Ship of Theseus:
Quantum Physics: What is real?
So let us take stock. We think of particles as tiny billiard balls, but the things that modern physicists call “particles” are nothing like that. According to Quantum field theory, objects cannot be localized in any finite region or space, no matter how large or fuzzy it is. Moreover, the number of putative particles depend on the motion of the observer. All these results together sound the death knell for the idea that nature is composed of anything akin to ball-like particles.