How do we know light travels at speed c?

[eoghan]

Hi!
Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

 

[Meir Achuz]

c is a constant in Maxwell's equations of Electromagnetism.
A simple derivation shows that this constant, c, is the speed of EM waves which describe the propagation of light.

 

[Passionflower]

Hi!
Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

c is defined as the speed of light in vacuum and is exactly 299792458 m/s.

 

[mathfeel]

Hi!
Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

SR asserts that there is a invariant speed. One consequences is that this is a maximal speed.

Light happens to travel at this speed (for good reason).

 

[HallsofIvy]

Hi!
Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

Special relativity states that nothing can travel faster than the speed of light. Which we happen to call "c".

 

[Drakkith]

Just to chime in, we have measured the speed of light, and it is c.

 

[Antientrophy]

Just to chime in, we have measured the speed of light, and it is c.

Lols

 

[HallsofIvy]

Hi!
Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

What, then, is your understanding of the meaning of c?

 

[Naty1]

Different measurements:

http://en.wikipedia.org/wiki/Speed_of_light#Measurement

 

[harrylin]

Hi!
Special relativity states that nothing can travel faster than c. But how do we know that c is the speed of light?

As you can see, there are different opinions as to what c officially stands for. This is because both in theory and experiment, Maxwell's electromagnetic constant equals the speed of light and this speed also equals the maximal speed.