Rear Flashing
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speed of light - train experiment - was Einstein wrong?
Can someone look here (http://homepage.mac.com/ardeshir/Einstein%27sTrain.html) and explain what's going on? I'm particularly confused by the fact that, if the speed of light is always c for all observers, then if the woman on the train sees the front flash first, then wouldn't she measure the speed of that light as being faster than the light from the rear flash? If not, why would she see the front flash first? If it reaches her first, she must measure its speed as greater than the light from the rear, non? (I understand from the diagrams why she should see the front flash first, I just don't get how the speed of the two beams of light, for her, could be measured as equal. If the train was traveling at the speed of light, she wouldn't even ever see the rear flash, non?
Would it make any difference if the lightning didn't come from the sky, but instead came from special "lightning machines" attached to the train (i.e. moving with the train)?
Remember the train is moving. ====> Both Time and Space dilate in the direction of motion. ====> To the OUTSIDE observer the distance the front photon travels is shorter therefore gets there quicker and the back photon travels a greater distance and gets there later. So to the person on the train the 2 events take place at different times AND the distances are different. To the OUTSIDE observer the distances are the same to the flashers ===> The flashes happen at the same time.
http://en.wikipedia.org/wiki/Time_dilation
http://physics.suite101.com/article.cfm/time_and_space_dilation
We start with the Train and pitcher thought experiment.
You are standing on the ground next to a train track. A train going 100 km/hr is going past. On a flat car is a baseball pitcher that you know can throw 195 km/hr fastballs throwing toward toward you. You have a radar gun so you can measure the speed of the baseballs.
What speed would you measure if the train was coming toward you? (100 + 195 = 295 km/hr )
What speed would you measure if the train was going away from you? (195 - 100 = 95km/hr)
Now we start Special Relativity:
Toward the end of the 1800s scientists measured the speed of light compared with the speed of the earth in orbit. They expected that knowing the speed of the earth going toward the source of light the velocities would add and that when going away from the source of light the velocities would subtract. BUT that is not what happened. It did not matter if they were moving toward the source or away from the source, they got the same value: roughly 3 * 10^8 m/s. VERY STRANGE! They were sure something was wrong. It was not possible, based on their assumption that Time and Space were absolute (unchanging) for that to be true.
Einstein's insight: He thought,"What if the speed of light IS absolute and Time and Space could change to make that true? What does that do to everything else? He worked it out for all the physical quantities. It works! What you get is consistent with what we observe in experiments.
Yes, if the train is going c, she will not see the rear flash.
If the flashes were on the train, then they would get there at the same time. Figure each light source is known to be 1 light second away ===> It would take 1 second for both sets of photons measured by a stopwatch on the train. The OUTSIDE observer would also see the flash a simultaneous, IF the light source was equidistant from the observer when it flashed. The person on the train and the OUTSIDE observer would still argue about the Time it took the photons to travel to the center of the train.
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