The principle of relativity tells us that all clocks must behave similarly and demonstrate identical time dilation. The advantage of the light clock is that it's easy to analyze.R Power said:This page http://en.wikipedia.org/wiki/Time_dilation clearly explains time dilation by exampling with the light clock. But how can it be explained if suppose there was a simple mechanical clock instead of light clock. So, now for moving observer there is no light (in light clock) to follow longer path and hence elongate one second but only a second hand that rotates.
You are right! but can you explain ? It will help me further understand time dilation.The principle of relativity tells us that all clocks must behave similarly and demonstrate identical time dilation. The advantage of the light clock is that it's easy to analyze.
I've tried it! In this case, second hand traces an arc at 6 deg/sec to show one second increment, so when an observer travels with speed of light c beside the clock, the second hand for him will trace the arc + the elongated distance (the locus will be a big arc) appearing due to motion of traveling observer(as in case of light clock light had to travel greater distance) but since velocity of second hand can't be "6deg/sec + c" with respect to traveler i.e it can't exceed speed of light..so it will take more time to trace 6 deg.I don't think there's any simple way of deducing time dilation using mechanical clocks, if that's what you're looking for. (At least I've never seen such a demonstration.)
R Power said:You are right! but can you explain ? It will help me further understand time dilation.
R Power said:What about my explanation in post #5?
I'm afraid that you confound gravitational time dilation with special relativistic time dilation; for a lucid discussion those are better not mixed up.questionpost said:I don't get what the problem is. Any clock measures time, so when the fabric of space is distorted, time will flow slower, and thus any clock measurement will be slower since the flow of events is slower proportionally to the gravity. Although I will admit I don't quite understand completely why the shape of a well actually makes time run slower, but we know that it does. That's why if you are in an airplane, your clock will run ever-so-slightly faster than clocks on the ground.
bahamagreen said:The request for an explanation is a good one.
If you take for granted that all possible clocks will be identically time dilated, then using the light clock as your generic clock in all subsequent though experiments is fine.
But all must admit that light is a very special entity with extraordinary properties, and if you are attempting to verify the universality of clock dilation in your own thinking before moving to just take it for granted, it makes sense to wonder what would be the effect on the actions of a mechanical clock - something with size and mass. It makes sense to wonder that different orientations of the oscillating and rotating parts of the clock might change their lengths and radii in one dimension, and therefore effect centers of mass, centers of rotation, and thereby effect linear and angular accelerations, etc.
This is not just "physical processes slowing down"... there are gross mechanical effects to account for, as well as smaller things in chemistry like molecular bonds, orbitals, and even smaller things, etc.
Surely someone has done this analysis and demonstrated that all these effects must balance out so that the mechanical clock may be replaced with the simple light clock without reservation?
R Power said:In case of light clock even, when observer travels at some speed, path of photon appears elongated to the moving observer now the velocity of observer should have been added to velocity of light which we know is not possible so the overall velocity of photon for the observer is constant i.e c (which causes dilation) but does this mean that photon has to slow its speed down in order to maintain total speed(photon speed + speed of observer) equal to speed of light?
The clock was relatively moving for the observer(for he himself was moving) and the photon in the clock which was traveling at speed c must now be moving with [ c+observer or clock speed] but that is not possible, so it travels with c. That means the photon in moving clock (to the observer) still travels with c for the observer which is only possible when the photon slows its speed down by an amount equal to the speed of clock (or observer) so that to observer it still moves with speed c.Consequently it is the observation of the observer that is altered by the observer's speed (together with his choice of clock synchronization), and not the photon which propagates unaffected by the observer.
To elaborate, it depends on the reference system that the observer chooses. Apparently you have him choose a system in which he is moving, which is less common in this kind of discussions; commonly one refers to a system in which the observer is in rest. In a system in which the observer is measured to have velocity v and the light velocity c, their relative velocity (in jargon "closing velocity") is the vector subtraction (c-v) - this is so by mathematical definition. As a matter of fact, that is also how GPS receivers calculate.R Power said:The clock was relatively moving for the observer(for he himself was moving) and the photon in the clock which was traveling at speed c must now be moving with [ c+observer or clock speed] but that is not possible, so it travels with c.[..]
Whether the clock is moving or the observer, its one hand same thing for the observer. I prefer taking observer to be mobile because if clock is moving (say at very high speed) then photon will not move along with clock and at some instance it will miss one of the reflectors. Moreover, the speed will be c+v (although that's not possible) which is why dilation occurs.To elaborate, it depends on the reference system that the observer chooses. Apparently you have him choose a system in which he is moving, which is less common in this kind of discussions; commonly one refers to a system in which the observer is in rest. In a system in which the observer is measured to have velocity v and the light velocity c, their relative velocity (in jargon "closing velocity") is the vector subtraction (c-v) - this is so by mathematical definition.
Sorry, that's simply wrong. Effectively you call "1+1=2" "not possible". Did you learn SR? A detailed presentation can be found in section 3 of:R Power said:Whether the clock is moving or the observer, its one hand same thing for the observer. I prefer taking observer to be mobile because if clock is moving (say at very high speed) then photon will not move along with clock and at some instance it will miss one of the reflectors. Moreover, the speed will be c+v (although that's not possible) which is why dilation occurs.
A vector addition isn't a system transformation - but these are often confused. In a single reference system, as Einstein phrased it in the section that I pointed at, "the ray moves relatively to the initial point of [the moving system] k, when measured in the stationary system, with the velocity c-v".questionpost said:It seems like the problem is how clocks measure time depending on their speed. If they are going fast, then relative to the speed of time, which is c, time flows slower, so to the clock other things would have time flowing at a faster rate and we wouldn't see the ticking go as fast, and with traveling very close to the speed of light, there's some property of space that only allows speed to increase in a sort of "asymtotic" way as to only come infinitely clsoe to c, so the way you add speeds in v=(u+a) in terms of vectors is only an approximation at low speeds, not high near-light speeds.
But in the light clock article, when the observer is moving the light should have traveled at c+speed of observer but according to STR its speed remains constant and hence dilation occurs. Thus basic velocity addition fails at speed of light.And of course, such basics of vector algebra has nothing to do with time dilation, the topic of this thread.
That "velocity addition" is a system transformation, as I already mentioned... moreover the "hence" confounds cause and effect (the observer's instruments cannot affect the light ray's speed!). And as you started with "but", it may be helpful if you can tell me why you think that the sentence that I cited from the SR derivation is not basic vector algebra.R Power said:But in the light clock article, when the observer is moving the light should have traveled at c+speed of observer but according to STR its speed remains constant and hence dilation occurs. Thus basic velocity addition fails at speed of light.
R Power said:But in the light clock article, when the observer is moving the light should have traveled at c+speed of observer but according to STR its speed remains constant and hence dilation occurs. Thus basic velocity addition fails at speed of light.
questionpost said:Isn't "velocity addition" not even the actual way your suppose to measurement and is nothing more than an approximation at low speeds? Why are people basing understandings off of it?
A.T. said:Another way to think about it: On the atomic level, a mechanical clock also depends on EM-force fields, in which changes propagate at c.
Saw said:the mechanical clock also suffers time dilation (as per the same pattern as the light clock) because a clock is a moving thing inside an enclosed space; the clock ticks when the moving thing bounces against the walls or otherwise changes direction. The cause for this "acceleration" is an electromagnetic interaction (light) or any another force that does its job in a manner that is analogous, at least for this purpose, to light.
This is a useless complaint because it applies to all of science. All science, including the principle of relativity, is a description of how nature works, not a reason why. If you are unwilling to accept such explanations then you do not want a scientific explanation.Saw said:the principle of relativity is a description of how nature works, it is not the reason why it works that way.
No. Circular reasoning would be something like: mechanical clocks time dilate, so by the principle of relativity light clocks time dilate, so mechanical clocks time dilate.Saw said:if we had found out TD first in mechanical clocks, we would then say that light clocks must conform to the same pattern or otherwise the principle of relativity would be broken. Isn't that circular reasoning?
It's not that no books at all ever mention it, for example it's just how Lorentz (post-relativity) and Bell taught physics in their books. However, regretfully it's a minority of books that values such physical, constructive explanations. IMHO, a good book provides both type of explanations.Saw said:[...] Why don't books ever mention this physical explanation? It is true that, if mechanical clocks did not suffer TD as per the same pattern as light clocks, the principle of relativity would suffer. But the principle of relativity is a description of how nature works, it is not the reason why it works that way. In this sense, it can be noted: if we had found out TD first in mechanical clocks, we would then say that light clocks must conform to the same pattern or otherwise the principle of relativity would be broken. [..]
Some of the greatest scientists of history were not satisfied with such lack of constructive explanations. Your suggestion that they did "not want a scientific explanation" doesn't make any sense to me; lack of explanation is not a scientific achievement. And his complaint is useful, as they suggested a solution which a few books do apply.DaleSpam said:This is a useless complaint because it applies to all of science. All science, including the principle of relativity, is a description of how nature works, not a reason why. If you are unwilling to accept such explanations then you do not want a scientific explanation. [..]
Can you provide an example? I am not aware of this. AFAIK, no "great scientist" has ever developed a scientific theory which was not a description of how nature works rather than a reason why it works that way.harrylin said:Some of the greatest scientists of history were not satisfied with such lack of explanations.
For example Newton, Lorentz, and likely Kepler. They did not consider such lack of explanation a scientific feature but instead as an incitement for further scientific investigation. For example, I read somewhere (sorry, don't recall where) that Kepler was himself not happy with his theory because he could not explain the "why"; one had to wait for the answer on Newton who provided a deeper level of insight (just one level deeper, as is usual with that kind of answers).DaleSpam said:Can you provide an example? I am not aware of this. AFAIK, no "great scientist" has ever developed a scientific theory which was not a description of how nature works rather than a reason why it works that way.