# If we filmed what happens on an extremely time dilated planet in realtime

Say there was a planet that experienced insane time dilation due to orbiting a black hole, say 1hr on there is 7 years on Earth (something like that), and that it was close enough to Earth for light to travel within minutes or hours. If we put a camera there and watched what happens on our computers in “realtime”, would we see things in slow motion? Like if we put a human there would we see him walking in slow motion or what?

Thought from remembering Interstellar.

Short answer: yes, we would see things in slow motion.

Let's say we put a video camera on the planet, this video camera records what's happening around. Camera saves data to a flash drive and at the same time broadcasts the video stream through wifi.

Standard wifi equipment on Earth would not be able to receive the transmission. Not because wifi is not suitable for a large distance data transmission (we can use a super big antenna to receive the signal), but because the frequency of radio waves received would be some 60000 time lower. Not 5 GHz, but less than 100 kHz. Still it would be possible to decode the signal and get the video stream. As data come very slowly we will get a new frame not several time per second, but about 1 new frame per hour. Each new frame would look normal, only we receive them too slowly.

When in several years the whole movie file is received we would be able to watch the movie and it would look normal. Or if the flash drive is delivered from the planet to Earth we would be able to view the recorded movie and everything on this movie would look normal.

What if we take a powerful telescope, point it to the planet and just watch what's going on on the planet?

We will see that it's very dark there. What was visible light reflected by some object on planet would reach as not visible radio-waves. If we do see some visible photons that would mean that on the planet these were deadly X-rays.

So, to "see" what's going on there we would need some kind of radiotelescope. And if we build such a telescope that would get radio waves, interpret them and transform into a picture, than we will actually "see" extremely slowly moving people and objects on the planet.

Though it's not directly related to question, my personal opinion is that it was not a very bright idea to relocate to a planet so close to black hole.

• Apart from the Doppler shift problem, another factor making it tricky to watch activity on the planet is its high orbital speed. Its orbit would be just outside the photon sphere (by less than a billionth of the Schwarzschild radius), so its orbital speed is a tiny fraction less than $c$. And I guess we need a huge BH to get a stable orbit there for a planet-sized body... – PM 2Ring Oct 23 '18 at 8:17

Over 60,000 times is quite a bit of dilation that would be challenging to achieve on a livable planet, but conceptually it is not impossible. For example, time is dilated with no gravitational forces inside an empty super heavy shell (if only anything could hold this shell from collapsing). The second challenge is that the radio transmission of the video signal would be red-shifted also over 60,000 times. So the transmission would have to be a very high frequency while we would receive it as a very low frequency.

Aside from the technicalities, the answer is yes, indeed we would see people there is a super slow motion in real time. In fact, at over 60,000 times slower, we would simply see them as if almost frozen in time. This article may be a good start on Gravitational Time Dilation.