why is speed of light constant?

Answer 1

The short answer is that we don't know. All we know is that experiments show that it is. Maxwell's equations suggest that the speed of light is a constant, but the equations contain physical constants that in principle could change, but in practice, don't.

Answer 2

This is an empirical observation of nature (read about the Michelson-Morely experiment). It is simply how the universe is . This question is akin to "why is energy (or momentum) conserved" and "why does force equal mass times acceleration instead of mass squared?"

Ole Roemer's observations of Io not only indicate the finite speed for the propogation of light, but also implied it is the same for all observers, regardless of radial velocity, or even his correction using a finite speed would have changed depending on the Earth's heading.

Michelson-Morely experiment: http://en.wikipedia.org/wiki/Michelson-Morley_experiment

Ole Roemer and Io's orbit: http://www.colorado.edu/physics/2000/waves_particles/lightspeed_evidence.html

The same

Answer 3

The speed of light is constant IN A VACUUM. However, it travels more slowly through air and even slower through water and glass.

Answer 4

The speed of light in a vacuum is an important physical constant denoted by the letter c for constant where in metric units, c is exactly 299,792,458 metres per second or 1,079,252,848.8 km/h.
Converted to imperial units, the speed of light is approximately 186,282.397 miles per second, or 670,616,629.384 miles per hour.

Answer 5

Because, in a vacuum, it never changes and it is always observed to be the same no matter what the observers inertial frame.


Doug

Answer 6

It is constant under specific conditions. See http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/speed_of_light.html