# Connection between velocity and time

I have some understanding that a relationship exists between time and velocity. As velocity increases, time passes slower for the person in motion at any significant velocity more than those at rest or moving slowly in relationship to the one moving significantly faster.

The example often given is the astronaut moving at half light speed to a distant planet returns to find everyone he knew has aged more than he has. I am comfortable that time can change with velocity as well as with gravity. I've read that a photon emitted from the first star has been traveling for billions of years at the speed of light but has experienced no time passing.

My question is 'Why?' Why does this relationship exist between time and velocity. Why, for example, doesn't time move more quickly when it's hot and more slowly when it's cold? Why isn't time temperature dependent?

Why doesn't time pass more quickly or slowly depending upon perturbations in the quark field?

What gives velocity the power to affect time?

• Motion clearly affects spatial coordinates, as in Galilean boosts. It should not be too surprising that we’ve found it also affects the “other coordinate”, time. Jan 28, 2020 at 6:54
• Time dilation is a direct mathematical result of Einstein's Theory of Special Relativity.
– Sam
Jan 28, 2020 at 6:54
• The example with the (twin) astronaut shows, that not the speed is relevant for the difference in aging but the gravity resp. acceleration. If the astronaut is simply passing by with constant speed vector, for symmetry reason one can not say if the planet is moving or both with half speed in opposite directions. Only the acceleration breakes the symmetry, f.e. flying a 180 degree curve for returning to the planet via swing by technique in the strong gravity field of a big mass. Jan 28, 2020 at 7:26
• In string and other theories the spacetime has more dimensions. As a result, passing by a planet moving "straight" with constant speed vector (in our 4 dimensions) would result in coming back to the planet from the opposite direction, similar like running on a circle. Also in this case, the symmetry should disable any difference in aging. Jan 28, 2020 at 7:36
• Mainly due to light speed constant in all reference frames; en.wikipedia.org/wiki/… Jan 28, 2020 at 8:21