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## escay's Journal: My sig has been answered

Journal by escay
The sig: "If your car is going at the speed of light, what happens when you turn on the headlights?"

by vistic (556838) on Tuesday April 17, @05:06PM (#18773319) (http://www.public.asu.edu/~corba3/)

You can not travel *at* the speed of light. And speed is relative.

I don't feel like doing the math, but as I recall from modern physics class... if you're standing still (i.e. you are the frame of reference) and you see a space ship traveling at 0.8*c, and then a ship undocks from that ship and travels forward (from *that* ships frame of reference) at 0.8*c... then from *your* frame of reference, the new ship is traveling at something like 0.95*c... not at 0.8*c + 0.8*c = 1.6*c. The relativistic effects don't work by simple addition.

Even if your car were going really near the speed of light, and you turn on the headlights... from your frame of reference the light still shoots forward at the speed of light. The speed of light limit is a speed limit for two things relative to each other... you always need some frame of reference.

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