There have been a lot of books, chapters and articles published about the meaning of time. Whether they are written by physicists, mathematicians or philosophers, most (except perhaps those based on process philosophy of Alfred North Whitehead) are based on the assumption that time is one-dimensional, whereas space is three. That seems to be the right answer because it takes three coordinates to describe a position in space and only one coordinate of time. And in all practical applications, that’s fine. It works to predict motion in 3-D space, which is what we usually care about. The problem is that it hides the nature of time itself. And folding 1-D time up with 3-D space as a 4-D manifold as in the Minkowski formalism creates a complex mathematical web that generates more questions than answers about the nature of time.
It may not even seem practical to ask “what is time” but some physicist, like Lee Smolin, consider it “the single most important problem facing science as we probe more deeply into the fundamentals of the universe.” (Smolin, 2013) The practical answer that I hope to support in this thesis is that time is nothing more than a measure of motion (as I explain in Timeless Epiphany). I don’t claim this as an original idea by any means. In fact, it is more of a reminder that this is what we were told in the introductory section of Physics 101. Any motion that consistently repeats itself can be used as a clock.
Time is a scale of motion that has been standardized for use as a denominator. It is used to denominate other measures of motion and that is what makes it seem to be different – to have a different meaning. This is in contrast to Smolin’s answer (that “Embracing time [as real] means believing that reality consists only of what’s real in each moment of time”), which may be true but is as impractical as the notion that time is a persistent illusion, as Einstein and many others have said. In his 1999 book, The End of Time, Julian Barbour said, “Time does not exist. All that exists are things that change. What we call time is – in classical physics at least – simply a complex of rules that govern the change.” (Barbour, p. Loc 2327) But that is not practical either. Time does exist, not as a complex of rules, but as a very simple tool. Newton was the tool-maker and the tool was used for nearly 300 years to advance physics to the point that we now realize the limits of its usefulness.
Back when Newton proclaimed time to be absolute and independent, before linear time was ingrained in everyone’s mind, it was considered by most to be a philosophical blunder. Isaac Barrow (1630-77), Newton’s predecessor at Cambridge, was quoted in E. A. Burtt’s book (originally published in 1924), The Metaphysical Foundations of Modern Science (Burtt 2003) as follows, “[He] takes up the question how, if the measure of time be thus dependent on motion, time may itself be, as defined, the measure of motion.” He explained in his “Geometrical Lectures”, published in 1735:
“Time is commonly regarded as a measure of motion, and… consequently differences of motion (swifter, slower, accelerated, retarded) are defined by assuming time is known; and therefore the quantity of time is not determined by motion but the quantity of motion by time: for nothing prevents time and motion from rendering each other mutual aid in this respect. Clearly, just as we measure space, first by some magnitude, and learn how much it is, later judging other congruent magnitudes by space; so we first reckon time from some motion and afterwards judge other motions by it; which is plainly nothing else than to compare some motions with others by the mediation of time; just as by the mediation of space we investigate the relations of magnitudes with each other.” (Burtt, 2003, p. 158)
It’s true that nothing prevents time and motion from rendering each other mutual aid, but considering time to be fundamental creates the question that no one seems to be able to answer; what is time? Clearly, as Barrow said, time is just “reckoned” from some motion – a repetitive motion such as the sun, moon, a pendulum, sands through an hourglass and eventually an international standard measured by the decay of radioactive isotopes. The standard was then “minted” as the approved denomination (the literal denominator in the equation for motion) to be used as a scale to judge other motions.
The more accurate and precise our time standard became, the more real and independent it seemed to be. And as the science advanced, the math got more and more complicated until it formed an intellectual trap. It’s a trap because only those who are smart enough to learn the enormous complexities of advanced math and physics can speak the language, but the language itself is based on the use of time as we know it.
Spacetime, or the space-time continuum, is an idea that most people credit to Einstein. But it was actually a mathematician named Hermann Minkowski, who presented it. Einstein even credited him in his book, Relativity, The Special and the General Theory:
“the world of physical phenomena which was briefly called “world” by Minkowski is naturally four dimensional in the space-time sense.” (Einstein, 1952)
In fact, before Einstein started using it he called Minkowski’s approach “superfluous learnedness”, that it just complicated the theory and said, “since the mathematicians have invaded the relativity theory, I do not understand it myself any more.” (Minkowski, p. 2) In a recent article published in Scientific American, entitled “What is Spacetime,” George Musser said
“People have always taken space for granted. It is just emptiness, after all—a backdrop to everything else. Time, likewise, simply ticks on incessantly. But if physicists have learned anything from the long slog to unify their theories, it is that space and time form a system of such staggering complexity that it may defy our most ardent efforts to understand”. (Musser, 2018)
My goal is to show that it is the math that is complicated, not spacetime. The idea of spacetime came from Minkowski’s lecture in 1908, “Space and Time” in which he stated:
“From this moment, space by itself and time by itself shall sink in the background, and only a certain union of these two shall retain substantiality.”
Isn’t speed – the measure of motion – a union of these two? It’s the ratio of displacement and time or the product of a unit of space with a unit of inverse time. But is that too simple? Is it more likely that nature is “a system of such staggering complexity that it may defy our most ardent efforts to understand”? I don’t think so. If I have learned anything from my 58-year (and counting) slog through life, it’s that the world makes sense. The reason that the math is so complicated, I submit, is that the four-dimensional spacetime equation itself is lopsided; it defines spacetime as a mixture: 3 parts space and 1 part time. But this definition creates a forgone conclusion and forces the interpretation to be lopsided as well.
It’s like a balloon animal, made from a single balloon that is twisted up into a figure. The real trouble with physics is that most people are trying to figure out how to make it smooth (unified) by adding more twists.