Can calculus find the momentum of light?

[matphysik]

A wave packet for a massive classical field has dispersion. Do I define v in p=γmv as dw/dk?

Dispersion, and apparent superluminal speed is off-topic.

 

[matphysik]

It is my opinion that the question by the OP had been answered by many users. Any further discussion seems useless and is just going off in circles. May I suggest a mod locks this thread.

You are right. But i think that this topic should be allowed to quiet down on its own. It doesn`t hurt anyone to discuss.

 

[atyy]

Yes.

Hmmm, I am really having trouble seeing this.

The equation for a massive free classical field is really like E²=p²+m². (Eq A)

The group velocity will be: v=dE/dp. (Eq B)

This gives: v²=p²/(p²+m²). (Eq c)

Rearranging: p=γmv. (Eq D)

If m=0, Eq B and C give v=1, which is correct. If we allow division by 0, Eq D gives an indeterminate form which is also correct, since p is not dependent on v for m=0. But that's fine since E=p by definition in Eq A. So I'm really not sure that the indeterminate form is wrong for a massless classical field, except for the division by 0 part. But if division by 0 is not permitted, then we can't even get to Eq D, let alone take its limit.

 

[bcrowell]

It is my opinion that the question by the OP had been answered by many users.

I agree. It was answered 141 posts ago, to be exact.

Any further discussion seems useless and is just going off in circles. May I suggest a mod locks this thread.

Done.