What are the photon/electron consequences of matter in a gravitational time dilation? So I saw the movie Interstellar, and it got me thinking. I won't even mention all the plot holes, but I wanted to ask about a planet orbiting a black hole. I always thought you had to travel near the speed of light in order to experience time dilation.


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*If you pointed a strong telescope at people on the planet's surface, will you see them moving very slowly?

*Since photons do not experience time dilation and always move at the same speed, will the surface of that planet and objects appear darker, almost dim and black?

*When a photon is absorbed by an atom on the surface and then discharged and reflected back, is the atom's electron orbital speed slower with respect to the speed of light, and absorption also slower with respect to the speed of light?

*Would more light hit a radiometer per unit time from the radiometer's perspective, and would it cause it to spin faster or slower (radiometer time, revolutions/s)? Wouldn't there be a build up of 'light pressure' because atoms could not absorb and reflect the photons as quickly?



 A: OK, let's take you questions one by one.


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*Theoretically, the answer is yes. If you manage to observe the people on the planet from an area not in the vicinity of any significant mass, you would see the people moving much slower, clocks running slower, etc. 

*Although the speed of light is a constant in a vacuum, the frequency of the light will be different to an outside observer. The entire scene would be redshifted. In essence, the light that you would detect would seem to have less energy than the light that left the planet.
If the planet has a large enough gravitational field, you may find that what you are able to 'see' is actually part of the x-ray or ultraviolet part of the spectrum, which has been redshifted into a frequency that can be perceived by the eye.
Since there are far less sources of x-ray and ultraviolet light, you would see a dim, almost black scene.(When I say sources of UV or X ray, I also imply that since no ultraviolet light reaches the planet's surface, there is none reflected. Also, light in the higher part of the spectrum is more easily absorbed than reflected.)


*When you say slower with respect to the speed of light, do you mean slower than what it would be for a surface observer. If so, then the answer is yes. Gravity is responsible for time dilation, which would make everything on the planet seem slower to an external observer. As I understand it, the speed of light here is only a reference speed. Correct me if I am wrong.

*Since the scene was redshifted, the photons that hit the radiometer (carried by an external observer), would have lower energy and hence, lower momentum. The radiation pressure would be less. At least to my understanding.
A: Due to gravitational time dilation, for an observer of the planet, the frequency of electromagnetic radiation would be slower.  Visible light emitted from the planet would appear as infrared or micro-waves.  The amplitude of the radiation would not change.  Since frequency decreases while amplitude remains constant, the radiometer would receive less cumulative energy and would spin slower.
I do not believe there would be any change in the rate at which an atom absorbs a photon.  The speed of light is infinitely faster than mass can travel.  Objects inside a massive gravity well absorb photons the same way objects in open space do.
