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Tuesday, December 14, 2010


Space 5E


As we may recall, one objection against my thesis was that we apply truly fundamental physics to settle issues in space astronomy and physics, not the other way around. This objection has two corollaries. First, our truly important scientific views are not likely to be affected in significant ways by what we do in space. Second, as a consequence of space science, some of our views of the universe may well change, but they are of such remote or esoteric phenomena that the opportunity for practical consequences, even in the long run is slim at best.

Let us take up first the matter of significance. There is a pecking order in the natural sciences, with physics clearly at the top. This is so because of three reasons. One is historical: physics led the way in the scientific revolution and presumably set the standards for subsequent science. A second reason is that physics deals with processes that are fundamental to the natural world; it deals with what all objects have in common. It is not surprising, then, that important changes in physics tend to be felt in many scientific places. The third reason is that the mathematical and experimental rigor of physics, coupled with extraordinary feats of the imagination, maintains the prestige of physics very high.

Even if such high prestige is well deserved, there is an unfortunate tendency to think that other sciences have much to learn from physics but little to teach it. And so we not only give priority to physics but even within physics we may downgrade what the received wisdom does not consider fundamental. For several decades, the most pressing problems were thought to reside in the very small, for the simple reason that the smallest components of matter are presumed to be the building blocks of the universe. These problems are the province of particle physics, and for some years the leading view to explain the nature of particles has been the Standard Model. This model contains 12 basic particles, fermions, which come in two classes: quarks and leptons. The theory of quarks goes by the strange name of “chromodynamics.” The name is strange because it appears to refer to the dynamics of color, but the “color” in question is a property of quarks that cannot be seen (charm is another whimsical property of quarks, and the name "quark" itself is a nonsense word from a poem by James Joyce). The word “lepton” means light, as the electron, the most famous lepton, is supposed to be. But now there are “heavy” leptons. To these whimsically named particles, proponents of the Standard Model have added the hypothetical Higgs particle, presumed to give mass to the other particles. Quarks are the building blocks of hadrons, e.g. protons and neutrons, which together with electrons form atoms. The model also accounts for three of the basic forces: electromagnetic, and the weak and strong nuclear forces. To do this it posits the existence of four force-carrying particles named bosons, which include the photon and the gluon, which “glues” quarks to other quarks.

The so-called fundamental physics contained in the Standard Model, however, does not account for gravity (more on this soon). A rather popular way to bring gravity and quantum physics together has been string theory, which supposes that particles are really little loops or strings. It requires the existence of many dimensions in its attempt to give a consistent account of quantum gravity. Unfortunately that account does not yet have any empirical evidence to support it, nor does it propose many experimental tests that would allow us to acquire that evidence. Even more fanciful views would have many universes existing side by side, so to speak, although such views boast of no more evidence to their credit than plain string theory.

The importance of quarks, and later of strings, was that they presumably explained the variety and properties of sub-atomic particles. More specifically they pointed the way toward a unified account of the basic forces that act between particles, which physicists often call the "basic" forces of nature, except, once again, for gravity. Fundamental research is then research about those forces, and that is the research done at gigantic and very expensive particle accelerators. Since space science is also expensive, there has been an uneasy feeling that space science has taken money away from truly fundamental research. Not that particle physics is the only kind of research a respectable physicist can undertake. But other physics shines by reflected glory, so to speak, and thus the more removed from the center of the discipline the less important it is thought to be.[1]

This uneasy feeling about space science has been losing ground dramatically, and for very good reasons. Let us leave aside, for the moment, the discovery of Dark Matter and Dark Energy, which force us to do fundamental physics in a way that requires the active participation of space science. Apart from those considerations, then, we should take into account the apparent goals of fundamental physics before the astonishing finds of the space-based telescopes. The basic forces of nature are, once more, the electromagnetic, the weak, the strong, and the gravitational. Current physical theory has brought a more or less unified account of the first two (the electro-weak), and there is hope that the strong nuclear force can also be similarly unified with those two. But gravity is not so tractable. The best hope for a unified account of all the forces requires a state of the universe in which all the forces are of comparable strength. But today gravity is far weaker.[2] Many proponents of the standard model trust that eventually in collisions at very high energies in new particle accelerators they will eventually find the so-called Higgs particle. To some extent, though, these ideas have been influenced by scientific beliefs about the beginning of the universe, for then we find a clear case of the required strong gravity, "supergravity," in interaction with the other forces.

Now, to study the beginning of the universe we first make hypotheses about it on the basis of which we predict how the universe should have evolved (e.g., how "lumpy" it should be, what kinds of galaxies should be born and how they should be clustered, what ratio of matter to antimatter should exist, and what other objects, say, quasars and black holes, we should find). We then must observe the universe in order to determine which of the competing hypotheses explains it better (again, this was in the “happy days” before the present obsession with Dark Matter and Dark Energy). It is obvious, though, that the sharper a description we have of the universe, the more sophisticated our testing of those hypotheses about its origin. It should be clear also that the more details we know about the universe the more hints we benefit from in trying to devise new theories to explain its origin and its evolution.

[1] For an account of the contemporary low status of the planetary sciences (until rather recently), see Stephen G. Brush, “Planetary Science: From Underground to Underdog,” Scientia, 1978, vol. 113, p.771.

[2] Taking the value of the strong force to be 1, the other values are as follows: electromagnetic, 10-2; weak, 10-6; gravity, 10-40.

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