I was wondering what a phone call would be like entering or falling t=into a black hole. Due to the massive density of the black hole and time would feel slower, how would that appear to the person on the other side of the call?
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1$\begingroup$ I don't think you can maintain a phone call while close or falling into a black hole. The gravity would very effectively disrupt whatever signal that you are to receive. $\endgroup$– CipherBotCommented Jan 19, 2016 at 3:30
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1$\begingroup$ Question: do you want to include the point of crossing the event horizon, or just leading up to it? (Leading up to it would be just standard relativity calculations I think, but with a very heavy "planet"...) $\endgroup$– AndyCommented Jan 19, 2016 at 14:36
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1$\begingroup$ Time wouldn't feel any different inside the blackhole than outside for the object inside the blackhole, though time outside of the singularity would appear to speed up.. External observers will see time slow to an almost halt for any object that approaches the event horizon. $\endgroup$– scrappedcolaCommented Jan 19, 2016 at 18:56
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$\begingroup$ Exactly the same as any other electromagnetic signal emitted by something falling into a black hole. Very well trodden ground. $\endgroup$– ProfRobCommented Jan 20, 2016 at 0:06
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$\begingroup$ I might be wrong here; however, I think you'd hear "Hello from the other side"!! $\endgroup$– DumbledoreCommented Jan 20, 2016 at 16:35
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1 Answer
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You and your phone will be destroyed before you get to the black hole, but If we pretend that you and your phone can survive being in the vicinity of a black hole ... And let's suppose this is a regular black hole of about 5 to 10 solar masses, and you are falling in, you are not trying to orbit it.
As you fall towards the black hole, at first there is no problem. As you get closer to the event horizon you will accelerate, but until the last second or so the relativistic effects are quite small. Your phone signal will be redshifted, so the receiver will have to adjust the frequency that they are listening in on.
The last second before you fall in will last forever. Your signal will become redshifted further and further, your apparent rate of speaking will slow down and the last second before you pass the Event horizon will, to the outside observer, last forever.
You however are doomed. You pass the Event horizon and reach the singularity in a fraction of a second.
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1$\begingroup$ Why don't you pretend its a supermassive black hole and then tidal forces are no problem at all. $\endgroup$– ProfRobCommented Jun 23, 2016 at 0:13