Total mass and/or future of dark energy = cyclic universe?

[mykamakiri]

In an article called "From big bang to big bounce" published in New Scientist in 2008, author Anil Ananthaswamy outlines two different theories that lead to our universe being cyclic.

1: "Cosmologists are still very much in the dark about dark energy. Some theoretical models speculate that the nature of dark energy could change over time, switching from a repulsive to an attractive force that behaves much like gravity. If that happens, the universe will stop expanding and the galaxies will begin to rush together."

2: "A question mark also hangs over the universe’s matter and energy density, which we have not measured with sufficient accuracy to be sure that the universe will not eventually stop expanding. If it turns out to be a smidgen greater than current observations, then it is a recipe for cosmic collapse."

He goes on to say that both theories describe a universe which expands and contracts indefinitely - a cyclic universe (or what Carl Sagan referred to as an oscillating universe in his Cosmos series).

Have we made progress on these two theories since 2008? Have they been thrown out? Is there, in your opinion, better contenders when it comes to describing a cyclic universe, or should the idea be abandoned altogether?

Input much appreciated.

 

[Chalnoth]

The idea of dark energy changing over time is still highly speculative. Switching to a negative value (which would cause it to become attractive) is more speculative still.

For the second point, this is only the case if dark energy eventually decays away to nothing. As long as dark energy remains, the universe will continue to expand.

Basically, the answer is they're theoretically plausible, but highly speculative and there's no evidence for either case.

 

[K. Doc Holiday]

Mykamakiri, great question. Chalnoth, great answer. As a lowly philosophy major i would like to add a few opinions. Logic is not empirical data and yet it can be used in order to narrow the search for observable data.

One of Newton's Laws is "an object in motion tends to stay in motion unless acted upon by an outside force. When astronomers used type 1a (standard candle) supernovae to "prove" that the universe is expanding the scientists of the world agreed that there must be a reason based upon Newton's Law. Personally, i think the expansion of the universe can be explained without creating an entirely new force called "dark energy" but if there is such a force and it adheres to the known physics of the universe then we can safely draw a few conclusions.

1st: We know very little about dark energy but it is logical to assume that it cannot spontaneously switch to a negative value without being "acted upon by an outside force."

2nd: When we calculate the overall mass of dark energy it conveniently makes up the exact total amount of mass needed in order to make our universe "flat". That suggest a causal relationship or at least more than a casual relationship between the known mass and the unknown mass.

3rd: The world of science and academia are by nature fixated on the status quo and it is very difficult to convince either of them that they need to revise their theories. I suspect that the clinging of some scientists to the cyclic universe theory despite all evidence now being to the contrary is due to this perfectly natural human preference.

Of course, I could be wrong. sincerely, k. doc holiday

 

[Chronos]

The oscillating universe model is attractive at one level. It solves the creation problem and allows time without end. The creation issue breaks the chain of causality which is near and dear to the heart of most scientists. And the notion of a 'beginning' to time is at least as causally repugnant. I favor a different explanation - the universe [or reality] is an unending series of phase changes. What preceeded our current universe is a deep mystery that has eluded our most ingenious efforts to explain, and what will follow is a similar mystery. We have apparent examples of phase changes in the current universe - e.g., inflation and accelerated expansion - that seriously challenge our notion of causality. What triggers such phenomenon and what prevents them from leading to the equivalent of an ultaviolet catastrophe? The answers appear to reside in the realm of modern mysticism we call quantum physics.

 

[K. Doc Holiday]

Chronos,
i love to hear different perspectives and yours is certainly a new one to me. thanks for sharing that.

I dabble in string theory and tend to agree with it.

There was a 10 dimensional universe that preceded ours. Instability caused the 10 to break down into a 4 (which is ours, height, width, depth and time) and a 6.
My personal view of cosmology is one of the never ending creation of 10 dimensional universes, thus negating the need for a beginning or end of time. So, my cosmology is cyclic but in a different way then the traditional "big bang - big crunch" model. The universe isn't slowing down. it is picking up speed and, in my opinion, heading for the reunification of the 4 with the 6.

I try to stay objective. If some sort of "creation" is involved i try to look at that concept objectively, without bias. I believe that is more scientific than throwing out a theory because it happens to upset me emotionally.

The real proof of the objectivity and/or validity of any theory is the ability to make predictions based upon it and to have them verified. That is where the "rubber meets the road." We live in an exciting age and i look forward to all discoveries, regardless of whether or not they happen to fit my particular theory. And, like yourself i try to always leave room for a little mystery. thanks again.

 

[PeterDonis]

My personal view of cosmology

Please bear in mind the PF rules about non-mainstream theories; discussion of them is not allowed here.

 

[PeterDonis]

There was a 10 dimensional universe that preceded ours. Instability caused the 10 to break down into a 4 (which is ours, height, width, depth and time) and a 6.

This isn't quite correct. String theory does not say that the 10-dimensional universe "broke down" into two separate universes. It says that 6 of the 10 dimensions are "compactified", so that they are not directly perceivable by us the way the 4 dimensions we ordinarily refer to as "spacetime" are. But the structure of the 3 non-gravitational interactions we observe (strong, weak, electromagnetic) is indirect evidence (according to string theory) of the existence of the 6 compactified dimensions.

 

[K. Doc Holiday]

Please bear in mind the PF rules about non-mainstream theories; discussion of them is not allowed here.

Dear Peter, If you are correct, I have to say that i am deeply disappointed in the rules of Physics Forums. I think that the only way to continue making progress in theoretical physics or any branch of science, for that matter, is to "boldly go where no one has gone before." If Albert Einstein had abided by your rule, we wouldn't be where we are today. I am seriously going to have to reconsider whether or not i will engage in any further discussions on this site. Still, i wish you only the best. sincerely, k. doc holiday

 

[PeterDonis]

I think that the only way to continue making progress in theoretical physics or any branch of science, for that matter, is to "boldly go where no one has gone before."

That's fine, but the purpose of PF is not to break new ground in science. It is to discuss theories that are already mainstream. PF is not a physics research site; it is a physics discussion site. If you want to do physics research, you should be looking elsewhere.

 

[K. Doc Holiday]

This isn't quite correct. String theory does not say that the 10-dimensional universe "broke down" into two separate universes. It says that 6 of the 10 dimensions are "compactified", so that they are not directly perceivable by us the way the 4 dimensions we ordinarily refer to as "spacetime" are. But the structure of the 3 non-gravitational interactions we observe (strong, weak, electromagnetic) is indirect evidence (according to string theory) of the existence of the 6 compactified dimensions.

Dear Peter, It appears that we are arguing about semantics. I've done my fair share of that and no longer enjoy it. So, I will let you determine how the terms are defined. I would like to add the following.

For centuries humans thought that our universe and solar system revolved around the earth. In order to make that approach work we had to believe that some planets stop in their orbits, go backward and then proceed forward again, for no apparent reason (going retrograde). The theory fit a lot of the data but it couldn't fit all of the data until we put the sun where it belongs, in the center of the solar system (heliocentric). I think the same thing is happening with "accepted" string theory. If you take the 6 dimensional universe and put it where it belongs then the mystery of the acceleration of the universe disappears, like the "planet dancing" did hundreds of years ago. My theory fits all the data and doesn't have to invent a new force, of which we know almost nothing. It is less complicated, more simple and more eloquent, so much so that a high school grad could understand it. In philosophy we learn that the more simple and eloquent the answer the more likely it is to be true. I didn't predict that the universe was accelerating but when astronomers discovered it was, it confirmed my theory instead of complicating it. That said, i will honor the rules of this forum and keep my opinion to myself. Your loss.

 

[PeterDonis]

It appears that we are arguing about semantics.

You said you were disappointed in PF's rules because they don't allow what amounts to research in physics to be done here. I explained why the rules are that way. But perhaps I should elaborate a bit.

Research in the frontiers of physics is essential; every regular here on PF would agree with that. But you can't do research in the frontiers of physics by posting threads on a discussion board like PF. We simply don't have the resources or the time to give you the kind of feedback you would need.

For example, you say:

My theory fits all the data

I have no way of knowing whether this is true, or whether any of your other claims about your theory are true. Even if you were to post your entire theory here on PF, I still wouldn't, and neither would anyone else here on PF. We might have opinions, but that is all they would be, opinions.

To get something more than opinions, you would need to actually take your theory and confront professionals in the field with it. You would need to publish peer-reviewed papers, go to conferences, etc. In short, you would need to defend your theory, not against random posters here on PF, but against the best that the professional physics community can throw at it.

If you were to succeed at doing that, then at some point your theory would become an acceptable topic here on PF, because it would be mainstream. But not until then.

I've done my fair share of that and no longer enjoy it.

That tells me something different than it apparently tells you. It apparently tells you that the professional physics community is closed-minded. It tells me that whatever theory you think you have has already been subjected to the process I described above, and didn't survive it. Discussing it here on PF won't change that.

 

[mfb]

My theory fits all the data and doesn't have to invent a new force

Publish it, get a Nobel Prize. You don't have to wait for step 2, you can discuss it here once it got through peer-review.

Here is a prediction from me: you do not have a proper theory. Over the years, we had hundreds of users thinking they had "a theory", posting them here. Not a single one of those was of any use.

 

[slatts]

In an article called "From big bang to big bounce" published in New Scientist in 2008, author Anil Ananthaswamy outlines two different theories that lead to our universe being cyclic.

1: "Cosmologists are still very much in the dark about dark energy. Some theoretical models speculate that the nature of dark energy could change over time, switching from a repulsive to an attractive force that behaves much like gravity. If that happens, the universe will stop expanding and the galaxies will begin to rush together."

2: "A question mark also hangs over the universe’s matter and energy density, which we have not measured with sufficient accuracy to be sure that the universe will not eventually stop expanding. If it turns out to be a smidgen greater than current observations, then it is a recipe for cosmic collapse."

He goes on to say that both theories describe a universe which expands and contracts indefinitely - a cyclic universe (or what Carl Sagan referred to as an oscillating universe in his Cosmos series).

After four years of following cosmological issues, I was astonished to read recently that, in a de Sitter universe (-the usual setting for inflation, although I've heard Minkowski spacetime mentioned once or twice as an alternative to it), a contracting phase precedes expansion! I don't see why the sequence would necessarily be in that order, and I've seen Vilenkin (in his 2011 essay "The Principle of Mediocrity") mention the probability that our region will eventually be engulfed in a "bubble" of "negative energy"--apparently, attractive gravity--that will cause it to collapse, even though the speed-of-light expansion of some portion of our metastable "local universe" will outrun that gravitational bubble and continue expanding.

You might want to look at Eric Lord's 1974 Geometry of the De-Sitter Universe for more details; the math in it is beyond me.

I realize this information only gets the universe you're wanting to visualize through its first cycle, and I imagine you've heard of the problems with the accumulating density of entropy that removes a lot of explanatory power from oscillating-universe models: Tracing them backwards through time leaves them with a beginning.

Special fields, or the possibility that the space contracting in each crunch "returns empty", work around this in an ad hoc way: The "ekpyrotic" universe of Steinhardt and Turok is probably the best-known example of such approaches, although I have to admit that I missed the "special field" I've heard it said that they hypothesized, when I breezed brainlessly through their book.

I've got to add that Penrose has a cyclic cosmology out, these past few years, that is certainly compatible with the 2nd Law of Thermodynamics: His book, called "Cycles of Time", describes a universe evaporating slowly until nothing remains but photons, which of course travel only in space (while everything else had been traveling in spacetime). It ends with a lone photon flying along, and leaves everyone wondering, "Why only one?".

Except me. I'm glad there will be only one, at least as far as the risks of an unpleasant collision are concerned. No one else seems to worry much about that.

 

[jearlrugh]

My question has to do with Mykamakiri's statement, ". . .the universe will stop expanding and the galaxies will begin to rush together" and the discussion of the center of the universe. When I was a boy I had a paddle. To it was attached an elastic string and on the other end of the string, a rubber ball. The object was to smack the ball (the universe) with the paddle (big bang). Once the ball reached the end of the tether and expanded the elastic in direct relation to the amount of force applied by the paddle, the ball returned to the source (gravity). Newton's law states, "What goes up must come down." Because the universe is bound together with gravity as Einstein's relativity posits, could it not also be said. "what goes out must comes back." If the universe as we know it is expanding, might their come a time when all this matter reaches the end of its tether and collapses in on itself? If that's true, and I understand that is the essence of the big crunch theory, then it would seem to imply that the center of the universe is the point from which the big bang singularity exploded (if that's the right word) in the first place some 14 billion Earth years ago. Is that logical?

 

[mfb]

Because the universe is bound together with gravity as Einstein's relativity posits

According to our measurements, it is not bound. The nature of dark energy could change in the future, but this is very speculative.
The universe is not made out of tethers.

then it would seem to imply that the center of the universe is the point from which the big bang singularity exploded

There is no such point. The big bang was not an explosion in space, it created spacetime itself. It "happened everywhere".