce collapse looks just like the post-bounce run backwards.

I suspect that is the source of your misunderstanding.

Chalnoth

Apr6-11, 01:48 AM

I don't understand, entropy has to be defined or there is no argument.
I don't see that it is necessary. This is a point about the symmetry of physical law. As long as LQC is time reversal invariant, then it should equally describe the universe's behavior backward in time as forward.

Nevertheless, you could use the simple definition used to describe the entropy during inflation of any Hubble volume as being proportional to the horizon scale. With this definition, entropy would indeed be decreasing as the universe collapses.

BTW I assume that by "generic" you mean what Loop cosmology people call "robust". That is it happens pretty much with any choice of parameters, does not require fine adjustment or special choices.

Indeed that has been found. The bounce is a robust feature.
If the previous universe doesn't look like a universe that came about as a result of inflation with the time coordinate set the wrong way, then the bounce isn't robust. If it does look like that, then it doesn't explain the low entropy boundary.

marcus

Apr6-11, 10:02 AM

I never heard anyone say that LQC model of bounce is time reversal invariant. What Ashtekar says is that you have a classical universe collapse (often called a "big crunch") leading up to the bounce. A crunch does not look like a bang movie run backwards. The Loop bounce has an obvious "arrow of time" directionality.

About microscopic reversibility of laws, note that the distinction between microscopic and macroscopic law becomes hazy during what A. calls the "quantum regime" or "Planck regime" phase of the bounce. It is definitely something for theorists to explore and get sorted out.

marcus

Apr6-11, 10:06 AM

About the need to have a definite mathematical meaning for the entropy. You do need this. Otherwise you have no assurance that the word has any meaning at all in the regime under consideration.

Chalnoth

Apr6-11, 01:32 PM

marcus

Apr6-11, 01:44 PM

What I am saying is that the expansion of our space-time would look like a collapse run backwards.

I think that is wrong, thought I made that clear earlier. I'm too lazy to look back and find where I made that point.

You are welcome to think that a classic universe collapse looks like the start of expansion run backwards. You must suit yourself. I don't want to argue with somebody's deep-set mental images.

marcus

Apr6-11, 02:18 PM

If anybody else besides Chalnoth (who seems to have a conceptual hangup) is following this thread, the obvious reason that classical expansion from a smooth intitial condition does not look like a classical crunch run backwards is basically just what Two-Fish said a few posts back.

As long as grav. is universally attractive the forward progression of time tends towards the grav field---the geometry of the U---becoming more lumpy and pock-marked.

The geometry gets more and more inhomogeneous as stuff coagulates and as structure forms.

I've said this before in this and parallel threads.

So the picture of a crunch has lots and lots of inhomogeneity.

On the other hand starting when the classical regime takes over in the big bang you have lots of uniformity, for 100s of thousands of years. Lots of homogeneity. It takes time for structure to begin to nucleate and start gathering.

So the two movies are quite different. One movie is not going to bear any resemblance to the other movie run backwards.

I will try to discuss this, and how this happens in bounce cosmology ( a research area that seems to be taking off) in that other thread.

"Eternal Inflation" is a much older idea (1980s? 1990s?) and this thread is supposed to be about "Falsification of eternal inflation". So I think to be considerate of people interested in that kind of thing we ought to discuss bounce cosmology, how it implements this, and the definition of entropy, and so forth in that other thread.

Here is the "Definition of entropy of the universe?" thread's link, so we can get out of this "eternal inflation" one:
http://physicsforums.com/showthread.php?t=487703

eloheim

Apr10-11, 08:58 PM

Hey just a quick (edit: okay maybe not) question in regards to this issue and the OP's question: (And I have to admit I haven't made it through this whole thread yet so I hope I'm not repeating what others have already said.)

Is the "youngness paradox" an example of the anthropic principle? My understanding (via Brain "String-bean" Greene) is that Steven Weinberg suggested in his '87 paper on the topic that, should there be a multitude of different universes with different cosmological constants, then the probabilities say we should inhabit one with a constant that has a value just low enough for us to be able to exist, and not much smaller.

Does the OP's criticism of eternal inflation follow the same path, by pointing out that, if true, then, given the odds, we should inhabit a universe that is just young old enough for life to exist?

(Hoping I'm on the right track) I take it that the reason this argument is presented as evidence against E.I. is that it seems we could have come about a lot earlier? And that is because there have been stars and galaxies, presumably with planets like ours, for a long time now?

My question then is, "How long do universes consistent with E.I. allow for the emergence of life?" If the answer were something huge, like a trillion, trillion, trillion, trillion, etc. years, then wouldn't the "youngness paradox" actually bolster the case for E.I. because, relatively speaking, we did evolve extremely quickly?