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Name: Jon
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Question:
Imagine a spaceship near a black hole. I have heard that time dilation may take place around the black hole due to its gravity warping space-time. My question is: what would an observer from a far-away distance see as the spaceship approached the black hole? I have heard
a) the spaceship would seem to disappear in an instant and
b) the spaceship would seem to hold its position near the edge of the black hole forever.
Which if either is right?



Replies:
Well, b is more correct than a, but in a qualified sense. Let us say you are observing the spaceship by reflected light. The light traveling from the spaceship to you is red-shifted as the spaceship approaches the event horizon of the black hole. This gravitational red-shift is an effect of time dilation, and, in fact, light from the ship at the event horizon will continue to be sent to you forever.

However, you will not be able to see the ship very well for very long. Because of the time dilation, the flux (brightness) of light will be very low, as the time between photons (for you, not the ship) will constantly increase. Also, the red shift will quickly stretch the light waves from the visible to infrared, then microwave, and finally very long radio waves. Not much to see there.

Richard Barrans
University of Wyoming



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