3 ms·

The trick is that we don't really have deeper understanding of "mass" and "time" so all we can talk about is the (classical) measurements we make. Paraphrasing

The trick is that we don't really have deeper understanding of "mass" and "time" so all we can talk about is the (classical) measurements we make. Paraphrasing Feynman: Physicist's definition of time: "it is what is measured by a clock" Philosopher's definition of time: "it is the thing that passes by when you wait!" (Or even all the way back to Saint Augustine: when you're living day-to-day, time is as natural and obvious as could be; when you're trying to explain time in words, it's a morass of tautologies and contradictions.) For non-relativistic classical mechanics these concepts plainly coincide. General relativity leads to unintuitive consequences but doesn't come into friction with "what passes when you wait" since humans are subject to GR. But humans are not meaningfully quantum-mechanical, and the philosopher's definition of time is meaningless for a photon. For QM, all we have is the physicists's definition; the negative time measurement observed in the lab is the only time it makes sense to talk about. When you say "not able to measure time appropriately" I think you mean more precisely something like "not able to phrase a subatomic theory of time which aligns with our classical intuition" - e.g. a quantum theory of causality itself where classical time "falls out," kind of like how some physicists are looking for information-theoretic approaches to gravitation where mass "falls out." But it's a much bigger problem than measurement of time - if we come up with such a theory the measurements of "second" would be the same up to a minor correction, but supplemented by additional measurements of physical properties we don't understand yet.

godelski 2y ago
> Physicist's definition of time: "it is what is measured by a clock" I hate this quote, because it makes people think there is something unique about time. There is, but not because of this. We could similarly say "a meter is what a ruler measures" (defined by how far light moves in 1/299792458th of a second; a second is defined as 9192631770 Hz, or the transition of 2 hyperfine levels of a CS-133 atoms). We can do this with any SI unit! What is an Ampere? You gotta define charge and frequency (time). What is a kilogram? You gotta define Planck's constant, the speed of light, and... frequency. Kelvin? Planck's constant, frequency, and kilo. Candela? Also depends on frequency. Mol? Well... actually this one is unique. Truth is that these are not as "well defined" as one might think. They're kinda made up and arbitrary, and that's perfectly okay. In particle physics you often set hbar = 2pi = c = 1 (or if you're Mills, you include i). If we meet aliens, they would very likely have a different set of units, but their physics would look identical (they'd be isomorphic, i.e. we could translate between them). So what is time? Distance? Mass? Energy? These are still very open questions at a base fundamental level. We treat them like axioms but even math still questions axioms and would love to remove them (and just like math, axioms are typically developed in hindsight). Someone might give you some definition for these things and you might be satisfied, but that doesn't mean there is a question one level deeper that's unknown. Beware this trick, as you'll fool yourself into thinking you know more than you do (it's quite common, and we all do it. I'm not trying to stand on a pedestal, every human does this and in abundance. Sweep things under the rug, but don't forget that you've done this). (also, this quote is usually attributed to Einstein, not Feynman) For info on SI units: https://www.bipm.org/en/si-base-units/mole https://www.bipm.org/en/si-base-units/mole

godelski 2y ago

> Physicist's definition of time: "it is what is measured by a clock" I hate this quote, because it makes people think there is something unique about time. There is, but not because of this. We could similarly say "a meter is what a ruler measures" (defined by how far light moves in 1/299792458th of a second; a second is defined as 9192631770 Hz, or the transition of 2 hyperfine levels of a CS-133 atoms). We can do this with any SI unit! What is an Ampere? You gotta define charge and frequency (time). What is a kilogram? You gotta define Planck's constant, the speed of light, and... frequency. Kelvin? Planck's constant, frequency, and kilo. Candela? Also depends on frequency. Mol? Well... actually this one is unique. Truth is that these are not as "well defined" as one might think. They're kinda made up and arbitrary, and that's perfectly okay. In particle physics you often set hbar = 2pi = c = 1 (or if you're Mills, you include i). If we meet aliens, they would very likely have a different set of units, but their physics would look identical (they'd be isomorphic, i.e. we could translate between them). So what is time? Distance? Mass? Energy? These are still very open questions at a base fundamental level. We treat them like axioms but even math still questions axioms and would love to remove them (and just like math, axioms are typically developed in hindsight). Someone might give you some definition for these things and you might be satisfied, but that doesn't mean there is a question one level deeper that's unknown. Beware this trick, as you'll fool yourself into thinking you know more than you do (it's quite common, and we all do it. I'm not trying to stand on a pedestal, every human does this and in abundance. Sweep things under the rug, but don't forget that you've done this). (also, this quote is usually attributed to Einstein, not Feynman) For info on SI units: https://www.bipm.org/en/si-base-units/mole https://www.bipm.org/en/si-base-units/mole