With whom are we sharing the rest of eternity?
December 4, 2011 11:57 PM   Subscribe

If I've gotten the right impression, much of our currently visible universe will eventually be expanded away from us, never to be seen again. Do we already know how much and what parts of our present neighborhood we'll be left huddling with?
posted by Anything to Science & Nature (12 answers total) 5 users marked this as a favorite
The jury is still out on what exactly the actual fate of the universe will be . New data brings new theories. I've lived through several - all contradictory. We probably won't know the real truths for several centuries at the very least. However if you are talking about the popular theory that our universe will expand forever , that theory says that we won't be left with any neighbors at all. Some tens to hundreds of trillions of years in the future space will expand to the point where the strong force will weaken and protons and neutrons will more or less dissolve away. Long before that happens our galaxy will have broken up and all of the baryon stars in the Universe will have gone out.

The good news is that it's only a theory and I'm sure that a new theory, based on a better understanding of the cosmos , will supplant it in another quarter century just as it always has. The bad news is that ultimate reality is probably a lot scarier and lonelier than anything men can theorize.
posted by Poet_Lariat at 12:11 AM on December 5, 2011

Recently I read an interview with a famous cosmologist (forget who), who said that there were six galaxies in our group who were generally going in the same direction, and if the expansion of the universe kept speeding up, then only these six would be visible. He postulated that any intelligent species which evolved during that time would look out and wonder what was special about the number "6."

I thought this was a pretty cool concept. :)
posted by zachawry at 2:35 AM on December 5, 2011

Do we already know how much and what parts of our present neighborhood we'll be left huddling with?

In what time frame? Eventually all matter in the universe is going to dissolve and there will be nothing left but some stray photons.

This paper goes over it in detail.
posted by empath at 3:44 AM on December 5, 2011

Best answer: Here is a picture of the "Local Group" the galaxies in our general vicinity.

Andromeda (#21 in the picture above) and it's little satellite galaxies are about 2.5 million light years away. And on a collision course with us. In a few billion years we'll merge with it.

According to this (a great site to follow for all sorts of physics related goodness) that's pretty much the fate of the entire local group. All those galaxies will merge into a single, massive elliptical galaxy and, eventually will be the only one left in the visible universe.

Short answer: We'll be sharing the rest of eternity with the local group. Sort of.
posted by Mister_Sleight_of_Hand at 3:48 AM on December 5, 2011

By the way, if memory serves, Ethan at Starts With a Bang has a better post specifically about the recession of galaxies beyond the horizon of the visible universe. I just can't seem to find it right now. But dig around, I'm pretty sure it's there somewhere.
posted by Mister_Sleight_of_Hand at 3:57 AM on December 5, 2011

Response by poster: Thanks for the answers!

Regarding which time frame, I'd say I'm looking for whichever time frame under which we can still expect matter to hold together, with the understanding that if matter is eventually going to dissolve, there will be some specific lump of matter which in our part of the universe will be doing the dissolving.

So the Local Group it is? I love that picture -- our rag-tag team of galaxies!
posted by Anything at 4:54 AM on December 5, 2011

Don't worry, the earth will get swallowed by the sun when it turns into a red giant, billions of years before we're alone with the local group.
posted by empath at 5:21 AM on December 5, 2011

Maybe not...
posted by BozoBurgerBonanza at 5:25 AM on December 5, 2011

Yup. The Local Group consists of those galaxies that are gravitationally bound to each other. Current cosmological theories suggest that inflation (well, dark energy to be precise IIRC) will take the rest of the universe over the horizon sometime in the next 100 billion years or so.
posted by pharm at 7:29 AM on December 5, 2011

The second law of Thermodynamics dictates that everything will gradually drift further and further apart, marching toward maximum entropy. This is referred to as the heat death of the universe.

This will occur on an even longer timeframe than the "expansion" of the cosmos, but is the ultimate endgame. (Or, maybe not, depending on who you ask)

Isaac Asimov wrote a short story that explains this concept far more nicely than I can. It's fiction, but definitely something you should read if you're musing on this topic.
posted by schmod at 7:42 AM on December 5, 2011

According to Gott et al., most of the universe is already "unreachable." (Check out at least the logarithmic map; don't be put off by the length of the manuscript, which is basically a ten-page caption for the log map preceded by a discussion of maps in general.)

The radius of the visible universe (in "co-moving coordinates," caveat emptor) is about 45 billion light years. Light emitted from the Milky Way now will only ever reach galaxies nearer than about 15 billion light years; accelerating cosmic expansion means that more distant galaxies will be receding from us faster than c before our message reaches them. If it's fair to talk about volumes in co-moving coordinates, then 90% of the volume of the presently visible universe is in the "unreachable" zone.

Presumably the same thing is true for our view of those galaxies. Not only do we see them now as they were when the universe was about 2/3 its present age, 8 gigayear or so from the Big Bang, but they'll redshift to invisibility before we see them at the universe's present age, 13 Gy from the Big Bang.

So that's the answer now. You have your longer-term answer already: until the unknown interaction causing the expansion of the universe to accelerate becomes more important than gravitational binding energy, we'll still be bound to the other members of the Local Group.
posted by fantabulous timewaster at 10:56 PM on December 5, 2011

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