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This is sometimes called the "Cheerios effect". It basically occurs because each floating object forms a meniscus, and other floating objects want to "move downhill" in this meniscus. The meniscus forms (roughly speaking) because the interfaces between the spheres, the water, and the air form a preferred angle, known as the wetting angle. If one could ...

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No, quantum/particle theory came later. What Einstein realized was that, travelling at the same speed as a light wave, the forward component of the fields "freeze", leaving only the lateral components able to vary. So the interplay between electric and magnetic fields which characterize electromagnetic radiation would be grossly affected. All of this takes ...

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These are two really great answers, so I don't feel the need to add much; only to supply that the rho can be thought of as an "excited" pion, like the Delta can be thought of as an "excited" nucleon. As the asker and @gcsantucci point out, the rho has a unit more spin than the pion. This means you could think of it as a light quark-antiquark system which has ...

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This is to be read in conjunction with the answer by Lubos The particle data group has compiled a lot of crossections in this paper, whence I have copied a particular plot, fig 49.5. Squareroot(s) in GeV The blue part are the resonances that were found during the sixties , and are typical of other resonances in scattering ...

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A resonance (in the particle physics or related physics sense) and an unstable particle is exactly the same thing. The object has some complex mass and the imaginary part determines the decay width (and decay rate). But these two terms describe different aspects of the same thing. "A particle" refers to the object, the particle species (in your URL's case, ...

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In the statistical mechanics of the grand canonical ensemble, one needs to allow for superpositions and mixtures of of states with different particle number. Thus one is naturally led to considering the tensor product of the $N$-particle spaces with arbitrary $N$. It turns out (and is very relevant for nonequilibrium statistical mechanics) that one can ...

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$\renewcommand{ket}[1]{|#1\rangle}$ Item #4 in your list is best thought of as the definition of the word "particle". Consider a classical vibrating string. Suppose it has a set of normal modes denoted $\{A, B, C, \ldots\}$. To specify the state of the string, you write it as a Fourier series f(x) = \sum_{\text{mode } n=\in \{A,B,C,\ldots \}} c_n ...

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