I have often wondered why it’s not possible to go faster than the speed of light. My reasoning has been “well, according to Einstein’s theory of relativity (E=MC^2), you would require an infinite amount of energy to increase your speed by an infinitely small amount.” Until lately I have been been satisfied by this response, but I’ve always been stumped by this apparent paradox: Imagine you are in the back of a train going 1 MPH less than the speed of light. Now you get up and run to the front of the train at 8 MPH, would you not be going 7 MPH faster than the speed of light?. The answer is no, and here’s why. When you start moving forward you are perceiving yourself as moving normally, but in fact this is far from the truth. The closer you get to the speed of light, the slower time is.  What this means to you on the train is that you feel like you are going the 8 MPH because you are also perceiving time more slowly than normally.  If you were timing yourself with a watch, you would indeed get to the front of the train in the 10 seconds or so that you thought it took; however, if I were stopped on the outside of the train looking in, it would appear to me that you took many hours — maybe even days to run across the train.  What this means is that it actually took you a very long time to travel the distance of the train, let’s say 50 feet in 24 hours.  This speed is added to the speed of the train, but it’s far less than the 8 MPH you thought you were travelling at.  What if you shoot a bullet towards the front of the train?  It doesn’t matter what you do, the faster you go, the slower time goes.  If you managed to get to the speed of light, time would stop completely, so you would not actually be moving.

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