Mirrors are amazing - they turn walls into
portals to another world!
Well, our world, only slightly different.
Like, you’ve probably noticed that words
look backwards in a mirror, but they aren’t
upside down - which is weird, because how
would a mirror know to flip left and right
but not up and down?
Well, the short, annoying answer is that mirrors
don’t flip left and right OR up and down
- if you look carefully at a scene in a mirror,
you’ll notice that everything on the left
stays on the left, everything on the right
stays on the right, everything up stays up,
and everything down stays down.
What does get flipped is the direction into
or out of the mirror - the things closest
to us end up farthest away, and the things
farthest from us end up closest.
Mirrors flip not left and right, nor up and
down, but depth - they flip in and out.
And mirrors invert in and out because they
reflect light according to the principle of
specular reflection: light coming into the
mirror at a given angle bounces back out at
the same angle.
This means that, after bouncing off a mirror,
light is behaving no differently than it would
have if instead of a mirror there were a window
into a parallel universe on the other side,
just like ours in every way except with in
and out reversed.
That’s why mirrors feel like windows into
another world - the light is behaving in LITERALLY
the same way as it would if they WERE windows
into another world.
Ok, but then what about the left-right flip
question?
How does that make sense if mirrors DON’T
flip left and right?
Well, you can literally see the answer for
yourself by writing on something transparent
- when the word is readable left-to-right,
its mirror image is also readable left to
right.
The reason words are usually flipped in mirrors
isn’t because mirrors flip them; WE flip
them.
Words, it turns out, tend to be printed on
or attached to objects that we have to turn
to face the mirror in order to see in the
mirror.
WE flip the words - and we normally do it
left & right.
We could just as well turn them vertically,
in which case the word would look flipped
top-bottom in the mirror, not left-right!
Again, not the mirror’s doing.
Here’s the deal: if a word is flipped in
a mirror, it’s probably flipped outside
the mirror, too!
We just don’t normally notice that the word
got flipped outside because we can’t see
through solid objects.
In order to see the word without looking in
the mirror, we have to go around to the other
side of the object and turn ourselves around.
Unless you have multiple mirrors - in that
case, in and out get flipped along two different
directions, which combines to mean that things
on the left indeed show up on the right and
right on the left - or, if we rotate the mirrors,
up gets flipped with down.
So if somebody tells you mirrors don’t flip
left and right - well, mirrORS actually CAN
- but not mirrOR.
A lone, single mirror has to get us to do
the flipping for it.
Hey, before you flip channels, I’ve got
a channel recommendation for you: MinuteBody.
Wait, but I thought this video was sponsored
by CuriosityStream, which has teamed up with
Nebula, a new streaming service featuring
original videos from independent and education-y
youtube creators?
Well yes it is - and those original series
include MinuteBody, produced by the MinuteEarth
team, or “The Logistics of D-Day” produced
by Real Engineering.
And you can get Nebula for free bundled with
a CuriosityStream subscription by going to
curiositystream.com/minutephysics, which gets
you access to the thousands of documentaries
on CuriosityStream AND all of Nebula for just
$20 a year.
So go to curiositystream.com/minutephysics
and you can watch Particle Fever, MinuteBody,
AND the logistics of D-day.
Oh, and new MinutePhysics videos are there
too, in case you want to watch without ads.
Thanks to CuriosityStream and Nebula for supporting
educational videos on the internet!
