# Why is time on earth and time in space different?

Mar 10, 2018

Because of gravity time dependence..

#### Explanation:

If you have heard of $\textcolor{red}{{F}_{g} = \frac{G M m}{r} ^ 2}$ and you think it is correct. Sorry to say but no it isn't. If you feel a little cheated in school, you are not the only one.

${F}_{g} = \frac{G M m}{r} ^ 2$ is literally a really good approximation but the fact that relativistic effects are not included in this formula can't be denied.

As per the newtonian concept time is absolute but then came Einstein "time isn't absolute but relative" . Einstein proposed the idea that gravity was just a curvature in spacetime ( a four dimensional stuff) and not a force. Heavy masses curve the spacetime more than the light ones. If there's nothing in space or say free space the time would move on faster than in region with gravity because gravity bends space-time.

Mar 11, 2018

Time on Earth and time in space are different because of relativistic time dilation.

#### Explanation:

Isaac Newton saw time as passing at the same rate for all observers. This was not quite true. Relativity says that time is the fourth dimension of spacetime. This has some profound consequences.

Albert Einstein showed that mass and energy are equivalent with his famous equation $E = m {c}^{2}$. He also showed that mass and energy cause spacetime to curve. Gravity is the effect of this curvature.

Both velocity and mass cause time to slow. An observer on a fast moving ship or in a strong gravitational field will experience time passing normally. An external observer will see time passing more slowly on the fast moving ship or in the gravitational field.

Something curious happens to time when in orbit around Earth or anything else. The orbital speed causes time to slow. The reduced gravity by being in orbit rather than on the surface causes time to speed up. These effects cancel out at an altitude of half of the radius of planet.

So, astronauts in low orbit on the ISS age slightly slower than people on the Earth's surface because the velocity component of time dilation is greater than the effect of reduced gravity.

The clocks on GPS satellites in high orbit run faster than on the Earth's surface because of the reduction in gravity has a bigger effect than orbital speed. These satellites have to have their clocks slowed down to match surface time.

Mar 27, 2018