Recent content by WernerQH

"Transition probability" is a somewhat misleading term, because it suggests a "thing" undergoing a transition. (Is time special?) We should treat space and time together, and generalize the idea of atomism ("There are only atoms and the void") from space to spacetime. Quantum theory lets us...

What does it mean to exist? Does the letter A exist on your computer screen, even though it's just a pattern of pixels, possibly refreshed 70 times per second? The term quantum "object" is based on a misconception: the idea that the continuity that we ascribe to classical objects must pertain...

Exactly. Since charge is conserved, most physicists would say that an electron must have continuous existence. But this need not be the case on a timescale of ## \hbar / mc^2 \sim 10^{-21} \rm s ##. I think this is the origin of the famous "Zitterbewegung". Why do the Feynman rules demand...

Do you think that the "basic principles" of quantum theory have reached their final form? I don't. Ballentine's two postulates depend on two notions that I find problematic: "state" and "observable". Ballentine emphasizes that they are not mathematical, but physical concepts and firmly...

What are the "basic principles" of Quantum Mechanics? In mathematics proofs start from axioms, which were once thought to be self-evident and didn't need further proof. But Euclid's fifth axiom turned out not to be "self-evident". Most physical theories have not been axiomatized, because of...

I just copied the wikipedia reference, and it seems to point to a nature paper with that title. Unfortunately it's behind a paywall. Have your read the wikipedia page?

Have a look at https://en.wikipedia.org/wiki/Hanbury_Brown_and_Twiss_effect The effect seemed puzzling at the time, because of Dirac's remark that "a photon only interferes with itself" in his textbook. But E.Purcell showed that the HBT effect can also be understood classically: E. Purcell...

Gentzen, thanks for investigating. :-) My copy of that arxiv paper is dated February 15, 2024. So I probably became aware of it also through Peter Woit's blog. But bhobba has been referring to it frequently.

A while ago @bhobba pointed to an interesting paper by T Padmanabhan: "Obtaining the Non-relativistic Quantum Mechanics from Quantum Field Theory: Issues, Folklores and Facts" (https://arxiv.org/abs/1712.06605).

I think the first alternative is better, but it depends on how you define ΔE and Δt. For ## \Delta t ## it is customary to use the lifetime of the decaying particle, and for ## \Delta E ## the full-width-half-maximum (FWHM) of the line in the energy spectrum. The line shape is typically fitted...

A vector ## \ket{\Psi} ## in Hilbert space, multiplied by any complex number(*), represents exactly the same state. That's why it is possible to call ## e^{iEt} \ket{\Psi} ## "stationary" even though the phase factor may vary rapidly. Then all expectation values are time-independent. But this...

Wavefunctions are usually written down in a coordinate system where the z-axis is singled out, i.e. the azimuthal quantum number ## m ## refers to the component of angular momentum in the z-direction. For p-orbitals having ## l=1 ## we have one wavefunction (## m=0 ##) proportional to ##\cos...

There is a difference between the Maxwell-Boltzmann distribution (applying to particles with mass) and the more general Boltzmann factor ## e^{-E/kT} ##. The mean energy of a single mode of the radiation field with frequency ## \nu ## can be written as a series of Boltzmann factors: $$ { h\nu...

What is considered real is important (physics is about the real world around us!), but it is subject to change. Every physicist considers the electric field real, but it once was a completely abstract concept describing stress in a hypothetical material medium (the ether). Everybody seems to...

I don't think this is a meaningful distinction. Of course we are talking about physical reality -- unless you give up on the idea that physics is concerned with the real world around us. As science evolves, what is considered real can change (caloric, ether, "lines of force", phlogiston, ...)...