Black holes/wormholes

[SM]

He nicked it from that godawful BSG ripoff.  I think it was called Battlestar Galactica.

Nice sentiment though. 

[SiL]

Forgive the use of Wikipedia!

Evaporation
Main article: Hawking radiation

In 1974, Stephen Hawking showed that black holes are not entirely black but emit small amounts of thermal radiation.[50] He got this result by applying quantum field theory in a static black hole background. The result of his calculations is that a black hole should emit particles in a perfect black body spectrum. This effect has become known as Hawking radiation. Since Hawking's result many others have verified the effect through various methods.[51] If his theory of black hole radiation is correct then black holes are expected to emit a thermal spectrum of radiation, and thereby lose mass, because according to the theory of relativity mass is just highly condensed energy (E = mc2).[50] Black holes will shrink and evaporate over time. The temperature of this spectrum (Hawking temperature) is proportional to the surface gravity of the black hole, which in turn is inversely proportional to the mass. Large black holes, therefore, emit less radiation than small black holes.

A stellar black hole of 5 solar masses has a Hawking temperature of about 12 nanokelvins. This is far less than the 2.7 K produced by the cosmic microwave background. Stellar mass (and larger) black holes receive more mass from the cosmic microwave background than they emit through Hawking radiation and will thus grow instead of shrink. In order to have a Hawking temperature larger than 2.7 K (and be able to evaporate) a black hole needs to be lighter than the Moon (and therefore a diameter of less than a tenth of a millimeter).

On the other hand if a black hole is very small, the radiation effects are expected to become very strong. Even a black hole that is heavy compared to a human would evaporate in an instant. A black hole the weight of a car (~10-24 m) would only take a nanosecond to evaporate, during which time it would briefly have a luminosity more than 200 times that of the sun. Lighter black holes are expected to evaporate even faster, for example a black hole of mass 1 TeV/c2 would take less than 10-88 seconds to evaporate completely. Of course, for such a small black hole quantum gravitation effects are expected to play an important role and could even – although current developments in quantum gravity do not indicate so – hypothetically make such a small black hole stable.

So all those people worrying about micro black holes have nothing to get worked up about. They would, theoretically, cease to exist almost the moment they were created. Theoretically.

[deezelboy]

Now, I believe the wormhole theory states that black holes could actually be used to travel into different universes. Right?

Yeah, an Einstein-Rosen bridge. It's basically a wormhole that connects a black hole to a white hole, a white hole being a black hole going backwards in time (relativity, as with most of physics, being time symmetric).

No white holes have ever been observed in this universe, so if Einstein-Rosen bridges occurred they'd be most likely to trasnsport you to another universe where white holes exist (assuming white holes are any different from black holes due to Hawking radiation - the jury's still out on that one).

The wormhole connecting the two holes together would be unstable, so you couldn't get from one side to the other before it closed off, even if you were going at the speed of light.  However, Kip Thorne proposed a way where the wormhole could be stabilised (which is where the exotic matter in your diagram fits in).

This idea is often dismissed because "everything a black hole consumes is destroyed", but how do we know this? AFAIK it's impossible to record what happens to an object inside a black hole.

Nothing is destroyed, because matter and energy can't be destroyed (they can be changed from one to the other, but never destroyed).  If you fell into a stable Einstein-Rosen bridge, everything you were made of would emerge on the other side.  But you wouldn't look like you!

But if you were the sort of highly advanced civillisation that could stabilise an Einstein-Rosen bridge, I don't see why you couldn't travel with exotic matter, effectively creating a Lagrange point where the gravity of the exotic matter and the gravity of the black hole cancel each other out.  This would allow you to sit at the Lagrange point and not get spaghettified and reduced to a stream of particles.  (Clearly this is hypothetical, 'cos I'm fucked if I'm even going to think of attempting the calculations!)

Forgive my ignorance, but if radiation is emitted by a black hole, then does that mean they don't swallow up anything and everything?

No, they swallow up everything and anything.

Adding to SiL's explanation, Hawking radiation isn't emitted from what fell in to a black hole's event horizon - escape is impossible!  The following lay-man's explanation may cause your brain to hurt.

At the quantum level, empty space isn't empty space by a writhing foam of virtual particles.  Occasionally these particles become slightly more than virtual, but usally only briefly.  So, for instance, a vacuum fluctuation causes a particle-antiparticle pair to pop into existence.  Usually the particle and anti-particle will collide, annihilate themselves and 'pay back' the energy of their creation with the energy of their annihilation, and nobody's any the wiser.  The laws of conservation are maintained, and all that.

But if a particle-antiparticle pair is created near the boundary of a black hole, you might have a situation where one particle falls into the event horizon and it's partner doesn't, and is able to escape.  The escapee particle we call Hawking radiation.

Because it can't collide with its partner and pay back the energy cost of its creation, there's an imbalance with how much matter and energy were in the universe before and after its creation - the law of conservation has been broken.  Except that (theoretically) it doesn't have to be.  To an observer outside the black hole, the black hole will appear to have lost just enough mass to produce the particle of Hawking radiation.  So from our perspective, the black hole evaporates and the law of conservation is maintained.

But - and this is where the mindfuck really begins - to a hypothetical observer inside the black hole's event horizon, it will appear that the universe, not the black hole, has lost just enough mass to produce the particle of Hawking radiation, and the law of conservation is maintained

So from the black hole's perspective, it's the universe evaporating.  Given enough time, the universe will cease to be, and there will only be the black hole.  Fun!

--EDIT--

Interesting idea... could radiation escape a gravity pull that light could not? Me wants to know!

No. 

Adding to Nel's explanation, gamma rays are photons, light.  Not the visible kind, but the nasty, high energy kind!

[BlackWatch]

So from the black hole's perspective, it's the universe evaporating.  Given enough time, the universe will cease to be, and there will only be the black hole.  Fun!

Learning about astrophysics always depresses me because it seems whatever the topic of discussion the end of the known universe is usually what it boils down to. Of course we'll all be dead and gone if and when enough particles get sucked into a black hole to end the universe but there's something disturbing about knowing that everything in existence today will one day be gone (including time and space!).

I guess ignorance really is bliss.

[fitzley]

Not necessarily...I've read theories about multiple universes...so ours dies, but it contributes to the existence of other ones.

Also watched an interesting show where physicists discussed that the end of our universe would return it to its original quantum state. Thus...another random occurrence such as the Big Bang (collision of virtual particles that deez discusses above) would create a new Big Bang and new universe (if I remember this correctly).

Then there is the oscillating universe idea...that eventually, the universe will collapse on itself (the Big Crunch) only to explode again (Big Bang).

Nothing ends...Nothing ever ends.

[SM]

But - and this is where the mindfuck really begins -

[SiL]

MAXIMILLIIAAAAAAAN!

Aherm.

How the diddly would the engine work in Event Horizon? Doesn't it create a black hole in the ship itself? The very end would suggest it doesn't, but that makes even less sense - How would a gravity drive inside a ship create a black hole outside?

[BlackWatch]

How the diddly would the engine work in Event Horizon? Doesn't it create a black hole in the ship itself? The very end would suggest it doesn't, but that makes even less sense - How would a gravity drive inside a ship create a black hole outside?

You're forgetting, SiL, that Paul Anderson is a twat.

[SM]

He didn't write EH though.

I'd just put it down to tachyons, SiL.  It's all tachyons.

[BlackWatch]

My bad, I thought he wrote and directed. Probably the only reason I actually like the film.

Either way he's still a twat.

[deezelboy]

How the diddly would the engine work in Event Horizon? Doesn't it create a black hole in the ship itself? The very end would suggest it doesn't, but that makes even less sense - How would a gravity drive inside a ship create a black hole outside?

We use a retaining magnetic field to focus a narrow beam of gravitons.  These, in turn, fold space-time until the space-time curvature becomes infinitely large and you produce a singularity...
...It folds space so that point "A" and point "B" coexist in the same space and time.  When the spacecraft passes through the gateway, space returns to normal.  It's called a gravity drive.

So basically it uses a gravity beam that's focused so that it creates a singularity/wormhole oustide the ship, through which the ship can then travel through.

Of course we'll all be dead and gone if and when enough particles get sucked into a black hole to end the universe but there's something disturbing about knowing that everything in existence today will one day be gone (including time and space!).

Well, bear in mind that in my example above, the universe and the black hole go their seperate ways.  An observer in each sees the other evaporate to nothingness, but both still continue to exist, just completely cut off from each other. 

But adding to Fitz, for every way the universe is theorised to end, there are usually three or four ways for new universes to theoretically arise from the ashes.

Bar one. 

A vacuum metastability event is a universe killer in every sense of the word.  There's a beautiful quote from the guys who thought it up:

The possibility that we are living in a false vacuum has never been a cheering one to contemplate. Vacuum decay is the ultimate ecological catastrophe; in the new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know it. However, one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy.

This possibility has now been eliminated.

[Neltharion]

Are you talking about Entropy?

Cause well thats seems to be a Universe Killer to me.

[deezelboy]

Nah, a vacuum metastability event.  Wipes out the universe at the speed of light.

A heat death isn't so bad.  Universe collapses and we get something akin to a big bang, like a yoyo universe.  Or it continues expanding, with the expansion either forestalling maximum entropy, or it flattens out to a spacetime so flat that a quantum event creates a big bang.

[Neltharion]

So when entropy reigns supreme and their is no order left in the Universe, that is not a Universe Killer. Unless Entropy reverses, and that, does not happen. Ever.

In the large scale of things at least. It does in certain biological processes.

[BlackWatch]

The possibility that we are living in a false vacuum has never been a cheering one to contemplate. Vacuum decay is the ultimate ecological catastrophe; in the new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know it. However, one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy.

This possibility has now been eliminated.