You may have heard that Einstein's theory of special relativity imposes a cosmic speed
limit: nothing can travel faster than the speed of light. Well, that's wrong. All that
Einstein said was that light moves at the same speed in every reference frame - and
while this implies that nothing with real mass can move faster than light, it doesn't
impose a cosmic speed limit.
Because you can break the speed of light in your backyard. All you have to do is point
a laser beam at the moon and flick your wrist. The spot of light from the laser beam will
travel across the moon's face in about half a millisecond, which means it's traveling
at twenty times the speed of light!
How is this possible? Well, think about a computer screen – what's the speed limit
for pixels on the screen? Zero. Pixels can't move.
But if you cleverly arrange a whole bunch of pixels to turn on and off in a special
way, you can make an image that appears to move across the screen, even though every
pixel stays put. So you've broken the speed of pixels!
The laser pointer on the moon is basically the same - each photon travels to the moon
at the speed of light, but the image of a dot that they form on the surface moves twenty
times faster! No physical laws are broken because nothing physical is actually traveling
faster than light - it's just an image.
And as you may have guessed, the red dot of a laser is pretty big by the time it gets
to the moon – depending on your laser, it might be five hundred or a thousand kilometers
across! So don't worry about blinding any astronauts.