Fate of Universe revealed by galactic lens

[hackenslash]

No, no, heat death. The theory is, eventually, the universe will reach maximum entropy. We've gotta stop it because the universe will become uninhabitable. Maybe we can trigger the big crunch.

I'd skipped this post, but it does require a response.

Maximum entropy is a very tricky proposition to deal with. Bear in mind that, in the classical big bang model (which is not established by any stretch of the imagination), our cosmic expansion began as an super-dense, super-hot point. In this model, the cosmos was at maximum entropy before the expansion began. The expansion, however, changes the game, because it increases the maximum value that entropy can reach.

In the 'heat death' scenario, what actually happens is that a maximum in thermodynamic entropy is reached, by attaining thermal equilibrium. What this means is, essentially, that the entire cosmos becomes the same temperature. At this point, all thermodynamic processes stop. This is problematic for several reasons. Firstly, the expansion will continue, which means that the maximum attainable value for entropy will continue to increase, which seems to contradict the idea of reaching maximum entropy. Further, gravity will still be in play, albeit reduced in influence massively as the expansion continues and bodies become more disparate.

As for triggering the big crunch, that idea has been dead in the water for some considerable time, since it was discovered that cosmic expansion is increasing. The best model we have at the moment is that the cosmos will continue to expand indefinitely, and eventually all matter will decay into a sea of photons. After that, who knows? It may be that at this point, another quantum fluctuation will trigger the next cycle. Maybe the world-branes will collide, triggering another phase of expansion. There are a few model on the table, and which, is any, are correct remains to be seen. I'm actually quite excited, because we live in the greatest era of discovery since the dawn of man, which is pretty incredible, given what we've already discovered. Perhaps the LHC will provide some answers. What the GWD experiments will almost certainly provide, if not the answers themselves, is a better idea of what the final answers will look like, and what features they must have.

I'm actually quite hopeful that, in the lifetimes of some of the members here, we will finally have a quantum theory of gravity. At that point, most of physics will be concerned with dotting the 'i's and crossing the 't's. Of course, they said the same just before the discovery of Special and General Realtivity, and Quantum Mechanics. Maybe the answers that are provided in the next century will only open up more questions. I certainly hope so because, while it is nice to have answers, it's much nicer to have questions, because questions drive knowledge forward.

[DropLogic]

/waits for one of our bible bunnies to exclaim "AH HA! See that is proof that God is there! You don't know what it is, it MUST be God! Praise the Lord!"

[DropLogic]

I'm not educated in physics or astronomy whatsoever...but couldn't all the mass we're missing be black holes that aren't in galaxies, and therefore invisible to us?  How could we possibly know how much mass should be in the universe?

[AnimatedDirt]

AH HA! See that is proof that God is there! You don't know what it is, it MUST be God! Praise the Lord!

[DropLogic]

AH HA! See that is proof that God is there! You don't know what it is, it MUST be God! Praise the Lord!

[hackenslash]

I'm not educated in physics or astronomy whatsoever...but couldn't all the mass we're missing be black holes that aren't in galaxies, and therefore invisible to us?

No, Read the post about dark matter/energy above, and it is all explained. Galaxies hold together too well to be accounted for by the mass contained within them.

How could we possibly know how much mass should be in the universe?

By how it behaves.