Can the Speed of Light be derived?

[friend]

Einstein postulated that the speed of light is the same for all observers. But it seems that this speed limit applies to more than just photons. It also applies to any massless particle. So I have to wonder if there is some way of deriving the speed of light from more general principles that applies to all massless particles. For example, could more general principles hide a maximum speed of information? Any thoughts are welcome.

 

[Khashishi]

It doesn't make much sense to derive a non-dimensionless constant. We _define_ the value of the speed of light. We don't derive it. Historically, it made sense to derive it, because we had a conventional standard for the meter. But we abandoned that standard and just define the meter based on the speed of light.

 

[friend]

It doesn't make much sense to derive a non-dimensionless constant. We _define_ the value of the speed of light. We don't derive it. Historically, it made sense to derive it, because we had a conventional standard for the meter. But we abandoned that standard and just define the meter based on the speed of light.

Yes, I'm sure a derivation would be in terms of other dimensionful constants like h-bar, charge of the electron, etc. So my question is whether there is some means of deriving the speed of light within the formulism that does contain other dimensionful constants.

PS. I'm not sure this thread belongs to SR&GR forum since the speed of light is assumed constant there in ALL there calculations. It seems actually deriving "c" would require a much broader theory that includes SR and GR and so would be beyond the standard model.

 

[elfmotat]

Well, historically Maxwell used his newly-corrected Ampere law to get an electromagnetic wave equation. When solving this equation, he found that EM waves travel at a speed given by:

$v=\frac{1}{\sqrt{\mu_0 \epsilon _0}}$

, where μ₀ and ε₀ are the magnetic and electric constants. When he calculated this value, he found that it was the same speed that light was known to travel at, suggesting that light consisted of EM waves.

 

[bcrowell]

Starting from certain symmetry principles, it is possible to prove that there is a universal speed which also acts as a speed limit: http://www.lightandmatter.com/html_books/0sn/ch07/ch07.html

 

[lugita15]

Starting from certain symmetry principles, it is possible to prove that there is a universal speed which also acts as a speed limit:
http://www.lightandmatter.com/html_books/0sn/ch07/ch07.html

But even Newton would have accepted the existence of a universal speed limit, he just thought its value would be infinite in all inertial reference frames.

 

[bcrowell]

But even Newton would have accepted the existence of a universal speed limit, he just thought its value would be infinite in all inertial reference frames.

Yes, you can consider Galilean/Newtonian spacetime as the limit of Einstein's spacetime as $c\rightarrow\infty$.

 

[friend]

Starting from certain symmetry principles, it is possible to prove that there is a universal speed which also acts as a speed limit: http://www.lightandmatter.com/html_books/0sn/ch07/ch07.html

It would help if you could give a reference to where to find these "symmetry principles" in the long article that you link to.

 

[bcrowell]

it would help if you could give a reference to where to find these "symmetry principles" in the long article that you link to.

7.2.1

 

[friend]

When solving this equation, he found that EM waves travel at a speed given by:

$v=\frac{1}{\sqrt{\mu_0 \epsilon _0}}$

, where μ₀ and ε₀ are the magnetic and electric constants.

Correct me if I'm wrong, but as I understand it, μ₀ and ε₀ are entities of the EM field only. This does not leave much room for confidence that other fields would propagate at a maximum speed of light.