C represents the speed limit of the universe rather than the speed of light

In summary, the speed of light is not necessarily equal to c, but it is often used interchangeably as the maximum speed of cause and effect in the universe. The equation e=mc^2 uses c to represent the speed of light, but if the photon were to have a non-zero mass, then c would represent the maximum speed limit in the universe. However, current understanding and experiments suggest that the speed of light is indeed the maximum speed limit, hence the use of c in equations.
  • #36
Neandethal00 said:
First of all, one unwritten universal law is 'everything in this universe has a limit', so does the speed of anything. But the question is 'how do we know maximum speed limit is c?' It is just 'one theory' that tells us c is the highest speed of things. A theory.

If we use E=mc2, and assume c is the highest speed of any object, doesn't it also mean 'the rest energy of mass m is twice its maximum kinetic energy?'
You're assuming rest mass is equivalent to obserrved mass.
 
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  • #37
Neandethal00 said:
If we use E=mc2, and assume c is the highest speed of any object, doesn't it also mean 'the rest energy of mass m is twice its maximum kinetic energy?'
No. You are assuming the formula for kinetic energy is ½mv2. But it isn't. That's an approximation that's valid only at low speeds. The accurate formula is

[tex]\left( \frac{1}{\sqrt{1-\frac{v^2}{c^2}}} - 1\right)mc^2[/tex]​

There is no upper limit on kinetic energy.

(I'm using the convention that the vast majority of physicists follow nowadays, that "mass" m means "rest mass".)
 

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