Why Do Mirrors Flip Left & Right (but not up & down)?

This video is about why words flip left & right (aka horizontally) in a mirror but not up & down (aka vertically). The answer has to do with specular reflection, mirrors being like windows into another world (alternate universes, just with in and out flipped!), and transparency of the things we write on.

REFERENCES
Specular Reflection

PhysicsGirl video about mirrors

Fermat’s principle

Thomas-Fermi screening

MinutePhysics is on twitter - @minutephysics

Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!

Created by Henry Reich

[MinutePhysics]

I know lots of people have made videos about this before, but I felt I still had something to add, so, well, here you go! Also, I'm working on a video about CP violation (aka mirror symmetry violation) in particle physics, so I've been thinking more about mirrors recently. That video should be out soon!

[iveharzing]

That transparant card you used really made it click for me!

[aidanbalac]

I’ve seen a lot of videos attempting to explain the mirrors flipping images, and this is the best explanation I’ve ever seen

[lassievision]

You took something really simple that I took for granted, and made me realise that actually, I know nothing at all. Well done. Flipping brilliant!

[Totone]

I love it when things are so "trivial" that you don't even think about them, but are very interesting the second you start to study them.

[TheRealGuywithoutaMustache]

Mirrors are really fascinating. I really needed some time reflecting on this topic.

[rsm]

Producing mirrors must be super fascinating and exciting


I could really see myself doing that

[ricardoalves]

I feel like an idiot for not understanding how words are reflected earlier

[tabaks]

I love the addition of transparencies! I knew that the "flipping" mirrors do is in "z" axis, but imagining it mentally is 10 times easier with your transparency idea. Excellent!

[brianpso]

Wow, using a transparent card was such a simple but mindblowingly powerful idea! I can't imagine the feeling of happiness that came when the person who thought of that had the idea. This was by far the best explanation about mirrors I've seen, short, simple and clear (pun not intended).

[oLuii]

When I read the title I was like "well this is pretty obvious" in my mind.
And then I saw the part about the word in plastic film and was like "well thats obvious too, why tf didn't I think of that?!"
The more we think we know all about a subject, the less we get to learn about different ways of looking at it.
Great video!

[dougmcguire]

When you did the word on the clear glass I was like “oh wow” and then when you explained that we flip it, I was like “son of a bitch” I literally said that. In a very sincere way. I hope you know this is a huge compliment

[yawer]

Feynman talks about this magic. Actually all that Feynman talks about is magic. Beautiful work, once again @minutephysics

[manik]

The way he says mirrors in the end sounds like Hermione Granger saying its leviosa not leviosar

[bencushwa]

I'm a physicist and a photographer, and this is by far the simplest explanation of this phenomenon that I've ever heard. Bravo!

[georgplaz]

This is so simple, I can't believe I have never figured it out myself. I feel very humbled 😂

[tbnrthebestneverrest]

me on a date: hey nice to meet you. how are you? oh im great! did you know that mirrors...

[Master_Therion]

Whoa! This is a deep concept. I need some time to... reflect.

[timgabby]

A third mirror, above those 2 at right angles, but closer to the observer and angled so that the rightangled mirrors can be seen via it, with a screen preventing direct observation of those 2 mirrors, allows for all combinations of left-right, up-down reflection, reversal or double reversal.. try it. I constructed this setup for an A level biology project in '76, here in the UK, showing how folks slowed in completing a reflected maze, depending on the combinations used.. :)

[AdityakrishnaMr]

This video makes me feel I've circled the youtube once, because years ago the first video i watched of Physics Girl was mirror flipping as well.