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When train moves at speed of light the time becomes slow. why it happens?

  1. Aug 9, 2011 #1
    if train moves at speed of light the passenger will do any work with very less speed as time becomes slow. why this happens?
  2. jcsd
  3. Aug 9, 2011 #2


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    Staff: Mentor

    Material objects cannot move at the speed of light. It would take an infinite amount of energy to accelerate a material object to the speed of light "c". So your question is meaningless.

    You can click on the boxes at this Hyperphysics page to learn more about Special Relativity:


  4. Aug 9, 2011 #3
    [ Answering original question: "when train moves at speed of light the time becomes slow. why it happens?" ]

    Imagine a closed tube held by a train passenger. The inside of each end of the tube is a perfect mirror. As the passenger holds the tube vertically, imagine a photon of light inside the tube bounces back and forth between the mirrors. Meanwhile, the train is accelerating closer and closer to the speed of light.

    To the passenger, the photon always bounces up and down in a straight line. But to a stationary observer, the photon actually follows a longer zig-zag path through space (if the stationary observer ignores the tube and the train and everything else inside the train). Because light must travel at 186,282 miles per second, no faster and no slower, it takes longer for the photon to bounce from one end of the tube to the other.

    But because the passenger is moving along with the tube and the train, everything in his body and brain and everything on the train is also forced to follow their own somewhat-longer paths--including every subatomic particle. They are slowed down in respect to whatever path they were supposed to follow, within what we would call the train's "frame of reference".

    So time is forced to slow down on the train. But nothing has changed for the passenger because everything is slowed down, including him: He still sees the photon in the tube move at 186,232 miles per second. From our stationary frame of reference, however, his second of time is longer than a second of time for the stationary universe.

    It naturally follows that if the train is moving at the speed of light, the photon's zig-zag path flattens out to a straight line. It can't move at all inside the tube. If it could, it would be travelling a longer path in the same amount of time, exceeding its speed limit, which it can never do under any circumstance. So at the speed of light, time stops in the train.
    Last edited: Aug 9, 2011
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