[General] On photon momentum

[Chip Akins]

Hi Dr Grahame Blackwell

 

One more observation.  The equation p=E/c is a bit misleading and not expressed in a completely transparent form.

The equation p=E/c taken literally means that momentum would increase if the velocity of the energy were slowed somehow. So I agree that this is not in any way a definition.

I know that this equation can be derived from p=mv= E/c^2 v, and if the v is c then simplifying gives p=E/c, but in simplifying that equation to read p=E/c, part of the information regarding any possible mechanism for the creation of momentum is lost.

 

Chip

 

From: General [mailto:general-bounces+chipakins=gmail.com at lists.natureoflightandparticles.org] On Behalf Of Dr Grahame Blackwell
Sent: Saturday, January 28, 2017 6:12 PM
To: Nature of Light and Particles - General Discussion <general at lists.natureoflightandparticles.org>
Subject: [General] On photon momentum

 

Dear All,

[Notably Chandra & Chip],

 

I'm having a bit of a problem over this question of: 'How does a photon carry momentum'? (or similar words.)

It seems to me that in order to even beginning to address this question, one needs a clear definition of 'momentum' that's applicable to the momentum carried by a photon.

I may be looking in the wrong places (if so please advise), but the only definitions of momentum that I can find either refer to 'mass' or refer to some other phenomenon which in turn refers to momentum - i.e. circular references.

If I'm going to figure, or be persuaded, how a photon carries momentum I first need to know what momentum IS in respect of a photon (yes, I know it's E/c, that's a measure it's not a definition).

Of course I'm aware of the paper "Light is heavy", but I don't feel it's appropriate just to extract from that some sort of mass-equivalence of a photon.  If we do, we get the result that 'm'=E/c^2, so 'm'c = E/c - gives the right result, but appears to be some sort of convoluted self-confirmation (i.e. a circular argument dressed up in fancy clothes).  It certainly doesn't DEFINE a photon's momentum, just evaluates it.

 

Does anyone have a convincing definition of momentum that's applicable to a photon?  One that can be used as a firm basis for theorising?

(I'd be glad if colleagues didn't use this as an excuse to yet again present their own personal theory/model - I'm looking for a definition that would be agreed by all, or at least most, physicists.)

 

Thanks in anticipation,

Grahame

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.natureoflightandparticles.org/pipermail/general-natureoflightandparticles.org/attachments/20170128/55e0fd47/attachment.htm>