- It is not possible to prove the point of origin of a photon
- It is not possible to prove the point of origin of a free electron
- It is not possible to prove that protons or neutrons exist inside a nucleus
Can anyone confirm?
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Actually in natural sciences, you can't prove anything. If you state a law of physics, i.e. "things fall down to the ground, when you throw them", you are never completely sure, that it will be true for all possible things in the world at all possible future times. You simply can't be everywhere every time, to check and verify, that it is ultimately true.
So we just made up some laws, that predict some things will happen, and it just worked every time we checked. We can't be better than that. If something doesn't work, we make further experiments, go back to pen and paper and make a corrections to these laws.
In particle physics it gets further complicated, because you have to use terms that are completely made up and disconnected from the macroscopic environment in which you live and that you understand. No one has ever seen neutron or proton, and probably no one will ever do. We just did some experiments, made some equations, that predict what will happen in different settings, and it just worked every time we checked. We use these equations in science, industry and all that. Sometimes we call some parts of these equations with silly names like "proton" or "neutron" or "curved spacetime", just to get better grip of it, imagine some things and get more comfortable with all the math involved.
But we can't prove anything. We just made up some useful equations that work.