Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I Relativity's "time dilation" or clock accuracy alteration

  1. Jan 5, 2017 #1
    i've seen the double slit experiment and the delayed choice . my mind rejected the conclusion, but the experiment setting and configuration of delayed choice is rational and holds water so i accepted the experiment outcome even if it means the world isn't real.

    i had to give that intro that sounds irrelevant to the topic just to show that i'm open minded.

    Now, for the relativity and time dilation , my argument starts with the light clock, it's designed and calibrated to "count" time in certain conditions same as those large old classic pendulum clocks that are calibrated in certain conditions and they measure time faster in winter as the pendulum rod shrinks or slower during high atmospheric pressure and humidity but we dont age faster in winter nor slower in humid thick air, so why should we say so if a clock that uses different theory gave altered reading??
     
  2. jcsd
  3. Jan 5, 2017 #2

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    Technically, yes, but they're much more consistent and repeatable conditions than you get with a pendulum clock. Basically you need light bouncing between two mirrors in a vacuum. Under those conditions there is no variability at all in a light clock.

    We don't actually use light clocks as our best standard of time, we use atomic clocks, but they are similarly calibrated and controlled to minimize variability.

    I'm not sure I understand the issue. Relativity does not predict that we age faster in winter or slower in humid thick air. It predicts that we age according to the rate of an ideal clock (a light clock or an atomic clock is a close enough approximation to this ideal for all practical purposes) that follows the same path through spacetime.
     
  4. Jan 5, 2017 #3
    i agree, "we age according to the rate of an ideal clock" but when those clocks are moving faster, they are not ideal or accurate thus they give wrong reading , so it's not us that age in different rate
     
  5. Jan 5, 2017 #4

    Nugatory

    User Avatar

    Staff: Mentor

    It sounds as if you are thinking that relativity says that "a moving clock runs slow". That' not right, and that's not what relativistic time dilation says.

    We age at a rate that is in agreement with the rate of an ideal clock that is at rest relative to us, which is another way of saying "following the same path through spacetime as we are". The fact that we and the clock may be moving relative to something or somebody else is irrelevant: right now you are moving at 99.999% of the speed of light relative to someone somewhere in the universe, but that doesn't mean that a clock sitting on the table next to you is any less ideal.
     
  6. Jan 5, 2017 #5
    what i'm saying is that speed (relative or actual) only affect the clock reading. the clock malfunctions, a clock that depends on the speed of light on its calculation would sure mess up if it travel at speeds close to the speed of light
     
  7. Jan 5, 2017 #6

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    Look carefully at what I said: we age according to the rate of an ideal clock that follows the same path through spacetime. In other words, we age according to the rate of an ideal clock that is not moving relative to us. (The technical term for this in relativity is "proper time".) The fact that the rate of such a clock looks slower to someone relative to whom it is moving doesn't affect the rate at which we age.

    Also, the time dilation of a clock as measured by an observer relative to whom it is moving does not make the clock "inaccurate". As above, it doesn't change the rate at which we age, or at which the clock ticks, at all. It is just a "perspective" effect in spacetime, similar to the way an object's apparent size can change depending on the angle from which you view it.

    A light clock doesn't "depend on the speed of light on its calculation". It doesn't "calculate" a rate. It just uses the bouncing of light pulses off a mirror to determine a rate.

    Are you familiar with the experimental evidence for time dilation? It is at least as strong as the evidence for the quantum phenomena observed in delayed choice and double slit experiments.
     
  8. Jan 5, 2017 #7

    Dale

    Staff: Mentor

    We can build a variety of clocks using a variety of different frequency standards. If we find that some condition affects one type of clock but not others, then we would say that the clock was inaccurate under those conditions.

    However, if all clocks of all mechanisms are affected by exactly the same amount then we may as well say that time itself has changed. There would be no detectable difference between the two, and it is simpler than positing many different effects of the same amount.

    The time dilation of relativity corresponds to the second case. We have tested it with clocks based on EM, the strong nuclear force, the weak nuclear force, and gravity. All exhibit time dilation as predicted by relativity.
     
  9. Jan 5, 2017 #8
    1. the light clock sounds to depend on the speed of light (the light source, mirror and sensor...etc) if it's 150,000 km between the mirrors then the tick will tick after 1 sec (coz the speed of light is 300,000 km/s) thats my understanding of the light clock

    2. i'm familiar with experiment , i've watched different videos much more than i watched the delayed choice, even though the delayed choice more complicated. but maybe there's a catch, the experiment ignore that the light beam should be aimed in angle where the mirror is not there yet, but i assumed the experiment supposes that we aim the light in that certain angle.

    3. when i said the clock will not be accurate , that wasnt to an observer or someone beside it , just meant the clock will count the ticks erroneously.
     
  10. Jan 5, 2017 #9

    Dale

    Staff: Mentor

    The point of the light clock is that it is easy to analyze. Don't get too hung up on it. The fact is that we have tested clocks of many different operating principles. They all behave as predicted by relativity, regardless of if it is EM, strong, weak, or gravity, or a combination. The evidence really is quite comprehensive and varied.
     
  11. Jan 5, 2017 #10

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    The speed of light in vacuum is a physical constant, so saying the clock "depends" on it is saying the clock depends on something that never changes. What's the problem?

    Please give specific references. And not to videos: to textbooks or peer-reviewed papers. (PF has rules on acceptable sources, please review them.) I'm unaware of any such issue with the light clock thought experiment.

    And what is your definition of "erroneously"? Remember that, as Dale pointed out, all ideal clocks that follow the same path through spacetime will tick at exactly the same rate. Remember also that according to SR there is no preferred state of motion, so the fact that two clocks in different states of motion tick at different rates does not make one of them "erroneous"; it's just a physical fact that we need to deal with.
     
  12. Jan 5, 2017 #11
    oh... i only know of the one actual experiment done with nuclear watch , no gravity watch if that's the case then i fully accept the theory of dilation . and for now i would just blame the the mirror (light clock) for confusing me
     
  13. Jan 5, 2017 #12
    1. the light clock counts time by dividing the distance/speed of light (constant) but if distance changed then it gives different reading
    2 erroneously means count wrong to what it should count but dale said all sort of clocks gave the same time variation , so that solves the problem. apparently the hypothetical light clock example is not the best way to introduce someone to relativity and time dialation
     
  14. Jan 5, 2017 #13

    PeterDonis

    User Avatar
    2016 Award

    Staff: Mentor

    No, it doesn't. It counts time by the number of bounces off the mirrors. We calculate its behavior by dividing the distance between the mirrors by the speed of light, but the clock itself doesn't have to do that; it just works.

    And how are you defining what it "should" count? Whether you realize it or not, you are implicitly assuming that there is one preferred state of motion which defines the time a clock "should" count. But relativity says there is no such preferred state of motion. There is no one rate that a clock "should" tick at. There are just ideal clocks moving on their own paths through spacetime, and the time they count depends on the path.
     
  15. Jan 5, 2017 #14

    Dale

    Staff: Mentor

    Here is one of the best compilations of experimental evidence regarding relativity.

    http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

    Sections 4 and 5 are particularly relevant, but part of the scientific appeal of relativity is the amazing breadth and depth of data that it explains. A theory that would replace relativity would need to explain all of these results and more.
     
    Last edited: Jan 5, 2017
  16. Jan 5, 2017 #15

    morrobay

    User Avatar
    Gold Member

    It was my understanding that stationary clocks and traveling clocks , of any mechanism, all 'tick" at the same rate. Ie. time between ticks. And the travelling clock records less proper time because it traveled a lessor path distance in spacetime.
    That Δt' = Δt/γ is referring to total elapsed time.
     
    Last edited: Jan 5, 2017
  17. Jan 5, 2017 #16
    It's not a real clock, it's a thought experiment designed to demonstrate something about the way real clocks behave. It turns out that real clocks actually do behave this way.

    It's true that things don't age faster or slower as a result of the precision issues you mention concerning a pendulum clock. It's also true that things do age differently by precisely the amount predicted by the light clock analysis.
     
  18. Jan 5, 2017 #17
    It demonstrates that time dilation is a consequence of the invariance of speed ##c##.
     
  19. Jan 6, 2017 #18

    stevendaryl

    User Avatar
    Staff Emeritus
    Science Advisor

    The significance of light clocks is that it demonstrates that a particularly simple way of measuring time that works correctly according to one frame shows time dilation according to another frame. So comparing with a situation in which physical conditions (cold weather) affect a clock's behavior isn't appropriate. The moving clock versus stationary clock is not about two different physical conditions, it is the SAME clock, looked at from two different reference frames.
     
  20. Jan 6, 2017 #19
    i know that in any experiment that has more than one variable/input , we have to hold all variables to get the measurement we need. in the hypothetical/theoretical light clock,all components are sped up except for the light , causing the distance traveled to be longer and so it's time measuring device that's kinda designed to give different reading as it speeds up. it doesnt make sense unless it's a clock that doesnt count on light or electricity which i found by accident yesterday , what seems to be the undisputed prroof for time dilation , it's the muon measurement , not actually a clock but particles that should decay before it reach the earth as it gets born on higher atmosphere (and should live only around 22 microseconds) yet we receive it on earth..the particle lives longer due to its nearly speed of light. i now believe the theory but not its proof
     
  21. Jan 6, 2017 #20
    thank you for your patience , i'll look into that link and may return with more questions than i already still have :) . i cant absorb what i doubt and i tend to be skeptic or understand things through fighting it rather than getting along with it
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Relativity's "time dilation" or clock accuracy alteration
  1. Twins Paradox (clock) (Replies: 43)

Loading...