The Nature of Time
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The Nature of Time∗ Jayant V. Narlikar This article is about the unidirectionality of time. We experience it in daily life and are conscious of the fact that time past is time irreversibly lost. Why is it that we can go back and forth in space but not in time? This time asymmetry can be related to basic physics by a rather ingenious approach. This was initiated by two scientists John Wheeler and Richard Feynman. In 1945, they explored how classical electrodynamics can be described as an action at a distance theory instead of field theory. This makes the formulation necessarily time-symmetric. Later in 1962–63 Jack Hogarth and later Fred Hoyle and this author showed that this approach makes it possible to explain the alignment of three arrows of time: thermodynamic, electrodynamic, and cosmological. Later work by Hoyle and I extended the idea to full-scale quantum electrodynamics.
Jayant V. Narlikar is a cosmologist and theoretical astrophysicist. He was a research student and a long-time collaborator of Fred Hoyle. He is the Founder Director of IUCCA and is currently an Emeritus Professor there. He has made strong efforts to promote teaching and research in
Introduction One important saying I first encountered as a schoolboy was, “Time and tide wait for nobody”. I was reminded of it several years later when I was visiting Japan with my wife. There in Kyoto, while traveling on the underground, she drew my attention to what looked like an advertisement...one of the many on the walls of the underground station. The only striking difference was that while almost all advertisements were in Japanese and hence beyond our ability to read, this one was in the Devanagari script. What was it trying to communicate? Getting down from the train, we went to read the advertisement and figure out its significance if any. We were surprised to see that ∗
astronomy in the universities. He has written extensively in English and Marathi to popularize science.
Keywords Time,
dimensions,
magnetism,
Wheeler–Feynman cosmological
electro-
thermodynamics, models,
theory, time
asymmetry.
Vol.25, No.8, DOI: https://doi.org/10.1007/s12045-020-1025-8
RESONANCE | August 2020
1083
GENERAL ARTICLE
the quote in Devanagari was from a verse in Sanskrit. Not ever in India does one see Sanskrit ads on our railway stations. From our limited knowledge of Sanskrit later supplemented by the help of a professor of Sanskrit, we got the gist of the statement. It was telling the reader that of all things around us, the most valuable one is time; we should not lose it, for we do not get it back. The scientist may call the above property the irreversibility of the flow of time. However, giving it a technical name does not imply that the phenomenon is understood! Just as we can move in space in any direction, top-bottom, east-west, north-south, can we likewise move freely into the past and future? We can’t. Otherwise, there would be logical problems like the proverbial one, wherein, Mr A goes into the past and kills his grandfather before he got married;
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