Dr. Fei Guo’s thesis, partially performed at the Paul Scherrer Institute and nominated for the best thesis award in physics at EPFL, proposes a new understanding of quantum time scales focusing on dimensionality, symmetry, and correlation. While quantum mechanics readily describes spatial position with a defined operator, it lacks a corresponding operator for external time coordinate, a parallel that highlights a fundamental difference in how time is treated compared to space. However, operators can define the internal time duration of processes; the Eisenbud-Wigner-Smith (EWS) time scale, for example, specifically describes the time scale for single-particle scattering or ionization. “Time, though ubiquitous in our daily experience, is a physical quantity not very well understood,” Guo writes in her thesis, available through EPFL’s information system. This research explores the complexities of quantum time, examining how it differs across physical paradigms from Newtonian mechanics to general relativity.
Internal Time Duration in Quantum Mechanics
The distinction between external time and internal time duration is a central challenge in quantum mechanics, as the framework lacks an operator to define time as it does for spatial position. Guo explains that in quantum mechanics, the inability to find an operator for time analogous to those for spatial positions indicates the impossibility of finding an observable which represents the external time coordinate, highlighting a fundamental asymmetry between space and time. This internal time isn’t a measure of when something happens, but rather how long a process takes from the perspective of the quantum system itself. Guo’s research, detailed in a thesis available through EPFL’s infoscience platform, seeks to refine understanding of these internal timescales and their relationship to fundamental quantum properties.
The investigation into these quantum time scales builds on the idea that time’s role varies across physical paradigms, functioning as a constant in Newtonian mechanics but as an internal property within general relativity. Understanding these differences may prove crucial in unifying these frameworks. For further information, contact Prof. Hugo Dil, Scientist and Subgroup Leader at COPHEE (EPFL) and the Paul Scherrer Institute PSI, at jan-hugo. dil@psi. ch.
Nevertheless, an operator can often be found to represent the internal time extit{duration} of some certain process.
The exploration of quantum time reveals a distinction between external time coordinate and internal time duration, a concept particularly evident in scattering processes. This research builds on the understanding that the absence of an operator for external time mirrors the ability to define position, suggesting a fundamental asymmetry in how space and time are treated within quantum physics. The EWS scale, as a specific example of an internal time duration operator, offers a concrete avenue for investigating these temporal dynamics in physical systems. The work presented by Guo and Dil contributes to a growing body of research attempting to reconcile our intuitive experience of time with its complex quantum reality.
