If we want to explore the whole universe
, we're in trouble. The universe is starting to expand exponentially. Luckily our local supercluster is held together by its own gravity, and that gives us roughly a trillion stars that will stay nearby. But our best evidence today says everything else will move away, and in 150 billion years fall behind a cosmic horizon
- meaning we'd have to go faster than light to catch it!
This horizon is roughly 18 billion light years away. When objects fall behind it, they won't immediately disappear. Instead, the last bit of light to reach us from them will get stretched out and become increasingly dim and redshifted. By about 2 trillion years, it'll be impossible to see this stuff at all.
This seems like a long time, but some red dwarf stars around today will last as long as 10 trillion years - so with plenty of luck, there could be thriving civilizations living near hundreds of billions of red dwarfs in our local supercluster, long after the rest of the universe has disappeared from view! Unless of course life figures out something more interesting to do: I like to speculate based strictly on the physics we know now, but if nobody knows anything shockingly new about physics by then, that'd be surprising.
To see more details, try:
• Lawrence M. Krauss and Glenn D. Starkman, Life, the universe, and nothing: life and death in an ever-expanding universe, http://arxiv.org/abs/astro-ph/9902189
Thanks to +Pedro J. Hdez
for pointing this out! #astronomy