I dislike this description of things existing in two places at once, this is because I believe that objects exist in one place, then they move to the next place.
The interference pattern only highlights the probability of where the particle will be when it's next observed, or "where it moved to". The object does not interfere with itself, it's the probability wave that is interfering with itself, and the wave is something separate from the object but is related to it.
The particle does not exist anywhere between its current position and the next. It does not travel in a "linear" or other way, if at time t it was at position 0 and at time tNext it was at position 1, at time tNext*0.5 you cannot assume it was at position 0.5, or both "position 0.5, slightly higher up" and "position 0.5, slightly lower down" at the same time.
In another way, in my mind, the object exists here, then it exists there, but it did not exist at the time between here and there, unless you happened to have observed it. Then of course "there" would be where you have made the observation because you have given it something to interact with.
I guess my issue is, at what moment does the article say that it exists in two places at once? Are they inferring this from the fact that there is an interference pattern?
To quote: "[1] Every particle or group of particles in the universe is also a wave—even large particles, even bacteria, even human beings, even planets and stars. [2] And waves occupy multiple places in space at once. [3] So any chunk of matter can also occupy two places at once."
I guess my problem is with [1] "is also a wave". I think that "there is a wave related to the object" but not "the object IS a wave". Then [3] does not follow.