Feynman: Mirrors FUN TO IMAGINE 6

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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/

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26 сен 2024

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Комментарии : 275

@lathem01 6 лет назад

They had a different definition of fraternity back then.

@RogerTheil 5 лет назад

Nowadays your fraternity brothers only teach you how to keep good grades while being a compete degenerate in every other way.

@realbrush 14 лет назад

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.

@CioranD 13 лет назад

his enthusiasm is contagious, would've loved to have him as a mentor.

@etiennealive 15 лет назад

Yes he is . I listen to some off his wideo's several times a week and he never gets boring. Everytime I'm "feynding" new things and other perspectives. And also motivating !

@Greig1424 14 лет назад

this guy is great i could listen to him all day

@alexreg 6 лет назад

2:30 - 3:08 is the particularly interesting bit. It really highlights how our psychological expectations fool us.

@GetMeThere1 15 лет назад

I'm proud to say that this question spontaneously occurred to me (right-left , but not up-down). I'm also proud to say I figured out the answer! Now, I have had a year of regular college physics. So I'd been through reflection/refraction, lenses, that crap. But you never remember that stuff.... And that's another reason education does a bad job. It doesn't teach you to think, and it doesn't ask HARD QUESTIONS. I've learned more physics by just thinking about things myself.

@IndigoIndustrial 2 года назад

Using your method, we would never have left the stone age. Sorry about the late reply!

@GetMeThere1 2 года назад

@@IndigoIndustrial LOL, sorry isn't good enough. Thirteen years and you miss the boat.

@IndigoIndustrial 2 года назад

@@GetMeThere1 I've been busy!

@DawarHusain 9 лет назад

2:50 - ".. and because people when they walk around don't turn their head for their feet" lol true. :)

@TravisMacMillan 11 лет назад

What an amazing teacher.

@sudarshanbadoni6643 3 года назад

The magic of this is what we are seeing as virtual classes in carina period where our mobile has become a virtual tool to bind the earth's humanity and progress. Thanks.

@meyes1098 7 лет назад

A good analogy here is pulling a glove inside out. You get a right glove from a left one that way, it's basically what "happens" in a mirror.

@emilbrandwyne5747 5 лет назад

Yeah or the foreskin of the penis

@bon12121 5 лет назад

@@emilbrandwyne5747 true that

@EGarrett01 16 лет назад

Yeah, I'm curious to see the rest of the video also. I liked thinking about the mirror problem, and I'd figured out that our ideas of "left" and "right" were a little messed up, but his insight was great. The second one doesn't seem that difficult. The track blocks the train from leaving. The left side stops the wheels from veering to the right, and vice versa for the other side. Once it gets going it probably has enough forward momentum to stay straight anyway...except when it turns.

@chrisofnottingham 14 лет назад

@Bananadine I agree. Despite RF's description being correct, the 'psychological thing' he speaks of it still quite a puzzle in its own right. It seems to depend on our preference for seeing things rotated about a vertical axis and the fact that a left-right reversed person still basically looks like the same person.

@51Cards 16 лет назад

What keeps a train on the track is that the wheels of a train are shaped like cones... the inside of each wheel is a larger diameter than the outside. As long as the train is centered on the tracks it runs straight. As soon as it moves at all off center one side of the train car is rolling on the smaller outside diameter and the other side is on the larger inside diameter. This then "steers" the train back to being centered on the rails.

@sebc2s 13 лет назад

I already love this guy.

@sidewaysfcs0718 14 лет назад

the fact that all the beauty of life all happened by chance is way more pretty that the idea of intelligent design could ever be.

@faraz1231 6 месяцев назад

Yeah but pretty doesn't make it right.. correctness could also be thought of as pretty

@chrisofnottingham 14 лет назад

@Bananadine I guess its understood that most objects, have enough symmetry (or are so random) that when we see a reversed version it is still recognisable as the non-reversed object. For me the heart of the answer, apart from the fact that mirrors flip front to back, is that we define left/right in terms of the front/back of a person. BTW, I'm not sure if "flipped about a horizontal axis" is a valid thing to say.

@goldencricket 11 лет назад

I always wondered about this as a kid. Despite the fact that I have a pretty full understanding of how mirrors work and why the image is reversed, it still seemed odd that they reversed one way but not the other. I concluded that they didn't really do that, but that it was just my psychological perception which made it seem that way, but I couldn't quite put my finger on why.

@YellowBricks1234 14 лет назад

THIS MAN IS A GENIUS!

@bluebomber81 14 лет назад

This is a clear example of the benefits to not really looking at things in just a different way, but rather, in the proper way.

@mnlg_yt 15 лет назад

OMG now I will never know about train tracks

@rozeboosje 16 лет назад

I'm delighted that the great Dick talked about this. I posted a vid about this myself a good while back and I've made it a video response to this one :-)

@DoctorFastest 12 лет назад

@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, ...

@equallyeasilyfuqyou 14 лет назад

awesome way of thinking about it.

@ironpirites 14 лет назад

Not bad. Feynmann is still (in all probability) one Nobel Prize ahead of you, though.

@chrisofnottingham 14 лет назад

@Bananadine I know what you mean but I think that even as a lobster, your first thought would be that the mirror swapped round the side your big claw was on. If you look at a familiar landscape in a mirror, you think it is reversed left to right, not front to back. Actually, I think the key is that we are used to rotating our view about a vertical axis as we move around, with up always being up. We could see our left hand in the mirror and say, "oh, the view is the wrong way up" but we don't.

@oldyoutubeaccount 15 лет назад

My first thought (

@F_khalid02 13 лет назад

If you're puzzled try this: Line up two mirrors- so that one is behind you and one is in front of you You should be able to see the mirror behind you in the mirror in front now wave your left hand if you look in you should see that in the mirror behind u, u r still waving your left hand NOT YOUR RIGHT. This is because its not left and right thats mixed up! pls tell me if you are still confused (after reading this replay the video- if u understand this u can understand wht he said!)

@sariusmonk 12 лет назад

My mind is blown.

@jackpullen3820 8 лет назад

IT's the little things that bring happiness...

@DutchDread 2 года назад

I always wondered this about mirrors, thought I was the only one. Turns out my answer was pretty close to his as well.

@Plerion 11 лет назад

The question about the train at the end is not about what forces keep the train on the ground, but what "concept" keeps it on the track (and not off the rails). Gravity, magnets, and such are the answer of the former question, not the latter.

@spearPYN 5 лет назад

Wise man speaks...

@GetMeThere1 15 лет назад

Yes! You're right, ollyk22! On your advice, I'll stop trying to think IMMEDIATELY!

@BrianPeiris 15 лет назад

Incidentally, I don't think that Feynman is inarticulate as some comments have suggested. I believe it is simply that our generation has a diminished ability to follow long trains of thought. Probably due to a lack of deep-reading skills and, indeed, a diminished imagination. Of course it doesn't help that the subjects Feynman often talks about are intrinsically rather abstract and confusing. (Which is why he tends to talk about them :D)

@RandomTomatoSoup 4 года назад

he keeps interrupting himself my dude

@slitheredxscars 12 лет назад

quick google search shows that mit has come up with a perfect mirror already. either way we need to make a perfect one way mirror now, because its just a matter of time before it all gets diffused in the same way it went in. anyways tank you for your input and theory. cheers!

@bscutajar 13 лет назад

i figured this one out when i was about 10 years old. this guy is awesome

@orobouros616 15 лет назад

"How is this hard?" This kind of question shows the difficulty many people have with understanding science. The easy answer is, "that's just what mirrors do." But science aims to go deeper and not just state an observation, but explain it. The real answer, explained here in easier words, is that mirrors cause a parity change. The key is that there is a difference between "left/right" which are relative directions and N/S/E/W which are absolute directions.

@RhinoAts51 15 лет назад

This is something we could've all figured out I suppose, if we didn't already know, however the way in which he explained how he analyzed it was great. I bet he loves pot.

@Bananadine 14 лет назад

@chrisofnottingham Good point about the landscape though. That is a different effect from what I'm thinking of. It doesn't rely on symmetry, although I think symmetry might help it sometimes.... If there's a convenience-of-symmetry effect AND a devotion-to-"up" effect, then it's tricky to separate and compare them in the case where the thing looked at is a human, because, again, humans always have both a pretty strong left-to-right symmetry and a strong sense of which way is "up".

@sachoslks 13 лет назад

Oh man i can write and read english but it's a lot more dificult to understand a person when is speaking, well i would love to be like him some day =D

@ramtinking 14 лет назад

I agree... and personaly i'd want to invest my time on something that can be scientifically experimented... when one understands the scale of the universe, and finds out that everything is working under simple and elegent laws, it's like a movie you have to watch it and enjoy it... because all that we are doing is trying to understand it... the laws of physics are for ever and unchanging... it just blows ur mind

@JukkaLiimatta 12 лет назад

@bicnarok No; your left hand is still your left hand and right hand is your right hand. They haven't swapped. Do experiment: look into mirror. Move your left hand. Your left hand moves. No swapping is taking place. Mirror does negate the z-axis. In terms of linear algebra, mirror is: [1 0 0] [0 1 0] [0 0 -1].

@snapsnapdik 11 лет назад

Sheldon I'm such a big fan

@Crocy 11 лет назад

That was confusing

@Ray2311us 4 года назад

All I know is that the mirror is a merely a reflection

@kylekeys4304 11 лет назад

superconductivity allows for some levitation and propulsion. superconductivity is used to to propel the molecules on the large hadron collider as well as some trains right now, im pretty sure. Micho Kaku talks about it in his video "the quantum revolution"

@sirishgi2597 5 лет назад

Blew my mind

@Kurnikowy 2 года назад

Suddenly I wanna know what keeps the train on track

@Bananadine 14 лет назад

@chrisofnottingham If you had a giant lobster claw on only one arm, then you wouldn't be symmetrical left-to-right anymore, and your mirror image would no longer appear to be a turned-around version of you. It would appear to have been reversed from your normal image, but not in a way that privileged one axis over the other. If we were totally irregular, we could still define left and right as you say, but the effect that motivates the question would be gone. Our internal symmetry is the key.

@saintmuse 15 лет назад

It's not that simple but to explain it to you would be a waste of time. Feynman is a great communicator of very complex ideas and often asks what may seem like childish questions when discussing certain topics. That is his way of covering all the bases. The man was an utter genius.

@kiemul136 14 лет назад

Looking in a mirror is really looking into another Universe where you are doing the exact same things. So you will find yourself, from a different universe, staring back at you... however in the other universe the front is back. This is my theory on mirrors.

@DigitizedSelf 12 лет назад

@sawmassacre13 'Mise en abyme'. Due to the distance between them the frames will be smaller and smaller and all contained within themselves reflecting the image back and forth (depending on the point from which you're looking though). Limiting factors are probably the quality of the mirror and the clarity of the air (at least at a macroscopical scale)

@Andreazor 14 лет назад

@chrisofnottingham I still can't get my head around this. Is it our perception that makes a mirrors image opposite?

@PoetlaureateNFDL 12 лет назад

Interesting guy for sure!

@pendejadafcc 14 лет назад

that was cool

@africanlegs 10 лет назад

Now that is a good explanation.

@TwistedLemniscate 13 лет назад

@sawmassacre13 The same thing that happens when you think about your thoughts, or when a video camera is pointed in the direction of it's own display.

@Trisscarro 13 лет назад

@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).

@lvecsey 15 лет назад

Imagine a plaster of paris mold, right in front of you. Your nose pushes in the most, and then parts of your face and the rest of your arms and body. When the artwork on coins is made there is a mechanism to trace out the depth from one scale to another, so maybe something similar could exist to transfer or invert the mold from a "left handed" to its corresponding "right handed" shape. Or use a 3D scanner and just invert the data, and print out your "mirror" self ;)

@Bananadine 14 лет назад

@chrisofnottingham Still, he doesn't quite get to the core of the matter. Yes, the "person" in the mirror appears to be a version of us that rotated about a vertical axis until facing us, rather than one that flipped about a horizontal axis, because that's how one would normally get into the apparent position of that "person"... but why is that? He doesn't say, though the reason is simple: Our bodies contain a left-to-right symmetry. That is the heart of the real answer.

@flawns 11 лет назад

weird, for me the train on the track one was easy, but the mirror one was hard

@jdm21339 11 лет назад

Gravity, wheels, and rails.

@gregorkorosec6131 3 года назад

In the other video he explains that he meant "what keeps the train on trackis on a turn"

@chrisofnottingham 14 лет назад

"He was right until ...like a person facing you." RF just means which way the person is facing, nothing more. The dominating effect of what we see in a mirror is that the person is looking toward us. So we imagine how a person would get to be facing us and normally that would be by turning round, rather than flipping front to back! You understand how it works but I think you just misunderstood what he meant at that point. Brilliant explanation. I had never heard it described like this before.

@creepindead 11 лет назад

Impurities in the glass. Usually you'll get a greenish haze

@mike198856 12 лет назад

either darkness or light, depending on how close they were together, and what space in the universe these mirrors are at

@jorgepeterbarton 12 лет назад

i don't quite get the problem. its just symmetry, if you line up all the points its where it goes if it was flipped up/down they wouldn't line up... like he says its front and back mixed up, not like you've turned around but all the points of light are just facing the other way.

@orbsandtea 12 лет назад

Haha! Either I'm too clever or too stupid to be puzzled by the question.

@luketurner314 2 года назад

When you see someone else's face in a mirror, they will see your face in the same* area of the mirror as you see theirs. If in doubt, using both of your own index fingers and thumbs, form an approximately circular shape and place it on the mirror around their face. Also works with cameras. * roughly, faces come in all sorts of shapes and sizes

@ramtinking 14 лет назад

i'm a physics student... i personally don't believe that this conversation is going to be worth anything when it's over... so sure you are right

@AtifHussain93 11 лет назад

He only pushed the problem further back than solve anything. Now the question is why we see our image inverted with our nose in the backs like that.

@Oydle 6 лет назад

For the answer to this problem, recall that images in mirrors are always perpendicularly opposite the 'object' they are images of, and the same perpendicular distance away from the mirror as their objects. For an explanation for that statement, draw a ray diagram with two different rays reflecting from an object off a mirror, trace them past the mirror to where they would appear to diverge from, and spot the 'similar triangles' created by the relevant distances involved to prove that the perpendicular distances are indeed the same.

@SpartaNate 14 лет назад

@EvTrev11 He's not explaining how it happens so much as why the image looks the way it does to us. I'm pretty sure Richard Feynman knew that mirrors reflect light.

@AdrianFacchi 11 лет назад

sigh.. I was going to sleep but now I have to know what keeps a train on the track

@DigitizedSelf 12 лет назад

@DigitizedSelf Ah, think I got the question now: When you say 'directly at each other' you mean in a line that's at right angles with both mirrors. Aside from the fact you can't look in this line, since you'd be blocking it, then it's an interesting question. Since mirrors are generally imperfect there's probably still some light that gets caught until it eventually escapes (might also be some quantum effect). In the 'perfect' mirror case I guess there's no light, so you'd see only darkness)

@ramtinking 14 лет назад

i know you weren't... i just used that as an example... light is very weird and intresting at the same time... when a mirror is involved, all it's doing is reflecting back the light of a 3 dimensional object, so the essence is 3 dimensional being reflected by a 2 dimensional object... this could go on forever... the most important thing is that we can enjoy having mirrors and we can enjoy having understood the nature of light...

@Fex. 12 лет назад

Light. And if you could see that. That´d be just light.

@bace1000 5 лет назад

How did he explain this better than a diagram

@VLK249 11 лет назад

See the inversion of the axis in 3D programs like Maya when trying to invert/reflect an object. You can call us Z1, where your reflection is Z-1. If you're trying to make Z-1 manually, just literally squish the object into the -Z direction and then eventually it will plop back at as a fully formed Z-1. It's neat.

@HolgersonCrusoe 11 лет назад

Yep!

@supergsx 12 лет назад

@sawmassacre13 An infinite repetition of the empty space between, fading off into blackness as the photons slowly get absorbed by the mirrors.

@richardthelionheart01 10 лет назад

Curvature - You are top/bottom swapped in a spoon.

@wtfuredead 8 лет назад

+richardthelionheart what if mirrors work because they are not perfect. like small curvatures that ondulates. There would be impossible to make a perfect flat mirror, or any surface, as in my opinion flatness is also relative

@sofia.eris.bauhaus 6 лет назад

the spoon flips your image in all three directions..

@pobinr 15 лет назад

If instead of having your back to the mirror then rotating 180deg about an axis going from your head to your feet so as to see yourself in the mirror, you instead stand in front of the mirror &rotate about an axis going across your hips.You'd need to grab hold of a gymnastics bar or some such thing to do so & you'd wind up being upside down.However you would have rotated in a completely different way to the way R.Feynman's refers to but youd still see left & right mixed up but not top &bottom!

@slitheredxscars 12 лет назад

i would think the beam of light would keep as straight as possible, yet by doing that it will reflect off of the curves of the sphere, yet as well as the beam is being reflected, the radiation of light as it passes is still being reflected as well, so would that make more light? -.- i wish we didn't have to theorize :(

@chrisofnottingham 13 лет назад

@PikPobedy "Left and right are relative to the observer." True, but when you point to your left your mirror image also points to your left. Left and right have not been reversed either. The mistake is in treating the mirror image as a person and defining left/right with respect to that imaginary person. In fact the image in the mirror has actually been reversed front-to-back, something that can't happen to a real person. If it did, we would have to redefine what we mean by left and right.

@KnowKnot 14 лет назад

@ramtinking That's what bothers me though. We tend to think that a person can WONDER, or a person can DO, or a person can APPRECIATE. That each are somehow mutually exclusive. I very much believe this isn't necessarily so... maybe it only requires a mind that can endure doubt, be present in experience, and produce (appreciate? enjoy? endure?) some degree of consecutive thought. Looking at things differently needn't mean rejecting common experience...

@slitheredxscars 12 лет назад

i have a question, if you have a sphere, made of mirrors inside, and one of the parts was a one way mirror, which could be switched on and off, from it being a mirror and a glass, if you had a bright light or lazer going through the mirror side, what would happen? would the lazer be infinitely reflected and contained within the sphere? or would it vanish?

@rubbermuck 13 лет назад

This guy looks like a mix between Irvin Kirshner and Dylan Moran

@Kowzorz 14 лет назад

What keeps a train on a track?!?! We'll never know!

@lobsterballoon 11 лет назад

Sure, you can seen them reflecting even looking at it from an angle. The reflection wont go on forever though. Any light not perfectly perpendicular to the mirrors will eventually bounce out and maybe replaced by incoming light.Mirrors only reflect about 99% of light, so after a couple hundred nanoseconds, any perpendicular light will die off. So what you'll see is endless shrinking reflections that get darker. If u have a special light source in the middle u can make a laser with this though :)

@ramtinking 14 лет назад

the mirror itself is 2 dimentional, but the image is 3 dimentional

@KatiHathor 11 лет назад

google "infinity mirrors"...they have that at my gym and i've seen it in various bathrooms. if you can view your reflection at a slight angle you can peer into it and see yourself repeated an infinite number of times.

@marcaxe 11 лет назад

Superconductivity is useful, but isn't a requirement of keeping the train on the track. you'd just need an awful lot of cooling.

@JesusChristSaves2024 13 лет назад

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

@RHawkeyed 12 лет назад

Cool, didn't know about those. But aren't they "only" 99.9999999% reflective? Maybe they are 100% reflective at specific wavelengths, I only had a quick look at it. Anyway, if the sphere is big enough you could shine a laser pulse in through a hole and then close the hole completing the perfect mirror sphere before the light escapes, right?

@sidewaysfcs0718 14 лет назад

im not sure they are unchanging .. cus in the beginning of the universe the first force to separate was gravity and the 3 other forces where combined in 1 force u could say that as the universe cools down , more structure , complexity and diversity emerges ...like in a snowflake , in the beginning its a round drop , if it cools down it gets a structure im curious however what happens when the universe will reach maximum entropy and reach zero temperature , the quantum fluctuation wound end

@xxAkatsukixSasorixx 15 лет назад

Linierly as in a photon from your right will be on your right when viewing it in a flat mirror. so in effect your viewing a projection of your outer self light from behind. imagine if you took all the atoms on your front. and created a slide and viewed these from behind. they're the photons you are seeing in the mirror.

@TNTforWISDOM 15 лет назад

I dont understand. What does he mean by the fact that the back and front have been reversed

@BrianPeiris 15 лет назад

Feynman is describing the psychological tendency to think that mirrors "swap" images horizontally. Imagine holding a ball in your *right* hand while looking at a mirror. Your brain sees a person who is holding a ball in her/his *left* hand. Since we are usually upright when looking into a mirror, we form the common fallacy that mirrors swap left and right. This is easily corrected if you look at a mirror while lying on your side. A mirror does not swap an image horizontally, but front to back.

@Redpilldown 14 лет назад

It does make me lol......this guy thinks in 10 dimensions opposed to most of us, including myself that only just manage 3D..........but some here having trouble with 1D. Watch the video again and try and understand........he is not tying to tell you how a mirror works. I so wish I had of had a teacher like him........amazing mind

@alcaz0r1 11 лет назад

The distance between your nose and the mirror is smaller than the distance between the back of your head and the mirror. Thus, if you imagine yourself morphing into your reflection, the back of your head goes farther than your nose, so your head gets flipped front to back. Feynman considered that part obvious enough to not be worth mentioning, but, well, he was Feynman.

@ollyk22 15 лет назад

Not really what I said (or mean't). Do you think the chap in the video above would agree that education does a bad job? NO. The chap above would have learn't everything he knew at school / university and then applied his unique translation to a language / way of thinking that some people struggled to understand.