Comment on 'Negative matter propulsion'

Abstract

F ORWARD'S discussion of negative matter propulsion is interesting and worth some additional comments. A discussion of negative mass would be incomplete without a reference to the work of Paul Dirac, who developed a theory of elementary particles which included negative energy solutions in 1928. Dirac's theory has been remarkably successful in explaining physical phenomena and is now considered a part of the model of physics. Dirac's discussion of negative energy states predates the work of Bondi by several decades. Although bare Dirac negative mass particles are not actually seen, if they could be seen their properties would presumably be much like those of the negative matter Forward discusses. There is no physical distinction between Dirac's negative energy solutions and the negative mass objects described by Bondi and Forward. Given m=E/c, a negative energy state is identical to a negative mass state. For example, the standard text on quantum mechanics by Messiah notes about Dirac negative energy states: it would be more correct to call them negative mass solutions; however, when the field is null, the distinction between mass and energy is illusory. The Dirac theory does predict antiparticles, but the antiparticles themselves are not the negative energy states (at least not in the conventional way of interpreting the Dirac theory); the antiparticles are holes where negative energy particles are not. Dirac's negative energy states, if they could be observed alone, have exactly the properties Forward supposes for negative mass particles : 1) The momentum is opposite in direction to the motion of the center of mass [ = , where E is negative, in units where c= 1]. 2) The acceleration is opposite in direction to the applied (electrostatic) force. 3) The gravitational mass is negative. The last point assumes that the gravitational mass of an antiparticle is positive—a fact that will soon be experimentally verified but which is not usually doubted. Since the antiparticle is the absence of the negative energy particle, if the antiparticle has positive gravitational mass the particle itself must have negative gravitational mass. By Newton's law of reaction, then, both active and passive gravitational mass must be negative.