Who isn't interested in cosmology? If people say they aren't, they probably confuse it with cosmetics. But even then, who doesn't like cosmetics? Seriously though, cosmology studies the origin, workings and ultimate fate of the universe. If someone's not curious and inspired by that, well then they're definitely not invited to poker night. Royal flush? Eh, boring.
So the universe is expanding. And it's expanding at a faster and faster rate. Based on the amount of mass in the universe, this should not be the case. The gravitational pull of all matter should be slowing the expansion of the outer frontier. Like holding up a sheet flat and setting some ping pong balls on the outside, then dropping a baseball or similar object in the middle of the sheet, it's weight will pull the ping pong balls closer to the middle. So Stephen Hawking says at least. So to account for this unpredicted fact, that the universe keeps expanding faster and faster, physicists add a fudge factor, known as dark energy. I don't know what's so "dark" about it, it's just the energy that must be contained in open space, that is counteracting the gravitational pull. The system clearly has some mysterious source of energy, so I guess if it's mysterious, it can be dark too. This seems a common route physics takes: the backwards route. Higgs-Bossom was inferred long before it was proven to exist. Dark energy doesn't exist in any tangible way, but it's inferred, because otherwise things just wouldn't make sense.
So can the universe expand forever then? If it really did expand forever, into infinite space, the distribution of matter and energy would be infinitely sparse. There would be a density of zero. This would spell the end of the universe as we know it, a cold, lifeless tundra where space consistently has nothing in it. And dead space is a dead universe. But this apparently won't happen, because before it can, the stars of the galaxies will consume all their energy and become black holes, swallowing up their solar systems and everything in their reach. In 100 billion years or so it's expected the whole universe will be one giant collection of black holes from stars that have fissioned their way to oblivion. So this means the universe is actually quite young in its current state. The big bang was some 15 billion years ago at current estimate, so we're a teenager who can expect to make it well into old age. That's good, I guess. I guess because I'll be dead and gone in a mere nanosecond by comparison, but it's reassuring to know that this grand operation, whatever it is, will continue for millions of my meager lifetimes. There's something beautiful in that, a sense of inherent modesty is imposed by the sheer grandeur and unimaginability of the scale that all of existence and matter operates on. So, ours is a universe with much longer to live.
But after these 100 billion or so years, apparently the models predict that, because of quantum movements (which still operate just fine in black holes) the black holes that fill the universe will eventually become unstable. These black holes are obviously really dense and energy rich, and the fluctuations in their quantum energy will eventually lead them to explode and separate. This explosion and separation will then, get this, lead to a period where the universe consists of their debris and leftovers for about 1 trillion years! For 1 trillion years, all of space will be a chaotic mess, a random distribution of all matter and energy (except maybe dark energy) spread all across the universe. Mind boggling.
How long is a trillion years? Well it's so long that the amount of crazy combinations that can occur over that period of time will lead to the end of this period. A trillion years is the predicted limit for the timeframe over which basically the universe can become one clump of matter. In a trillion years it's predicted that the universe will basically order itself into non-existence. If there's enough random movement, enough experiments of different ways that things can organize themselves, eventually really cooky things will happen. Like if you could live a million years and stay in your house that whole time, eventually the air in the room would organize itself, randomly, in such a way that all the air is a more or less perfectly organized lattice above your head, and it's weight would crush you to death. Crazy, unlikely things like this creep into the picture over seriously long timeframes. The events that are 20 standard deviations from the norm, happen.
So after a trillion years, the universe will basically do what the room does. It will form a lattice of energy and matter that is highly organized and dense. Everything will basically clump up really tight. I think this comes from entropy. That more chaotic systems will lose energy and come undone, while more organized ones will become more energetic and more organized, in a feedback loop. But who knows. And what's really, really, really, and I mean, really, interesting about this is that this structure is very similar to what the universe is thought to have been like in the instant before the big bang. Very smooth. Very dense. All of existence and matter in the space of a thimble. And then it exploded to be what it is now. So then after this trillion years of basically random experiments of organization, that leads to a very tightly packed concentration of all material, what happens? Does it explode into another big bang? Does it create another universe, out of the same energy and material of the one before, but a different permutation? And if so, how many times has this happened? How many universes have their been? And how many are there? Maybe it's not a universe we live in, but a multiverse.
As a caveat, I don't really know what the fuck I'm talking about, at all, I pieced this together from watching and reading stuff online. But then again, who really does know? That's the fun, beauty and awe of it, for me. The universe I believe will remain well outside out comprehension until, when, well, who even knows that.
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