As Neil DeGrasse Tyson puts it in his book Death by Black Hole and Other Cosmic Quandaries:

With or without warp drives, the long-term fate of the cosmos cannot be postponed or avoided. No matter where you hide, you will be part of a universe that inexorably marches toward a particular oblivion.

Yikes. So what are the particular oblivions that we can expect?

1. Total heat death
If you're like me, chances are your thermodynamics class stopped being pure fun right around the time you learned about the second law. The second law introduces the concept of entropy, often described as a measure of disorder in a system, but really a measure of the system's unavailability to do work — the evenness with which energy is distributed. Once an ice cube melts in a glass of water, for example, there's no way that ice cube will ever be able to go back and do any more work. It's finito.

The same goes for most of the processes in the universe. The second law of thermodynamics tells us that any process, when it occurs, can either increase the entropy of the universe or leave it unchanged; it can't ever decrease the entropy. So when you think about it that way, it's only a matter of time until the entropy in the universe is at its maximum, and there's no room for any more processes to occur — including any kind of life.

2. The big freeze
As the Big Bang was occurring, the temperature of all the matter in the universe was extreme, on the order of trillions of degrees. In the approximately 14-billion-year history that's followed, however, the universe has continued to gradually expand, and so its average temperature has decreased along with it. Today astrophysicists estimate it to be about 2.7 degrees Kelvin.

Astrophysicists, however, will also tell you that the universe's expansion hasn't stopped. And physics mandates that with expansion comes cooling. Eventually, the average temperature of the universe will get all the way down to absolute zero; no matter how fantastic parka technology gets by that time, life will have to stop.

In case 2.7 degrees sounds to you like it's pretty close to zero, here's a nice thing to remember: Experts in the field agree that the heat in the universe should last us at least 10^10^26 more years.

3. A big crunch / big bounce
Our universe started with a big bang, didn't it? Well, perhaps that big bang was just the end of a previous universe's big crunch — it existed for some amount of time, happy and innocent, and then began to slowly shrink into itself until it collapsed. Collapsed, mind you, with a bang.

If this theory is true, it could mean that we're living in an oscillatory universe; whenever one clump of galaxies has run its course, it contracts and explodes to form another. The major difficulty astrophysicists have had supporting this theory is that it doesn't explain how a recurring universe like this would avoid total heat death. There's also the increasing evidence that the universal expansion will continue indefinitely, but our universe has certainly surprised us before.

4. The big rip
So the universe is continually expanding. Some postulate that it's expanding with increased speed toward a moment where everything in the universe will tear itself apart. First, gravity will become too weak compared to the overwhelming cosmological forces pulling everything out, and galaxies themselves would separate. Then, individual stars and planets would unbind; in the final end, every atom in the universe would lose that essential gravitational imperative holding their elements together, and all of creation would separate into total destruction.

For this, my friends, we've got about 50 billion years to go.

Honestly, though, despair is not the proper reaction to these theories. If you feel like studying quantum mechanics (and who doesn't?), there are plenty more exciting ways to look at the fate of our existence — you could be the one with the next great proposal for what will happen when we drop into a lower energy state, or what exactly we can expect from the supremely mysterious dark energy that occupies 73% of our universe. And if you've been reading io9, you know we've got your back: we're fans of the multiverse theory, and not just because it means that Doctor Who's Billie Piper is having her way with David Tennant in another plane of existence.

All of this is a problem for your distant future relatives anyway. Turn your brain on and give it your all, but you know these cosmic solutions will truly find their answers when the kids are listening to the 10^10^75 offspring of the Jonas Brothers.

Image from Wikipedia.

Describing itself as a movie "about a girl who can walk through walls," the official synopsis of the movie's plot goes a little something like this:

Rebecca is a disgraced scientist conducting illegal experiments to confirm the existence and initiate travel between parallel universes, who accidentally cracks the problem. Her counterparts in neighboring universes are also working on the same problem, but they have their own agendas.

It quickly becomes apparent that the rifts in the space-time continuum caused by inter-dimensional travel can bring about the merging of the affected universes, so it becomes a race against time to close these rifts and save the planet.

Physicists disagree violently as to whether more than one version of our universe may exist. The usual fantasy of alternate universes comes from shows like Star Trek or Doctor Who, where you visit another universe and everything's the same except evil, and with more eyepatches or different facial hair. Here's the evil Worf from an alternate universe enjoying some fun leash-play with Garak, from Star Trek: Deep Space Nine:
DC's current weekly comic, Countdown to Final Crisis, featured a long backup feature called "History Of The Multiverse," in which a group of identical men with weird hair tried to summarize every comic in which someone had visited an alternate universe.For some reason, in DC Comics, the only people who are different in the alternate universes are superheroes, so that Batman is married and has kids, or is a pirate, or was around during World War II. We never see an ordinary person who has different versions in different universes, except maybe for the mail-carrier who starred in that weird crossover between the Milestone and DC universes in the 1990s.

So I was super curious to hear what DiDio, who masterminded the return of the multiverse, would say about its appeal. Is there a philosophical background to the obsession with seeing how things could have turned out differently? The first time I asked DiDio, at the DC Nation panel, he said "Good question" and then didn't really answer. I pressed him a bit more, and here's what he said:

The DC Universe has been built on the multiverse concept. We wanted to bring it back to show the strength of that concept and the multiple interpretations of the characters. And now we're going to focus on the current universe and the current versions of the characters.

These answers made sense (especially the part about nostalgia) but they didn't really satisfy me. I wanted to know what it was about alternate timelines that so fascinated a group of writers and editors in their thirties and forties. Was there some intrinsic appeal to the idea of being able to see how your life might have shaped up if you'd made a different set of decisions?

So I cornered DiDio in the hallway a while later, and asked him again what he thought was so intrinsically fascinating about the multiverse. This time, he said it's all about business. He hadn't wanted to give that answer on the panel, because it's boring, but it's also true. DC Comics went on an acquisition binge during the Silver Age, buying up Charlton Comics, Fawcett Comics and a host of other publishers. Because each publisher had its own stable of superhero characters (like Fawcett's Shazam), who barely fit in with the DC characters, it made more sense to pretend that each cast of characters came from a different universe. And then, as the crossovers between the different acquisitions' "universes" became more colorful, they became a fun thing in their own right. As for why DC is revisiting the idea of different universes now, it still seemed to come down to nostalgia, and trying to recharge some old properties.

I never quite got the answer I was hoping for, about the reasons why alternate universes might seem glamorous and exciting to the DC crew. But maybe if I corner Grant Morrison or Dan Jurgens next time, I'll have more luck.