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Re: Evaporation

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Posted by Gideon Yu/">Gideon Yu on August 27, 1997 15:54:33 UTC

: : : Hello, : : : : : : Can someone explain to me what the evaporation of the black hole means? What happens when it is fully evaporated?

: : : Also I was wondering that id we could survive inside the horizon and we get to the center.....would we not hit the mass in the center and die anyway.....why does everyone think that we would travel in time?

: : : Blaise

: : You know, you should really read the book by : : S. Hawkings - A brief history of time. i think : : people talk about travel back in time because : : that's what we all like to fantasize about. : : and since all laws of physics as we know it : : breaks down, time travel is not excluded.

: Evaporation: Steven Hawking hypothesized that black holes actually emit energy in the form of radiation. Clearly, this is a controversial theory as it is impossible to test with current technology. Many believe that the radiation would stop before the mass is fully evaporated, leaving a newly stable remnant. However, I don’t think that anything has been proven mathematically.

: Surviving Inside the Horizon: For a black hole with a sufficiently large mass, it is possible to get beyond the event horizon without instantly dying. However, once you start drifting towards the singularity, tidal effects tend to rip you apart (this is akin to the tidal effects that the moon has on the earth’s oceans, causing them to feel different gravitational pulls at different areas – resulting in tides). Remember, once inside the event horizon, you cannot leave, and in fact, reaching the singularity becomes your "future." So, your survival, once past the horizon, will be at most a few seconds.

: Hitting the Mass in the Center: The idea of a black hole’s singularity being at the center of the event horizon sphere only works with black holes that have no spin. However, if the black hole has a spin, the singularity can be shaped like a flat ring. Ignoring the extreme tidal effects that would undoubtedly cause you to disintegrate, you could conceivable reach the "center" of the black hole without hitting the singularity.

: Time Travel: There are hypothetical arguments that we can travel between universes and indeed, through time via something known as a wormhole. To picture a wormhole, imagine two sheets of paper with a straw through it – the straw is the wormhole. Wormholes are inherently unstable and creating one would call for the creation of a new type of matter and/or a tremendous amount of energy. Professor Kip Thorne and several colleagues recently wrote a paper in one of the top Physics journals describing that, given a civilization with sufficient resources and technology (not ours!), time travel could be possible. If fact, NASA is supposedly setting aside funding to look into the possibility of time travel.

: Oh yeah, to answer your question, the reason people seem to think that we would travel in time when we hit the center of a black hole is that one theory states that a wormhole is made up of a black hole (to suck you in) and a white hole (to spit you out). Conceivably, if you were able to survive the tidal effects, and if you were lucky enough to hit a black hole that was the "portal" into a wormhole, then yes, you could travel through time.

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