There’s a new book out this week by Marcelo Gleiser, entitled A Tear at the Edge of Creation. Gleiser blogs at the NPR site 13.7, and that site also has a review of the book from his fellow blogger Adam Frank.
Gleiser started out his professional life as a string theorist, enchanted by the prospect of finding a unified theory, and for many years that motivated his research:
Fifteen years ago, I would never have guessed that one day I would be writing this book. A true believer in unification, I spent my Ph.D. years, and many more, searching for a theory of Nature that reflected the belief that all is one.
Over the years he began to become disillusioned with this quest, not only with string theory, but also with other closely associated ideas (e.g. GUTs and supersymmetry) about how unification is suppose to happen. Hopes that GUTs would give predictive theories of inflation or proton decay have fallen by the way-side, and about supersymmetry he is “very skeptical”:
The fact that the [lightest, stable superpartner] particle has so far eluded detection doesn’t bode well. To make things worse, results from the giant Super-Kamiokande detector in Japan and the Soudan 2 detector in the United States have ruled out supersymmetric GUT models, at least the simpler ones, based again on the proton lifetime. If SUSY is a symmetry of Nature, it is very well hidden.
About string theory itself, Gleiser refers to my book and Lee Smolin’s, and comments that:
Responses from notable string theorists were of course highly critical of the books and their writers. Some were even offensive. I find this sort of dueling pointless. People should be free to research whatever they want, although they should also reflect responsibly on whether their goals are realistic.
Ultimately, Gleiser came to the point of view that all hopes for a unified theory are a misguided fantasy, and explaining this point of view is the main goal of the book. In an interview on his publisher’s web-site, he says:
After years searching for a “final” answer, as a scientist and as a person, I realized that none exists. The force of this revelation was so intense and life transforming that I felt compelled to share it with others. It completely changed the way I think about Nature and our place in it.
In his book, he argues repeatedly against the fundamental nature of symmetries in our understanding of physics, seeing the failures of GUTs and supersymmetry as a failure of the idea of getting unification out of larger, more powerful symmetry laws. For him, symmetries are always just approximations, never exactly true principles. He claims to be more interested in asymmetries, in failures of symmetry laws, seeing in asymmetry a fundamental explanatory principle about the universe and humanity’s role in it.
Personally, I find myself in strong disagreement with him about this, and don’t see much evidence in the book that the abandonment of the search for symmetries that he advocates leads to any positive route to greater understanding of the universe. I agree with him about the failure of the most popular ideas about how to use symmetry to get beyond the Standard Model, but disagree with him about the implications of this.
The problem with both GUTs and supersymmetry is that one posits a new symmetry only to be faced immediately with the question of how to break it, with no good answer. To be successful, any new symmetry principle needs to come with a compelling explanation of how it is to be realized in fundamental physics. A repeated lesson of the development of the Standard Model was that major advances came not only from coming up with new symmetry groups, but through coming up with unexpected ways of realizing them (e.g. spontaneous symmetry breaking and confinement in gauge theory). I don’t believe that the gauge symmetries of the Standard Model are approximations, but rather that they are among our most powerful and fundamental physical principles, and that much work remains to be done to understand their full implications. The failures that have discouraged Gleiser have also discouraged many others, and a resulting abandonment of symmetry-based attempts to find a better, more unified, fundamental theory would be a shame.