[Atmos (Colin)]

I personally believe that the big freeze is coming. One of the main things that we discovered from the 7 year WMAP data was further proof that the universe is flat by looking at it geometrically. Further evidence to this has been put forward by large scale surveys calculating the mass and size of galaxy clusters and superclusters, voids and super voids. Big job.

The universe could theoretically have been in one of three states, Open, Closed or Flat - these are all factors to do with the critical density of the universe as a whole, the amount of matter contained with its area.

If the universe is open, gravity is not strong enough to slow it and the universe continues accelerating expansion forever. This is sometimes known as the Big Rip.

If the universe is closed, gravity is strong enough to, in time, over come expansion and we end up with the Big Crunch.

If the universe is flat however, it is sitting on the Critical Density where the universe just continues the way it is. Bring on the Big Freeze.

Everything so far points to the universe being flat. In time, all galaxies outside of our local group (some 50-60 galaxies) will slowly drift away from us due to the expansion of the universe. Gravity is strong enough to hold things together if they're close enough, our local group is but nothing out side of that. Estimates put it at 10-100 trillion years before the closest galaxies outside of our local group disappear from our skies forever. After that... The universe will be black... At this point there is no new star formation, virtually every star has died, white dwarfs have cooled down into black dwarfs, every planet has died and exhausted all of the heat that it can pull from gravitational contraction. This, my friends, is the Black Hole Age. In time, even they will disappear with nothing left to absorb, they will continue to evaporate over the next trillions of years.

As it is currently considered that even protons have a half life, given enough time every particle in the universe will decay leaving no trace that it ever existed.

This is the Big Freeze....

Sleep well my friends for the universe will die in 10 million billion billion billion years...

ADDITIONAL:
Just pulled out my trusty calculator. After 10 million billion billion billion years the universe would have ~0.0001% of the amount of matter as it does now.