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Time & measurement

  1. Oct 16, 2009 #1
    This may seem like a silly question, so I shall offer my apologies in advance.

    I wish design an empirical experiment to show time.
    I should be able to use a stopwatch to obtain a time value, say 1 s.
    In order to show that the value which I have measured is not due to (my) bias, I must also devise a control.
    Using my heart rate (about 60 pulses/min = about 1 pulse/s) could I show that the stopwatch has actually measured about 1 s of time? - or would I have used the stopwatch to measure the approximate rate of my heart? - or conversely, used my heart as a clock to approximately measure a 1 s count of the stopwatch?

    Confusing!
    Can anybody suggest an experimental method allowing for an objective and empirical measure of time?
     
  2. jcsd
  3. Oct 16, 2009 #2
    Unfortunately your heart rate varies, so isn't a realiable time keeping device.
     
  4. Oct 16, 2009 #3
    True, though it is reliable enough for my purpose here. You may imagine using any device.

    The actual instruments used are irrelevant to me, it is the principle (objective test showing the passage of 1 s) which I am trying to understand.
     
  5. Oct 16, 2009 #4
    I guess you could have a look how atomic clocks work or how quartz crystal timers work.

    Atomic clocks work something along the line of measuring the time between radioactive decay which is constant for different isotopes. (not sure exactly, but you could google it)
     
  6. Oct 16, 2009 #5
    Is that in principle different from measuring the time between the swings of a pendulum?
     
  7. Oct 16, 2009 #6
    no, if you know what the gravitational acceleration is that is affecting the pendulum, you can get a reasonable accuracy of time.

    your heart beat is not objective, it does not beat as a result of some time dependant factor, so your heart rate can not be used to objectively measure time.
     
  8. Oct 16, 2009 #7
    Again, measurement precision does not concern me here.
    I am interested to find what is it that I am actually, objectively measuring.

    To make the dilemma clearer I have re-written the problem:

    I wish design an empirical experiment to show time.
    I should be able to use a stopwatch(a) to obtain a time value, say 1 s.
    In order to show that the value which I have measured is not due to (my) bias, I must also devise a control. Using another identical stopwatch(b), could I show that stopwatch(a) has actually measured 1 s?
    - or would I have used stopwatch(a) to measure the rate at which stopwatch(b) is running? - or conversely, used stopwatch(b) to measure a 1 s count of stopwatch(a)?

    I can not imagine that this is actually clearer! But there you go!
     
  9. Oct 17, 2009 #8
    The following definition of 'experimental control' is given by http://en.wikipedia.org/wiki/Experimental_control

    "Scientific controls are a vital part of the scientific method, since they can eliminate or minimize unintended influences such as researcher bias, environmental changes and biological variation. Controlled experiments are used to investigate the effect of a single variable on a particular system. This variable is applied to the treatment group in a controlled experiment. All other conditions besides this variable are applied to the control groups. Negative controls are designed to produce no result and positive controls are intended to produce the result expected in the treatment group. If both the treatment group and the negative control produce the result we know another variable acted on the experiment and the data is discarded. Similarly, if the positive control fails, we know there was something wrong with our procedure so we discard any results and begin again. If both controls behave correctly, we can confidently accept the results of the experiment as the effect of the desired variable. Scientific controls are vital because they ensure that data are valid."

    According to this definition, one may use three stopwatches (a)-dependent variable, (b)-positive control and (c)-negative control.

    During the time measurement experiment, as before, (a) and (b) are started at the same instants and stopped when the counter on (a) reads 1 s. (c) is not started but is 'stopped' at the same instant as (a) and (b), thus reading 0 s.

    As both controls have behaved correctly, we may confidently accept the results of the experiment as the effect of the desired variable (time).
    - or can we?

    Again, my question is: what has actually been measured here?
    - I fail to see that time has been made the dependent variable in this exp.

    - perhaps I'm wrong...
     
  10. Oct 17, 2009 #9
    I don't really get it. You can't do an experiment to test a clock against anything else apart from a better clock as a clock is a calibrated peice of equipment design to measure the passage of time.


    Contol groups are used where there are multiple variables, so eliminate unwated changes in an undesired variable. For example in drug trials, there are many variables within the bodt. So in drug tests they use:
    unhealthy people + medicine (test group)
    healthy people + medicine (as a control)
    Healthy people + placebo (negative control)


    A clock only has 1 variable, and you can control it. So there is never any need to have a 'control' watch or indeed any experiment at all. The entire exercise is totally pointless, that;s probably why you fail to see why time has been the dependent variable.


    The only way to measure time, is with something very regulat that doesnt rely on us measuring it.

    EG your heartbeat BPM is a useless clock for two resons.
    1. Your heart rate changes without you having any control over it. There mere fact taht you are thinking so hard about your heart beat will probably raise the speed of it.
    2. To know how fast its beating the beats are measures against a clock. The flaw of having a clock that is determined by a second clock should be obvious.

    A good example of a clock would be anything liek an atomic clock. Something that has a unique regular property.
     
  11. Oct 17, 2009 #10

    Dale

    Staff: Mentor

    The second is a unit of time defined as follows: http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html" [Broken] To determine if what you measure is a second you compare it to the defined standard.
     
    Last edited by a moderator: May 4, 2017
  12. Oct 17, 2009 #11
    "You can't do an experiment to test a clock against anything else apart from a better clock as a clock is a calibrated peice of equipment design to measure the passage of time."
    - it is exactly the 'passage of time' that I wish to measure objectively. I'm not interested in the subjective standard s.

    If I understand you correctly: when I measure time objectively using a clock as the instrument of measurement, what I am actually measuring is the clock's mechanism, i.e. nuclear decay or the swing of a pendulum.

    The clock's mechanism being calibrated against a subjective 'standard' measure.

    A clock only has 1 variable, and you can control it.
    - I assume you mean 'can not control it'?
     
  13. Oct 17, 2009 #12

    Yes, this is precisely what you are measuring.

    You can control it, thats the whole point of a clock. The only variable is what the mechanism 'counts' each time it 'ticks', which can be set by us.

    So there is no 'bias' with a clock mechanism, and therefore no need for control.


    However, If you compared a stopwatch to say an atomic clock. You woulds be measuring your perception of a second (if you could not see the display) or your reactions/anticipation if you can see the dial. I dont know if this is what you meant or not. If this is the case you are measuring you, not time.
     
  14. Oct 17, 2009 #13
    Thank you for your clarity Chris.
     
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