no swansont...you don't have to "close the loop" to achieve time dilation.

and neither have i made a flawed clock.


both einstein and myself use a single set of inputs denoting a single leg of a light path (eg: a tick).

and the reason is because in this einsteinian model it is "a given" that the second leg (the tock) will be symmetrical with the tick...it is not required to repeat the exercise and then divide by 2.

being a model based on a symmetrical effect makes the exercise superfluous.

But when the direction of travel of the photon and the direction of relative motion are not perpendicular, the second leg is not symmetrical. That does not lead to a failure of Relativity, because Relativity does not depend on that symmetry.

In fact, as I said, Einstein's first mention of light pulses in his 1905 paper was in reference to pulses travelling parallel to the direction of motion. He specifically points to the lack of symmetry of the second leg as being indicative of the failure of absolute simultaneity.

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SeanF

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I didn't say you have to close the loop to achieve time dilation - you need to close the loop to measure it, i.e. make a clock. You need to answer the question of how the clock "knows" when to send the next light pulse in order for the clock to work.

The model does not depend on the symmetry, it's just done that way to make it easier to analyze. Do the analysis with the clock constructed as I described - and see for yourself: what is the elapsed round trip time for your last gif example, and what is it for the perpendicular case?

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SeanF

i did not say relativity relies on symmetry...i have instead pointed out that the gamma formula does.

swansont

that is also a given in einsteins method.

when the light pulse reaches a mirror...it reflects (and that's when it knows).


i can't agree...we have a formula (gamma) based on a rigid geometry that speaks only for a single leg.


@ 0.5C
*******************************
standard light-clock

1.155 + 1.155 = 2.31

*******************************
light-clock angled at 90dg (the gif you mentioned)

2 + 0.68 = 2.68

********************************

it doesn't match




i did another version for on paper for a light-clock angled at 45dg....it doesn't match either.

1.7 + 0.77 = 2.47 (roughly)

**************************

standard light clock = 2.31
one angled at 45dg = 2.47
and one at 90dg = 2.68


********************************
********************************
ps: if you read this reply shortly after i posted it you wouldn't have seen the last bits i wrote...somehow they weren't saved...so i've edited this post to include them (i think another app i was running interfered).

Then the information has to travel instantly to the emitter for it to "know" to emit another photon. How does it do that?



It does if you do it correctly. The other observer sees the lengths contracted by 0.866: 2.67 * 0.866 = 2.31

__________________
"I have a cunning plan that cannot fail."
S. Baldrick

madman,

First off, it should be clarified that the bouncing light pulse clock experiment was designed after-the-fact as a demonstration of the time dilation. It was not used to develop the original equations.

Read Einstein's original SR paper (it's available online here). You can see how all the equations were developed, and the symmetry of that vertical light clock is not required.

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SeanF

"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

The contents of this post are ©2008 by SeanF and may not be copied or retransmitted in any form without the express written consent of SeanF

swansont
no it doesn't.

you asked "how the clock "knows" when to send the next light pulse"

it is an automatic reaction in the experiment...light pulses reflect from the mirrors.

there is no "instant travel" effect.

look at anybody's example of a light-clock (including mine)....the light takes time to travel to a mirror...when it reaches it, it reflects.

so you are asking me to explain something that nobody else questions...and since there is no difference between mine and others'...i wonder why you are doing it?


there is no "other" in the exercise...there is just the one light pulse moving from mirror to mirror.

it takes 2 unit time periods to reach the first mirror..and then 0.68 unit time periods to "close the loop" by returning to the first mirror.

no "other" is required to "cast their opinion" on what happens.


but according to you, no time dilation is allowed to occur until we have 2 legs of a light clock...in other words time must "tick-tock" and not just "tick" along.

and so a single photon exchange is not good enough?

and then you need to bring in some observer as well?


swansont..explain why these details are not included in the gamma formula...if they're so important.

There are often several different ways to prove a theorem.

I still like the one I posted earlier on this thread, because it doesn't need more than one spacelike dimension, and therefore could be used in a onedimensional world.

I would also like to point out that all chemical and biological phenomena (like getting sleepy, waking up again, growing hungry, growing up, growing old) are built from electromagnetism (forces between charged particles moving inside atoms). And every electromagnetic phenomenon is governed by Maxwell's Equations. And if Maxwell's Equations must yield themselves in all inertial frames of reference, they must transform by the Lorentz Transformation. (If they don't yield themselves in all inertial frames of reference, the variable motions of our dwelling place around the Earth and around the Sun would work havoc with our bodies.) Therefore, the rates of all processes inside our own bodies will, in every inertial frame, have the same ratios to the rate of a clock made from a light pulse (or something else with speed C) bouncing up and down a tube. Because the rate of such a clock will also transform by the Lorentz Transformation.

As for the twin paradox, perhaps we should consider triplets. At the start of the experiment, one of them (Nicholas) is sitting in a fast northbound train, one (Simeon) is sitting in a fast southbound train, and one (Percival) is sitting on the platform of a station which both trains are going to pass at full speed (and at equal speeds).

Let us say that Nicholas flashes by the station first. Some time afterwards he will flash past Simeon, who is riding a train in the opposite direction. Some time after this Simeon flashes by the station. There are three encounters, and it's easy to see that the second encounter should come halfway in time between the first and the last.

At the start of the experiment, all three triplets have their wristwatches set to random times. As the pairs of triplets encounter each other, they do not synchronize their watches, they merely record any difference in the times they read. (And of course they will agree about this difference, because they read each others watches while they are next to each other.)

First, Nicholas encounters Percival, and they find that Nicolas' watch was reading, say, 16:03 while Percival's watch was reading 16:21. So, both record a difference: P - N = 18 minutes.

Next, Nicholas encounters Simeon. By this time, Nicholas' watch is reading 16:45, but Simeon's watch is reading 14:08. So, both record a difference: N - S = 2 hours, 37 minutes.

Last, Simeon encounters Percival. We already know that Simeon's watch will read 14:50. But Percival's watch is reading 17:55. So, both record a difference: P - S = 3 hours, 5 minutes.

Somewhat later, the triplets get off their respective trains and join at home to compare their results.

P - N (at the station) was 18 minutes.
N - S (somewhere north of the station) was 2 hours, 37 minutes.
P - S (at the station) was 3 hours, 5 minutes.

These differences don't add up. Juggling the numbers somewhat, the triplets find that Percival's watch ticked through 1 hour and 34 minutes while first Nicolas' watch and then Simeon's watch ticked through 42 minutes each, for a total of 1 hour and 24 minutes. Ten minutes remain unaccounted for.

The virtue of this way of rendering the twin paradox is that no wristwatch gets accelerated here; the triplets set their watches after boarding their trains and read their watches before leaving their trains again.

Madman, there is much more to Relativity than just time dilation. There's also Lorentz contraction and simultaneity disagreement to contend with.

Consider the simple case where a light pulse is sent from one point to another, then reflected back to the original point. We have three events. We'll call them:

A) photon emission (photon at point one)
B) photon reflection (photon at point two)
C) photon return (photon at point one)

In a reference frame that is stationary relative to the two points, the amount of time between A and B will be the same as the amount of time between B and C.

In a reference frame with relative motion along the line between points one and two - that is, parallel to the path of the light pulse - the amount of time between A and B will not be the same as the amount of time between B and C. One will be longer than in the first reference frame, the other shorter. This is due to the simultaneity difference, and is rather distinct from the time dilation.

In other words, what you are talking about is not something nobody ever noticed before. It is an inherent part of SR! In fact, if you will please read the Einstein paper I linked to, you will see that it's the first thing Einstein discusses.

The demonstration of time dilation usually uses a light clock arranged perpendicular to the direction of motion because then there is no simultaneity issue to contend with, so the time dilation is more readily apparent.

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SeanF

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Yes, it reflects, and has to return to the point of origin for the next pulse to be sent. You aren't doing that. One can build a clock where you have a detector at each end, and a new pulse is sent as soon as a photon hits the detector, but that will not work symmetrically (much like the counter for a pendulum clock could be set at some angle other than vertical - the round-trip time is the same, but the left side vs right side times would differ). To do a proper comparison, you have to be counting the round-trip time, which is equal for any orientation of the clock when relativity is properly applied to the situation.

I can't speak to anybody else's motive. Once the question has been asked, there is no need for anyone else to ask it again, unless you were to fail to respond. You are responding, though you are missing a crucial step. SeanF is also addressing this, but from a different angle - the asymmetry of the tick vs tock he is calling a simultaneity issue.


Of course there is an "other" observer - there is one at rest with respect to the clock, and one that is moving with respect to the clock (or sees the clock moving with respect to him). There is no time dilation within a single reference frame, it is always in one frame compared to another.

The person at rest sees one unit of time between the forward and backward transits of the photon, separated by a distance L. The person who sees the clock moving does not see the forward motion take 2 units, because the distance is not 2L, it is 2L/gamma because of length contraction. Similarly, the backward motion is not .67L - you need to divide by gamma there as well. Once you do that (i.e. properly apply relativity) then the round-trip times are equal for any orientation of the clock.

The reason you must "tick-tock" is because of the asymmetry that you have introduced, and I explained above. You have to do an apples-to-apples comparison of the elapsed time.

__________________
"I have a cunning plan that cannot fail."
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swansont
i told you why i didn't do that...because the exercise is symmetrical, the second leg would be a mirror image.

this is the same reason why it is not dealt with in gamma.


you've asked me to deal with asymmetrical effects too..and i am.



no....there's 2 mirrors (eg: atoms) and one light pulse.

the exercise produces time dilation by altering the frequency of transmission through velocity.

it is an inherent effect.




you have shown that if we only consider light-clocks that are aligned perpendicularly to the direction of motion...then all we require is the gamma formula to calculate the effect of velocity.

but if the light clock is angled at <>perpendicular...then we need a special observer to sit at some sweet spot and give us the thumbs up that it all "looks right to him".

You have a "special observer" in the first instance, too, madman. The term "velocity" has no meaning unless it is a velocity relative to something else. That "something else" is your "special observer" in both cases.

When the light pulse is perpendicular, there is no simultaneity nor Lorentz contraction to deal with, so you can use the simple gamma formula to get the time dilation.

When the light pulse is not perpendicular, then you do need to consider simultaneity and Lorentz, and so calculating the time dilation is more complicated.

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SeanF

"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

The contents of this post are ©2008 by SeanF and may not be copied or retransmitted in any form without the express written consent of SeanF

aye that's a very "special" observer.....even if it's just empty space you'll still use it as an observer.


swansont thinks of it as "a person" at rest with respect to the clock (even though i've been talking about actions at the atomic level).

SeanF calls it "a something else".

swansont clarifies by saying...."There is no time dilation within a single reference frame, it is always in one frame compared to another."

but that's not true....you only use that "something else" to clean up a supposed mess with asymmetrical effects.

and that's because you view simultaneity as a "preferred state".



did you ever consider it might be natural that the bulk of the effects be non-simultaneous experiences?.....like night and day?

and that you should not be forcing events to be simultaneous?

Have you considered providing us with some other actual observation or experiment that doesn't match SR's predictions (not a animation you've produced). Or maybe showing us in the actual paper where you think SR is wrong? Or is it just possible that the problems you think you've found may simple be a misunderstanding on your part?

__________________
Some try to tell me, thoughts they cannot defend,... - Moody Blues.

there's an interesting point made at the beginning (of the paper) that i thought might have some bearing on the concept of testing motion of a reference frame.

remember Relmuis' train example?...and the statement..."The Principle of Relativity states that no experiment done within the train can ascertain whether the train is standing still or moving at some constant speed in some arbitrary direction."

couldn't we take a strong magnet and place it on the floor of the train (as close as we can get it to the rails...which i take as being "conductors")

the magnet would express an electric field, betraying the fact that it is it that is moving...and not the rails.

The 'on a train' scenario means 'in a sealed chamber unable to interact with the outside universe'. there are all sorts of tests you could do to check the conditions of the world around, but that is not the point of the thought experiment. The point of the thought experiment is to say that if you are in an inertial frame and cannot see around you, you cannot find your velocity.

No, the point of the thought experiment is that you cannot say who is moving - all you can say is that the two systems are moving with respect to one another. You most certainly are allowed to interact with the outside world. If you have a magnet, you measure a magnetic field. You won't measure an electric field unless that magnet is moving with respect to you, but you get the E if you are moving with respect to the magnet, too.

__________________
"I have a cunning plan that cannot fail."
S. Baldrick