Can Particles be in two Places?

Hello there. I read that particles can be in two places at the same time, I would like to know if that's a well-established fact with high confidence among the scientific community, or if it's possible that's the result of some kind of 'interference' for example from the measurement equipment or some other problem with (or effect of/in) the actual measurement. I remember for instance that the orbital model for the electrons which was later discovered not to be a good representation of what actually happens, not that I'm suggesting it's a similar matter, just justifying the legitimacy of my question since errors like that occurred in the past. Thank you in advance.
- Alan Q. (age 27)
Coral Gables, FL, US

Yes, there are  many, many quantum experiments which contradict common-sense interpretations in which reality is represented by particles that exist at single places. Among those particle-at-a-place models that cannot be right is the early Bohr orbital model, still unfortunately taught at some places. The problem with the Bohr model was not some experimental glitch, but rather that it gave wrong answers to all but a few questions that might be asked experimentally about small-scale things. For discussions of experiments that show that an even broader class of models must be wrong, search this site and elsewhere for "Bell Inequality", a relation obeyed by any local realist model but violated by our world.

There may be possible ways of saying that particles have specific positions without violating experimental facts. One example would be a proposal called Many Interacting Worlds, in which in each version of reality particles have positions but there is a swarm of different versions of reality (including ones where the particles are elsewhere) with interactions between the versions. I don't think that idea has yet been definitively ruled out, but even if it succeeds it is not exactly a return to the common-sense picture.

Mike W.

(published on 09/08/2016)