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Time is a tool we've invented to measure changes of state. What evidence do we have that it is a natural phenomenon?

Mitch
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    Time would still pass even if there were no humans around to measure it. The Earth would still orbit the sun in one year, the Earth would rotate once a day. Humans invented years and days, but not time itself. I'm not sure I understand what evidence you're asking for? – Dan Pollard Jan 18 '21 at 13:52
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    Is this question philosophical? I guess it is. – lee Jan 18 '21 at 13:57
  • What kind of evidence would convince you that any particular thing is a natural phenomenon rather than "invented"? Philosophically you can always claim solipsism, turning anything into your own invention, but few people maintain that position. – Anders Sandberg Jan 18 '21 at 14:41
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    Yesterday my knees hurt. Today they don't. – WillO Jan 18 '21 at 14:46
  • @DanPollard Those things you've mentioned are not evidence of time, they are evidence that there is present moment. I'm asking if there is evidence that reality is composed of more than the present. – Mitch Jan 19 '21 at 20:42
  • @AndersSandberg Natural phenomona exist. Space is a natural phenomon. Air is a natural phenomenon. It seems to me that we treat time as a natural phenomon, but it is an invention, not something we've discovered in nature. – Mitch Jan 19 '21 at 20:44
  • Dear moderator who closed my question: Please tell me where you see this question answered on https://physics.stackexchange.com/questions/235511/what-is-time-does-it-flow-and-if-so-what-defines-its-direction?noredirect=1&lq=1 – Mitch Jan 19 '21 at 21:25
  • Related meta discussion: https://physics.meta.stackexchange.com/q/13334/2451 – Qmechanic Jan 19 '21 at 22:01
  • @Mitch - Why do you think the sentence "space is a natural phenomenon" is true while the structurally similar sentence "time is a natural phenomenon" might be false? Can you explain what property of space makes it natural, that time lacks? Saying it exists is a non-starter, because I can just make the same claim about time. Saying time would not exist without measurement allows me to claim the same about space - seeing things in different locations is also a form of measurement. – Anders Sandberg Jan 20 '21 at 00:25

2 Answers2

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Things actually do change, and change happens naturally.

The idea of time is inseparable from the idea of change. When we say that we are measuring how much time some process takes, what we actually mean is that we are comparing the rate of the process to the rate of some "standard" process (e.g., the rate of the Earth's daily rotation, the rate of vibrations of a quartz crystal in a stopwatch, the rate of oscillations of microwave energy emitted by cesium atoms under carefully controlled conditions in an atomic clock.)

Solomon Slow
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  • We know that reality is a state of continuous change, and we use time to descibe the change. Physicists describe space time and discuss time travel as if time is a unique component of our reality - like space or matter. Do we have evidence of that? – Mitch Jan 19 '21 at 20:51
  • @Mitch, I'll say again, we define time by comparing rates. If we say that an object is moving at one meter per second, we're really saying (as of the year 201x) that the object moves one meter for every 9,192,631,770 periods of an electronic oscillator that is regulated by a Cesium-133 fountain. The whole idea of "spacetime" and how it is "warped" by the presence of energy is a mathematical trick. So far as I know, the only evidence that it is objectively real is that the trick works. – Solomon Slow Jan 20 '21 at 14:57
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A clock is certainly a natural phenomenon. A good clock measures time in at least two ways: a metric (duration) and a phase (when). But what is a clock? What does it actually do? I would suggest everything is a clock if we get loose enough with the defintion, some are just better at their job than others. How many heartbeats passed while you wrote your question? How many degrees did the sun process in the sky? How many atoms of potassium decayed in the ambient air in you room? Your computer's clock is subject to the same laws of physics as everything else in your room and above, however it regularly passes through much more arbitrarily close to the same states than "non-clocks". That's the only difference. And via GR, all clocks dilate the same under gravity/acceleration, no matter what they are made of. If the notion of seconds is obfuscating the similarness of clocks and "non-clocks", a second is just "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom".

So your heartbeats are natural and are clocks, and clocks tell time. Time is a natural phenomenon. Time is change.

The experience of time passing and/or the flow of time is something else entirely, but it seems like you were focused on the time is change idea of time.

J Kusin
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  • A clock is a human invention. Even using a natural phenomon like a heartbeat as a measuring tool is us choosing to correlate and accumluate discreet samples of the present - this we know is true. From this scenario what data would you present to postulate that time is a unique phenomenon? – Mitch Jan 19 '21 at 21:01