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tldr - Can we reject the notion of the passage of time, but still accept that motion is real?

This question is a follow up to comments between myself and the author of this answer to the question, What is time, does it flow, and if so what defines its direction?.

The proposition is that time does not flow on the basis that:

No it does not. Water flows. You can see it flow. But when you try to see time flowing, all you can see is cogs turning or a crystal oscillating. The notion that time flows is just a figure of speech, an abstraction. Light moves, planets move, blood moves, electrochemical signals move, cogs move. Everything moves, and you can see this motion. But you can't see time flowing. Because it doesn't.

My counter argument is that the definition of motion involves the passage of time. From wikipedia:

In physics, motion is a change in position of an object with respect to time.

Therefore, if we want to reject the notion of the passage of time, we must also reject motion. If time does not flow, then it is like the spacial dimensions, and what our brains interpret as motion and time flow are really just fixed coordinates in spacetime.

Furthermore, that you can't see something doesn't prove that it does not exist. We cannot see an inverse square law, but we can deduce it from observation of things we can see. It is an abstract concept, but we accept it as reality (or at least until an alternative theory replaces it, but the issue here isn't whether or not today's science is correct).

The response argument runs as such:

When you define motion as a change in position of an object with respect to time, remember what a clock really does.

My issue with this is that it appears to involve circular reasoning:

1. Motion is a change in position with respect to time.

2. The passage of time is not real, because when we observe a clock we are really just observing its cogs.

3. The cogs are undergoing motion - go back to line 1.

So, who is right? Can we have motion, without the passage of time? If so, what is a more accurate definition of motion, which does not contain a circular reference to motion itself?

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    $\begingroup$ This is philosophy not physics. $\endgroup$ – John Rennie Mar 10 '16 at 20:51
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    $\begingroup$ And as with most philosophical questions, they're only problems because the language is ill-defined. If you give a rigorous definition of 'motion' and 'flow' then the problem will almost certainly disappear. $\endgroup$ – lemon Mar 10 '16 at 20:56
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    $\begingroup$ @John Rennie : this is physics, this concerns hard scientific evidence. And as you said in your answer to your question What is time, does it flow, and if so what defines its direction? time doesn't flow. $\endgroup$ – John Duffield Mar 10 '16 at 21:56
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Take a slightly different example and it may help a bit with your confusion:

  1. A slope is a change of height with respect to position.
  2. Take the surface of the earth (without water) as an example and you will see that neither the position nor the height are "flowing".
  3. We can be sure that slopes do exist - if you don't believe it, go to your nearest Mountain and walk to its top.

Using this analogy consider someone sitting in a moving black box with no way to look outside and no way to visit the same position twice. But he has a device that measures his height and his position. How should he describe the change of height?
He could use the definition of a slope we have, in which case he says that height is dependent on the position and his position is changing due to some reason he does not know.
He could as well describe both height and position as "magically changing (flowing) parameters".
However independent of his description why or how those parameters are changing, he can still recognize a slope by just measuring both parameters and looking at their correlation.

It is the same with motion. We can see that objects are at different positions at different times. The correlation between both is what we call motion.
It is not relevant if "time is moving/flowing" or if it is a "static dimension" that we are moving along or that we just experience to move along.

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Can there be motion without the flowing of time?

Yes, in that "the flow of time" is a figure of speech. It is an abstract thing. There is no actual thing called time that's literally flowing. Instead light moves, planets move, people move, hearts move, blood moves, lungs move, air moves, electrochemical signals move in nerves and brains, and so on. Everything moves, including pendulums and cogs in clocks, and oscillating quartz crystals and electrons in the circuitry within the watch upon your wrist.

Can we reject the notion of the passage of time, but still accept that motion is real?

Yes, because you can't see this passage of time, but you can see things moving. This is the empirical ontological science of it. When you open up a clock you don't see time flowing through it. A clock is not like your gas meter. There is no time flowing through it.

My counter argument is that the definition of motion involves the passage of time. From wikipedia: In physics, motion is a change in position of an object with respect to time.

There's nothing wrong with that definition. Provided you remember Einstein's operational definition, and what a clock really does. It's a device that features a movement, wherein some kind of regular cyclical "local" motion, such as that of a pendulum or a rocker or a piezo-electric crystal, this motion being accumulated and/or converted to present some kind of analogue or digital display that we call the time. So motion is a change in position of an object with respect to the change in position of another. Or if you prefer, its gradual change in position.

Therefore, if we want to reject the notion of the passage of time, we must also reject motion.

I disagree. Don't reject what you can see with your own eyes because you're rejecting something you were never able to see.

If time does not flow, then it is like the spatial dimensions, and what our brains interpret as motion and time flow are really just fixed coordinates in spacetime.

No they are not. Those fixed coordinates are an abstract thing, and so is the "block universe". Ours is a world of space and motion. The map is not the territory.

Furthermore, that you can't see something doesn't prove that it does not exist. We cannot see an inverse square law, but we can deduce it from observation of things we can see. It is an abstract concept, but we accept it as reality (or at least until an alternative theory replaces it, but the issue here isn't whether or not today's science is correct).

We accept it as reality because forces really do diminish such that when you double the distance, the force is reduced by a factor of four. We refer to this as the inverse square law as convenient shorthand. But we understand why it applies, and nobody has an issue with it as far as I know.

My issue with this is that it appears to involve circular reasoning: 1. Motion is a change in position with respect to time. 2. The passage of time is not real, because when we observe a clock we are really just observing its cogs. 3. The cogs are undergoing motion - go back to line 1.

Note that I'm not saying time isn't real at all. I think it's best to think of it as something like heat. Heat is real, heat will burn you. But it's an emergent property, not something fundamental. Think about the kinetic theory of gases, wherein "the temperature of an ideal monatomic gas is proportional to the average kinetic energy of its atoms". The faster those atoms move, the hotter the gas. The temperature of that gas is akin to an average measure of motion:

enter image description here GNUFDL image by Greg L, see Wikipedia

Time on the other hand is more like a cumulative measure of motion. And it's just as real as heat, in that a hundred years will kill you just as surely as a hundred degrees C. It just isn't something that literally flows or passes, or through which you can move. You don't literally climb to a higher temperature and in similar vein you don't literally move forward through time, and nor does time literally flow or pass.

So, who is right? Can we have motion, without the passage of time? If so, what is a more accurate definition of motion, which does not contain a circular reference to motion itself?

When you measure the motion of that object, you use a clock. And that clock really does feature other things, moving. That's the science of it. That's the physics of it.

NB: You might be interested in reading this popscience article I wrote a couple of years back explaining why time travel is science fiction. You "travel" to the future by not moving at all whilst everything else does.

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    $\begingroup$ This answer does not represent the standard practice in physics. Time is a parameter of solutions of "equations of motion" in classical mechanics, and a coordinate in relativistic mechanics (proper time is again a parameter of solutions - that of worldlines). You may interpret a parameter as "a cumulative measure of motion", but that's just word games. Beyond that, standard physics makes no statements about the nature of time, although individual physicists may. $\endgroup$ – ACuriousMind Mar 10 '16 at 21:52
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    $\begingroup$ This answer is in line with Einstein and the hard scientific evidence. If you think the standard practice in physics is to define reality as consisting of abstract mathematical things that do not exist, you are mistaken. Time is not "a parameter of solutions". And it certainly isn't word games to point out what a clock actually does. $\endgroup$ – John Duffield Mar 10 '16 at 22:14
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Time in itself is not an entity. It is a measure of events in terms of other type of events. The events involve motion at some level (visible, or not). For example, if you have a blinking clock, (instead of oscillating, or rotating), there is no visible motion but there is some kind of underlying motion that regulates the sequence of blinks. The interval itself is in terms of underlying events. Thus, time is a measurement, and it must involve some events, which must have motion/action at core.

Therefore, measurement of time (it's flow) is not possible without involving events (motion).

That also implies that there can not be motion without measurement (flow) of time. Because, detection of motion, implicitly involves other events which take form of flow of time.

We can say, that time flow, and motion individually do not make sense. They both exist together, or neither does. Needless to say, an observer is involved.

The direction of time flow is same as the sequence of events used to measure its flow. Which happens to be always forward, per perception of any observer.

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