# How can it be that a person on earth and a person on another solar system will view time differently ie: one hour on the distant solar system will be 7 years on earth?

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How can it be that a person on earth and a person on another solar system will view time differently ie: one hour on the distant solar system will be 7 years on earth?

In: Physics

That’s not how it works. Time stays the same on both planets. You might be thinking of orbital differences. A year is just the amount of time it takes for a planet to go around its star, so 1 year on earth is different for any planet with a different orbit

This is a concept called “time dilation”, put simply the speed of light is constant. It covers the same distance in the same time (in a vacuum) no matter what according to the prospective of the light. But time and space are interconnected, so if space changes then time changes. Space can be changed by large masses, like a black hole. If something big pulls on space and makes it longer, the light has to “speed up” to maintain its constant, but it can’t speed up otherwise it would not be constant. The solution is to slow down time relative to an outside observer. Its a complicated interconnectedness, but if light cannot go faster or slower in a vacuum when the space is stretched or squeezed then time bust change to keep things even.

Gravity changes space and time to keep light constant. Likewise, the speed of light is the same even if a spaceship was going 99% light speed, therefor, time as measured by the ships passengers and an observer on earth would be very different.

On earth, the effect is pretty small but noticeable. We have to take this into account to keep gps reliable, because a stopwatch on earth and a stopwatch on a gps satellite have ever so slightly different measurements.

Ah, you’re talking about the movie *Interstellar*.

The premise of that movie is that they go to a planet near a black hole, which is a very unusual set-up to highlight some aspects of gravity, space, and time in General Relativity.