h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I was just idly wondering (like you do)about what would happen if two black holes collided.
Also, is it possible for the entire mass of the universe to end up inside a black hole?
I know that I'll get at least seven conflicting answers, in which case I'll think of it as 'no one knows'.

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They would cannibalize each other...black holes are gravity gone mad, so they wouldn't escape each others' gravitational pull.

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It's possible that that's what caused the first Big Bang, because we don't know what came before.

<<'no one knows'>> yes but it's fun to speculate!

Two black holes colliding would merge and form one bigger hole.

It is possible that all the matter in the universe would end up in a black hole. That's one of the two possible endings of the universe and is known as the Big Crunch. It appears, though, that there is not enough matter in the universe to cause this to happen. It's more likely that the universe will continue to expand until everything is very very far from everything else.

Like northern Scotland.

B

but without the shortbread.

Naw! The critical mass of Scotland's far to high for that to happen...

All those deep-fried Mars Bars - the original 'dark matter'.

I think Northern Scotland follows the Steady State theory..

If black holes are emitting Hawking radiation (has this been observed? I thought it had, but can't find anything to back that up), then they will eventually evaporate. This will take a very very long time (possibly never if that emitted stuff comes back in later? Or if the universe somehiow ends first? Who knows?). I don't think at any point it could contain all the mass of the universe, since Hawking radiation is constantly emitted.

Hawking Radiation happens in the space around a black hole. At the Big Crunch, there won't be any space, as it will all be sucked into the hole too. So that'll be the end.

Stephen Hawking has recanted the theories put forward in 'Brief History' (so glad I never fell for that fad!) and is now proposing an alternative. Although the alternative does still have hawking radiation, it alters the nature of the blackhole as well so that information is now not lost in it.

From what little I have heard of the new theory, it does sound like a bit of a bodge.

As I understand it, Hawking radiation and his model of the blackhole have been providing problems for many people and there are now several replacement theories floating around.

http://news.zdnet.com/2100-9584_22-6062605.html

Apparently space turns to jelly as well. Which is a very Adamsesque thing to happen.

What flavour is it?

Probably cheese.

Arguably, the entire universe is already a black hole, since as far as we know no information can escape from it.

Noggin

What flavour is it?

It's available in up, down, strange, charm, bottom and top... Take your pick.

I'll take the bottom, please, Bob.

good point Noggin. In Cosmos, Carl Sagan says if you want to see the inside of a black hole, look around, you may be in one already!

if somehow a black hole was became large enough to draw other galaxys in it would come in conflict with the supermassive black hole at the center of the galaxy which it was in

this would ultimatly end up in them combining and starting to "feed" until it got too big the matter arround it would start spinning too fast for the black holes gravity to hold on to and it would stop untill something similar to happend again

remember though black holes rarely move enough to "feed" form the place where the star collapsed because it has exaclty the same ammount of gravity as the sun that made all the planets continue to orbit normaly

I think based on measurements of the Hubble constant, the situation you describe won't happen.