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You make a good point. The problem is interacting with the particles, e.g. the photons bouncing off them. Don't poke the particle -- it only interferes with itself. Poke the particle -- now it is entangled with your measurement device, that means zillions of other particles, which changes the interference patterns. But it is more complicated that this. Consider https://en.wikipedia.org/wiki/Elitzur%E2%80%93Vaidman_bomb_t... -- if you only poke the particle in a "parallel universe", that also changes its pattern in this one. At the end, quantum physics says there are multiple "versions" of how the particles move, and those versions interfere with each other. By interacting with each other, particles become entangled, which means that the "versions" of their states are no longer calculated independently, but together. There are disagreements of what exactly this means: some people believe that reality only has multiple "versions" on a microscopic level, but when the entangled configuration becomes large enough (how large? no one knows), the parallel computation collapses, one of these "versions" is randomly selected to become the actual reality and the remaining ones disappear. Other people believe that multiple "versions" is the whole story; that observing the outcome means that you (being composed of particles that follow the laws of physics) also become entangled with the particles in the experiment, and now there are multiple "versions" of you, each observing a different outcome. So, I'd say you got it half-right. Yes, it is about "observation = interaction"; and "observer" is just a shortcut for "the thing that poked the experimental particle, optionally also a display connected to that thing, optionally also a person observing the display". (That is, you could also have a completely impersonal "observer", e.g. a machine that measures the particle but no one is looking at its display.) But quantum physics is a different thing than mere classical physics where you correct for photons being actual things that hit the measured particle. It means there actually are multiple outcomes, which then interfere with each other, at least on the microscopic level. |