Once any one of them is discovered and identified, it will imply the existence of the rest of them, and set the agenda for experimental particle physics for several decades to come–maybe even make a compelling case for a new improved Superconducting Supercollider (SSC) project. There is no direct sighting of any of these particles as yet, though there are a number of indirect observational indications that support a belief in their existence. Supersymmetry (at “low energy”) implies that every known elementary particle should have a supersymmetry partner, with a mass that is about 100 to 1000 times the mass of a proton. The third general prediction, not yet confirmed experimentally, is the existence of supersymmetry at low energies (the electroweak scale). The second is the fact that superstring vacua generally include Yang–Mills gauge theories such as those that make up the “standard model” of elementary particles. No other quantum theory can claim to have done this (and I suspect that no other ever will). The first is the existence of gravitation, approximated at low energies by general relativity. In the absence of this kind of confirmation, we can point to three general “predictions” of superstring theory that are very encouraging. It is very difficult to assess whether this level of understanding is just around the corner or whether it will take many decades and several more revolutions. In my opinion, success in such enterprises requires a better understanding of the theory than has been achieved as yet. In the case of superstring theory there have been no detailed computations of the properties of elementary particles or the structure of the universe that are convincing, though many valiant attempts have been made. When a new theoretical edifice is proposed, it is very desirable to identify distinctive testable experimental predictions. Indeed, there are indications that someday quantum mechanics will be viewed as an implication of (or at least a necessary ingredient of) superstring theory. Most string theorists expect that the theory will provide satisfying resolutions of these problems without any revision in the basic structure of quantum mechanics. The relativist’s set of issues cannot be addressed properly in a perturbative setup, but the recent discoveries are leading to nonperturbative understandings that should help in addressing them. The latter, if true, would imply a breakdown in the basic structure of quantum mechanics. There are also a host of problems associated with black holes such as the fundamental origin of their thermodynamic properties and an apparent loss of quantum coherence.
Strings theory still string how to#
A relativist might point to a different set of problems, including the issue of how to understand the causal structure of space-time when the metric has quantum-mechanical excitations. By replacing point-like particles with one-dimensional extended strings, as the fundamental objects, superstring theory certainly overcomes the problem of perturbative nonrenormalizability. The field theorist would point to the breakdown of renormalizability-the fact that short-distance singularities become so severe that the usual methods for dealing with them no longer work. There are various problems that arise when one attempts to combine general relativity and quantum field theory. (When there seemed to be five such theories, we found that disturbing.) This gives a philosophically satisfying picture: there is a unique theory that can give rise to a number of consistent quantum solutions and that contains gravitation. Even though a fully satisfactory formulation of the underlying theory remains to be completed, it is already clear that this theory is unique-it contains no arbitrary adjustable parameters. Moreover, another special limit corresponds to a sixth consistent quantum vacuum, this one having Lorentz invariance in eleven dimensions (ten space and one time). † It is now clear that they are better viewed as five special points in the manifold (or “moduli space”) of consistent solutions (or “quantum vacua”) of a single underlying theory. It also appeared that they are the only mathematically consistent quantum theories containing gravitation. Until a few years ago, it appeared that there are five distinct consistent superstring theories, each one requiring ten dimensions (nine space and one time) but differing in other respects. String theories that have a symmetry relating bosons and fermions, called “supersymmetry,” are called “superstring” theories.
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