They don't have measure zero. Their contributions cancel out, because the lagrangian involves derivatives, and the action diverges. Its easiest to show that in the case of a Euclidean path integral, where the integrand is e^{-\infty}=0 for a non differentiable path.
The probability of traveling from one point to the other is the sum over all paths between them of the probability of traveling along that path; The path integral is basically just that sum over paths.
It also implies that electric charge is quantized(this is basically the particle in a ring problem in quantum mechanics).
Extra temporal dimensions(whether or not they are large) would imply the existence of tachyons; so far experiments have not detected tachyons.
The exchange of virtual photons is what QED is all about. Schrodingers equation can tell you how a charged particle acts in an external electromagnetic field, but does not tell you anything about the electromagnetic field produced by the particle. Classically the function satisfying a wave...
If a quark were to emit a spin-1/2 fermion, by conservation of spin it would change into someother type of particle(a boson with either spin 0 or spin 1). The color charge would also have to go somewhere. If the spin-1/2 particle has color charge, it is probably just a quark. The most well...
According to general relativity it is. That is especially clear in the tetrad formalism, in which there are vectors fields(collectively referred to as the tetrad), e^a_\mu with the property that \eta_{ab}e^a_\mu e^b_\nu = g_{\mu \nu}, where η is the minkowski metric, and g is the metric...
Because light is massless it must go at the speed of light(yes, this term sucks for this purpose)
If you look at the formulas for lorentz transformations you might notice they look almost like rotations. You can introduce 4-vectors(the name comes from the fact that they have 4...