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One way speed of light and simultaneity 
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#1
Feb2312, 01:45 AM

P: 215

Hello,
There are two observers. A is stationary and B is on train. Train is moving. B is at middle of train. If B flashes a beam to front and back, and at the both end there are detectors, then what does B measure one way speed of light in both direction? Thanks. 


#2
Feb2312, 06:11 AM

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P: 17,202

Assuming that the detectors are synchronized using Einstein's convention then they measure c, by definition.



#3
Feb2412, 03:52 AM

P: 215

Ok, We assume left end of train as A, right end is B and middle is M. Observer is at M.
When train is at rest. O flashes two pulse in direction of A and B to synchronize both clocks with O's clock. clock of A and B has some little difference with respect to O's clock because of time taken by light to reach at ends. Suppose, that O flashes two pulse to both clocks at [itex]t_{o}=0[/itex]. pulse reaches to both clock and set [itex]t_{a}=0[/itex] and [itex]t_{b}=0[/itex], but now O's clock displays [itex]t_{o}=1[/itex]. (We can say that the values of t is in timeunit, and train's length is 2 lighttimeunit). Now, train is moving to the right with the speed of 0.5 lighttimeunit/timeunit and suppose O flashes two pulse in both direction at [itex]t_{o}=5[/itex]. We know that reading of both end clock should be [itex]t_{a}=4[/itex] and [itex]t_{b}=4[/itex] now. When pulse reach to the clocks, is both clocks reading different or same? If different that what would be values of [itex]t_{a}[/itex] and [itex]t_{b}[/itex]? 


#4
Feb2412, 04:22 AM

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P: 41,435

One way speed of light and simultaneity



#5
Feb2412, 04:36 AM

P: 215

Two event occurs simultaneously, but train observer have no way to prove it. So he has to conclude that the event was not simultaneous because speed of light is always c. But, if in moving train both light pulse take same time to reach clocks, then why simultaneous events occurred in rest seems one by one in moving frame? 


#6
Feb2412, 04:56 AM

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#7
Feb2412, 05:16 AM

P: 215

Suppose, train is moving, if lightning happens at the two ends simultaneously with respect to rest frame what is the clocks' reading in train frame? same of different?



#8
Feb2412, 05:36 AM

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P: 41,435




#9
Feb2412, 05:53 AM

P: 215




#10
Feb2412, 06:02 AM

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P: 41,435

According to the ground frame, the train clocks are not synchronized. (The clock in the rear of the train is ahead of the clock in the front of the train.) So if the lightning strikes the ends of the train at the same time according to the ground frame, the train clocks will show different times. 


#11
Feb2412, 06:32 AM

P: 215

I understand that clocks on the train is not synchronized with rest clock. But the two clocks have same dilation effect with respect to rest clock. Two train's clock is not synchronized with each other with respect to rest observer is strange to me. Can you please explain me why does it happen? 


#12
Feb2412, 07:02 AM

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P: 17,202

Einstein synchronization is described in section 1 of this paper: http://www.fourmilab.ch/etexts/einstein/specrel/www/ 


#13
Feb2412, 07:37 AM

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P: 41,435




#14
Feb2412, 08:29 AM

P: 215

@Doc Al
If train observer synchronize the clocks when train at rest, both observer agree that clocks are synchronized. If we accelerate the train to some speed and then make speed constant. Now, both frame are inertial. Train observer doesn't synchronize the clock in the moving frame. Is both clock still not synchronized with each other with respect to rest observer? 


#15
Feb2412, 08:33 AM

P: 215




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