[General] On photon momentum

[John Duffield]

Grahame:

 

I think of photon momentum as something like the momentum of an ocean wave.  See  <https://en.wikipedia.org/wiki/Wind_wave#Wave_formation> wind waves on Wikipedia and look at the gif:

 



 

The wave is motion. Take away the motion and you take away the wave. Note that energy and momentum aren’t two totally different things. One is a distance measure of energy-momentum, the other is a time measure. You can’t take the momentum away from a cannonball without taking away the kinetic energy too. The same applies to a wave. Also note that when an ocean wave moves through the sea, the sea waves. And that when a seismic wave runs through the ground, the ground waves. So when an electromagnetic wave moves through space… space waves. That’s what Maxwell said. See Einstein’s Leyden Address <http://www-history.mcs.st-andrews.ac.uk/Extras/Einstein_ether.html> . He didn’t think of space as nothing. Also see the stress-energy-momentum tensor <https://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor>   which “describes the  <https://en.wikipedia.org/wiki/Density> density and  <https://en.wikipedia.org/wiki/Flux> flux of  <https://en.wikipedia.org/wiki/Energy> energy and  <https://en.wikipedia.org/wiki/Momentum> momentum in  <https://en.wikipedia.org/wiki/Spacetime> spacetime”. It’s got a shear stress term:

 

 

 

I think it’s because space is like a ghostly gin-clear elastic. Waves run through it, and matter is made of them.   

 

Regards

JohnD

 

From: General [mailto:general-bounces+johnduffield=btconnect.com at lists.natureoflightandparticles.org] On Behalf Of Dr Grahame Blackwell
Sent: 29 January 2017 00:12
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

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