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I recently watched a documentary about relativity and time travel. It explained how time slows down close to massive objects and then it tried to visually show it by showing people moving in slow motion around the pyramids (after clarifying that pyramids are not massive enough for time to slow down that much and that pyramids were assumed to be much more massive for that example).

That made me wonder - If pyramids were indeed massive enough for time in the immediate vicinity to slow down by let's say one-tenth and people were walking around it and if an observer was looking at them from far enough to be only negligibly affected by the mass of the pyramids, would that observer actually see/observe people walking around the pyramid in slow motion? If not, what will the scene look like to him?

Note: For this question, lets ignore other side effects of that unnatural mass of the pyramids, lets assume that people are able to normally walk around, the pyramid doesn't suck everything around it etc. Lets also imagine that the observer is able to visually see the people near the pyramid regardless of the distance (for example, he may be using some sort of telescope).

Achilles
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Yes, one would observe it as slow motion. Another complication would be that the light would become red-shifted as it escapes the gravitational potential.

There is the muon decay experiment where one knows the lifetime of muons to be very short from other, stationary experiments. Then you can measure the muon flux from the atmosphere/solar winds on a mountain and on the sea level. Knowing their velocity (significant part of speed of light) and their lifetime, one could estimate the flux on the sea level. However, the flux is way larger due to special relativity time dilation. So there one can indirectly observe the muons in slow motion because they decay slower.

A thought experiment that can be calculated with the machinery of general relativity is dropping a clock into a black hole. If the experiment is set up that at 12:00 the clock will pass the event horizon, you will observe like 11:54, 11:55, 11:56, 11:57:30, 11:58:00, 11:58:30, 11:58:45, 11:59:00, 11:59:10, 11:59:15, ... 11:59:59, 11:59:59.5, ... 11:59:59.9999.

The closer the clock comes to the event horizon, the slower time will pass. You will never be able to observe it passing through the event horizon, instead the events just before that will become more and more stretched out.

Martin Ueding
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