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Time difference in relation to elevation

  1. Apr 3, 2009 #1
    I have been thinking about the the experiment of 2 accurate clocks, one at ground level, and one elevated a the top of the tower, to show time dialation.

    I am a much better musician than I am an amateur physicist. And I understand the impact of pressure, rigidity, air pressure, and temperature have on musical instruments. If you take a drum, and start tightening the head, 2 things will happen. First, the pitch will go up when it is struck. The frequency at which that drumhead will resonate will increase. Second, the recoil or bounce of the stick will increase, as more energy is returned. My guitar hates it when I pull it from my 70F humid basement to a 85F dry porch. The tuning will change.

    Pressure, humidity, temperature, and gravity changes have a direct impact on mechanical devices and the frequencies they produce. This also applies to crystal oscillator used to keep time such as quartz. If this reliance on mechanical devices is to keep a frequency of time, how can this be deemed reliable?

    Could it be that perhaps the reason clocks that orbit the earth are slower is because the material they are built out of are susceptible to air pressure changes and gravitiational pressure changes that will occur as you increase altitude?

    In the twin paradox, twin A is out in space while twin B stays on earth, and 20 years later, twin A returns and might look younger because time slowed down.

    Now lets assume that mars had the same mass and atmosphere as earth. Would this apply if twin A camped out on mars for 20 years, or would they appear the same age again? The distance from them would be great.

    Should high altitude alternative cooking recipes really be labeled, "time dialation cooking instructions?"
  2. jcsd
  3. Apr 3, 2009 #2


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    Let me assume that by "time dialation" you mean "time dilation".
    Probably the effects you mention are relevant when producing mechanical clocks and undoubtedly people take them into account (for example, if you need a high-precision clock, you can link it with another clock to keep it synchronised and if you want you can even take into account the time needed to transmit the synchronisation signal).

    However, in physics, "time dilation" is usually meant in the context of special relativity, where it describes a fundamental effect of moving clocks running slower. There are two key words in that sentence. One is fundamental: a clock with no mechanical components at all (for example a light beam reflecting between to oppositely placed mirrors) would also experience it. The other keyword is moving: time dilation is an effect for clocks moving with respect to someone stationary. Just putting a clock at the top of Mount Everest would not be enough, however putting one in an airplane at that altitude would (and has been done, matching the prediction from special relativity).

    For the twin paradox which you mention it doesn't matter if A camps on Mars for 20 years or not, because - neglecting the relative motion of planets in the solar system - he would be stationary for 20 years with respect to B, so both of their clocks would tick at the same rate. The difference only occurs while A is moving with respect to B (and the paradox is resolved by the fact that not only he is moving, he is accelerating with respect to B).

    Satellites orbiting the earth are a bad example because they are also accelerating with respect to the earth.
  4. Apr 3, 2009 #3
    Sorry, yes I did mean dilation.

    I am reading Stephen Hawkings A Brief History of Time, and on page 43 it talks about 2 clocks on a water tower, and how Einstein's prediction was tested and the findings agreed with general relativity. It doesn't say that the above clock was accelerating.

    I have also read that this has been confirmed on commercial planes using caesium atomic clocks.

    Here is my question, are they measuring the light speed, or light frequency?
  5. Apr 3, 2009 #4


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    I would say that they are locking frequency.
  6. Apr 4, 2009 #5


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    No, but it is in a gravitational field, which is (locally) equivalent.
    This is a general relativistic effect, whereas the twin paradox is a is related to special relativity.

    This experiment involves both special relativistic (relative movement) as general relativistic (difference in gravitational potential energy) effects. It is commonly known as the Hafele-Keating experiment.
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