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Einstein notion of time and the oscillation of the cesium atom

  1. May 23, 2013 #1
    I just read the thread entitled: "How did Einstein Define Time" and I'm very confused.

    At school, I was taught that time was an abstract representation of movement meaning that the word "time" can only be used to represent movements.
    For example, when earth has completed a cycle around the Sun, that is called "one year". So in this example we see that the "one year" (concept of time) represents a movement (the cycle of Earth going around the Sun).
    So the definition of time for me has always been that it's an abstract representation of some movement and nothing else.

    Now, in the Hafele–Keating experiment where Cesium atomic clocks where used to test Einstein's theory of relativity, they state that the clocks going eastward in the airplane jets "lost time" and the clocks going westward "gain time". These conclusions (of clocks gaining and losing time) can only be considered in regards to a specific definition of the notion of time which I think Einstein has lacked to provide. One thing is for sure, considering the definition of time that was taught to me, it is absurd to think that a clock can gain or lose time, it just makes no sense at all.

    What does makes sense tough is that while the air plane jets goes eastward, the speed of the cesium atoms oscillations slows down and when the air plane jets goes westward, the speed of the cesium atoms oscillations increases. But that's it !!!! Nothing else can be said about that experiment. The jet planes moving eastward or westward has absolutely NO direct effect on the clock, they only affect the speed of oscillation of the cesium atoms and it is that speed of oscillation of the cesium atoms that's speeding or slowing the clock !!! So the "time" shown on the clock is totally dependant on the speed of oscillation of the cesium atom.

    For Einstein to say that the clocks are "losing or gaining time" relative to those clocks travelling at some speed is to make a direct relationship between "time" and the speed of the oscillation of the cesium atoms. So why bother confusing people using the word "time" instead of simply saying things as they are: "it is the speed of oscillation of the cesium atom that is relative" ?

    Time is NOT relative to anything unless your definition of time is : "the speed of oscillation of the cesium atom" !!!

    I think that Einstein biggest problem was to talk about time without ever giving a specific definition of what he considered time to be. He gave the definition of: "time of an event" but that's different from the notion of "time" alone by itself.

    Does my above explanations makes sense to anyone ?

  2. jcsd
  3. May 23, 2013 #2


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    The second is defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom". This is in the reference frame of the cesium atom. If you took two cesium atoms, one on a flying jet and the other on the ground, by the time the atom on the ground produced 9,192,631,770 periods of radiation the one on the jet will have produced say 9,192,631,769 periods of radiation. This is because the atom on the jet experienced less time compared to the atom on the ground.
  4. May 23, 2013 #3
    There is indeed a difference between time as something that locates an event in space-time ("coordinate time") and time as something measured by clocks ("proper time"). Einstein understood—as do all physicists who are now acquainted with relativity—the difference, specifically that only the latter is physically significant, and was very clear on this point.

    That is not what happens. According to either reference frame, time is running slowly in the other frame. This is possible precisely because of the difference between coordinate and proper time. However, when all the clocks are brought back together for comparison, it is found that different amounts of proper time elapsed for each.

    It doesn't matter what physical process you define time to elapse by. It is not just the Cesium clocks that disagreed with one another. Any clocks aboard one jet would have disagreed with clocks on the other jet by the same amount, were they precise enough. The pilot who flew eastward aged less than the pilot who flew westward by the same amount as the two clocks disagreed. Note that were also general relativistic effects that had to be taken into account (gravity also causes time dilation) but the overall effect was the same as that predicted by special relativity alone. Time dilation isn't something that just happened to the atomic clocks; it happened to every dynamical process.

    Of course, it's always good to bring a critical eye to new concepts since that often brings better understanding; however, I think you have the wrong attitude. You're not going to disprove Einstein—if indeed he is wrong—without many years studying advanced physics. I'm sorry, but it's just not going to happen. I understand that these are challenging ideas because they're so different from every day life. However, these are ideas that have withstood some very critical inquiry by some very smart people for a long time, and you're not going to get anywhere if you decide right off the bat that these ideas are wrong. You just have to accept that you might not always understand things as well as you might like. If you do that, perhaps it will motivate you to work a bit more at it until they do make sense. We all went through it. On the other hand, folding your arms and going, 'Hmph, well Einstein was wrong,' will not lead to understanding.
  5. May 23, 2013 #4


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    Why is it absurd? The definition of time according to you is "an abstract representation of some movement". To the best measurements possible today, any movement that you would care to measure slows down the same amount as the atomic clock. So in what sense is it absurd under your own definition of time?

    I think that you are having a visceral reaction to the idea of time slowing down, rather than a reasoned response. It is understandable, I think that every student of relativity has faced that same reaction at some point. It is counterintuitive, but the data supports it very strongly.
  6. May 23, 2013 #5
    You seem to be ignoring the fact that speed is a function of position (magnitude only) over time. So any change in speed means that there was either a force exerted or something not quite right with perceived time. Einstein defined time as a part of a fourth dimension cT. An observers perception of time varies based on their relative speed to each other.
    The interesting thing is how the two clocks observe the other.
  7. May 24, 2013 #6
    QuantumPion, what is your definition of "time" ? I cannot understand objectively what you're saying when you mention that the atom on the jet experienced "less time" (I understand where you want to bring me with this explanation but it still makes no sense to me).

    On the other side, I think I've come up with an (probably not doable but interesting) experiment that could maybe prove that “time being relative” is simply a misunderstanding of what is really going on. I hope this doesn’t sound pretentious; I’m open to any suggestion.

    Let's assume we’re measuring Earth position (around the Sun) in the precision of a billionth of a meter, let’s say Earth is at position (x1,y1,z1), and at the same moment (in regards to Earth position) we’re taking note of the “time” displayed on the reference atomic cesium clock on Earth. We then ask 2 air plane jets (having on board atomic clocks that’s showing exact same time as the reference one on Earth) to take off (one Eastward the other one Westward) and after, let’s say, 48 hours of flight (Earth position measured to be (x2,y2,z2)) we press on a button that would stop all three clocks (the one on Earth, the one in the plane going Eastward and the one on the plane going Westward) at the exact same moment, what will each clock show?

    First of all, QuantumPion would probably argue that this experiment resembles very much the Hafele–Keating experiment. One of the difference being that the clocks in the Hafele–Keating experiment were never stopped but only compared to one another after the experiment.
    The reason why I would stop all 3 atomic clocks at exactly the same moment (let’s assume that’s possible) is that I would want to see if the “time” displayed on the 3 atomic clocks are different taking into account that they have been running for THE EXACT SAME AMOUNT OF TIME. I’m putting emphasis on the fact that all 3 clocks ran for THE EXACT SAME AMOUNT OF TIME before they were stopped and no one can argue that. Why? Because the time that has elapsed between Earth position (x1,y1,z1) and position (x2,y2,z2) can only take one unique value. Also, we made sure that when Earth is at position (x1,y1,z1) all 3 clocks showed exact same time and we also made sure that when Earth arrives at position (x2,y2,z2) all 3 clocks are stopped at precisely the same moment. So this necessarily implies that the 3 clocks have all experienced THE EXACT SAME AMOUNT OF TIME.

    This experiment resemble so much the Hafele–Keating experiment that I’m 100% confident the results would be the same: the clock going eastward in the airplane jet would seem to have "lost time" and the clock going westward would seem to have "gain time" compared to the reference atomic clock on Earth. But that doesn’t mean time is relative. What the LCD screen of the atomic clock is showing is something very different of why it’s showing what it’s showing.
    The argument of QuantumPion, following the Hafele–Keating experiment, is that “the atom on the jet experienced less time compared to the atom on the ground” is now, in my experiment, totally invalid because all Cesium atoms (on Earth, on plane 1 and on plane 2) have experienced THE EXACT SAME AMOUNT OF TIME like I explained above. That being said, what could now possibly explain why 3 clocks don’t display the same “time”? Well it’s so obvious to me at least: the ONLY explanation is that the speed of oscillation of the cesium atom has been perturbed during the flights. During the Eastward flight, the speed of oscillation of the Cesium atoms has decreased and during the Westward flight, it has increased.

    This increase or decrease of the speed of oscillation of the Cesium atom makes a difference in what is sent to the LCD screen of the atomic clock. Why? Because the electronic board of the atomic clock is programmed to add a second to the time displayed on the LCD screen only when it counted a precise number of periods of the cesium atom (9,192,631,770). So if the speed of oscillation of the cesium atom slows down, like in the scenario where the air plane flew eastward, it then takes more time for 9,192,631,770 periods to occur resulting in the clock giving the impression of “slowing down” or showing to have “lost time” which is not the case. For the other scenario where the air plane flew westward, the speed of oscillation of the cesium atom increased, it then took less time for 9,192,631,770 periods to occur resulting in the clock giving the impression of “speeding up” or showing to have “gain time” which is also not the case.
    In the above explanation, I took into assumption, of course, that the definition of “time” is the one I learned in school in which “time” is only an abstract representation of movements. If you take any other definition of time, all the explanations above make probably no sense. It’s interesting to see that it all comes down to definitions!!!

    One last thing, they say the GPS systems are programmed to take into account the theory of relativity. What I think is really happening is that the GPS system in the satellites compensates for the increase or decrease of the cesium atom oscillations (depending on the direction the satellite is moving), that's it !!! These GPS system need to be synchronized with atomic clocks on Earth and since the speed of oscillation of the cesium atom is modified on a satellite moving at high speed, if no correction is made, the GPS system on the satellites would lose their synchronization with atomic clock on Earth. But again, this correction (on the GPS system on the satellites) has nothing to do with some fancy notion that, at high speed, "time" is modified. Time is never modified, the GPS system is only compensating for the cesium atom oscillation that is perturbed by satellites moving at high speed.

    I'm opened to all comments or suggestion. If you want to throw at me that all of this is crap, you might as well. I'm a truth seeker and I don't believe in any magical non-sense explanation too many times offered by actual science.

    jonathan azoulay
  8. May 24, 2013 #7


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    Which one? The ones at Greenwich tick at a different rate than the ones at Boulder due to the difference in gravity at different altitudes.
    The GPS system is set up to keep track of a time that no actual clock ticks at.

    You haven't been reading the previous posts carefully. You're dreaming. If you want your ideas to be taken seriously, you will have to decide which clock in the universe is going to be the standard and you're going to have to convince every one else in the world why your choice should be taken seriously.

    Simple question: which clock is going to be the standard?
  9. May 24, 2013 #8


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    You can't do this if the clocks are spatially separated. More precisely, if the clocks are spatially separated, stopping them "at the same moment" will be frame-dependent; it can only be done with reference to one particular frame.

    Yes, and the whole point of doing that is to take away the frame dependence; the clocks are all at the same spatial location both before and after the experiment, so any difference in the amount of time elapsed on them is an invariant--it's the same in every frame.

    Bad assumption; it's not possible. See above.
  10. May 24, 2013 #9


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    You sure used a lot of words to ask what happens if we stop a clock on a plane after 48 hours of flight. It's a good idea to keep things short if you want people to read your posts.

    The answer is that it depends on whose 48 hours we're talking about. If we stop the clock after 48 hours has elapsed on the plane, then the answer is obviously that the clock will show that 48 hours has passed, because we simply chose to stop it when it displayed that number.

    But if we wait until a clock on the ground shows "48 hours, minus the time it will take a radio signal to reach the plane", and then send a "stop the clock now" message by radio to the plane, then the clock on the plane will stop before it has reached 48 hours.
  11. May 24, 2013 #10


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    Yes, it does come down to definitions and your definition is the one that leads to relativity unless you want to limit it to the movement of the atoms in a single atomic clock.
  12. May 24, 2013 #11


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    Then you are contradicting yourself. The oscillation of a cesium atom is every bit as valid a movement as the motion of the earth around the sun. If you consider the latter to be an accurate measure of time then why not the former? You need to use some logic, not just your emotional reaction. You cannot logically say that time is an abstract representation of movements and then escape the inevitable conclusion that time slows down for a clock in motion.
  13. May 24, 2013 #12
    I'm indeed not a specialist of Einstein theory. I still wish to understand his definition of "time" and time only. Maybe that would be the basis of my understanding of his theory.

    I found this interesting article on the web (A NEW INTERPRETATION OF THE HAFELE-KEATING EXPERIMENT): http://www.shaping.ru/congress/english/spenser1/spencer1.asp

    thanks again for all your comments,
  14. May 24, 2013 #13
    I would encourage you to read Einstein's original paper on special relativity. There's nothing particularly hard about the definitions, the concepts, the reasoning, or the math. Special relativity is simple and obvious. If you read the paper and still don't get it, it's because you don't want to get it and you are trying very hard not to. I can't help you with that.

  15. May 24, 2013 #14


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    In that case, time is a more general concept than you were taught. It has meaning even in situations where no movement is involved.

    Example: a muon at rest lives for about 2 microsecs, and then decays into an electron and a pair of neutrinos. A muon does this without the need for a pocket watch!
  16. May 24, 2013 #15


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    You should read section 1 of the paper mrspeedybob linked to.
  17. May 24, 2013 #16
    I have a side question to the OP.

    In a few replies I read that time is thought to go either faster or slower in the examples given. However, is it not more appropriate to say that time is either a shorter or longer number relative to some entity that is in faster or slower motion ? That is, if some entity has faster relative motion up to limit of speed of light then time is relatively shorter; conversely, if entity has slower relative motion time is relatively longer. For an entity in motion at speed of light such as photon, time reaches the limit of the concept slow, e.g., time stops. Some help with this appreciated.

    Edit: To support my suggestion that it is the entity, and not time, that moves slow or fast, we read in his 1905 paper that Einstein said this..."hence we conclude that a balance-clock at the equator must go more slowly, by a very small amount, than a precisely similar clock situated at one of the poles under otherwise identical conditions." Clearly Einstein claims that the entity, the arms of clock, 'must go more slowly'...not that time must go more slowly. Thus, as the clock arm must go more slowly, time must be longer.
    Last edited: May 24, 2013
  18. May 24, 2013 #17


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    Azoulay, one thing that might help the conversation is to distinguish coordinate time and proper time. These are two different, but related, concepts. Proper time is essentially the time as measured by some clock, and it is considered to be the "length" of the clocks path through space-time, and it is only defined on that path. Coordinate time is a number that is assigned to an event to describe when the event happened, events with the same time coordinate are simultaneous.

    It is an experimental fact that if you set up a coordinate system according to Einstein's convention, then any clock's proper time is slow compared to the coordinate time if that clock is moving in that coordinate system. It is also an experimental fact that if two different clocks take different paths through spacetime between the same pair of events that the amount of proper time they experience may be different.
  19. May 24, 2013 #18


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    That is Einstein's way of saying that time goes more slowly. Remember his definition of time from section 1. He defined time as the pointing of the hands of a clock, together with a simultaneity convention.
  20. May 24, 2013 #19
    Thank you. Yes, I read that, but Einstein also presented the concept of the time interval related to light path and velocity. By definition, along any path, an interval measurement (such as time) would be long or short, and a velocity measurement, slow or fast. Consider a horse race, and the second place horse is one track length measurement behind winning horse. Do we not say the second horse was slower than the first because it took a longer time to reach the finish line ? I do not see why Einstein would grant 'time' as a concept the same physical status as 'horse' and say that both move slow or fast ? Sorry for being so dense.
  21. May 24, 2013 #20


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    Of course. It would be hard to have velocity without time.

    The words slow and fast do not exclusively refer to velocity. You can have a song with a slow or fast beat, nothing has a higher velocity. You can have slow or fast chemical reactions, but no higher velocity (at least not macroscopically).

    Slow and fast refer to rates of change wrt time. It can be the rate of change of position or volume or chemical concentrations.

    Time slows down because the rate of change of proper time wrt coordinate time goes down.
  22. May 24, 2013 #21


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    Is there any entity, according to your suggestion, that we can use to keep track of time?
  23. May 24, 2013 #22
    But, because the rate of change of proper time wrt coordinate time is SLOWER (e.g., goes down), time is LONGER for the clock that measures proper time wrt the clock that measures coordinate time..correct ?
  24. May 24, 2013 #23


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    All clocks, by definition, measure proper time.
    There's no such thing as a clock that measures coordinate time (except in the trivial sense that there is always some coordinate system in which the coordinate time between two events is equal to the proper time between them, so the clock measuring proper time will happen to report coordinate time in that coordinate system, for those two events).
  25. May 24, 2013 #24


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    I don't know what you mean by longer. The English doesn't matter, what matters is the math. If τ is the proper time on a clock and t is the coordinate time in an inertial frame where the clock is moving then dτ/dt is less than 1. Call that what you will in English.
  26. May 24, 2013 #25
    Is this a trick question ? I'll assume you are asking about entities internal to humans, and not clocks, etc ? Not sure how humans internally keep track of time. However, there is a gene in some plants called ELF4 that allows the plant to keep track of time based on day length, long periods of daytime vs short periods. For a plant, the amount of time that the sun shines in a 24 hour period is NOT fast or slow, it is long or short duration. The only suggestion I make is that time is not a measure of fast or slow wrt to motion of entities, it is either (1) a measure of long or short, or (2) a measure of many or few, depending on what sense of time is being discussed as relates to motion.
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