Physicists reveal the mystery of the arrow of time

A new study by theoretical physicists has made progress toward determining how particles and cells trigger the large-scale dynamics we experience over time.

The central feature of how we experience the world is the flow of time from the past into the future. But it is a mystery exactly how this phenomenon, known as the arrow of time, arises from microscopic interactions between particles and cells. Researchers at the City University of New York’s Graduate Center for Theoretical Sciences (ITS) initiative are helping solve this mystery by publishing new research in the journal. physical review messages. The findings could have important implications for a wide range of disciplines, including physics, neuroscience, and biology.

Essentially, the arrow of time stems from the second law of thermodynamics. This is the principle that the microscopic arrangements of physical systems tend to increase in randomness, moving from order to chaos. And the more disordered the system, the more difficult it was to return to an orderly state, and the stronger the arrow of time became. In short, the universe’s tendency toward chaos is the primary reason we feel the flow of time in one direction.

“The two questions our team asked were, if we look at a particular system, will we be able to determine the strength of its arrow for time, and will we be able to determine how it appears from the exact scale, and where the cells and neurons interact with the whole system?” said Christopher Lane, postdoctoral fellow. in the ITS program and first author of the research paper. “Our findings provide the first step toward understanding how the arrow of time that we experience in everyday life emerges from these microscopic details.”

To begin answering these questions, physicists figured out how the arrow of time can decay by observing certain parts of the system and the interactions between them. For example, segments can be neurons that run within the retina. Looking at one moment, they showed that the arrow of time can be divided into different parts: those produced by parts that act individually, in pairs, in triplets, or in more complex configurations.

Armed with this method of analyzing the arrow of time, the scientists analyzed current experiments on the response of neurons in the salamander’s retina to different films. In one movie, one object was randomly moving across the screen while another film depicted the full complexity of scenes found in nature. Across both films, the team discovered that the arrow of time arose from simple interactions between pairs of neurons — not large, complex clusters. Surprisingly, the researchers also observed that the retina showed a stronger arrow of time when viewing random movement compared to a landscape. Lin said this latest discovery raises questions about how our internal perception of the arrow of time corresponds to the outside world.

“These findings may be of particular interest to neuroscience researchers,” Lin said. “It could, for example, lead to answers about whether the arrow of time works differently in typical neurotic brains.”

“Chris’ decomposition of local reflection – also known as the arrow of time – is an elegant general framework that may provide a new perspective for exploring many non-equilibrium high-dimensional systems,” said David Schwab, lead author on the study and professor. Physics and Biology at the Graduate Center.

Reference: “Local Arrow Analysis of Time in Interacting Systems” by Christopher W. Lin, Caroline M. Holmes, William Bialik and David J. Schwab, physical review messages.

Authors in order: Christopher W. Lin, Ph.D., Postdoctoral Fellow, City University of New York Graduate Center; Caroline M. Holmes, PhD student, Princeton; William Bialik, Ph.D., Professor of Physics, City University of New York Graduate Center; and David J. Schwab, Ph.D., Professor of Physics and Biology, City University of New York Graduate Center

Funding sources: National Science Foundation, National Institutes of Health, James S McDonnell Foundation, Simons Foundation, Alfred P Sloan Foundation.