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View Full Version : Big Bang. Big Rip? Big Contraction?? Endless cycle???



red supergiant
2009-Feb-19, 05:58 AM
Hi guys, just read an article which says that after the BB and subsequent expansion, there's going to be a Big Rip. The matter in the universe moves faster and farther. Once it slows down, the whole thing is drawn back due to gravity to form the same particle from which the BB occured and again a BB. This cycle repeats every 80 billion years or so. Does the particular space where BB occured, have so much gravitational force to pull all matter back? Or is there a black hole in that place which the swallows the whole thing?? Need some help here...

astromark
2009-Feb-19, 06:41 AM
Greetings; red supergiant...
Hi guys, just read an article ...end quote.

That article you read was wrong.

I have not found any descension, or disagreement with the wildly excepted notion. That this universe is expanding ever faster. The driving force been aptly named 'Dark Energy' No, We do not know what it is. We do know that it as a force has overcome gravitational contraction. My blind acceptance of this is based on the fact that it is true. You might want to argue with this and me. This I would welcome but would also ignore.:)mark, the astronomer.

NickW
2009-Feb-19, 06:43 AM
Agreed. I thought the expansion of the universe to be caused due to dark matter instead of explosive forces caused by the big bang, hence the subsequent speeding up of the expansion of the universe.

gzhpcu
2009-Feb-19, 07:02 AM
Agreed. I thought the expansion of the universe to be caused due to dark matter instead of explosive forces caused by the big bang, hence the subsequent speeding up of the expansion of the universe.
No, dark matter has been envoked to explain the missing mass needed in the calculation of rotating galaxies. Dark energy is responsible for the accelerated expansion of the universe. These are two different things.

Apparently, 5 percent of the universe consists of the ordinary matter that we are made of and that we can see. 70 percent of the universe is thought to consist of dark energy. 25 percent of the universe is dark matter, a form of matter that hasn't yet been detected directly.

red supergiant
2009-Feb-19, 07:15 AM
But how can there be a contraction and condensation into a particle with infinite mass if the dark energy/matter is only acccelerating the outward movement? my query is: will there be a contraction after the dark energy is expensed?

tnjrp
2009-Feb-19, 07:26 AM
Yep, "dark matter" and "dark energy" are names for different observed phenomena. As I understand, the jury is still out on what is the ultimate cause of these so they may or may not be actual "matter" and actual "energy", respectively.

That said, one potential result of the dark energy phenomenon is indeed the Big Rip in which the said phenomenon envetually overcomes every form of attraction, tearing the matter itself apart at the lowest observable level (and possibly below, if any).

It has also been suggested, based on Turok & Steinhardt's work on cyclic universe model, that the universe can "come back empty" for another go from the very verge of the Big Rip, essentially sheding its entropy. It's a kinda poetic thought that dark energy is both the force that destroys the current state of the universe and the one that enables the following state to start afresh.

Caveat: I'm not up to speed as to how these hypothesis are fairing in the lobster pot of cosmology discussions.

NickW
2009-Feb-19, 07:27 AM
No, dark matter has been envoked to explain the missing mass needed in the calculation of rotating galaxies. Dark energy is responsible for the accelerated expansion of the universe. These are two different things.

Sorry, I did mean dark energy, just got confused with the terms. :)

Tarkus
2009-Feb-19, 07:57 AM
Yes even the big brains struggle with this. All we have is the science process to guide us to clarity. So sit tight and wait and see what develops over the next few years.

astromark
2009-Feb-19, 08:32 AM
But how can there be a contraction and condensation into a particle with infinite mass if the dark energy/matter is only acccelerating the outward movement? my query is: will there be a contraction after the dark energy is expensed?

Please read and understand what you are being told...

[Quote=gzhpcu]; Apparently, 5 percent of the universe consists of the ordinary matter that we are made of and that we can see. 70 percent of the universe is thought to consist of dark energy. 25 percent of the universe is dark matter, a form of matter that hasn't yet been detected directly. [end quote].

Yes the early universe did expand explosivly... and slowed. It then and still is accelerating ever faster. We as yet have no reason to assume any slowing will ever be detected.
This universe is expanding to become a cold dark spars place. Its going to take eternity to do this....
Do you understand the gravity force at a local level is not part of this expansion. Clusters of Galaxies. Nebula's, Star clusters and Galaxies are all gravity bound as this solar system is. Only those more distant unbound objects seem to be accelerating away. Like the rest of them are shy...

Tzarkoth
2009-Feb-19, 10:27 AM
I wonder how old the OP's article is. The Big Crunch received a lot of airtime a number of years ago until observational evidence from distant supernova and detailed studies of the CMB lead us to rethink/refine our Theories/Models.

The process is ongoing and we are a long way off being able to describe what exactly the Universe is doing. We can only model, theorize and refine.

More data is required, which requires more missions, bigger and better telescopes, etc etc.

As Tarkus said, 'All we have is the science process to guide us to clarity.'

speedfreek
2009-Feb-19, 08:21 PM
Here is a brief simplified synopsis, as I understand things (and I could well be wrong!).

We think that the universe is expanding, and for a long time our measurements of distant galaxies indicated that the rate of that expansion had been slowing down since the Big Bang. It was theorised that the slowing of the expansion rate was due to the gravitational attraction between galaxies. The mass of the things in the universe was slowing down the expansion of the universe.

The question was, how much mass is there? Is there enough gravity to halt the rate of expansion or not? If there was a lot of mass, not only would the rate of expansion slow to a halt, but the universe would start to contract, as gravity started drawing things together again. If this was the case, the fate of the universe would be a big crunch.

But about a decade ago we found that the rate of expansion seems to have been accelerating for the last 5 billion years or so. For the first 8 - 9 billion years the expansion was slowing down, but around 5 billion years ago it levelled out and then the rate started to increase! So it seems as if gravity was slowing things down for a while, but once all the clusters of galaxies were far enough apart another factor has come into play, something that accelerates the rate at which distant galaxies recede from each other.

It is as if there is something, perhaps a form of energy, that acts like repulsive gravity in the background. When clusters were close enough to each other, their gravity worked to slow the rate at which they separated, but once they were far enough apart for their gravity to have a negligible effect, this "background" energy came to the fore and started to accelerate the rate at which they separate.

We call it dark energy, for want of a better name. As I said, it seems to be some form of process working in the "background" and by this I mean that the effect it has doesn't seem to be decreasing as distant galaxies recede - it acts like a cosmological constant, with a constant energy density.

But, if there were an increasing dark energy density (this is known as phantom energy) then we have a Big Rip scenario, where even atoms end up being ripped apart by that "repulsive gravity". Currently however, I think the consensus is that dark energy is more likely to work like a cosmological constant than like phantom energy. I think it depends on whether dark energy had always been there, or only appeared 5 billion years ago and started to increase in density, both of which might explain our observations, but the second might also seem less likely.

I seem to remember some speculation for what might happen after a Big Rip, including the idea that phantom energy might tend towards infinite density, but in a finite amount of time. There were suggestions of new Big Bangs, a kind of cyclical universe, but I can't find a reference for this.

Grey
2009-Feb-19, 09:33 PM
Nice summary, speedfreek.


Currently however, I think the consensus is that dark energy is more likely to work like a cosmological constant than like phantom energy.For this scenario, which I think is currently deemed the most likely, we get a "Big Chill". Things that are gravitationally bound, like galaxies and probably clusters as well, stay together. However, anything else continues to recede at an ever increasing rate, so eventually you would not see any galaxies beyond the local cluster. Within an individual galaxy, star formation gradually drops off as gas is used up, and the stellar population gradually gets older, redder, and fainter. Eventually (after a hundred billion years or so), we reach the end of life for even the red dwarfs, and the universe becomes a very cold, very dark place. One of my cosmology texts says that the obligatory quote at this point is from T.S. Eliot's The Hollow Men: "This is the way the world ends/ Not with a bang but a whimper."

gzhpcu
2009-Feb-19, 09:52 PM
An M-theory-based cosmology, rhe Ekpyrotic Model of the Universe proposes that our current universe arose from a collision of two three-dimensional worlds (branes) in a space with an extra (fourth) spatial dimension. The Big Bang occurs over a large area. The energy resulting from the collision results in a Big Bang which populates our brane (universe). The branes recoil from the collision. Everything disperses, and trillions of years later, the branes attract each other again, collide and a new Big Bang occurs ad infinitum.

Tzarkoth
2009-Feb-20, 08:33 AM
Isn't there a lot of disagreement against String theory?

Critics claim that there is a lack of empirical correlation and testability in these theories and thus they are without hard physical evidence and must therefore be considered unfalsifiable, currently outside the methodology of scientific investigation to confirm or disprove, and therefore more mathematically theoretical and metaphysical than scientific in nature.

Could you not claim Plato's Allegory of the Cave as equally plausible as as M Theory?

Cougar
2009-Feb-20, 06:11 PM
Isn't there a lot of disagreement against String theory?

Yes, indeed.

Argos
2009-Feb-20, 06:18 PM
The Big Crunch scenario is currently about as outdated as Hoyle´s Steady State universe.

gzhpcu
2009-Feb-21, 04:40 AM
Isn't there a lot of disagreement against String theory?

Critics claim that there is a lack of empirical correlation and testability in these theories and thus they are without hard physical evidence and must therefore be considered unfalsifiable, currently outside the methodology of scientific investigation to confirm or disprove, and therefore more mathematically theoretical and metaphysical than scientific in nature.

Yes, but there is some promise:


One of the biggest criticisms of string theory is that its predictions can’t be tested experimentally–a requirement for any solid scientific idea.
That’s not true anymore.
At a AAAS session on Sunday, physicists said string theory is making important contributions to the study of two extreme forms of matter –one heated to trillions of degrees, the other chilled to near-absolute zero. In both cases the matter became a “perfect liquid” that ripples and flows freely, like water. String theorists analyzed the results by applying what they had learned from pondering how a black hole might behave in five dimensions. Then they went on to calculate just how free-flowing these liquids might be, predictions that the experimenters are using to guide the next stage of their work.
source: http://www.symmetrymagazine.org/breaking/2009/02/16/a-first-string-theory-predicts-an-experimental-result/