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Time confusion

  1. Jul 22, 2014 #1
    We measure time based off of atomic vibrations, so time dilation from gravity and velocity are nothing more than pressure applied to the atoms, slowing their vibrations.

    This isn't an accurate measure of what we consider time, but more of a measure of the reaction of atomic vibrations under pressure.

    Is this not true, and if so, why do we claim time dilation exists when what we are actually referring to is atomic movements?
     
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  3. Jul 22, 2014 #2

    edguy99

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    I think most time keeping with atomic clocks is based on using the microwave signal that electrons in atoms emit when they change energy levels. The frequency of the signal (or another way to put it "the time it takes to go through 1 complete cycle") represents a very accurate measure of time.
     
  4. Jul 22, 2014 #3

    Matterwave

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    This is very not true. Why in the world would moving at a constant velocity "apply pressure" to an atom? How does a gravitational force "apply pressure" to an atom? In what way, and why, would "pressure" affect "atomic vibrations"? Moreover, we define the SI unit second as X-number of periods of the radiation (emitted light) from two hyperfine levels of a Cesium atom. But we can measure time in many different ways. Anything that is periodic can be used to measure time basically. And under time dilation, ALL of these periods will be longer (as viewed by a different observer of course) than usual.

    Where did you read this?
     
  5. Jul 22, 2014 #4

    Simon Bridge

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    We can measure pressure in a crystal. If time dilation was a result of pressure, then you could tell what absolute speed you are doing by measuring the pressure in the crystal.
    You'd also have to explain why the pressure bears that exact relationship with relative speed, how it results in the established twin's paradox, why the pressure appears only in clocks and nothing else, and why different crystals with different materials show exactly the same response under the pressure?

    Then - there are different ways to build clocks, and yet the clocks that do not depend on vibrations in crystals agree with the crystal vibrations. So this "pressure" would have to act the same way to change the rate of nuclear decay and the way light travels.
     
  6. Jul 22, 2014 #5
    Yes, but the electron movement is also affected by pressure. The resonance frequency would change under different conditions. This difference is what we are measuring when we do all the time dilation experiments. Correct?
     
  7. Jul 22, 2014 #6

    Matterwave

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    No, incorrect. Motion at a constant velocity does nothing to the pressure of a system.
     
  8. Jul 22, 2014 #7

    I didn't read this anywhere, really, but let me think about what you said. I may just be missing a basic concept somewhere.
     
  9. Jul 22, 2014 #8

    Simon Bridge

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    One of the principles in ckassical physics is that inertial reference frames are equivalent - in Newton's physics, this means that absolute velocity cannot be determined. You have probably already heard this. (Acceleration can result in a pressure.)

    There are crystals which vibrate differently when they are put under pressure - the pressure squashes the crystal changing the spacing between the atoms.

    If a constant velocity produced pressure, then it would be possible to tell what velocity you are going by observing the way the crystal changes it's "tone". It's a simple experiment with cheap components... observing that tone-change would overturn hundreds of years of established physics.

    But that's all Galileo and Newton stuff - special relativity is odd isn't it?

    In special relativity, the "time dilation" is what one observer sees of another observers clock.
    If Alice and Bob are moving as relative speed v, the A will see B's clock time dilated and B will see A's clock time dilated. Neither notice anything special about their own clocks.

    i.e Bob could look at Alice and, not knowing about SR, could deduce that there is some influence on Alices clock making it slow down. He could assume that Alice's clock is under some sort of pressure and, after a lot of experiments, work out how the pressure varies with speed. This would be a valid way to investigate the phenomenon.

    This does not prove the clock is under pressure from the speed - it just investigates the relationship between the observed dialation and the speed. The trick in science is to try to come up with an experiment to disprove the idea that speed produces a pressure.

    The first sign comes when Alice is stationary and Bob is moving - Bob still sees the same time dilation happening to Alice's clock! In order to feel the right amount of pressure to show the right amount of dilation, Alices clock needs to know how fast Bob is going. How can this be?

    So Bob asks Alice about it - it's her clock so she should know what's "really" going on. But Alice denies that anything funny happened to her clock. Instead, she says, it is Bob's clock that has been running slow all this time.

    We check all these things with atomic clocks, and verify the resulting models with other clocks - like the half-life of muons. Have you seen the Mt Wellington muon experiment?
    http://www.scivee.tv/node/2415
     
    Last edited: Jul 22, 2014
  10. Jul 22, 2014 #9

    ghwellsjr

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    I'm sure you know that observers cannot see the Time Dilation in a distant moving clock but the OP may be confused by your statements. In fact, if the two observers are moving toward each other, they will see each others clock running faster than their own.

    Don't you think it would be better to point out that Time Dilation is a coordinate effect and is dependent on the speed of the clock according to a particular coordinate system and has nothing to do with what any observer actually sees or observes? In fact, just like we can transform any scenario from one frame to another and change all the speeds of the various observers and their clocks, we are also changing the Time Dilation on their clocks but what they can see does not change.
     
  11. Jul 23, 2014 #10

    Simon Bridge

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    It would be better to use a more precise statement yes.
    The trick is not to describe what time dilation is, but to describe why the OPs description is not it.
    It is very common at the level that OP is writing at to talk about someone "sees" another's moving clock as a kind of shorthand. It is usually more effective to buld on what the student already knows than to completely change a paradigm.

    But we'll see.
    In these forums there are many people able to put forward different approaches so one person has to do all of them ... if nobody else was replying I'd be more concerned ;)
     
    Last edited: Jul 23, 2014
  12. Jul 24, 2014 #11
    what if time moves independent of motion. and motion is independent of distance.
     
  13. Jul 24, 2014 #12

    Matterwave

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    What?
     
  14. Jul 24, 2014 #13

    Dale

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    This site is about learning and understanding the current professional scientific explanations of time dilation and so forth, not about coming up with new explanations.
     
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