The Real Armageddon

• Finally, and perhaps most unusual of all, once we realize that empty space has energy, nothing forbids this energy from being negative. If this is the case, then even an unimaginably small negative energy in empty space will ultimately cause the Universe to recollapse, independent of how much matter now exists therein.

NASA The Perseus cluster of Galaxies is accelerating away from us, every hour the Universe grows a billion miles in every direction

A year ago, Michael Turner, of the University of Chicago, and I demonstrated that there are no observations one can hope to make in any finite time which will allow us to unambiguously determine the ultimate future of our expanding Universe. At least one cosmic mystery therefore appears to remain safe.

The only way out would be to develop a "Theory of Everything" that precisely predicts, in the absence of experimental input, all of the fundamental parameters of the Universe. But there are no signs whatsoever that such a development is in the cards.

We will therefore have to make sure that we, or our descendants, can hang around long enough to witness the final reel in this cosmic drama. However, other recent work suggests that while the Universe may expand forever, life cannot persist forever. (As any salesman for long term care insurance will happily tell you)

In fact, an accelerating universe turns out to be precisely the worst possible universe that anyone can inhabit - in the long term, at least. My colleague Glenn Starkman and I have recently described what our descendants would see in the far future. In an accelerating Universe, distant stars will slowly blink out of sight, as the space that is carrying them away expands faster than light-speed. In an imaginable time, about 150 billion years - during which stars will still be burning and one may imagine life existing around Earth-like planets - all of the galaxies outside our local supercluster will become invisible even to the most powerful telescopes. We will become ever more alone in the Universe.