Simultaneity - Albert Einstein and the Theory of Relativity

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Imagine two observers, one seated in the center of a speeding train car, and another standing on the platform as the train races by. As the center of the car passes the observer on the platform, he sees two bolts of lightning strike the car - one on the front, and one on the rear. The flashes of light from each strike reach him at the same time, so he concludes that the bolts were simultaneous, since he knows that the light from both strikes traveled the same distance at the same speed, the speed of light. He also predicts that his friend on the train will notice the front strike before the rear strike, because from her perspective on the platform the train is moving to meet the flash from the front, and moving away from the flash from the rear. But what does the passenger see? As her friend on the platform predicted, the passenger does notice the flash from the front before the flash from the rear. But her conclusion is very different. As Einstein showed, the speed of the flashes as measured in the reference frame of the train must also be the speed of light. So, because each light pulse travels the same distance from each end of the train to the passenger, and because both pulses must move at the same speed, he can only conclude one thing: if he sees the front strike first, it actually happened first. Whose interpretation is correct - the observer on the platform, who claims that the strikes happened simultaneously, or the observer on the train, who claims that the front strike happened before the rear strike? Einstein tells us that both are correct, within their own frame of reference. This is a fundamental result of special relativity: From different reference frames, there can never be agreement on the simultaneity of events.

Channel: News & Politics
Uploaded: May 5, 2007 at 10:09 pm
Author: MyEarbot

Length: 0:02:03
Rating: 4.78
Views: 282,292

Tags: Science Physics Simultaneity Albert EinsteinTheory of Relativity

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Video Comments:
Uejji (Tuesday 18th of November 2008 03:00:20 PM)
It would depend on the bomb's frame of reference. Is the bomb on the track or on the train? These are two separate frames of reference, just like with the man and woman.
owenmalta (Tuesday 18th of November 2008 10:18:06 AM)
Ah ok, my mistake was that of assuming that the lightning strikes were initially simultaneous for both reference frames (which cannot be the case, right?). Makes sense now :) thanks to all for the clarifications!
Pulsar89 (Tuesday 18th of November 2008 02:37:59 AM)
(cont) To formulate things a bit more formal: The simultaneity of two events happening at two SEPARATE locations (front and rear of the train) can be different for two different observers. That's relativity. But the simultaneity of two events happening at the SAME location (the woman) is always the same for every observer (herself or the man). That's logic.
Pulsar89 (Tuesday 18th of November 2008 02:32:54 AM)
"he will see the front beam hit her before the rear" correct. "From her point of view, both beams will reach her at the same time" No. You see, that would lead to a contradiction. Let's play a James Bond villain: place a bomb underneath the woman. If both beams hit it at the same time, the bomb goes off. If they don't, nothing happens. Now, does the bomb go off, yes or no? It can't be both. In other words, the man and woman have to draw the same conclusion: the front beam always hits her first.
brodighiero (Tuesday 18th of November 2008 12:23:18 AM)
Lol my professor showed this exact video in my Black Holes class, it's correct.
techphy100 (Monday 17th of November 2008 11:43:39 PM)
Well not exactly how he invented television, but his theories led to it.
techphy100 (Monday 17th of November 2008 11:37:19 PM)
t0--t1 \t1 (spacetime-the light carrying the colors of the event is going to your eye and travelling in space and reaches you in a certain time over the distance of your position, the mans distance stays the same, but the womans distance is constatly changing so her views of the event will be messed up). this is how he invented television!!
techphy100 (Monday 17th of November 2008 11:22:35 PM)
For example, Einstein said 'time, past and future' doesn't exist, its only created by man. What he means what you see has already happened but will happen because you havent seen it yet. When you see someone do something, they have already done it, relative to your position to the speed of light, and who sees it first is future relative to who sees it second. so future and the past dont exist, in these terms. i have many more explanations relative to einstiens.
techphy100 (Monday 17th of November 2008 11:11:50 PM)
your missing vector quantity and your thinking in terms of the train moving relative to the lightning strike, its seeing the event happen is also traveling to your eye at the speed of light. at time t0, she is 0, at time t1 she is +1 which makes the front bolt 0 and the rear bolt +2. but he is not moving so his distance is the same left side and right side, at t0 he is 0, at t1 the light is going to him from the t0 point(space time) and he is still, so both lights will reach at the same time.
RatkoUSA (Monday 17th of November 2008 08:25:52 PM)
The Simms experience simultaneity on a bullet train as envisioned by Albert Einstein, somehow fascinating, yet very creepy.