String theory gives physicists reason to believe that particles are 1-dimensional strings because the theory has a purpose – unifying gravity with the gauge theories.
So why is it that it's popular belief that particles are 0-dimensional points? Was there ever a proposed theory of them being like this? And why?
What reason do physicists have to believe that particles are 0-dimensional points as opposed to 1-dimensional strings?
Best Answer
In the standard model (as in all traditional relativistic quantum field theory), particles are pointlike. All experimentally available facts about microphysics seem to be consistent with the standard model. This is the (fully sufficient) reason for believing that particles in Nature are pointlike.
Pointlike is a technical term that refers to the fact that in the standard model, the Lagrangian is a function of fields at the same point (rather than of integrals over fields in some small neighborhood of this point, described by form factors specifying the ''form'' of the particle).
The main reason why, nevertheless, many physicists speculate that (at much higher resolution) particles might not be pointlike is that there is no known way how to harmonize quantum field theory with gravitational forces, whereas string theory (where particles are stringlike) seems to offer a potential way of doing so. Nobody knows to which extent these speculations will turn out to be correct.