Hurkyl said:
Don't complain about a statement being vague if you don't want to see it written more precisely.
Shall I try again? τ is the time on the clock under analysis, and t is the time given by the coordinate system.
Are you serious that you would like to see a derivation, or are you trying to deflect attention from the fact that you offered to try and prove something first, and have yet to make that attempt?
I really am serious. I know what has to be done to accomplish the proof. The first step is going to be to derive the time dilation formula. What is going to happen, is that you will set up two coordinate systems in relative motion at speed v. Then we can constantly refer to the way you set up the coordinate systems in order to make comments about the times in either system.
I tried to search the web for the exact derivation I am referring to, so that neither of us would have to repeat the work, here is a site that uses the derivation I am referring to, but I don't like the guy's symbolism.
Derivation Of The Time Dilation Formula
Here is the specific experiment (an experiment to measure the speed of light) we will need analyzed:
You are going to make a measurement of the speed of a photon. The photon is going to be fired from a photon gun, straight to a mirror, and then be reflected back to you. So you have a clock (clock A) at rest in this lab frame F1 which will mark the precise moment the photon is emitted, and the precise moment the photon returns. Denote this time by \Delta t. Now, you have a ruler set up just sitting at rest in the lab frame. It runs from the photon gun to the mirror. Let the distance from the photon gun to the mirror be measured to be D. Thus, the total distance the photon travels is 2D. Let c denote the speed of the photon in this frame. Thus, the speed of the photon in F1 is by definition:
c = \frac{2D}{\Delta t}
Now, consider this event as viewed from a reference frame F2 which is moving at speed v relative to F1. In this frame, the path of the photon is not a straight line, but rather the path is triangular (that is how the pythagorean theorem enters the derivation). Let it be the case that if you are at rest in F2, that you see the photon gun moving from left to right. So you see the photon travel diagonally upwards until it strikes the mirror, and then diagonally downwards until it strikes clock A(which is attached to the photon gun). There is a second clock (clock B) at rest in F2, and let the time it takes the photon to move from the photon gun to the mirror and back to the photon gun in F2 be measured by clock B to be \Delta t^\prime
Thus, the total distance traveled by the photon in F2, is the sum of the two sides of an isosceles triangle. Let the side length of this triangle be denoted by S. Thus, the total distance traveled by the photon in F2 is 2S. Let c` denote the speed of the photon in F2. Thus, the speed of the photon in F2 is by the same definition as before:
c^\prime = \frac{2S}{\Delta t^\prime}
Now, the base of the isosceles triangle is the product of the relative speed v between the two frames F1,F2, and the total time it takes the photon to strike the mirror and return to the photon gun, as measured by clock B. Thus, the base of the isosceles triangle is:
v \Delta t^\prime
This is certainly enough information for you to use the pythagorean theorem to derive the time dilation formula. The height of the isosceles triangle is D, hence the following equation is true:
S^2 = D^2 + (\frac{v\Delta t^\prime}{2})^2
In the derivation of the time dilation formula, the fundamental postulate of the special theory of relativity is invoked the moment you equate c with c`. In classical mechanics they are unequal, in SR they are equal by hypothesis. The exact equation you get (by hypothesizing that c=c`) is:
\Delta t = \frac{\Delta t^\prime}{\sqrt{1-v^2/c^2}}
Once that is done, all quantities in the formula are clear. Once you have carried out the derivation, more discussion will be necessary. Let me show you the logic I am after by asking you to do this for everyone:
Fundamental postulate of SR: The speed of a photon in any inertial reference frame is c=c`= 299792458 meters per second. (Keep in mind that in the derivation both F1, AND F2 are inertial reference frames. F1 is inertial by stipulation, and since F2 isn't accelerating relative to F1 and F1 is inertial, it follows that F2 is inertial.
Here is what is being perfectly proved:
Theorem(contingent knowledge): If the fundamental postulate of SR is true then (\Delta t = \frac{\Delta t^\prime}{\sqrt{1-v^2/c^2}})
Now, at this point reason alone cannot yet determine whether or not the fundamental postulate of SR is true. More reasoning will have to be done.
In order to prove that the fundamental postulate is false, you now have to prove the following theorem:
Theorem(contingent knowledge): If the fundamental postulate of SR is true then NOT(\Delta t = \frac{\Delta t^\prime}{\sqrt{1-v^2/c^2}}).
At that point you will have proven the following:
There is at least one statement X, such that:
Theorem(contingent knowledge): If the fundamental postulate of SR is true then (X and not X).
At this point, you can now prove the following:
Theorem(Absolute knowledge): The fundamental postulate of SR is false.
The main purpose of this excercise, is so that we can both have the same exact thought experiment in mind simultaneously, using the exact same letters to denote the variables and constants which are crucial to the time dilation formula.
Kind regards,
StarThrower
P.S. Here is a possible
enstasis(enstasis is a greek word and means objection). For the appearance of mathematical terms like postulate, lemma, enstasis see Heath's translation of Euclid.
Enstasis:
Clock B is at a fixed location in F2, and the photon gun only passes near to clock B once during the event.
Solution: Let there be a third clock (clock C) which is also at rest in F2. Let the photon leave the photon gun at the precise moment when the apparatus passes by clock B, and let the photon return to the gun at the precise moment that the apparatus passes by clock C. Thus, observers at rest in F2 will know the clock readings of clocks B,C at the moment the photon gun passed them. Let clocks B,C have been synchronized. Thus, the time \Delta t^\prime can be computed by subtracting the reading of clock B from the reading of clock C.
Additionally, let it be the case that all three clocks are of identical construction, therefore they all tick in the same unit (let the unit of time on these clocks be the second). Since all clocks are of identical construction, we can be certain that they have the same rest rate (the rate they tick when they are at rest with respect to one another). Thus, if any two of these three clocks are at rest with respect to one another and have been synchronized, then they will remain synchronous.
In order to synchronize clocks B,C, we can imagine that a rigid ruler connects them, and that we have located the midpoint, and then a spherical light pulse goes off there, and travels to both clocks, setting them to zero simultaneously in reference frame F2. They therefore remain in sync forever in reference frame F2.
Incidentally, here is a link to Euclid's proof of the Pythagorean Theorem
Euclids Proof Of The Pythagorean Theorem
The above site is excellent.
There should be no objection to the use of the Pythagorean theorem in the derivation, because it is certainly true of rulers at rest with respect to each other in an inertial frame. My favorite proof of the Pythagorean theorem can be seen at the following site:
Simple Proof Of Pythagorean Theorem