# Imagine a place where gravity is slower than on earth,there 1 second is equal to 10 seconds on earth.There, will light cover more distance than that on earth in 1 second? How will you measure its speed?

##### 1 Answer
Jan 2, 2018

Light always travels at the speed of light for all observers.

#### Explanation:

Even if gravity is strong enough to slow time by a factor of ten, the speed of light will be the same for an observer in the strong gravity and another outside.

Gravity is caused by spacetime being curved by matter and energy. Photons of light always follow geodesics which are the four dimensional equivalents of straight lines.

Photons have zero mass and always travel at the speed on light. This is completely independent of the velocity of the observer or the strength of the gravitational field the observer is in.

So, for an observer in a time dilation field such as gravity, light travels the same distance in a second as it does for any other observer.

The rule $v = \frac{x}{d}$ showing that velocity is distance divided by time doesn't work in relativistic conditions including gravity. From the perspective of an observer in a gravitational field, time and distance are unchanged. An external observer sees gravity causing time to slow down and distance to contract which cancel out when measuring velocity.