Universe to Disappear From View?

May 22, 2007 — It sounds crazy, but as the universe expands faster and faster, it will eventually get to a point where the cosmos seen through a telescope will look a lot smaller than today, say physicists.

That's because in a few hundred billion, or perhaps a few trillion years, all but our local group of galaxies will have moved so far away they will be lost forever.

As a result, any cosmologist of that distant time who tries to figure out the history of the universe will have no clue to the Big Bang or the existence of the vast clusters of galaxies we can see today in every direction with powerful telescopes. Not even the microwave background radiation — the subtle and surest sign of the Big Bang — will remain within reach.

"They'll still be out there," said cosmologist Lawrence Krauss of Case Western Reserve University. "But space will be expanding faster than the speed of light," and so the light from those galaxies will never reach us again.

This is possible despite the universal speed limit being that of light, Krauss said, because the galactic clusters won't actually be moving; it's the space between them that will be expanding at a rate faster than light can traverse it.

Krauss and Vanderbilt University physicist Robert Scherrer have written a paper on the matter, which will appear in the October 2007 issue of the Journal of Relativity and Gravitation.

The cause of all this is the bizarre but critical component of the universe called dark energy.

Dark energy is the growing tendency of empty space to spontaneously create more empty space — thereby distancing anything in the universe that's not bound together with gravity. No one can fully explain dark energy, but without it the universe we see today makes no sense.

"We know it's allowed (by physics), but we have no idea what it is," said University of Michigan cosmologist Fred Adams, co-author of the book "The Five Ages of the Universe."

By the year 3,000,000,000,000, all that will be left for astronomers to observe will be the stuff that today makes up our gravitationally-bound "local group" of galaxies: The Milky Way and Andromeda, the Large and Small Magellanic Clouds, and a few other puny galaxies.

These are all close enough that their gravity overcomes the expansion of dark energy, and so they can stick together and eventually become one of many "island universes" that can no longer detect each other.

Within any of those islands, the visible universe will appear to be neither expanding nor contracting, but relatively small and static, Krauss told Discovery News.

One implication of this time-travelling exercise, said Krauss, is that even today we may be suffering from similar blinders and don't know it. Adams agreed.

"It could be there's some event that happened in the early universe that's (undetectable)," said Adams. "It's very important for all cosmologists to be very humble."

There's even the possibility that dark energy itself will change in the distant future, said Adams.

"We're always assuming that the universe will continue accelerating," Adams told Discovery News. But even that weirdness might moderate.