THE MEDIUM

The difference is that these stronger oarsmen are tough and will take no nonsense from obstacles like water molecules; if instead of being meekly absorbed or deflected like photons or, for that matter, like their weaker brothers (particles with low energy, such as alpha and beta particles in radioactivity), they will knock them aside; and there is reason to believe that once they are beyond a certain energy threshold, the vanguard of the beam will blaze a trail through which the subsequent particles will propagate with comparatively small losses. (There is little in the open literature on this; but the mechanism may be not unlike a lightning bolt, which is a discharge of electrons through an ionized path blazed by a precursor discharge or "leader.")

The particles used could be electrons, protons or neutrons, of which the first two carry an electric charge. The advantage of electrons is that they are easily generated and easily beamed by means of magnetic fields; protons have only the second advantage (plus their roughly 2000 times greater mass), and neutrons, not having an electrical charge, have neither; yet there are ways of producing neutron beams, which have the additional advantage of deep penetration into matter even at low energies, and there are reasons why neutron beams may be the final choice for directed energy weapons; but it is time to face the ultimate obstacle, whose conquest will probably time (or "pace," as the weapons people say) the rate of development of directed energy.