# Tag Info

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I will bring an example from classical electrodynamics. In EM(electromagnetism) you have to consider that the fields(electrical and magnetic) also have energy and momentum. A classical example is to apply the third law of Newton(each action has an equal counter-action) to two moving charges. Then you'll conclude that the third law does not hold-thus the ...

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If you consider things classically (for the moment forgetting about virtual particles as mediators of the force) things get more clear. For instantaneous forces (which do not exist in nature), momentum conservation comes from the fact, that the forces in nature fulfil Newtons axiom actio = reactio, meaning, that for two particles, that interact we have the ...

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To add to the previous answers. Particles such as the Higgs field and the quarks are, in the modern theory, understood as excitations/waves/perturbations of the underlying quantum fields. The fields permeate the whole of space and time and the way they interact with each other determines the physics of the universe. Arguably, the fields are more ...

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If the electron is supposed to have a finite size, then it has has to be a rigid body. If not, then it wouldn't be an elementary particle, it would have some inner structure that you can further investigate. So, if the electron is indeed an elementary particle and it has a finite size, then it must be a rigid body. But a rigid body can be used to create ...

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At school, and when studying classical physics, one assumes that particles have no size. This is done because it massively simplifies equations, and it is a good approximation if the size of the particle is believed to be significantly small than the other important length scales involved. Actually, there are unwanted consequences when one assumes that a ...

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What is the smallest actually observable structure in the universe? The smallest structure that I have seen is the electron cloud around an atom.

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Your question comes with an extra difficulty: the meaning of distances and sizes at the quantum level. From the current understanding of particle physics, all particles are point-like and hence volumeless. Of course this is an interpretation of the theory and this statement would require the experiments to probe arbitrarily small distances, which does not ...

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It depends on what you mean by observable. The smallest confirmed particle is the electron neutrino. Observation/measurement is another discussion in itself.

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The matter doesn't disappear - it still exists, but we can't access it without entering the black hole ourselves, and then we'd be trapped. Due to Hawking radiation, over time (assuming the black hole is small enough) all of the energy that went into the black hole will be released again as the black hole evaporates. The bigger conservation issue at stake ...

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See explanations on Quarks and Gell-Mann's Quark Model.

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It is because they only lose there energy when accelerating. A moving electron or proton with a constant velocity won't emit EM radiation. The electronmagnetic radiation only takes away the aceleration, slowly the proton or electron down to a constant velocity. The reason they have charges is much more complicated. For the proton example it is because ...

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It depends on the probability of interaction. This probability is computed using Fermi's golden rule, and it involves the strength of the interaction and the number of allowed final states. Weaker interactions means higher probabilities of going through the atom. Some examples: Neutrinos only feel the weak interaction, so their probability of going ...

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Any sufficiently fast particle can go through the atom since the repulsing force is finite and you can prepare a projectile with a high enough energy.

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Most sub-atomic particles can. In the Rutherford gold foil experiment, alpha particles (helium nuclei) often went through atoms. Beta particles (high speed electrons) can go through paper. There are more than a billion neutrinos going through you every single day.

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A proton is described as a combination of three valence quarks, each with a bayrion number of 1/3 and a charge that adds up to the +1 of the proton, two up and one down. That is a primary constraint from data. Now in QCD, the theory we have developed to describe the strong interactions of quarks, it comes about that overall, in the constraining "bag" ...

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When I first started to study quantum mechanics, my physics text book told that particles have spin of either 1/2 or -1/2. That's wrong. Particles can have any integer or half-integer spin. (There are some deeply technical reasons that fundamental particles are expected to have spin ranging from -2 to 2, but if you include composite particles, any ...

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I know of no collective noun that includes only the electron, proton and neutron and excludes all other particles. Possibly you could use stable subatomic particles, but the neutron is only stable when it's in a nucleus so that doesn't really work (and I suppose it should include photons and neutrinos). As ACuriousMind suggests in a comment, nucleons and ...

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We can describe them as quark combinations. A neutron is a u-d-d and a proton is a u-u-d. Also, by charge, we have +1, -1, 0.

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An early bit of evidence for the neutron as an uncharged constituent of the nucleus, with approximately the mass of the proton, actually comes from the exclusion principle, and the low-temperature heat capacities and excitation spectra of atomic gases. The argument is a little bit subtle, so you'll have to bear with me. First, we have the exclusion ...

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Susskind says (in his Stanford lectures on string theory) that subatomic particles are not point particles, they have a spatial extent. This does not depend upon his contention that they are really extended string objects. It's just a consequence of the fact that even the electron is "fuzzy" due to being embedded in a little cloud of virtual photons and ...

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The neutron is in no way "composed" of a proton and an electron. It can decay to a proton, electron, and an antineutrino. But that doesn't mean that these three particles literally co-exist inside the neutron at the beginning. Instead, the decay involves some real transmutation of elementary particles. The only thing that one can say because of the decay is ...

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