Finding ‘‘real’’ time in quantum mechanics

A. Ruschhaupt, Reinhard F. Werner

Bhushan Bhoja Poojary

Time has always been a fundamental yet enigmatic concept in physics. From the arrow of time in thermodynamics to the timeless nature of quantum mechanics, understanding time's essence has challenged the foundations of modern physics. In this paper, we propose a novel interpretation of time in quantum mechanics, distinguishing between real time as observable events (wave function collapse or address changes) and imaginary time as the continuous evolution of the quantum state. By connecting this framework with the holographic principle, we aim to provide insights into the nature of time, its arrow, and its relationship with quantum mechanics. Keywords Thermodynamics; Wave function; Quantum mechanics; Holographic principle

Craig Callender

This article is an introduction to and advertisement of Erwin Schrödinger’s little-known real-valued wave equation, the first published time dependent Schrödinger equation. I argue that this equation is not merely a historical curiosity. Not only does it show that quantum mechanics need not be viewed as essentially complex-valued, but the real formalism also provides a deep insight into the puzzling nature of time reversal in a quantum world. It is hoped that this observation will stimulate the discovery of other areas where ‘keeping it real’ will prove pedagogically or foundationally useful.

Valia Allori

Sungwook Lee, Lawrence R. Mead

Update: A time-independent $n\times n$ PT-symmetric (and symmetric) Hamiltonian is diagonalizable since it has all distinct real eigenvalues and the resulting diagonal matrix is a real symmetric matrix. The diagonalization results an isometry so there shouldn't be any issue with unitarity and unfortunately this very elementary mathematical fact somehow did not draw the authors' attention. However, PT-symmetric quantum mechanics is not out of trouble. For time-dependent PT-symmetric (and symmetric) Hamiltonians (even $2\times 2$ ones) the authors observed that there is a violation of unitarity. Moreover, the first named author showed in his recent article arXiv:1312.7738 that PT-symmetric quantum mechanics is indeed a certain kind of Hermitian quantum mechanics and that in order for time-evolution to be unitary with respect to $J$-inner product (one that gives rise to a Hilbert space structure on the space of state functions), the potential energy operator $V(x)$ must be real. This means that those complex PT-symmetric Hamiltonians that have been studied by physicists are unfortunately unphysical. The first named author discussed in a subsequent article arXiv:1401.5149 that while finite-state PT-symmetric quantum mechanics with time-independent Hamiltonians is not physically any different from Hermitian quantum mechanics, PT-symmetric quantum mechanics exhibits a distinctive symmetry from that of Hermitian quantum mechanics.

Juan Gonzalo Muga, A. Ruschhaupt, A Del Campo