Unified field theory

"There was a period when cosmology got started. There were some important works in the 30s—the Einstein-Infeld-Hoffman ideas [equations]. ...Unified Field theories were the bane of GR in those days. Einstein... was convinced that physics should be primarily geometry... about 10 years later, maybe 15, Steven Weinberg was convinced that geometry was irrelevant... the important stuff is just field theory. ...Weinberg, later... collaborated in proving that physics really is geometry. Except not the geometry of space-time... its the geometry of the graph paper on which the properties of space-time are conceptually plotted... the idea of a curved connection. If you want to plot... any physical quantity... like a , s, s, etc. you need to plot it on curved graph paper. But Einstein... didnt have that broad an idea of geometry..."

"Until the end of the thirties, the only accepted fundamental interactions were the electromagnetic and the gravitational, plus, tentatively, something like the “mesonic” or “nuclear” interaction. The physical fields considered in the framework of “unified field theory” including, after the advent of quantum (wave-) mechanics, the satisfying either Schrödinger’s or Dirac’s equation, were all assumed to be classical fields. The quantum mechanical wave function was taken to represent the field of the electron, i.e., a matter field. In spite of this, the construction of quantum field theory had begun already around 1927. ...Nowadays, it seems mandatory to approach unification in the framework of quantum field theory."

"Seventy-five years ago this month, The New York Times reported that Albert Einstein had completed his unified field theory — a theory that promised to stitch all of natures forces into a single, tightly woven mathematical tapestry. But as had happened before and would happen again, closer scrutiny revealed flaws that sent Einstein back to the drawing board. Nevertheless, Einsteins belief that hed one day complete the unified theory rarely faltered. Even on his deathbed he scribbled equations in the desperate but fading hope that the theory would finally materialize. It didnt."

"When Einstein, Weyl, and others began their work on unified field theory, it was natural to assume that this task consisted exclusively of the union of gravitation with electromagnetism. To be sure, the separateness of these two fields posed no conflicts or paradoxes. There were no puzzles such as the nor curious coincidences like the . Nevertheless, it seemed physically well-motivated and appealing to ask, Do natures only two fields of force, both long-range in character, have a common origin?"

"Einstein’s dissent from quantum mechanics and immersion in the search for a unified field theory were not failures but anticipations. After all, even if many string theorists would disagree with Einstein about the incompleteness of quantum mechanics, much of what goes on in string theory these days looks a lot like what Einstein was doing in his Princeton years, which was trying to find new mathematics that might extend general relativity to a unification of all the forces and particles in nature."

"With Mies view of matter there is contrasted another, according to which matter is a limiting singularity of the field, but charges and masses are force-fluxes in the field. This entails a new and more cautious attitude towards the whole problem of matter."