1:29 AM
4

I am working on solving problem 5.24 from the $3^{\mathrm{rd}}$ edition of Goldstein's Classical Mechanics: A wheel rolls down a flat inclined surface that makes an angle $\alpha$ with the horizontal. The wheel is constrained so that its plane is always perpendicular to the inclined plane, but i...

3

From high school physics we are taught that photons are both waves and particles, and that they do not need a medium to travel through, being transverse waves. In QFT, we learn that particles are simply excitations of their respective fields. In this sense, is it correct to say that the medium in...

5 hours later…
6:13 AM
3

In Breuer and Petruccione's Theory of Open Quantum Systems Eq. 3.359, they arrive at the master equation for the evolution of a system's density matrix, after interaction with a pointer via a typical measurement interaction Hamiltonian $H = \theta \hat{A} \hat{Q}$ where $\hat{A}$ acts on the syst...

6 hours later…
12:04 PM
2

I have a question that feels obvious, but I have been having trouble proving it. In words, the question is: If a unitary is close to the identity, will it leave any state it acts on unchanged? This, to me, would necessarily be the intuitive definition of a unitary "being close to the identity", s...

4 hours later…
3:49 PM
3

I understand the diproton form of helium, helium-2 has a half-life of about a nanosecond. It seems safe to assume it's mass cannot be measured experimentally, yet I understand there is a way to calculate what it's mass should be. Is this true?