Feynman 'Fun to Imagine' 6: The Mirror

Richard Feynman amuses himself with an old puzzle - why do mirrors seem to switch left and right, but not top and bottom? From the BBC TV series 'Fun To Imagine' (1983). You can now watch higher quality versions of some of these episodes at www.bbc.co.uk/archive/feynman/

Category:

Science & Technology

Tags:

• feynman
• mirror
• science
• physics
• imagination
• fun
• cool
• puzzle

[realbrush]

I could listen to Feynman all my life and never get tired. He is such a down to earth guy and a great character. A great scientist and a great human being. I miss him alot.

[sawmassacre13]

I've got a question. If you put two mirrors opposite to each other. What would they reflect directly at each other ?

[DoctorFastest]

@rhcquant ...and then boom, laser!

Haha, in other words you let some of the light out through a hole in one of the mirrors, and a beam of intense light can escape. As long as the 'stimulated emission' from the gain medium (the extra light that the gas between the mirrors is emitting) exceeds the amount of light which you're shooting out, you can sustain the beam.

[DoctorFastest]

@rhcquant Thanks for the response! To solve the problem of the light escaping, you can use mirrors that are slightly curved, like this. ( )

Pretty cool. And it turns out, this is actually how lasers work! Between the mirrors is material called a 'gain medium', a gas that emits extra light when light shines on it. So you shine some light between the mirrors (just like your idea!), it bounces back and forth, the gain medium releases even more light which also bounces back and forth, ...

[rhcquant]

@DoctorFastest it's an interesting question... mabey you have one hole in a mirror that has a flashlight in it. If the light just keeps bouncing back and forth then eventually you'd have an infinite energy density. If course, the problem woud be if you ever tried to do this is that variance in the parallel-ness of the mirrors woils soon send a light ray off the edge, unless you had infinite-sized mirrors - in which case you'd have zero energy density.

[preecejon]

@sawmassacre13 i wanna know!!! and dont say infinite mirror frames, i wanna know what the middle would reflect!

[sawmassacre13]

@sinachiniforoosh ...My question itself is flawed. It's like questioning how old is god, supposing that god created time, the question would just not apply. Mirrors reflect image of light that bounces off of objects. If there are no objects and no light, than there's nothing to reflect. But again, ''nothing'' is hard to imagine as we are used to the idea of something always being somewhere. I mean what if we could see what the mirrors ''see'' when they face each other closely ?

[sinachiniforoosh]

@sawmassacre13 I think it depends on their distance.

[eahazell]

oh god when he asked left right vs up down my brain hurt

[DoctorFastest]

@sawmassacre13 The light would just keep bouncing back and forth. So light could come in from the side maybe, and it would keep bouncing back and forth until it missed one of the mirrors.

Extension of the idea - since it just keeps going back and forth, what if you kept adding more light, so there was more and more light bouncing around in between them? I guess it would get really bright in there! You could make it easier by using curved mirrors.

[CarlosCMTF]

Chameleon + mirror = ???

[Trisscarro]

@sawmassacre13 exactly the same they would if they where side by side.

a mirror doesn't reflect certain things, it reflects everything we just don't see everything a mirror reflects(like you can't see everything that's on the other side of a window).