Monday, May 10, 2010

Doubts About a Final Theory

Physicist Marcelo Gleiser at New Scientist:

Modern incarnations of unified field theories come in two flavours. The more traditional version, the so-called Grand Unified Theory (GUT), seeks to describe electromagnetism and the weak and strong nuclear forces as a single force. The first of these theories was proposed in 1974 by Howard Georgi, of Harvard University, and Sheldon Glashow, now at Boston University. The more ambitious version seeks to include gravity in the unification framework. Superstring theory tries to do this by abandoning the age-old paradigm that matter is made of small, indivisible blocks, substituting them with vibrating strings that live in higher-dimensional spaces.

Like all good physical theories, GUTs make predictions. One is that the proton, the particle that inhabits all atomic nuclei, is unstable. For decades, experiments of increasing sensitivity have looked for decaying protons and failed to find them. As a consequence, the models have been tweaked so that protons decay so rarely as to be outside the current reach of detection. Another prediction fared no better: bundled-up interacting fields called magnetic monopoles have never been found.

For superstrings, the situation is even worse. In spite of its mathematical elegance, the theory is so detached from physical reality that it is exceedingly difficult to determine what a measurable string effect might be.

I now think that the very notion of a final theory is faulty. Even if we succeed in unifying the forces we know, we can only claim to have achieved partial unification. Our instruments have limits. Since knowledge of physical reality depends on what we can measure, we will never know all there is to know.


Thomas said...

Yeah, physicists talk about a "Theory of Everything," but they don't necessarily mean that it will answer all questions.

For example, if String Theory is "correct" in some sense, it is also ridiculously complicated compared to particle theories of the universe. It might explain how all known forces in the universe spring from one aspect of the universe, but it leaves open tons of mathematical problems that are quite intractable.

Just imagine all the shapes you can make with a string in 3 dimensional space, and consider all the ways it could vibrate, and you see how much more complicated this model is, compared to a particle model.

John said...

Yes, I enjoyed reading about how many million different possible solutions there are to some of the equations.