Brilliantly written but, like Tom W, I have more chance of getting my head round the plot lines of Christopher Nolan's films*. (At least Tom studied this stuff).Simon(*Except Dunkirk. I followed that one). -------- Original message --------From: Tom Windmuller via Mifnet <[email protected]> Date: 06/10/2025 07:58 (GMT+00:00) To: [email protected] Cc: Tom Windmuller <[email protected]> Subject: [Mifnet 🛰 74414] Re: NNN What Time Is It? (It's Later Than You Think) Thank you, David. Unfortunately, I understood almost as much of your description of General Relativity today as when Professors Hans Bethe & David Mermin tried to explain it to me at university over 50 years ago.  I got a D- in the course back then; would probably get an F today.  Glad my life took a different direction than into science.  All best wishes,tomOn Mon, 6 Oct 2025 at 06:26 David Wardell via Mifnet <[email protected]> wrote:"Now he has departed from this strange world a little ahead of me. That signifies nothing. For those of us who believe in physics, the distinction between past, present and future is only a stubbornly persistent illusion." - Albert Einstein (1879-1955), German Theoretical Physicist    This is the statement by Einstein that is oft misquoted to say, "Time is an illusion." Apart from the variance between the misquote and the original, we are faced with the problem that one cannot be sure what he meant.  Einstein wrote the above lines in a private letter to the family of a close friend who had just died. We assume he intended it by way of condolence. People have been arguing about the meaning since the statement began circulating.  The notion that time is an illusion isn't new. There is even a quite legitimate and credible paper, written many years ago, which argues that, simply from a logical perspective, time does not exist.  We know that time does exist (or we believe that we know) because we define it as the inevitable progression from past to present, and then to future. We sequence our lives to harmonize with our observations, and we synchronize our clocks so that we may coordinate with other humans as well. While this process works reliably across the sequence of events that we observe, there are some flaws that we overlook because they are beyond our experience. For example, there is no means by which we can perceive “now.” Indeed, there is no definition of “the present” that works in all situations. Although we assume that “now” is what we are currently experiencing, we are continually living only with what has gone before. Our eyes perceive light that is reflected by objects within our field of vision. Even though the interval is very small, our perception is nonetheless delayed because light does not propagate instantly. Further, our visual perception must be transmitted to our brains (a much slower process) and understood, based upon how much attention we may be paying (still more time). Beyond this, we know that time exists because General Relativity teaches us that time is an integral part of our understanding of space and matter. Accordingly, space and time are relative, and in some respects, they are the same. According to General relativity, every point in space associates with a point in time. Massive objects distort space, and we experience this as gravity. Such distortions also affect time. All this can be observed consistent with the predictions of General Relativity.  One of those predictions (also confirmed by observation) is that time is perceived differently based upon the observer’s frame of reference. Hence, there is no “now” that can apply to all observers in all situations. An extreme example may illustrate how this works: We know that “black holes” exist (they have been observed more than once), and these result from extreme effects of gravity distortions. Such distortions cause the passing of time to slow for observers in a different frame of reference. The effects of gravity beyond what is called the “event horizon” of a black hole are so extreme that no form of matter or energy can escape. The effect of a black hole on time would manifest in a way would prevent an external observer from ever seeing an object cross the event horizon. The passing of time would become so distorted that it would effectively cease, making observations of objects crossing the event horizon impossible, as this would require infinite time. It is not time that is an illusion, it is our perceptions of time.  We insist, even unconsciously, that all things must have a beginning, as this is our experience. Most interpretations of current physics (although there is disagreement here) require that existence has a beginning.  General Relativity can be interpreted to say that all the universe may be understood as a box, bounded by the three spatial dimensions and a fourth dimension of time. Existence is defined as whatever is inside the box.  To continue the "black hole" example, General Relativity suggests that, were it possible for an observer to look outward from past the event horizon (this could never happen), said observer could view the entire history of the universe from beginning to end, owing to the extreme distortions of time by gravity.  General Relativity does not of itself, however, make predictions which require a beginning of existence. It primarily describes the relationship between matter, energy, space, and time. Still, inconsistencies remain. General Relativity is not consistent with quantum mechanics, one instance being that the latter requires that there must be a fixed definition of "now." It has been known since quantum mechanics was first defined that our understanding of it is flawed (or at least incomplete). Much thought and energy continue to be expended to develop a theory that reconciles our understanding of existence at all levels and that resolves such inconsistencies.  Yet, incomplete though our understanding may be, the predictions of our theories work well enough to enable truly astounding technologies, which demand the measurement of time intervals with extreme precision. We synchronize our clocks so that contemporary society and technology can function. One basic unit of our time calculation is the second, which is defined by atomic clocks measuring a given number of microwave oscillations of cesium atoms. We then align seconds with other standards, to include minutes, hours, days, and so on. Unfortunately, this process is not without its flaws. Human society has grown comfortable (over thousands of years) with synchronizing time to astronomical events. We divide years into days required for the earth to circle the sun. Days are further grouped into months, which are loosely derived from the phases of the moon and early lunar calendars. Days are also grouped into weeks, which are a logical construct without an astronomical parallel. Days are defined in various ways—coordinating these can be challenging. For most, a day is the time required for earth to rotate on its axis relative to the sun. As this definition is difficult to precisely measure in practice, a different definition uses sidereal reckoning based upon the apparent motion of stars. The fixed definition of a day, relative to what is known as International Atomic Time (TAI), as measured by atomic clocks, is 86,400 TAI seconds. The astronomical definition adopted in the 1950s defines a second as a fraction of a sidereal year. The length of a day based upon earth’s rotation varies considerably over long time periods. Over the last 53 years the length of the astronomical day has been increasing, which has necessitated the periodic announcements of “leap seconds” which preserve the coordination of an astronomical day with TAI. Two leap second updates annually are possible, with the accumulated change enacted by all such leap seconds now totaling 27 seconds since 1972.Not everyone is happy with leap seconds. Software errors occur periodically as systems (including airlines) that incorporate time coordination do not update correctly, or are not designed to accommodate leap seconds at all. The most straightforward solution to this challenge would be for all systems to simply align with TAI and ignore alignment to astronomical time. The U.S. GPS standard does not recognize leap seconds, while those of some other countries do. Current international proposals call for relaxing leap second requirements beginning in 2035—which would allow a larger variance to accumulate before considering an adjustment. This is partly owing to a recently observed increase in earth’s rotation speed, which may require a negative leap second sometime before 2035.If the reader is wondering, there are theories, but no one really knows why earth’s rotation speed changes. The most compelling speculations center on changes in the earth’s molten core.Thus, we see that there remains no universal definition of “now” and the agreed conventions we employ to coordinate time are not so agreeable as we may assume. Was Einstein right? Time will tell. Old Man WardellFailed Mad Scientist David Wardell(757) [email protected]   -------------------------------------------------------------------------- Revised: 20250507
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