Recent content by A. Neumaier

yes, and a very poor one in most cases, except when a system is nearly in the ground state (as for molecules in much of quantum chemistry), or when the system is stripped of its spatial degrees of freedom and only has a small number of energy levels. Hence it usually describes nothing at all...

In the present paper I don't use the term q-expectation. All terminology used in the paper is explained there. The Born rule is derived in Section 5.2 from a physically simpler and more intuitive postulate, the detector response principle (DRP). Why does the DRP not make sense to you? It is an...

In the Stern-Gerlach experiment discussed on p.15, <P_+> and <P_-> are the propensity for a single silver atom to appear on the left or right spot, respectively. One of the two cases happens, we cannot predict which one, and talking about probability for a single case is meaningless; hence...

Your question is ill-posed. Since this hydrogen atom interacts with other atoms, it is in a mixed state, obtained from the state of this atom + other atoms by forming the reduced density matrix. Thus ''this hydrogen atom which is in a superposition (in energy or spin for example)'' is...

No. I am using the standard unitary formalism of QM applied to QFT for the whole universe. Then I draw consequences for it's physical subsystems. Since the subsystems are not completely isolated, their dynamics is no longer completely unitary. This leads to decoherence and other well-known effects.

For a physical system in a pure state ##\psi##, the matrix elements ##\langle X \rangle=\psi^*X\psi## may be regarded as providing its properties. For example, if ##X## is an orthogonal projector then ##\langle X \rangle## is a propensity, and can be approximately measured as relative frequency...

This link now contains a significantly expanded version, ready for publication. New additions are (in addition to other small improvements throughout the paper) more details of the connections to cosmology, the similarities and differences to other interpretations of quantum mechanics, a...

??? How can the observer's brain solve the Schrödinger equation in real time?

It would mean that the Schrödinger equation (or whatever differential equation the state is assumed to satisfy) breaks down somewhere.

More interesting (and applicable to QFT) is the book A. Hobson, Fields and Their Quanta, 2024. It also gives a realist account, but in 4 dimensions!

See, e.g., the discussion in the last two sections of D. Wallace, The quantum theory of fields, and his Reading List in Philosophy of Quantum Field Theory. See also my own paper here.

I tried to define everything that is not in typical textbooks. For a single field ##\phi##, the N-point function is simply the map (and in fact for ##N>1## the distribution) defined by all quantum values $$W(x_1\ldots,x_N):=\langle\phi(x_1)\cdots\phi(x_N)\rangle.$$

A (classical or quantum) particle is a quantum field concentrated at each time in a small region of space. I tried to avoid the use of ''particle'' in any other way; if you see other uses, please let me know. Yes. Without interaction no measurement. And an interaction works in both directions...

It is finished for submission, and I put it online to get some early feedback before actually submitting it (in a few weeks). So the submitted version will perhaps be a little different.

Based on the thermal interpretation, I developed a quantum version of the classical, mechanical universe suggested by Laplace over 200 years ago. Abstract. The purpose of this paper is to propose a quantum version of the classical, mechanical universe suggested by Laplace over 200 years ago...