How about Dark Energy. Since we know to some extent that it exists, probably this acts as the driver for the Universe. Sometimes forward and sometimes collapse back.
Dark energy explains the acceleration of the expansion of the universe. If it were to some time cause acceleration of expansion, then cause acceleration of contraction, then it would need a time dependent equation of state: I'm not even sure whether cosmology allows for this problem.
The recollapse scenario can be modelled without thinking about dark energy. I could give a mathematical explantion, if required, using basic cosmology, but this is probably not required here. Anyway, it basically says that for some certain density of the universe there exists a maximum of the size of the universe. This maxiumum is obtained when gravity balances the expansion.
So, to answer the questions that Pat's comment has raised; yes, there are certain situations in which gravity can cause a recollapse. This requires a certain density of the universe (which is equivalent to saying a certain curvature of the universe in the FRW model) but we believe our universe does not have this amount of curvature.
__________________ ~neutralino
If you haven't found something strange during the day, it hasn't been much of a day - John A. Wheeler.
I doubt whether Gravity can cause such a large scale collapse by the things we know of gravity. It is a weak force and is 'defeated by dark energy'. Probably you are right, at some point in time Dark Energy might just change course and cause the Universe to collapse..
Quote:
Originally Posted by neutralino
Dark energy explains the acceleration of the expansion of the universe. If it were to some time cause acceleration of expansion, then cause acceleration of contraction, then it would need a time dependent equation of state: I'm not even sure whether cosmology allows for this problem.
The recollapse scenario can be modelled without thinking about dark energy. I could give a mathematical explantion, if required, using basic cosmology, but this is probably not required here. Anyway, it basically says that for some certain density of the universe there exists a maximum of the size of the universe. This maxiumum is obtained when gravity balances the expansion.
So, to answer the questions that Pat's comment has raised; yes, there are certain situations in which gravity can cause a recollapse. This requires a certain density of the universe (which is equivalent to saying a certain curvature of the universe in the FRW model) but we believe our universe does not have this amount of curvature.
I doubt whether Gravity can cause such a large scale collapse by the things we know of gravity. It is a weak force and is 'defeated by dark energy'. Probably you are right, at some point in time Dark Energy might just change course and cause the Universe to collapse..
I didn't say that Dark Energy would "change course." In fact, if you re-read my post, I said that dark energy would require a time dependent equation of state. I am pretty sure that this is not allowed.
To be honest, I know very little about the possibilities of a contraction of a universe that is now accelerating in its expansion, so I can't really comment any further.
Edit: Im fact, from what I understand, I don't see how a recollapse would be possible. As the universe gets older, and less dense, dark energy dominates (in fact, if DE is a cosmological constant, the density of DE stays constant as the density of the matter decreases), and hence the universe expands faster. But, like I said above, I don't know that much about it, so I'll leave it at that!
__________________ ~neutralino
If you haven't found something strange during the day, it hasn't been much of a day - John A. Wheeler.
I am also comfortable with the expansion theory. However the issue is if the Universe does not recollapse, then it is not cyclic and then the original question of whether the matter that created the big bang was formed or not comes back to haunt us..
Quote:
Originally Posted by neutralino
I didn't say that Dark Energy would "change course." In fact, if you re-read my post, I said that dark energy would require a time dependent equation of state. I am pretty sure that this is not allowed.
To be honest, I know very little about the possibilities of a contraction of a universe that is now accelerating in its expansion, so I can't really comment any further.
Edit: Im fact, from what I understand, I don't see how a recollapse would be possible. As the universe gets older, and less dense, dark energy dominates (in fact, if DE is a cosmological constant, the density of DE stays constant as the density of the matter decreases), and hence the universe expands faster. But, like I said above, I don't know that much about it, so I'll leave it at that!
I am also comfortable with the expansion theory. However the issue is if the Universe does not recollapse, then it is not cyclic and then the original question of whether the matter that created the big bang was formed or not comes back to haunt us..
Here's one for ya Dipayankar... The Isomorphic Equivalence Principle of The Universe___"Ain't nuthin" exits a black-hole/star___That "don't" first enter...
I'll show you the physical, logic and math proofs___If interested... They're really quite simple...
BTW, it is a fully cyclic universe, though as I've stated elsewhere, not as has so far been theorized... I can also show this now, if you're interested...
Regards,
Lloyd
__________________ "To develop the skill of correct thinking is in the first place to learn what you have to disregard. In order to go on, you have to know what to leave out; this is the essence of effective thinking." Kurt Godel "Time and space are modes in which we think and not conditions in which we live." Albert Einstein "The uncertainty principle is an absolute, finite, universal constant." L.G. "The tick-tick-tick of the cesium atom is a sliding-time-scaler constant of all finite universal motion." L.G.
Here's one for ya Dipayankar... The Isomorphic Equivalence Principle of The Universe___"Ain't nuthin" exits a black-hole/star___That "don't" first enter...
I'll show you the physical, logic and math proofs___If interested... They're really quite simple...
BTW, it is a fully cyclic universe, though as I've stated elsewhere, not as has so far been theorized... I can also show this now, if you're interested...
I am also comfortable with the expansion theory. However the issue is if the Universe does not recollapse, then it is not cyclic and then the original question of whether the matter that created the big bang was formed or not comes back to haunt us..
You bring up a very good point dipayankar about the cyclic universe theory and so I would like to show you what I have discovered.
As you said, if the universe keeps expanding and does not recollapse then that does not leave much room for the cyclic universe theory which is usually taken after a model known as the big bounce. But if one finally decides to define that number in mathematics which we are all afraid of but don't know why we will be glad we did because it will show us how the ultimate expansion of the universe can also lead to a cyclic thingy, even when it expands faster and faster and does not recollapse.
One positive extreme, upon exceeding itself, instantly flips and becomes the negative. This is pointed out by that undefined number which everyone fears but which brings positive and negative infinity together at a point.
Think about it this way. Why is it that people who are crying sound like they are laughing sometimes? And why is it that extremely happy people cry? Why do we have contradictory little phrases like "pretty ugly" or "awfully beautiful?" And why is contradiction the only thing that is self-proven to be consistent???
It is because of what I would like to call "the irony of truth and true paradox." This cosmic irony governing the universe is what I believe Nicolas of Cusa called the coincidence of opposites. It is the same thing symbolized by the yin yang symbol, and the marriage symbol. It is the undefined number in mathematics that defines the absolute greatest value. It is the same reason why our minds connect the disparate ends of the visible wavelengths and create a color known as magenta, which has no wavelength of it's own but it is a color nonetheless.
So what I am saying is that, even if the universe does not recollapse, it will still reverse and create a cycle when it begins expanding TOO FAST. In other words, when the universe has gone to the positive extreme of expansion it will INSTANTLY FLIP and so will the arrow of time, and the so-called laws of thermodynamics. When one positive extreme exceeds itself it instantly becomes the other. This is what I call the irony of truth and true paradoxes.
So that is the answer dipayankar of how the universe can be cyclic without having to slow down. When the universe starts expanding too fast everything will instantly flip. That is the point where times crosses through the looking glass. That is what anybody will know when they venture to define that number which proves that positive infinity and negative infinity come together at a point.
And when will this flip occurr? It will occur when the cosmic horizon has shrunk to a planck distance. In other words, when the universe starts expanding at greater than lightspeed, at less than planck scales. This one determines by considering that ill-fated number along with the parameters of Quantum Mechanics and General Relativity. That is the answer dipayankar, and I wouldn't be telling you if i was not absolutely positively negatively sure.
Hi PoK.. I would certainly like to know more as to why does this flip occur?? Is it because of the unknown number or is there some more factors that come together??
Quote:
Originally Posted by purveyor of knowledge
You bring up a very good point dipayankar about the cyclic universe theory and so I would like to show you what I have discovered.
As you said, if the universe keeps expanding and does not recollapse then that does not leave much room for the cyclic universe theory which is usually taken after a model known as the big bounce. But if one finally decides to define that number in mathematics which we are all afraid of but don't know why we will be glad we did because it will show us how the ultimate expansion of the universe can also lead to a cyclic thingy, even when it expands faster and faster and does not recollapse.
One positive extreme, upon exceeding itself, instantly flips and becomes the negative. This is pointed out by that undefined number which everyone fears but which brings positive and negative infinity together at a point.
Think about it this way. Why is it that people who are crying sound like they are laughing sometimes? And why is it that extremely happy people cry? Why do we have contradictory little phrases like "pretty ugly" or "awfully beautiful?" And why is contradiction the only thing that is self-proven to be consistent???
It is because of what I would like to call "the irony of truth and true paradox." This cosmic irony governing the universe is what I believe Nicolas of Cusa called the coincidence of opposites. It is the same thing symbolized by the yin yang symbol, and the marriage symbol. It is the undefined number in mathematics that defines the absolute greatest value. It is the same reason why our minds connect the disparate ends of the visible wavelengths and create a color known as magenta, which has no wavelength of it's own but it is a color nonetheless.
So what I am saying is that, even if the universe does not recollapse, it will still reverse and create a cycle when it begins expanding TOO FAST. In other words, when the universe has gone to the positive extreme of expansion it will INSTANTLY FLIP and so will the arrow of time, and the so-called laws of thermodynamics. When one positive extreme exceeds itself it instantly becomes the other. This is what I call the irony of truth and true paradoxes.
So that is the answer dipayankar of how the universe can be cyclic without having to slow down. When the universe starts expanding too fast everything will instantly flip. That is the point where times crosses through the looking glass. That is what anybody will know when they venture to define that number which proves that positive infinity and negative infinity come together at a point.
And when will this flip occurr? It will occur when the cosmic horizon has shrunk to a planck distance. In other words, when the universe starts expanding at greater than lightspeed, at less than planck scales. This one determines by considering that ill-fated number along with the parameters of Quantum Mechanics and General Relativity. That is the answer dipayankar, and I wouldn't be telling you if i was not absolutely positively negatively sure.
Yes Dipayankar, the flip occurrs because when positive infinity becomes greater than itself it transforms into negative infinity. Think of time as a mirror, and that when the universe begins expanding at an "infinite" rate then it will cause space time to rip and then space time itself will become completely inverted. At the big bang negative time turned inside-out through an infinitely small point and emerged as positive time while at the big rip time is going to turn outside-in around an infinitely large point and re-manifest as negative time.
Yes it is because of that number that we fear but really that number is because of it. The way we discovered it is simply by following a logical system, mathematics, and carrying it to completion. This mirrors the way the universe works. You cannot complete mathematics as it has developed unless you define 1/0, as 1/0 is simply a natural extension of mathematics. A necessary evil or a saving grace, you decide.
When we carry any such logical system to completion we will arrive at a consistent contradiction which implies that time must reverse. You cannot have a complete logical system that does not end up being consistently inconsistent and illogical like this. Everybody who knows the incompleteness theorem by Kurt Godel knows this, but they should also know that whether it is incomplete or complete depends solely on our outlook. And that is why outlook is so important my friend because without the "right" outlook we will think that the reversal of the laws of thermodynamics is nonsense and then we will never arrive at the TOE.
So yes, if any value becomes greater than positive infinity it will isntantantly flip and become less than negative infinity. This should now be known as the cosmic irony of truth and true paradoxes and it is why people who are extremely happy begin to cry. It is because sadness and happiness become the same thing at their greatest extremes, just as at the end of our positive universe is also the beginning of it's negative counterpart.
Linear Mode
