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What does a clock measure?

  1. Mar 12, 2008 #1
    All clocks measure the intrinsic motion of matter using a counter to assign a number to the present at the arbitrary rate of one per second. This allows us with a calendar, a circular table or chart, to relate to the past and plan for the future. This makes me wonder about matter, and how it exists relative to me, the embedded observer, in the present. I think of all intrinsic motion as a clock without a counter, and each observer as a clock and all the matter that makes up each observer as a clock. When we discuss time dilation are we not talking about matter and its intrinsic motion in the present? Does this mean there is time like properties of matter? Matter exists from the outside in, and I imagine that I see all the way back to the past the further inward I gaze, an inward look at the big bang maybe?
  2. jcsd
  3. Mar 12, 2008 #2


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    Clocks have to be periodic in order to tick, so I don't think all motion 'is a clock without a counter'.

    I can't make sense of any of these questions. Explain.
  4. Mar 12, 2008 #3


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    Clocks measure time via counting the known intervals between events in a cyclical/repetitive natural process.
    Some clocks measure motion, some don't. And the rate is rarely one event per second.
    Sounds more or less reasonable.
    We're talking about time and comparing time in different reference frames.
    Time is a dimension sorta like length and width, so I guess that would be like what you mean.
    That sentence really doesn't mean anything that I can discern.
  5. Mar 13, 2008 #4
    Clocks measure change. This can be change in distance (motion), change in energy (photon absorptions), etc. If nothing changes, then there's nothing for the clock to measure.
  6. Mar 13, 2008 #5
    Clocks dont measure change... a clock is somthing that was made for a function, we are the one's that see that function and we measure what we see and use it as a tool as it has allways been, but there are alot more implications of perception of the matter of what a clock dose. So to re-cap a clock measure's nothing and that nothing is somthing and that somthing is a preset gauge of entervauls of time that we measure and applie to the task thats at hand -.-
  7. Mar 13, 2008 #6
    allso nothing would be what we say it is or what we make that of which it is so hence forth it wouldnt be nothing it would be somthing that is nothing that is said -.- blame english lang and the mild perception of the words of the english lang for questions and answers such as this but i hope its to peoples liking and pass your time
  8. Mar 13, 2008 #7


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    Clocks measure the d/dt in all of those physics equations!
  9. Mar 13, 2008 #8
    Sorry, Noone, I hope that your post reflects only a language barrier, because I cannot make heads or tails of what you're trying to say. But to say that clocks don't measure change, well, I'd like you to tell me what they measure then if not change, and I'd like you to tell me how time could exist in a totally static universe.
  10. Mar 15, 2008 #9
    If you demand a physical interpretation then measuring time is counting events. If you presume nature has a most fundamental event of some sort it wouldn't need to be perfectly periodic by some absolute scale, but rather a mean value with respect to an inertial frame. If the mean value varied locally then it would be locally undetectable because all measures of space and mass/energy depend on this self referential time measurement for their definitions. Global anisotropies of these mean values would however be detectable.

    This interpretation has problems though. Primarily these problems can be summed up in the Robertson-Walker metric.
  11. Mar 15, 2008 #10
    To say that time is a measurement of change is true. Clocks only reguire a relatively constant rate of change or a predictably changing rate to be accurate. Thus, a clock can be anything that uses a rate (change over time). The rate of just about any change can be used as a clock, atomic decay, biological functions, orbitl motions, whatever....as long as the rate is constant or changing predictably, it will be possible to make a meaningful measurement of time in that frame or any other frame relative to it.
    So the answer to the question:

    "Does this mean there is time like properties of matter?"

    Yes, to fully describe interactions of matter it is necessary to describe all of its dimensions, one of those being time.
  12. Mar 19, 2008 #11
    I can't think of a clock without motion, can you give an example? The rate is different for all intrinsic motion, the second is relative to the motion of the earth, and the element cesium has over nine million events per second. The meson, is a clock with a lifespan that increases as it travels into a gravity well, do you think that the dilation rate set by its intrinsic motion is dilating as it travels into the earths gravity well?

    No I am talking about what a clock measures. The best thing I have found to describe the intrinsic motion that a clock measures, in my mind, are the laws of thermodynamics, it may be just me but every time I read them I think of clocks.
  13. Mar 19, 2008 #12


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    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.

    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.
    What is "intrinsic motion"? It sounds like an attempt at absolute motion. But a moving object is only moving when viewed by some outside observers. The only "intrinsic" thing about an object's motion is that it is always stationary with respect to itself.

    And that last sentence doesn't make much sense to me. What GR says about it is that time may pass at different rates in different reference frames.
    In the quote I responded to you said you were talking about time dilation.

    Clocks measure the passage of time. That's the definition of the word "clock".
    Last edited: Mar 19, 2008
  14. Mar 23, 2008 #13
    Clocks measure the quantity of time but are totally ignorant of its quality.
  15. Mar 23, 2008 #14
    Clocks are arbitrary delineations of periods, that's it really. Nothing more can be said unless you are talking about relative motion. Clocks do not measure this, they still measure delineations of periods, we however might notice that they differ in their periods, but the clock are pretty much measuring the same thing and are unaware of their surroundings or relative frames of reference. Ask yourself: what is time?

    Caesium clocks measure the decay of matter, the principal is the same as for a sundial as it is for a caesium clock, taking into account all relevant factors.
  16. Mar 23, 2008 #15
    Hello, S dog. You've given me a thought after reading your post.

    It might be instructive to see what happens if "clock" is replaced with "ruler". So I hope you can excuse the hatchet-job on your words.
    Yardsticks are arbitrary delineations of intervals

    ...we however might notice that a yardstick and a meter-stick differ in their lengths.

    Any instances where this replacement trick doesn't translate well should be the most interesting, such as a yardsticks measures d/dx.

    But a "Cesium yardstick" has me stumped.
  17. Mar 23, 2008 #16
    I'm not sure what you mean. But yes, in the same way as a clock measures d/dt I suppose if you want to put it in terms of a differential.


    Last edited: Mar 23, 2008
  18. Mar 23, 2008 #17
    If we compare measuring distance to measuring time, there is one big difference. To measure time, one will need energy. I have had the same meter stick for years and have never had to change the battery, because it was losing distance. But my clocks are different in that they all need some form of energy input. If there is not enough energy in the battery, it starts to lose time or stops measuring time, altogether. To me this seems to indirectly show a relationship between time and energy. It is sort of what one might expect since a photon has frequency and carries a quanta of time. This is sort of the photon's spring that contains all its potential energy. The wavelength is an artifact of the spring so it does not require energy to measure (assuming a meter stick).
  19. Mar 23, 2008 #18
    excellent! :rofl:

    So there are some notable differences between the measurement of time and distance. The Cesium clock still has me going. Another would be an "entropy clock" with a time interval based on how fast something cooled, say. The first is based on quantum statistics, and second on classical. I don't see any yardstick replacement for either of these.
  20. Mar 23, 2008 #19
    Precisely. Because time is a measure of _change_.

    If everything in the universe was in the precise state it was in 10 minutes ago, there would be no physical difference whatsoever between now and 10 minutes ago. No clock could possibly measure the time between then and now because there's been no change.

    And what is necessary for change? Energy. That's why clocks need energy, and distance measurements don't.
  21. Mar 23, 2008 #20


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    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).

    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.
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