This is one of the sentences in my physics book: "Coulomb discovered his law without knowing the explicit magnitude of the charge. In fact, it is the other way round: Coulomb’s law can now be employed to furnish a definition for a unit of charge. In the relation, $F = \dfrac{k}{r^2} \big|q_{\ 1}...

I don't quite understand why 2-loop pure graviton scattering is divergent. It looks UV finite to me when I naively compute the superficial divergence $$D=dL-2I\tag{1}$$ for $d=4, L=2, I=5$. Consider the 1PI diagram built from 3-vertices below, we have $D=-2$ and the integral would look something...

I saw a question like this in an AS-level physics paper (consisting of 40 questions given to ~17-year-olds, with a 75-minute time limit): Two identical balls, x and y, are thrown up from the earth's surface with the same velocity. x is thrown in the air and y is in a vacuum. Which ball reaches a...

The reason mankind does not now have a sub-picometre microscope is generally attributed to the inability to create a perfect optical system. The question is, is this true? Consider a perfect optical system with 1fm / 1am resolution, based on γ-ray. We should expect to observe debris resulting fro...

Usually, we say that the Lorentz force is a vector. However, in group theory, we make a distinction between vectors and pseudovectors based on how they transform under $O(3)$. Vectors and pseudovectors transform similarly under rotations but not under reflections. For example, the magnetic field ...

I feel silly asking because deep down, it just seems that a simple hydraulic pump (such as two syringes connected via a fluid-filled tube) has to be considered a simple machine... with two different-sized syringes, you can multiply force to gain mechanical advantage, or you can sacrifice a greate...