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Talk:Book of Elements (3.5e Sourcebook)/What is Magic?

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I believe there is a logical error in the following quote: "In the real world, if nothing else gets it first, the universe is eventually going to reach a "heat death" where entropy is maximum, all energy is either evenly distributed over the entire universe or in one single black hole,". Specifically, black holes dissipate over time in the real world (due to Hawking radiation and quantum physics) which means that if the entire universe was swallowed up into a single black hole, it would over time, dissipate into a state where particles are getting sparser and sparser. As such, there is no need for the phrase "or in a single black hole". --Havvy 21:52, August 30, 2010 (UTC)

The physics on this part is actually a bit over my head, but apparently gravity being significant might make fitting everything into a black hole the high entropy state. I'm not actually sure how Hawking radiation works into this; maybe it's a dynamic equilibrium or something where nothing actually escapes for long, or maybe the all-containing black hole has its temperature drop enough that it stops radiating (T = 0 K at infinite mass, but I'm not sure how this works out with finite values). It might be simpler to just give the no-black-holes picture, though; this isn't a physics textbook. --IGTN 23:21, August 30, 2010 (UTC)
<Puts on physics hat> Hawking radiation works via short term bending of one of the uncertainty relations (time and energy) near the event horizon. The vacuum spontaneously generates a matter / anti-matter pair (go vacuum fluctuations!) and one of them gets swallowed. This is generally the anti-matter particle for rather arcane symmetry reasons, and that still interacts with the black hole to reduce it's mass slightly while the other matter particle is now outside of the event horizon and goes on it's merry way. Net result, a particle appears to have escaped from the black hole.
I'm actually unclear if this even functions in a "universe as a black hole" state, since the space outside of the event horizon would not be very similar to the regular space we're more familiar with. I'm tempted to suggest that there is no "outside" of the event horizon in such a universe and so hawking radiation wouldn't occur, but I'm dangerously close to making unsupported statements at that point. - TarkisFlux
The space outside a black hole would still exist as per dark energy not being sucked up into a black hole. "From Eternity to Here" (which explains everything I know about entropy and quantum physics) supports my statements. --Havvy 01:22, August 31, 2010 (UTC)
While that's true, it's not particularly relevant and deserves it's own babbling. Dark energy is not independent of space. In it's current incarnation it will preclude the giant black hole scenario in the first place by pushing galaxies outside of the light cones of other galaxies. In that scenario, space grows so fast that other galaxies almost don't exist for each other (because the intervening space is growing faster than light can cross it) but space still stretches out towards them, so at best you get galaxy holes surrounded by near infinite space and you can hawking radiate into them until the heat death of the universe. If you go with a varying value of dark energy, then you could eventually stop stretching space and instead start compressing it, eventually causing a big crunch and likely generate the universe hole on its own (there are other problems with this . In this later scenario, it's unclear if there's even any space left outside of the event horizon for there to be hawking radiation into. And this latter scenario is the only one in which the universe hole happens, so dark energy doesn't really enter into it because it's probably not out there in the first place. The option you're considering, in which there's one universe hole that somehow doesn't comprise all of known space, isn't really compatible with dark energy in the first place. - TarkisFlux 04:45, August 31, 2010 (UTC)

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