[sjastro]

Originally Posted by CraigS

Ouch !
Brutal !

perhaps true, too .... but why not ?

Cheers

The paper is here.

There are a couple of questionable statements made by the author.

First of all is his example from electrodynamics using the Lorentz force law.
He uses CPT symmetry and finds the Lorentz force for a particle/particle interaction is the same as an antiparticle/antiparticle interaction.
In other words the equation doesn't change sign for each interaction.
The particle/antiparticle interaction changes the sign of the force through the charge conjugation (C) operation due to opposite charges.

This is a valid for the electromagnetic force as it has the unique property of being a repulsive or attractive force. Applying the CPT symmetry to the strong nuclear force doesn’t change the nature of the force. Changing the charge conjugation doesn’t change its direction. This is supported experimentally by Mesons which are composed of quark/antiquark pairs bonded together by the strong force.
The strong force would serve as a better model for gravitational forces as both are forces of attraction. Since the strong force does not change from an attractive to a repulsive force under a CPT transformation, then it is hard to see how this would apply to gravitational forces.

The other issue is the T transformation in the CPT symmetry. The author assumes the Feynman-Stuckelberg interpretation where an antiparticle is simply a particle travelling backwards in time. This defines the T transformation which is a time reversal operator.
The reversal of time when applied to the Universe (through GR) has serious consequences as it violates the second law of thermodynamics.

Regards

Steven