Recent content by wacki

Yes, this is indeed my problem. You’ve described it through an intermediate virtual state, which makes sense to me. I also like your argument for ruling out the process: Energy conservation is not enough and of course you need to respect conservation of angular momentum as well. I have to admit...

Guys, thanks for your replies. The Raman scattering goes a little bit in the direction I suggested, but as far as I understand it, it only works for scattering on the surface of solids and not for gases and it also uses an energy level as intermediate state. But most importantly: The Raman...

Thanks PeroK for your reply. QED is quite heavy machinery. I was looking for a simpler argument (maybe not as water tight as QED). There might be a certain breadth of the absorption line due to doppler shift, but let’s keep it simple and let’s assume the real absorption spectrum is discrete (or...

If an atom absorbs a photon it can only do it if the incoming photon has precisely the energy of the required electron excitation (difference between 2 energy levels of the atom). The very basic question: Why can't an electron (bound in an atom) absorb the incoming photon with an energy...

Apart from the giant nucleus. Why is it not possible to have a 2 neutron bound state. (I'm not sure if that should be asked in a separate thread, but it is so closely related). For the 2 neutron bound state there is no electric repulsion and if they have opposite spin they could both sit in the...

Ahh yes, thanks Orodruin. I clearly lack experience and intuition with non-Levi-Civita connections.

I’ve read about the exponential map that for Lie groups the exponential map is actually the exponential function. But the exponential map is based on the geodesic ODE, so you need Christoffel symbols and thus the metric. But usually nobody gives you a metric with a Lie group. So how can I get...

Thank you! I've just skimmed it, but it's exactly what I was looking for. Happy new year!

I’m searching for an introduction to relativistic Boltzmann equation. (Sorry, I know this is a question about learning material) I’ve read an excellent script from David Tong about non-relativistic kinetic theory (from Liouville to Navier-Stokes using Boltzmann equation (see link below)...

Yes, that's it, thanks!

Hi, I think there was a forum called "Learning Material" or similar, which seem to have gone. That forum was not just about books, but much broader. I can't say when it disappeared. Why was it closed? I can't find anything equivalent to it here.

I’ve just read Schutz: “Gravitation from ground up”. He says that there are 4 (not all independent) sources of gravity: 1. density of active gravitational mass = (rho + 3 P) 2. active curvature mass (generating spatial curvature) = (rho - P/c^2) 3. ordinary momentum...

The best visualisation of curved space-time I came across are the three papers in https://www.physicsforums.com/showthread.php?t=381683 see post #7 (from A.T.) they are mathematically sound (at least for me) and it gave me a bit of intuition. I think one can't hope for more than...

Hi the_pulp, I was always wandering why a real valued wave function can't be used in QM. The title "Origin of Complex Quantum Amplitudes and Feynman's Rules" sounds very interesting. Unfortunately it costs $25 to download :-( Could you give a "light weight" version of it in this forum?

Thanks Julian, for all your replies! Let me know when your book is ready. There is another thread in this forum related to the hole argument and diffeomorphisms called "Active diffeomorphism". However I found your explanation a bit clearer. And below is a short doc about the hole...