Question: If you were going at the speed of light in a car and then turned your headlights on, what would happen? o:

Evan Keane answered on 22 Jun 2011:

Great question. I like the way you’re thinking. The answer is that you cannot travel at the speed of light. Only light can! You can NEVER reach it. It is impossible. Ok, well what if you changed the question to a car travelling at 99% the speed of light or something. That would be possible. If you were driving towards me at 99% the speed of light and you turned on the headlights I would see the light come at me with the speed of light!!! NOT 1.99 times the speed of light! Welcome to the world of Special Relativity! This is not what you might expect from your everyday experiences but it something realised by Einstein. Everyone that measures light will measure it at the same speed, regardless of whether they are stationary, moving towards the light or moving away from it. Once you realise this you also realise lots of cool things that go with it. Such as from my point of view, when you are driving at me at 99% the speed of light it appears to me that time is running slower for you than it is for me. This is “time dilation”. Also, you would measure the distance you travel to be less than what I would. This is “length contraction”. There are lots of weird and wonderful effects like this in relativity when things start moving fast! 😀