**Time part 2** ---- Given the following grid: absolute time relative time Newton Einstein Where would you place the check marks? Something like this? absolute time relative time Newton X Einstein X That's what I would have said too. After all, Einstein's Relativity says that time is relative, not absolute. So it is commonly believed today that time is relative, and there is no such thing as absolute time. Turns out, that's a simplistic version of physics history. Consider what Newton wrote in the beginning of the Principia: >I do not define time, space, place, and motion, as being well known to all. Only I must observe, that the common people conceive those quantities under no other notions but from the relation they bear to sensible objects. And thence arise certain prejudices, for the removing of which it will be convenient to distinguish them into absolute and relative... >I. Absolute, true, and mathematical time, of itself, and from its own nature, flows equably without relation to anything external, and by another name is called duration: Relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time; such as an hour, a day, a month, a year. By sensible, Newton is referring to what appears to the senses. Notice here that Newton provides a definition for relative time, as a "measure of duration by the means of motion". The moving hands on a clock, for instance, tell us relative time. So Newton believed in both absolute and relative time: absolute time relative time Newton X X Einstein X It should be said that the tradition of absolute and relative didn't begin with Newton. He did however, believe his mathematics represented absolute time. Maybe because clocks were inaccurate while he lived, he didn't believe they could produce "true" time. Yet even back then, Leibniz contested that position, saying the mathematics were of relative time. Einstein also contested that position (as did Mach and others). A clock reading, and the mathematical equations we use to represent them, are both relative time. Here is a discussion with Einstein as told by Heisenberg: >"But you don't seriously believe," Einstein protested, "that none but observable magnitudes must go into a physical theory?" >"Isn't that precisely what you have done with relativity?" I asked in some surprise. "After all, you did stress the fact that it is impermissible to speak of absolute time, simply because absolute time cannot be observed; that only clock readings, be it in the moving reference system or the system at rest, are relevant to the determination of time." >"Possibly I did use this kind of reasoning," Einstein admitted, "but it is nonsense all the same. Perhaps I could put it more diplomatically by saying that it may be heuristically useful to keep in mind what one has actually observed. But on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality, the very opposite happens. It is the theory which decides what we can observe." While it is understood clock readings do not reveal absolute time, notice that the implicit existence of absolute time persists from Newton's era into Einstein's. The original solution to the physicist/time grid, that Newton believed in only absolute time and Einstein believed in only relative time, reveals an assumption: time can only come in one flavor. If the time we measure is relative, and if there is only one flavor, then there can be no absolute time. That assumption and conclusion seems to have appeared in the education of physics in the 1960's. It doesn't seem to be consistent with what Newton or Einstein actually said. If the question was, check the column for which kind of time each physicist felt was described by their mathematics, then the original two check mark solution is correct. On the other hand, if this question is which kinds of time exist (in whatever way they do), then both physicists belong to the tradition of relative time being a measurement and absolute time being more fundamental. absolute time relative time Newton X X Einstein X X While the absolute and relative topic has been of interest to philosophers long before Newton, to modern physicists what really matters is what can be described mathematically. That means, if there is room for only one kind of time in the mathematics, it should be the kind we observe, which is relative time. ---- Next > [Space](space.htm) ---- ### Bibliography * Newton, Isaac (1687) [Philosophiae Naturalis Principia Mathematica](http://plato.stanford.edu/entries/newton-stm/scholium.html) Second printing, University of California Press, 1946. p. 6 * Heisenberg, Werner (1971) Physics and Beyond, Harper & Row, p. 63