# Foundations of quantum physics III. Measurement

## TL;DR

This paper discusses the measurement problem in quantum physics through the thermal interpretation, proposing that measurements yield uncertain values approximating expectations, with no explicit collapse and a new understanding of quantum phenomena.

## Contribution

It introduces the thermal interpretation as a novel framework for understanding quantum measurements, emphasizing uncertain values, environmental influence, and deriving aspects of Born's rule without collapse.

## Key findings

- Measurements yield uncertain values approximating q-expectations.
- Detection events are statistically related to particle beam intensity.
- The interpretation explains features of Copenhagen and minimal statistical interpretations.

## Abstract

This paper presents the measurement problem from the point of view of the thermal interpretation of quantum physics introduced in Part II. The measurement of a Hermitian quantity $A$ is regarded as giving an uncertain value approximating the q-expectation $\langle A\rangle$ rather than (as tradition wanted to have it) as an exact revelation of an eigenvalue of $A$. Single observations of microscopic systems are (except under special circumstances) very uncertain measurements only. The thermal interpretation * treats detection events as a statistical measurement of particle beam intensity. * claims that the particle concept is only asymptotically valid, under conditions where particles are essentially free. * claims that the unmodeled environment influences the results enough to cause all randomness in quantum physics. * allows one to derive Born's rule for scattering and in the limit of ideal measurements; but in general, only part of Born's rule holds exactly: Whenever a quantity A with zero uncertainty is measured exactly, its value is an eigenvalue of A. * has no explicit collapse -- the latter emerges approximately in non-isolated subsystems. * gives a valid interpretation of systems modeled by a quantum-classical dynamics. * explains the peculiar features of the Copenhagen interpretation (lacking realism between measurements) and the minimal statistical interpretation (lacking realism for the single case) where these interpretations apply -- in the microscopic domain. The thermal interpretation is an interpretation of quantum physics that is in principle refutable by theoretical arguments leading to a negative answer to a number of open issues collected at the end of the paper, since there is plenty of experimental evidence for each of the points mentioned there.