russ_watters said:
You didn't read what I said. What I said was some clocks do and some clocks don't measure motion. I would venture to say that very few clocks measure motion. Most clocks count intervals between events. See the difference? Ie, a clock based on the rotation of the Earth is not measuring the rotation rate of the earth, it is counting the number of rotations.
But when you look at it in details, a clock always uses motion to measure the flow of time. A clock always ends up measuring the position of something.
You are right that a clock measures intervals between events but what are those events? They correspond to position measurements.
a clock based on the rotation of the Earth is based on th eposition of something coming back to its initial position (a Foucault pendulum, the Sun, the stars, etc).
I just want to make sure that's clear because we've had people in here saying that who meant it literally. But a swinging pendulum clock, for example, does not measure how far the pendulum swings. The clock rate does not depend on the displacement, only the frequency of the motion.
This sounds like circular reasoning to me. The clock measures the frequency of what, exactly? Of something to repeat itself. But what is that "something", specifically? It is for the pendulum to get back to its initial position. So in the end, the measurement is one of position.
as far as I can see, the only thing we ever measure are positions. Now, som ethings repeat their behavior in what seems to be predictable manenr and we start assigning this extra quantity we call "time" to count those repetitive behaviors. And we insert this extra label to everything, but time is something added on to what we actually measure. In principle, we could, say, write all our physical quantities in terms of the *position* of some chosen system. For example we could write everything in terms of the position of a chosen pendulum in a certain gravitational field).
As far as I can see, everything boils down to measurement positions. Time is something we added as an extra label because it makes things so much simpler to calculate. There is *change* in the physical world and and it was convenient to introduce this extra continuous parameter as if there was this underlying structure that we could build on. But then relativity and quantum mechanics made us realize that this extra label is not as well defined as we once thought it was. And I think that modern approaches will eventually have to do away with time as a basic ingredient but this is just my opinion.