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Same old twin paradox 
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#19
Jun2507, 07:50 AM

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And if you want to say that time dilation is not "real", then you have to say that the age difference at the end of the trip is not "real" and that the results of said experiments are not "real". If you try to hold on to the concept of absolute time, you will never grasp Relativity, as Relativity abandons that concept. 


#20
Jun2507, 08:00 AM

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#21
Jun2507, 04:52 PM

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how do you measure time ?
how do you measure distance ? how can you see the clock of your twin ? the satelites of GPS can measure the earth's frequency ? if these questions are very stupid, simply ignore. if anybody answer, please, in plain english. 


#22
Jun2507, 10:52 PM

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Time can be measured with a clock.
Distance can be measured with a ruler  a very long one. You can see the clock of your twin with a telescope, but of course you will see a delayed image. Focusing on what you actually see yields the "doppler shift" explanation of the twin paradox, which I rather like because it avoids abstractions. Understanding the issue of how one determines what time the twin's clock reads "NOW" (as opposed to what I see through my telescope). is very important to a full understanding of the paradox, however, though one can attempt to avoid the issue by avoiding the notion of simultaneity alltogether and focus instead on what one can see. The confusion arises because the notion of "NOW" is different for every observer in relativity. This is known as the relativity of simultaneity, and is one of the classic stumbling blocks that students have in understanding relativity. 


#23
Jun2607, 02:43 AM

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let A & B synchronise their clock.(A is at rest and B is travellingforget about any accelerationthey synchronise clock when they pass each other). A's reference frame. After 5 seconds passed in A's clock ,say the time in B's clock is 3seconds,due to time dilation(forget about calculations,we are analysing the situation logicaly). B's reference frame. After 3 seconds passed in B's clock,What will be the time passed in A's clock. if the time dilation equation is applicable to B's frame(remember there is no acceleration involvedso it is applicable),it should be of course less than 3 seconds(some figure). But we know,as from A's frame,if realy the time was dilated in B's clock,the time in A's clock should be 5 seconds. so could anybody explain me ,after passing 3 seconds in B's clock,what will be the time in A's clock. if it is 5 seconds . why? if it is less than 3 seconds(dilated ,as from B's frame) .why? 


#24
Jun2607, 03:12 AM

P: 106

To avoid this,we have to put A in a place and B travelling in a closed loop.This is because we are concerned about the relative speed only. if we can make the loop a circle,we can eleminate one more factor from the problem.The acceleration now restricted to direction only.Speed can be kept constant. Now if we give a solution to the problem,we can find ,at the end of the loop,both the clocks are showing same time.(i am a lazy man.it will take months for me to make an illustrated example with figures.).Say after every 22.5 degree of the loop ,let B flashes light to A,and A notes the time in his clock and vice versa. 


#25
Jun2607, 04:34 AM

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#26
Jun2607, 04:56 AM

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#27
Jun2607, 05:13 AM

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To make clear where the resolution of the "paradox" lies, suppose that A has an assistant (A2), and that both of them carry clocks. They are at rest with respect to each other, separated by the distance that B travels in 5 seconds. They synchronize their clocks so that both read zero (in A and A2's reference frame) when B passes A.
As I noted in my previous posting: in A's and A2's reference frame, 5 seconds elapse on A's and A2's clocks while 3 seconds elapse on B's clock; whereas in B's reference frame, 1.8 seconds elapse on A's and A2's clocks while 3 seconds elapse on B's clock. Nevertheless, if A and B set their clocks so that both read zero when B passes A, then everybody will agree that when B passes A2, A2's clock must read 5 seconds and B's clock must read 3 seconds! Why doesn't A2's clock read 1.8 seconds when B passes him? It's because in B's reference frame, A's and A2's clocks are not synchronized. This is because of the relativity of simultaneity that pervect mentioned. In B's reference frame, when B passes A, A's clock reads zero, A2's clock reads 3.2 seconds, and B's clock reads zero; and when B passes A2, A's clock reads 1.8 seconds, A2's clock reads 5 seconds, and B's clock reads 3 seconds. 


#28
Jun2607, 05:30 AM

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Is there any logic or just to match the final reading of 5 seconds after elapsing 1.8 seconds. or is there any time forwarding mentioned in SR? 


#29
Jun2607, 05:44 AM

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If two clocks are at rest with respect to each other and separated by a distance L in one reference frame, then in another reference frame moving (along that same line) with speed v, those two clocks are out of synchronization by the amount [itex]vL/c^2[/itex]. The clock whose position is "ahead" (in terms of the motion of the two clocks in the second frame) runs "behind" in time. This can be derived from the Lorentz transformation equations, the fundamental source from which the lengthcontraction and timedilation equations are also derived.
In your example, the timedilation factor corresponds to a speed of 0.8c, so A and A2 must be separated by 4c in their reference frame. Therefore the amount by which their clocks are out of synchronization in B's frame is [itex](0.8c)(4c)/c^2 = 3.2[/itex]. 


#30
Jun2607, 06:22 AM

P: 106

could you please give me some links to learn more about this out of synchronisation. 


#31
Jun2607, 07:57 AM

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A2's clock reads a later time than A's clock does, in B's frame, so A2's clock is "ahead." 


#32
Jun2707, 01:54 AM

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#33
Jun2707, 02:28 AM

P: 106

So somebody has to find an equation for that.The equation contains v(not a),which is the relative velocity(not acceleration) 


#34
Jun2707, 07:37 AM

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They already exist: [tex]t = \frac{c}{a} sinh \left( \frac{aT}{c} \right) [/tex] [tex]T = \frac{c}{a} sinh^{1} \left( \frac{at}{c} \right) [/tex] They are derived from the standard Relativity equations. 


#35
Jun2707, 07:47 AM

P: 106

And please explain me how somebody knows,who is accelerating? 


#36
Jun2707, 10:17 AM

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