No known process can make it happen world wide. It is possible that pockets of the process might happen.
There have been suggestions of an external neutron source. To produce fission you will need low energy neutrons, not high energy. U235 wants neutrons in the thermal range to produce significant fission.
The problem with external neutron sources is shielding. Uranium is currently mined at least 100's of meters deep in some locations. So any external neutron source that could produce significant fission would not be able to do it uniformly. 100 meters of rock is going to be a quite good neutron shield, preventing the deeply buried stuff from being affected.
Also note that, unless you have a situation with the Uranium quite closely and densely packed, you need (nearly) one neutron per Uranium fission. Without that close packing, the neutrons produced by fission are nearly all wasted.
Changing physical constants is currently at the "speculative" end of science. We don't know if it is possible, though several unification theories indicate it should be.
The problem with changing physics constants is that it might affect the thresholds for critical mass and such. But to get it to remove U235 from existing ore bodies is pretty much impossible. Ore comes in a wide variety of concentrations. And anything over 1% is probably a useful commercial product. To get 1% ore to start to fission would require such grotesque changes that it is quite likely many other things would start to fission as well. Thorium for example, which is far more plentiful than Uranium. The result would be a bright flash, and no more Earth.