NikolajK
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 2d awarded Notable Question Jan 29 comment Proving that Planck's Law is dimensionally homogeneous Why is it called dimensionally "homogeneous" if the opposite would just be "wrong"? Jan 26 answered What does $L^2(S^1,\mu_H)$ mean? Jan 9 comment Startups for astrophysics You can surely also find information if you search "introduction to..." here in the search bar. Jan 8 awarded Popular Question Jan 5 awarded Nice Question Dec 14 revised How does time look relatively in a gravity well? deleted 9 characters in body Dec 14 revised How does time look relatively in a gravity well? added 232 characters in body Dec 14 answered How does time look relatively in a gravity well? Oct 6 comment How do Hubble Units work? Found this Wikipedia reference. Oct 1 comment Yang and Mills' (and others') justification for local gauge invariance @ACuriousMind: Maybe that's the answer for him, then. Oct 1 comment Yang and Mills' (and others') justification for local gauge invariance I'm certain OP is aware of the first point and is just asking if a global-only field theories must be ruled out for describing physics if locality principles are assumed. Sep 23 awarded Yearling Sep 16 awarded Popular Question Sep 13 comment Harmonic Oscillator propagator I'd say the second equation with the derivative is not so evident, is it? Sep 13 comment Harmonic Oscillator propagator From one perspective, you just ask how $\frac{∂}{∂t}\langle x|e^{At}|y\rangle=\langle x|Ae^{At}|y\rangle=A\langle x|e^{At}|y\rangle$ should be made sense of. Is the case without the term $\frac{p^2}{2m}$ clear? Sep 9 comment Intuition for spin 1/2 and 1 propagators $\frac{1}{p^2-m^2}$ is $(\Box+m^2)^{-1}$ in Fourier space, in that it solves $(\Box+m^2)\,\phi=j$ for $\phi$. The spin 1/2 case $\frac{\gamma\,p+m}{N}$ solves $(\gamma\,\partial-m)\,\psi=j$, and so on. Aug 25 awarded Nice Question Aug 19 comment Kinetic energy as $\pi k_B T$ @LubošMotl: The question is if it matters as long as you keep on using a temperature-unit that's formally distinct from an energy unit. Sure, you may take the reductionist approach and fix all factors using the deeper theory, but "I haven't seen what the energy (...) is converted into" and so if all quantities in the theories account for this strange $\pi$, it may end up not ruining any results. I agree that it's odd that a particle should carry an irrational energy-quantity - I'm not advocating it. But apparently people have used this quantity for some time and it worked for their use. Aug 19 comment Kinetic energy as $\pi k_B T$ @LubošMotl: You don't need to violate any exact entropy expressions or the absolute temperature scale. Just consider $k_B^*\equiv \pi\,k_B$ the auxiliary constant. Some like $k_B=1$ and electron volts, and some might find $\approx 10^{-23}J/K$ and kelvins or "pi-kelvins" useful. That's why I said I don't know what would be the merit of adopting another $3.14$ to get energy out of temperature. I showed OP where $\sqrt{\pi}$ pops up. In expectation values, it will pop out anyway, because the density $\rho\propto{\mathrm e}^{-H\,/\,k_BT}$ gets normalized.