Name: 如何打破光速（How to break the speed of light）
Uploaded: 2022-07-17T04:42:04.000Z
Duration: 1 min 27 s
Description: 你可以在你的後院打破光速！ （不過別擔心，愛因斯坦還是對的）

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

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

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

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.