Recent content by LittleSchwinger

Conditional entropy in classical probability is always positive because the entropy of the total system is always greater than or equal to the entropy of its parts. This is no longer true in QM and it can be negative because you can have maximum knowledge of the whole system (it's in a pure...

The worked model in chapters 7 and 8 of Roland Omnes book on quantum mechanics is probably the easiest place to study decoherence in detail (do the exercises as well!)

To low orders. At higher orders the electromagentic field about the electron will contain corrections from interactions with the electron field itself, involving electron-positron bubble terms.

My view would be that "non-local" in particle physics either means literal action at a distance, i.e. dynamical coupling between spacelike separated degrees of freedom, or that the fields in the Lagrangian are not point functions of spacetime. In quantum foundations and quantum information it's...

A nice worked model is here, done in the non-relativistic limit: https://arxiv.org/abs/2212.02599 The general theory is covered in Frohlich's proceeding papers, which include references to Buchholz's previous works on the topic. I prefer this because the other papers are "advanced" mathematical...

Just to add decoherence isn't really the main factor responsible for the classical limit. Even before the investigation of decoherence in the 1970s there were detailed models of classicality being caused by ergodic effects or kinematic effects reducing the algebra of observables, such as in the...

Even if one added stochasticity atop of a chaotic evolution you would still not replicate quantum theory. Classical Probability and Quantum Probability are simply different mathematical structures.

Yes essentially. The best guide to this is the 2018 book "Fundamentals of van der Waals and Casimir Interactions" by Bo Sernelius. Part III is all about the Casimir effect and dispersion interactions.

No, in fact that's the point. Time evolution in QED is not unitary, but a contractive Markovian process. This is at the non-perturbative level. Perturbatively time evolution is unitary.

Note that this approach does not produce an actual Hamiltonian evolution. The "unitary" evolution produced does not obey: ##U(t_{3},t_{1}) = U(t_{3},t_{2})U(t_{2},t_{1})## Hence it's an approximation of the true time evolution breaking some of the true evolution's properties. This goes for many...

Wow, we get to meet celebs on this forum. I just wanted to say I loved the account of Quantum Logic in your textbook. Several points that many people miss about the relations of logics in general. The book in general is wonderful.

A very nice paper is: Buchholz, Detlev. (1986). Gauss' law and the infraparticle problem. Physics Letters B. 174. 331–334. 10.1016/0370-2693(86)91110-X. I recommend this because it is short and close to typical QFT language as opposed to mathematical physics language. Buchholz gives an...

Trying to read about Logic, which I never covered in much depth as a physicist. Currently on "First Steps in Modal Logic" by Sally Popkorn. I really recommend Schechter's "Classical and Nonclassical Logics: An Introduction to the Mathematics of Propositions"

I am understanding the OP's question to refer to the fact that QFT texts rarely discuss what form finite time evolution might take in QFT. In other words why we generally seem to avoid formulating a state ##\rho(T)## at some time ##T## in even a semi-explicit manner and solving for its...

The "shape" of a particle is often derived from scattering processes by integrating functions called form factors. Such a manipulation of scattering form factors in classical physics would allow you to figure out the shape of a particle, but in quantum theory you have different "shapes" result...