• Question: If you were travelling at the speed of light in your car. What will happen if you turn your headlights on?

    Asked by meg123 to Amy, Karen, Sarah, Vijay, Will on 19 Jun 2012.
    • Photo: Karen Reed

      Karen Reed answered on 19 Jun 2012:

      Hiya Meg – a clasic question this one… you would’t be able to tell they were on as the you and the light would be traveling at the same speed.

    • Photo: Sarah Martin

      Sarah Martin answered on 19 Jun 2012:

      Hi meg – you wouldn’t be able to travel at the speed of light in a car, because it has mass, and only light (made of mass-less photons) can travel a the speed of light! So whatever you do, you’ll always be a little bit slower… So there is actually no answer to your question!

      If you want to know what happens when you are driving at very nearly the speed of light, an answer can be given. Within your car you observe no unusual effects. You can look at yourself in your mirror which is moving with the car and you will look the same as usual. Looking out of the window is a different matter. The light from your headlights will always go at the speed of light in your reference frame. It will strike any object in its path and be reflected back. Everything else will be coming towards you at nearly the speed of light, so the light reflected from it will be Doppler shifted to very high frequencies—towards the ultraviolet or even further into invisible light. If you have a suitable camera you could take a snapshot. The objects passing are contracted in length but because of the different times of passage for the light and effects of aberration, the snapshot will show the objects you pass as rotated.

      All clear?
      🙂 Sarah

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