While studying black body radiation, I saw that most of the textbooks and videos I watched mentioned that there was a contradiction between the classical model of black body radiation and experimental data, which created the ultraviolet catastrophe. They all said that the classical model predict...

Why is Mercury considered a planet at 15329km in circumference when Callisto is not at 15144km? Pluto is 7232 km in circumference... If it was once a planet, why not Callisto?

We can practically consider that the microscopic interactions are symmetric with respect to time(as we can neglect weak force for many cases which is the only interaction that can violate T symmetry). So I thought that the asymmetry might be due to the irreversibility of quantum measurements. But...

I had some confusion about the idea of cutting the path integral to define states in quantum field theory. There are two versions which I have seen: We do the path integral with an unspecified 'final' b.c. This would define a state at the cut. We do the path integral with both b.c specified an...