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Most Likely Ending

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I've been reading a bit lately about the possible fate of the universe. So far I've seen a few models, and they all seem interesting to me. I've seen threads about these prophecies individually, but I'm not entirely sure which one is most plausible, so I'm curious as to your ideas. First off is the Big Crunch, the idea that when there is enough matter in the universe, gravity will cause the expansion to move backwards, thus collapsing the universe into a black hole singularity.The next one I found was called the Big Chill, the idea that as the universe is expanding, matter will get spread more and more thinly, until the temperature approaches absolute zero.After that, there is the Big Rip, which says that since the fabric of the universe is constantly expanding, the observable universe is shrinking, and that when the size of the observable universe is smaller than any particular structure, tearing will occur.Finally there is the Big Bounce, which says that we live in an oscillating Universe, and that everything moves in a cycle, and after our universe collapses, there will be another Big Bang.

 

These are all very brief summaries that I pieced together from several different resources. I'm not so sure of how accurate they are, but it has been interesting to read. Seeing as I don't know much about astronomy, I'd like to hear everyone's opinions on which one is more likely, and any possible corrections to the summaries that I've given.

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...The next one I found was called the Big Chill, the idea that as the universe is expanding, matter will get spread more and more thinly, until the temperature approaches absolute zero...

 

This is what you get from the standard mainstream cosmic model.

 

I haven't seen a professional research paper about "Big Rip" for several years. The idea is either dead or taking a nap. Some new discovery could conceivably revive it.

 

Same for "Big Crunch". Barring some new discovery it doesn't seem to be in the cards. It might appeal to the imagination.

 

I don't think you report the "Big Bounce" idea accurately. The idea is not cyclic. It is not about the future. There has been an explosion of interest in the idea that the big bang could have been a rebound from an earlier collapse. So many new researchers have gotten into this and there are many more papers appearing about it, than say 2 oer 3 years ago.

 

But when people talk about Bounce cosmology or non-singular cosmology they are normally not talking about the future. They are just talking about mathematical models of what happened 13-some billion years ago. There could be a bounce in future but that is conjectural and would depend on dark energy decaying (something we have no evidence of) or some other surprising aspect of the universe that we have no clue of as yet.

 

So the focus of attention is on the possible past Bounce, where we may be able to observe aftereffects in the cosmic microwave background.

 

A quick way to get current research literature on Bounce cosmology models is just do a keyword search on "quantum cosmology" recent papers, like this:

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=FIND+DK+QUANTUM+COSMOLOGY+AND+DATE+%3E+2006&FORMAT=www&SEQUENCE=citecount%28d%29

Edited by Martin

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didnt the wmap come state that there isnt enough data even including the possible dark energy for the universe to actaully contract? and that was after another satelitte that got similiar, less precise results. doesnt that support the supposed big chill?

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.. doesnt that support the supposed big chill?

 

Sure does!

Big chill (if I understand what you mean by it) is the standard picture of the longterm future. Our galaxy will be bigger then (due to merging with other galaxies like Andromeda). Stars will burn out*. Dark and cold. Other darkening galaxies drifting away gradually fading out of sight.

 

Surprises could of course happen. This dark cold picture just happens to be what is predicted by the best model so far devised. Why couldn't future discoveries change the model? and thereby change the forecast?

 

 

*If we are still around, in some form or other, we will have to figure out how to eat dead stars. There will be a lot of dead stars in our vicinity.

According to the standard model, expansion does not affect individual galaxies, so the galaxy won't drift apart (it will in fact merge with some others) so there will be billions of stars around.

Edited by Martin

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Sure does!

Big chill (if I understand what you mean by it) is the standard picture of the longterm future. Our galaxy will be bigger then (due to merging with other galaxies like Andromeda). Stars will burn out*. Dark and cold. Other darkening galaxies drifting away gradually fading out of sight.

 

If stars burn out, won't there be other stars? Even if the other galaxies start drifting farther away, how will that really affect us? I was under the impression that most of the other galaxies don't affect us quite as much (except gravitationally).

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If stars burn out, won't there be other stars? Even if the other galaxies start drifting farther away, how will that really affect us?...

 

Stars form out of gas clouds. Our galaxy still has some dense gas clouds where stars are forming. Not as fast and abundantly as in earlier times, but still. So you are right: there will be other stars replacing burned out ones, for a long long time.

 

You are also right about other galaxies. Not many galaxies are even visible with naked eye. As long as there are stars in our own galaxy, and enough around us in our immediate neighborhood, the sky will continue to be beautiful.

 

However after a very long time, after the star-forming gas clouds are depleted, and all the stars that have formed have burned out, this will present whatever life-forms remain with a considerable challenge. This is why I mentioned having to find some way to extract energy from dead stars.

Edited by Martin

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Well, if we live in an isolated universe then it might be heat death.

 

Everything (as far as we know) follows the second law of thermodynamics.

 

Not totally sure on that though, could be areas of the universe that follow a reverse law- in which everything moves towards order. <don't laugh

 

I think the universe will eventually just run out of energy(-heat)

 

Or we might "rip a hole in the space time continuum!" As Doc Brown loves to point out..

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Well, if we live in an isolated universe then it might be heat death.

 

Everything (as far as we know) follows the second law of thermodynamics...

 

You might enjoy Roger Penrose talk about what came before the big bang and what to expect to happen far into the future.

 

He gave the talk first in 2005 in Cambridge and there is online slides and audio.

 

Later he gave it other places (UC Berkeley, Perimeter Institute...) and an October 2007 version is also on YouTube.

 

I would recommend following the Cambridge (slides and audio only) version first, but you can take your choice.

 

November 2005 Cambridge version:

http://www.newton.ac.uk/webseminars/pg+ws/2005/gmr/gmrw04/1107/penrose/

 

October 2007 George Mason University version. The first segments are his talk and the last ones are him responding to questions from the audience.

 

http://www.youtube.com/watch?v=ghbDGBOYp1g

 

http://www.youtube.com/watch?v=0upkexD9Tf8&feature=related

 

 

 

 

 

 

 

September 2006 Perimeter (Canada) version

http://pirsa.org/06090005/

Before the Big Bang: an Outrageous Solution to a Profound Cosmological Puzzle

 

Personally I think Penrose is wrong to trust the 2nd Law to hold thru a LQG bounce----when spacetime geometry and matter collapse and then rebound due to quantum gravity effects. I think that an observer is necessary in order for the Law to hold. During the bounce, space as we normally experience it ceases to exist. Classical space and matter re-emerge shortly after expansion starts. But there is a break during which the physical machinery that one assumes in order to verify the 2nd Law simply does not exist.

 

So I think he is wrong. But that doesn't matter. It is a great talk! Much is presented with exceptional clarity.

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I think the universe will eventually just run out of energy(-heat)

 

How would that happen?

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Does not gravity itself generate heat energy just from the pressure? How can that heat pressure ever decay to a non-energetic state? After all the red dwarf stars have burned out and cool, there will still be places deep inside massive objects that will eternally create heat from pressure.

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How would that happen?

 

I think what he meant to say is the universe runs out of neg entropy.

 

That is it runs out of available energy---energy in some form that life and other processes can use.

 

Would that way of putting it satisfy you? There is no mystery how that happens---we see energy being degraded all the time:

e.g. the planet absorbs highgrade 5000 kelvin sunlight and radiates off an equal amount of lowgrade 300 kelvin waste heat.

 

Everything of interest having been accomplished by degrading that energy from 5000 down to 300 (approximately or whatever).


Merged post follows:

Consecutive posts merged
Does not gravity itself generate heat energy just from the pressure? How can that heat pressure ever decay to a non-energetic state? After all the red dwarf stars have burned out and cool, there will still be places deep inside massive objects that will eternally create heat from pressure.

 

White dwarf stars (finished fusing but not massive enough to collapse to neutron or hole) gradually cool.

 

Yes compaction generates heat energy. The core of the dead star does generate heat as long as it is becoming more compact. But eventually it cools down and becomes as compact as it is able to be and thats it: cold inert material.

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I think what he meant to say is the universe runs out of neg entropy.

 

That is it runs out of available energy---energy in some form that life and other processes can use.

 

Would that way of putting it satisfy you? There is no mystery how that happens---we see energy being degraded all the time:

e.g. the planet absorbs highgrade 5000 kelvin sunlight and radiates off an equal amount of lowgrade 300 kelvin waste heat.

 

Everything of interest having been accomplished by degrading that energy from 5000 down to 300 (approximately or whatever).


Merged post follows:

Consecutive posts merged

 

Heat death would only work though if we lived in a closed universe to begin with, which it's not known if we do or not, right?

 

And the videos are much appreciated, I've yet to watch them though :)

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Yes compaction generates heat energy. The core of the dead star does generate heat as long as it is becoming more compact. But eventually it cools down and becomes as compact as it is able to be and thats it: cold inert material.

 

Is it possible that large orbiting masses may be able to maintain heat from movement created by tidal forces?

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Is it possible that large orbiting masses may be able to maintain heat from movement created by tidal forces?

 

I'd imagine so, but I'd presume that unless their relative masses were significantly asymmetric (think of the mass difference between Io and Jupiter, for example) that the temperature increase from tidal forces alone would be pretty negligible. In other words, I'd expect there to be a heating effect from tidal forces, but not much of one if the masses of the orbiting objects were similar (it seems they'd be more likely to find quick equilibrium). [/conjecture]

 

 

It probably depends greatly on specific circumstances, but the simple answer is, "Yes, it's possible."

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Is it possible that large orbiting masses may be able to maintain heat from movement created by tidal forces?

 

Any heat it would create would decay the orbit. The net result would be a further increase in entropy.

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Yes compaction generates heat energy. The core of the dead star does generate heat as long as it is becoming more compact. But eventually it cools down and becomes as compact as it is able to be and thats it: cold inert material.

 

I find it hard to believe that a dead star will ever become cool all the way to its' core. There will always be pressure, and therefore heat energy. That is why mines get hotter the deeper they dig. Intelligent beings that are still living Trillions of years from now could dig tunnels into dead stars to mine the heat energy.

 

Or they could build a fusion reactor that never cools. All they need to do is add a little hydrogen to it now and then. E=mc^2. Energy could always be extracted from matter, as long as there is matter in the universe.

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I find it hard to believe that a dead star will ever become cool all the way to its' core. There will always be pressure, and therefore heat energy. That is why mines get hotter the deeper they dig. Intelligent beings that are still living Trillions of years from now could dig tunnels into dead stars to mine the heat energy.

 

Or they could build a fusion reactor that never cools. All they need to do is add a little hydrogen to it now and then. E=mc^2. Energy could always be extracted from matter, as long as there is matter in the universe.

 

A dead star will cool to its core...eventually. Yes it will take much, much longer than trillions of years, but it will happen. As long as it radiates heat away (and it will do so as long as it is warmer than the surrounding space), it loses energy and therefore cools. Pressure only generates heat when it changes or causes something else to change (think about PV=nRT - although I'm sure we both realize the inside of a star isn't an ideal gas). Once everything stabilizes at a constant Pressure, Volume, and Temperaure (equal to surrounding space, just an iota above absolute zero), there is no more energy to be had out of the star.

 

Unless of couse you can harness the gravity waves generated by the mass of the star; and if this is possible (we don't understand gravity waves so we don't know if this would be possible to do), then the implication is that eventually the star, and in fact all matter which can generate gravity, will dissipate since E=mc2 and a loss of energy must then equal a loss of mass.

 

As far as fusion, where do you propose to get the hydrogen for fusion? And as far as that goes, only very small atomic number elements "fuse" with a surplus of energy. Likewise only very large atomic number elements will produce energy by fission. If you only have iron available (or if nothing is available), you cannot do either.

Edited by SH3RL0CK
Added thought regarding gravity

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Interesting explanation SH3RLOCK. I suppose a cold dead star would be solid all the way to the core. That is hard to visualize, but it must be so.

 

As for where do they find hydrogen for a fusion reactor? Space will always be full of hydrogen gas and other kinds of dust that never gets compacted into stars. Not all matter gets pulled together into stars. They would need to sweep thru space collecting free hydrogen, and that supply of free hydrogen atoms is everywhere in the universe, nearly limitless.

 

I believe that there is more gas and dust in the universe than all the stars, black holes, planets, asteroid, and comets combined.

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True, there will always be hydrogen present (even if very spread out) as long as the proton does not decay. http://en.wikipedia.org/wiki/Proton_decay

 

I think that given the immense timeframes we are discussing here, such hydrogen must be VERY spread out indeed (or it would have collapsed into a star long ago). As such, it would require more energy to gather the hydrogen than is recoverable by fusion; unless you pick the spots where the hydrogen is just then collecting into a cloud and I'm not sure that would be the case after this length of time in an expanding universe. It could be that at some point the negligible gravitational attraction by the hydrogen atoms to each other is not as strong as the force driving the expansion of the universe.

 

At any rate, given a finite number of atoms in the universe and sufficient (near-infinite) time, this fuel source too must eventually run out.

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Here's my question. If the multiple worlds interpretation of quantum mechanics is true, wouldn't the universe reach more than one possible outcome, like a big freeze and a big crunch? I guess to be more specific, if all our evidence leads to a big freeze scenario, does that rule out a big crunch scenario, or is it dependent on circumstances that led the universe to one end or another? Or vice versa? Is there more than one possible end for the universe?

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How can there be both a big freeze and big crunch? Seems like a big freeze means even after Trillions of years gravity was not sufficient to overcome dark energy, and expansion continues "over the hill" and never stops. Either big freeze or big rip.

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I'm talking about the everett multiple worlds interpretation of quantum mechanics. Let me try to clarify.

Whether the Big Freeze or the Big Crunch happen to our universe based on circumstance, was the alternative ever possible?

At the time of the big bang, was it possible that, assuming MWI, either outcome could have happened based on the way things went?

Would it have been possible that the universe split into an alternative universe where it crunched and one where it froze?

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Yes. It's possible. How likely it may be is another question entirely.

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#1 - Whether the Big Freeze or the Big Crunch happen to our universe based on circumstance, was the alternative ever possible? At the time of the big bang, was it possible that, assuming MWI, either outcome could have happened based on the way things went?

 

#2 - Would it have been possible that the universe split into an alternative universe where it crunched and one where it froze?

 

You are asking two questions. The first is essentially "Did the universe have freedom of choice about it's destiny, or was it predetermined at the moment of the Big Bang? I think it was predetermined, based on all pre-existing conditions. But maybe it is possible that during the course of the evolution of a universe, it could take different courses depending upon unforseeable events.

 

Is anything possible? Sure, why not? ;)

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