Suppose you drop a clock toward a black hole. As you look at the clock from a high orbit, what will you notice?
A)Time on the clock will run slower as it approaches the black hole, and light from the clock will be increasingly redshifted.
B)Time on the clock will run faster as it approaches the black hole, and light from the clock will be increasingly blueshifted.
C)The clock will fall faster and faster, reaching the speed of light as it crosses the event horizon.
D)The clock will fall toward the black hole at a steady rate, so that you'll see it plunge through the event horizon within just a few minutes.

Question

Quizplus · Accepted Answer

As the clock approaches the black hole, it will experience stronger and stronger gravitational forces, which will cause time to appear to slow down (due to general relativity's time dilation effect). Additionally, the light emitted from the clock will become increasingly redshifted (stretched to longer wavelengths) due to the extreme gravitational field. This combination of effects means that from a high orbit, observers would see the clock ticking more and more slowly, and with redder and redder light, until it eventually disappears from view as it passes the event horizon.

Suppose You Drop a Clock Toward a Black Hole