Tuesday, April 24, 2018
Remembering Joe Polchinski the modest physicist who conceived a multiverse - PHYSICS
Creativity and modesty are two of the qualities that made Joe Polchinski an extraordinary theoretical physicist. The early pioneer of string theory died this month at age 63.
Polchinski was an early pioneer of string theory, the mathematical apparatus picturing the basic particles of matter and force as supertiny wriggling strands of energy known as superstrings. His contributions to the field were immense. As a young professor at the University of Texas at Austin in the 1980s, he developed a branch of superstring theory involving objects called supermembranes.
Superstrings are one-dimensional objects (like lines, hence “strings”) vibrating like rubber bands in multidimensional space. (String math presupposed more dimensions than the usual three.) Polchinski explored the possibility that those multiple dimensions could contain two-dimensional membranes, kind of like the film forming the surface of a soap bubble. He and his students derived the math describing such supermembranes living in 11 dimensions (10 of space, one of time).
Maybe, string/brane/M theory would explain the amount of that mysterious “dark” energy in space and all would be well. But no. Working with physicist Raphael Bousso, Polchinski found that string theory did not specify how much energy the vacuum of space contained. Instead the theory predicted a virtually countless number of vacuum states, with nearly any amount of repulsive energy you could imagine. In other words, string theory described a multiverse.
Polchinski’s modesty manifested itself in his reaction to this situation. He hated the idea of a multiverse, because it implied that some questions had no answers that physicists could calculate. No equation could specify the amount of dark energy; it would just be luck — determined by which universe had the right amount of dark energy to make it hospitable to life (an idea known as the anthropic principle).
Source: Corina Marinescu