Re: [Phys-l] Absolute four-momentum of massless particles

[Moses Fayngold <moshfarlan@yahoo.com>]

Fine.
In this case, out of the two possibilities to interpret your result for a 
photon:
1) P = m U , vector equation; your conclusion: |P|= m |U| = 0  (Scalar equation, 
True)
2) P = m U , vector equation, your conclusion: P = m U = 0, (vector equation, 
Wrong)
only the wrong one, 2), remains in your calculations.

Moses Fayngold, 
NJIT  



________________________________
From: John Denker <jsd@av8n.com>
To: Forum for Physics Educators <phys-l@carnot.physics.buffalo.edu>
Sent: Fri, October 1, 2010 10:13:45 PM
Subject: Re: [Phys-l] Absolute four-momentum of massless particles

In the context of
  https://carnot.physics.buffalo.edu/archives/2010/10_2010/msg00011.html

On 10/01/2010 09:28 PM, Moses Fayngold grasped at the following straw:

>   1)  The symbol U is used as the norm |U| of 4-velocity (and the same for P).

Absolutely untrue.
No such thing occurred in the calculation I did.
I have reviewed the message, and cannot imagine how
anyone could misinterpret in this way.
The equation P = m U is a vector equation.
When I write P = 0 it means every component of P is zero.
If I had meant |P| I would have written |P|.

> this is one of the most elusive 
> and thereby most dangerous errors,

It is particularly elusive in cases where it did not occur and could 
not possibly have occurred.

Bottom line:

Understanding arithmetic is a prerequisite for understanding relativity.
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