In Schwarz's Introduction to QFT and the standard model they say that because there are no finite-dimensional unitary representations of the Lorentz group we must have fields and not particles. However, for a single particle quantum state the basis of the Hilbert space is still infinite and so th...

In classical physics (classical electrodynamics), electromagnetic waves don't interact. In quantum mechanics, they could. In this article on light-by-light scattering: https://arxiv.org/abs/1702.01625 , the introduction states that there is a connection between linearity of equations and possibil...

I know that we can use transducers that are glued to a surface to achieve this. If I want, for example, to have 200 watts of actual acoustic power in the audible range in the granite, is a transducer the easiest cheapest way? Are there other methods?

I was studying simultaneity of events and there was a line which quotes that "The relativity of simultaneity is a direct consequence of the invariance of the speed of light in all frames of reference". I wanted to ask that if the invariance of light's speed is false(I know it's not but if we just...

Clearly, the Earth is accelerating (as it has centripetal acceleration), and thus it is a non-inertial frame of reference. Then, why don't we use pseudo forces all the time? My teachers told me that the effect produced by the centripetal acceleration of the Earth on our calculations is negligible...