I am not expert at all in this subject, but I am willing to suggest that time is a theoretical concept that is defined by the various theories that use it.

General Relativity defined time as you mentioned above based on the finite speed of light and it is also dependent on the mass of objects in the universe.

String theory in 26-D has two time dimensions. I have no idea what this means.

Superstring theory in 9, 11, but mainly 10 dimensions has one time dimension.

Loop theory derives time as well as space coordinates from loops. That theory is still incomplete.

Probably the most fundamental meaning of time is that we cannot see the entire universe. So it prevents us from knowing how big the universe is. It is also why the sky is dark at night.

Regards,

Richard

• and physical definitions - something - March 27, 2002 - 19:19 UTC