This is a very interesting question. The short answer is that time slows down near a blackhole.
In the diagram ,the effects on spacetime (the blue mesh) from different very heavy objects are shown. Black holes are the very extreme examples of space-time dilation because of how extremely dense and heavy they are. Because of this distortion, light is observed traveling a longer distance near the black hole. This is shown by the red arrow in the diagram and is seen by someone at the black hole. The blue arrow is the path of light we would observe from earth.
If we assume the blue arrow has a length of 300,000 km, light would travel that distance in 1 second. Let’s say the red arrow is five times the length of the blue arrow (1,500,000 km), then light would take 5 seconds to travel that distance because the speed of light is constant. So compared to us on Earth, the person on the black hole would perceive time fives times slower. These are just random numbers to illustrate a point though. If you wanted to calculate the exact time dilation, you can follow the equation in the diagram.
This phenomena (called gravitational time dilation) can also happen with the earth! If a clock was placed on the top of Mount Everest and one placed at sea level when the earth was formed (4.6 billion years ago), the clock on Mt. Everest would be 39 hours ahead of the clock at sea level. The effect is really small (nanoseconds) per year so we hardly notice it.
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