Q & A

When will the universe stop existing?

Dagmara - Warsaw, Poland

Well, Dagmara, thanks for my first question - and I'm glad you are enjoying the site.

When will the Universe cease to exist? Well, to all intents and purposes, I think the answer is 'never'. You will see, at the end of BANG!, a section where we look at possible final states of the Universe. The point where we think all the stars will have run out of fuel to make them shine is at about 10¹³ years from now. This number is quite quick and easy to say, but represents an unimaginably long time - about ten thousand times as long as the Universe has already been in existence - which as we have seen is reckoned to be more than thirteen billion years. If this distantly future universe, a bleak, scattered population of black holes, dead stars, and the remains of planets, continues to expand, as at present most cosmologists think it will, then there is still no real 'end' in sight. Locally the gravitational pull of black holes may continue to absorb some of the scattered debris, but even the black holes do not seem to be the end of the line, since "Hawking Radiation" given enough time, seems to give a mechanism for the ultimate dispersal of black holes into pure energy.

At 10²⁰ there is still a Universe of sorts, but the density is so small that, if you were put into it at a random point, you would be highly unlikely to see anything in your sky. But the Universe would still be out there, going about its business, expanding, it seems, at an ever-increasing rate. This is all so long after my 35th birthday that personally I am refusing to worry about it !

Cheers

Brian May

Will the Universe continue to expand indefinitely?

Phil - Northern Ireland

Currently, we believe that the Universe's expansion is accelerating (rather than slowing down under the influence of gravity), thanks to the mysterious 'dark energy'. As we don't understand this force at all, it's difficult to say what it will do in the future. Even if it turned off today, though, there is not enough stuff in the Universe to provide enough gravitational pull to reverse the expansion.

Chris Lintott

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