• Question: Why can't anything go faster than the speed of light?

    Asked by binladenjr to Arttu, Ceri, James_M, Monica, Philip on 14 Jun 2011.
    • Photo: Arttu Rajantie

      Arttu Rajantie answered on 14 Jun 2011:

      Imagine being on a really fast train, but you got a really cheap ticket so your carriage has no windows and therefore you cannot see outside. There is a lamp on the rear wall to give you some light.

      The special principle of relativity states that the laws of nature (including the speed of light) are the same for every observer moving at constant speed. It is therefore impossible to tell without looking outside how fast the train is moving.

      If the train were able to move faster than light, the light from the lamp would be moving slower than the train and would therefore not reach you. You would see the carriage being completely dark, and therefore you would be able to tell that the train is moving faster than the speed of light. According to the special principle of relativity this is not possible, and hence, if the principle is correct, the train cannot move faster than light.

    • Photo: Ceri Brenner

      Ceri Brenner answered on 14 Jun 2011:

      Arttu’s right, it’s all governed by the laws of special relativity. Another way to think about it, is to use einstein’s equation, e=mc^2. That tells us that as something with a given mass increases in energy and so moves faster and faster, so too must it’s mass increase. It turns out that in order to reach the speed of light, c, then the ‘something’ would end up also being infinitely heavy which doesn’t work so anything with mass can’t reach and break the light speed barrier. Light particles (photons) are massless so they can go at the natural speed limit.

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