• Question: Hypothetically, if you were in a car going at the speed of light, what would happen if you turned on the headlights?

    Asked by selmae to Andrew, Ash, Gem, Paige, SJ on 29 Jun 2012.
    • Photo: SarahJayne Boulton

      SarahJayne Boulton answered on 29 Jun 2012:

      OOOOO a physicsy one…and a toughy to answer.

      Here’s what I think (watch and Ash and Andrew prove me wrong…;))

      The speed of light is relative to the observer. Kind of like, if you’re on a motorway in a car, and the car driving next to you is driving at the same speed, RELATIVELY it’s like you’re both together not moving. Does that make sense?

      So if you’re in your car zooming along at the very very nearly the speed of light, so when you flip on your headlights, the light coming out of them is travelling AWAY FROM YOU at the speed of light (regardless of how fast the car is going, the light is still travelling away from it’s source which is the headlamp on your car) so to you, in the car, your headlights work just fine and dandy.

      Apparently though, that where it all gets a bit weird, because you would think that if someone was watching you do this, to them, the light would look like it was travelling at ‘the speed of the car’ + ‘the speed of light’ however this is not the case. when you approach the speed of light, all the units of measurement you have start shortening, for some reason that I don’t completely understand, so it’s impossible to tell how fast you’re actually travelling as the point at which you’re measuring your speed from isn’t constant.

      There were some experiments at CERN called OPERA that claim to have made particles travel faster than the speed of light, but ths is still under investigation. In fact – it might have been disproven. I’m not sure…

      Here’s the link ::

      http://press.web.cern.ch/press/pressreleases/releases2011/pr19.11e.html

    • Photo: Paige Brown

      Paige Brown answered on 29 Jun 2012:

      WOW! Awesome question!!!

      I would think that to an observer, it would look like the light from your car headlights was not moving any faster than your car! It is all about relativity though… I’ll have to bend to an expert in physics!

    • Photo: Andrew Thomas

      Andrew Thomas answered on 29 Jun 2012:

      SJ is right because nothing can travel faster than the speed of light you can’t add up the speed of the car and the speed of the light coming out of the headlamps. For example if you were rowing a boat at 5 km/h on a river flowing at 5 km/h your total speed would be 10 km/h. This doesn’t happen if you’re travelling at light speed.

      There are two weird things that happen when something moves at the speed of light, time gets longer to an observer and distances gets shorter. I used to have to teach this to first year Physics students and it still scrambles my brain when I try to think about it.

      This fact in particular is mindbending- If you look at a star 1000 light years away it has taken the light 1000 years to reach your eyes. When that light set off, to an observer in England, William the conquerer wasn’t due to invade for another 54 years. However, because the photon of light is moving at light speed it experiences no time at all. It sets off and arrives instantly!

    • Photo: Ashley Cadby

      Ashley Cadby answered on 1 Jul 2012:

      Yep SJ is correct. Nothing beats light, so for an observer watching light from another reference frame time or distance has to change to keep the speed of light constant across all reference frames. Crazy eh.

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