Electromagnetic Interactions at Very High Energy*

It is easy for a theorist to talk about expectations for particle reactions at higher energies. He knows the answer: he will be wrong. Nevertheless, he is derelict in his duty if he doesn't try to guess. These days the word tTpredictionll is often meant to be the explanation of last year's experiments. We should strive for more, lest it be said that the science of high-energy physics is more backward than meteorology. What can we expect at higher energies? In the realm of pure quantum electro-dynamics, we have an essentially complete theory to tell us. Higher energies will allow extension of conventional QED tests' to shorter distances; in addition, the dominating role of p-beams for proton machines will allow p-trident production (cl-I-pdp+ + ~1~ + CL-+ hadrons) to join scattering, pair-production, and brems-strahlung as good electrodynamics tests. But the high-energy storage rings with their high center-of-mass energy will very likely provide the greatest progress in this field. In processes directly involving hadrons, theory is not so reliable. A guide, useful from both the pragmatic side and from the point of view of theory per se, is the search for scaling-laws which suggest how to extrapolate to higher energies. The first part of this talk will deal with such scaling laws which have some basis from the experimental facts. This includes two-body (and quasi two-body) photo-production and the deep inelastic electroproduction. The second part of the talk will consider scaling behavior based more on theoretical conjecture than on facts. Such scaling laws include the predictions for single-particle spectra a la Feynman-and Yang, and conjectures regarding hadron yields in colliding-beam experiments.