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arXiv:2110.06392

The Origin of the Born Rule from Spacetime Averaging

Nikodem J. Popławski, Michael Del Grosso

Published Oct 12, 2021• 0 citations
arXivHTMLPDF

Abstract

The Born rule postulates that the probability of measurement in quantum mechanics is related to the squared modulus of the wave function $ψ$. We rearrange the equation for energy eigenfunctions to define the energy as the real part of $\hat{E}ψ/ψ$. For an eigenstate, this definition gives a constant energy eigenvalue. For a general wave function, the energy fluctuates in space and time. We consider a particle in a one-dimensional square well potential in a superposition of two states and average the energy over space and time. We show that, for most cases, such an energy expectation value differs by only a few percent from that calculated using the Born rule. This difference is consistent with experimental tests of the expectation value and suggests that the Born rule may be an approximation of spacetime averaging.

DOI
10.48550/arxiv.2110.06392

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The Born rule postulates that the probability of measurement in quantum mechanics is related to the squared modulus of the wave function ψψψ. We rearrange the equation for energy eigenfunctions to define the energy as the real part of E^ψ/ψ\hat{E}ψ/ψE^ψ/ψ. For an eigenstate, this definition gives a constant energy eigenvalue. For a general wave function, the energy fluctuates in space and time. We consider a particle in a one-dimensional square well potential in a superposition of two states and average the energy over space and time. We show that, for most cases, such an energy expectation value differs by only a few percent from that calculated using the Born rule. This difference is consistent with experimental tests of the expectation value and suggests that the Born rule may be an approximation of spacetime averaging.
In order to make the quantum mechanics a closed theory one has to derive the Born rule from the first principles, like the Schroedinger equation (SEq), rather than postulate it. The Born rule was in certain sense derived in several articles, e.g. in [1] and [2]. In this work some arguments of previous authors are simplified and made more “physical”. It is shown how to derive the Born rule using the conservation of quantum state norm (Ψ|Ψ) that is the unitary evolution property determined by the SEq. It is this property that makes the probability equal to the square of the amplitude modulus. Possible modification of the Born rule is briefly discussed in the case when the evolution of the system is described by a nonlinear Schroedinger equation. We also present arguments in the spirit of the Many-World Interpretation to explain the origin of probabilistic behavior. Simply speaking, the randomness appears as a result of representing the wave function by using a detector of discrete nature that is found only in one state at a time, out of two or more possible states.
The Born’s rule to interpret the square of wave function as the probability to get a specific value in measurement has been accepted as a postulate in foundations of quantum mechanics. Although there have been so many attempts at deriving this rule theoretically using different approaches such as frequency operator approach, many-world theory, Bayesian probability and envariance, literature shows that arguments in each of these methods are circular. In view of absence of a convincing theoretical proof, recently some researchers have carried out experiments to validate the rule up-to maximum possible accuracy using multi-order interference (Sinha et al, Science, 329, 418 [2010]). But, a convincing analytical proof of Born’s rule will make us understand the basic process responsible for exact square dependency of probability on wave function. In this paper, by generalizing the method of calculating probability in common experience into quantum mechanics, we prove the Born’s rule for statistical interpretation of wave function.
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One of the most successful, yet most puzzling, structures of quantum mechanics is Born's rule:P(\mathbf{x},t)=|\Psi(\mathbf{x},t)|^2.It establishes, with extraordinarily high experimental accuracy, the connection between the quantum wave function and the statistical distribution of actual measurement outcomes. Yet a more fundamental question remains worth asking: Why is probability given precisely by the modulus squared of the complex wave amplitude? Standard quantum mechanics uses Born's rule as a fundamental rule. This paper instead poses an open research question: Could Born's rule be not an irreducible probabilistic axiom, but a statistical emergence resulting from the combined action of continuous wave-amplitude superposition, quantized energy exchange, and local interaction dynamics? We propose a candidate physical picture:wave-amplitude superposition->spatial interference structure->local interaction->quantized energy exchange->discrete events}->probability distribution The central mathematical question is \Gamma(\mathbf{x})\stackrel{?}{\propto}|\Psi(\mathbf{x})|^2 where Γ(x)\Gamma(\mathbf{x})Γ(x) denotes the occurrence rate of localized discrete detection events. This paper does not claim to have completed such a derivation. Instead, it explicitly formulates the problem as an \textbf{open, computable, testable, and falsifiable research challenge}. We particularly invite young physicists, mathematicians, and researchers skilled in AI and modern computational tools to explore this problem.
A physical experiment comprises along the time trajectory a start, a time evolution (duration), and an end, which is the measurement. In non relativistic quantum mechanics the start of the experiment is defined by the wave function at time 0 taking into account the starting conditions, the evolution is described by the wave function following the Schrödinger equation and the measurement by the Born rule. While the Schrödinger equation is deterministic, it is the Born rule that makes quantum mechanics statistical with all its consequences. The nature of the Born rule is thereby unknown albeit necessary since it produces the correct ensemble averaged measures of the experiment. Here, it is demonstrated that the origin of the Born rule is the projection from the quantum frame (i.e. wave description) to the classical mechanics frame (i.e. particle description) described by a Ehrenfest theorem-oriented Fourier transformation. The statistical averaging over many measurements is necessary in order to eliminate the unknown initial and end time coordinate of the experiment in reference to the beginning of the universe.
Abstract In terms of its time trajectory, a physical experiment is comprised of a preparation time, a start time, a time evolution (duration), and an end time (point at which the measurement actually occurs). In non-relativistic quantum mechanics the start of the experiment is described by the wave function at time t = 0 taking into account the starting conditions, the evolution is described by the wave function according to the Schrödinger equation and the measurement is described by the Born rule. While the Schrödinger equation is deterministic, it is the Born rule that renders quantum mechanics stochastic with all its consequences it entails. Still, the nature of the Born rule is unknown yet it is useful since it produces the correct ensemble averaged measures of the experiment. Here, it is demonstrated that the origin of the Born rule is the projection from the quantum frame (i.e. wave description) to the classical mechanics frame (i.e. particle description) described by a Ehrenfest theorem-oriented Fourier transformation. The statistical averaging over many measurements is therefore only necessary in order to account for the unknown preparation time and thus starting time of the experiment because only the experimental duration (time between start time and end time) can be known.