Okay, here's one that keeps me up nights. If you were driving a car traveling at the speed of light and you turned on the headlamps, would any light project ahead of you? And would it make a difference if you used the high beams?
-- Marianne, Escondido
Could this be from our "Huh? Wha...Where Am I? How Long Have I Been Out? Oh, Man, and I'm Late for Physics Class" file? If you do one day find yourself traveling at the speed of light, pull over to the shoulder, whip out the cell phone, lock the doors, and call the nearest theoretical physicist. (To reach their emergency line, dial pi.) I assume you know that the word from the science guys is that you can't travel at or beyond the speed of light. That's their story, and they're sticking to it. Unless you count the believers in tachyons, our favorite hypothetical subatomic particles that will move at speeds beyond light and can be found in mathematical calculations and in "healing tachyon-radiation crystals" currently very hot in natural-remedy emporiums. (Maybe if you sit under one today, it cures the headache you had yesterday?)
If you're driving the Mariannemobile and the speedometer hits 186,000 miles per second, light will still be emitted from your hypothetical headlights. As it strikes objects, they will look blue because the light will be shifted to a higher frequency at the blue end of the visible spectrum. Go fast enough and it heads beyond blue into the X-ray frequencies. At that point you can't see anything because there's no visible light to reflect off other objects. If it's daytime, you'll be sticking your head out the window, gawking like a retriever at the weirdness around you as all the blue objects flatten like playing cards, compress, and morph into a long tunnel. Everything behind you would be red (the slow end of the spectrum, as you move away from things) then disappears as light slows into infrared. At least that's how it pencils out, according to the physics phanatics.