Paul Dirac devised a relativistic wave equation - an equation that did not only apply to particles with a velocity considerably less than c, the velocity of light. The particles described therefore obeyed the relativistic formula for their energy:
E2 = p2c2 + m02c4
Here energy is squared so its value could be either positive or negative. E.g. if x2 = 4, then x = 2 or x = -2.

Because of his extreme "rationalism" he insisted there must therefore exist particles with negative energy.

Such particles would have outlandish properties. By E = mc2 a particle with negative energy would have negative mass. If, for instance, two particles, one of positive mass the other negative, were each given a static electrical charge one would pursue the other with ever increasing velocity. Nothing of the sort has ever been observed.

To get round this problem Dirac argued that all negative energy levels were full up (Sporus does not understand why this stipulation is necessary). Further, everything was made of energy - somethingness, such as matter, was made of positive energy and nothingness, such as empty space, was made of negative energy. Hence if you zap some emptyness with sufficient (+ve) energy some of the nothingness is promoted up into positive energy and some somethingness blinks into existence. (This is how new particles appear in Cern type machines.)

This predicted anti-matter. Zap some emptiness with +ve energy and some somethingness appears, some matter. It moves off leaving a hole in the emptiness. This hole is anti-matter. When the matter comes back and meets the hole it falls in, releasing the original zapping energy. You get total anihilation. (The anti-matter has positive mass - it is an absence of negative mass; two negatives make a positive so it is positively massive.)

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