stuck.Here is a thought experiment: Alice is traveling in a ship towards a BH. Alex, well outside the reach of BH, is recording her progress with a detector. Will he see Alice headed to BH ever disappear?No black holes anywhere, so who cares. Not I.
Arindam:Regards
Anyway, suppose we have a lossless tunnel of light from Earth to an object - say a working clock - moving away.
At the speed of light, whatever time the clock shows remains fixed so far as we on Earth are concerned. It is like, frozen. For the same image (phasefront) is coming at us. it is not that the clock has got stuck. It is that it appears to have got
Beyond the speed of light, the clock vanishes, for the clock is travelling faster than light and light from the clock cannot reach us.
Below the speed of light, the clock slows down to some value between rest and speed of light.
Arinda:okay.This has nothing to do with Einstein's relativity, just practical matters.I don't understand the relativity part in your last sentence. When clock is moving at c, and the observer is moving at c then the clock works fine when the relative velocity is zero.
However if the observer is at rest, all bets are off.Why should that be?
I don't understand the part the clock appears frozen when it is moving at c.And the observer is at v=0, yes?
Look at it this way.Still don't get it. So if a star is moving at light speed, its light will never reach us?
Light comes to you at speed c normally.
When the object is receding at c, information via light won't come to you, or keep on coming to you.
Just one frame will be seen in a lossless pipe type scheme, say.
That is the time information, frozen.
When it is going beyond c, then not even that frame will come to you as the clock is travelling faster than light so the information via light can never reach.
Perhaps its arrival on earth will be delayed by some factor. But me thinks it will sure arrive.
This is like saying if a source of sound moves faster than sound, its sound waves will never reach us, which is not true. For example when the concorde used to fly above us, its sound got to us much after it has flown away from us.
Pray, enlighten me, O Master!
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