Blackholes and FTL

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Lost Soal
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Blackholes and FTL

Post by Lost Soal »

The stupid Voyager Episode where they get trapped inside the quantum singularity was on today, and it got me thinking. In many sci-fi series I see they go with the normal line, "gravity so great that even light can't escape".
So what about any of these hyperthetical FTL drives. If you can travel faster than light shouldn't there be a possability of being able to escape the pull of a blackhole?
In any documentary where blackhole's are mentioned they stick with established physics of FTL being impossible so I haven't seen any mention of what speed would be required to escape. Has there been any kind of genuine attempt to quantify what the force of a blackhole would be?
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Admiral Valdemar
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Re: Blackholes and FTL

Post by Admiral Valdemar »

Lost Soal wrote:The stupid Voyager Episode where they get trapped inside the quantum singularity was on today, and it got me thinking.
I somehow got stuck watching that too. I see Five now has the privilege of showing what BBC2 showed years ago.
In many sci-fi series I see they go with the normal line, "gravity so great that even light can't escape".
So what about any of these hyperthetical FTL drives. If you can travel faster than light shouldn't there be a possability of being able to escape the pull of a blackhole?
In any documentary where blackhole's are mentioned they stick with established physics of FTL being impossible so I haven't seen any mention of what speed would be required to escape. Has there been any kind of genuine attempt to quantify what the force of a blackhole would be?
It would be possible, if FTL travel worked. I would imagine you'd never find out given you get spaghettified long before you get fully swallowed up to try breaking out. Something "Parallax" neglected to show.
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Post by Ford Prefect »

At least the boys from Red Dwarf got turned into living spaghetti when they launched themselves into a black hole. Of course, I can't really admit that the rest of that event was all that scientific, but still.
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Kuroneko
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Re: Blackholes and FTL

Post by Kuroneko »

Lost Soal wrote:The stupid Voyager Episode where they get trapped inside the quantum singularity was on today, and it got me thinking. In many sci-fi series I see they go with the normal line, "gravity so great that even light can't escape".
They were trapped in an actual singularity? That doesn't even make any physical sense. Inside a black hole, yes; inside a singularity, none whatsoever.
Lost Soal wrote:So what about any of these hyperthetical FTL drives. If you can travel faster than light shouldn't there be a possability of being able to escape the pull of a blackhole?
Well, in the case of warp drives... maybe. The warp-drive metrics studied so far have been in an flat spacetimes, except for the bubble itself, of course. I'm not sure how a general warp bubble would behave in a strongly curved spacetime, but I wouldn't expect this to work if it the drive was 'turned on' after crossing the horizon. As for Voyager, it might be the case that whatever warp treknology Voyager possesed was insufficiently effective under such conditions.
Lost Soal wrote:In any documentary where blackhole's are mentioned they stick with established physics of FTL being impossible so I haven't seen any mention of what speed would be required to escape.
Well, if your technology allows you to ignore the local speed-of-light limit (i.e., travel on spacelike paths and somehow ignore the causality problems involved), then you can simply use Newtonian gravity to find the requisite speed for a Schwarzschild black hole.
Lost Soal wrote:Has there been any kind of genuine attempt to quantify what the force of a blackhole would be?
The problem with talking about gravitational force in a relativistic setting is that, properly speaking, there is no such thing. What one can interpret as force on some particle depends on who is doing the observing and how he or she is moving--unlike Newtonian gravity, this kind of 'gravitational force' is dependent not only on position but also on velocity. Still, let's take a particularly simple case. Suppose that there is a particle/rocket at some Schwarzschild coordinate r > 2m. How much radial engine thrust is required to keep the particle/rocket stationary? Well, radial infall is Newtonian in proper time, but the particle/rocket's light cone is boosted near the horizon--its radial coordinate R is not the Schwarzschild r. The boost is the gravitational redshift factor (to the Schwarzschild observer at infinity), so that dR²/dτ² = [-m/r²][1-2m/r]^{-1/2}. Note that the first term in the product is Newtonian and that the event horizon is that r = 2m. Note that the engine thrust diverges to infinity there--it is not possible to be stationary at the event horizon.
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Post by Ford Prefect »

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