- Thank you to Brilliant
for supporting PBS. Hey, smart people. Joe, here. I need to talk to you about a bird. - Our biggest wow factor is probably this crimson topaz here and so- - That's not real. Hold on a second. Did you see that? - The camera.
- That looks fake. I also need to talk to you about a bone. - [Jeffrey] So this is
actually a whale bone from Australia that in
fact has been opalized. - Every part of what you
just said is ridiculous. That's probably the coolest
fossil I've ever seen. And we need to talk
about all these beetles. Turns out you can order
dead bugs off the internet. (Joe laughs) (beetle clatters) I've been ordering a lot. All of these have one
incredible thing in common, and it is nature's greatest color trick. In past videos, we've taken a deep dive into some really mind-blowing
ways that nature makes color. We've looked for the blackest black. We've asked why blue is
the rarest of all colors, but I've been saving this
color trick until now because, well, I think
it might be the best one. (curious music) This is a phenomenon called iridescence. It means rainbow colored. We find iridescence in loads of places. Here, here, here too. And there, also there, even in that dirty puddle
out in the parking lot. But why? Now, color has many functions in nature. Sometimes it's for getting attention, sometimes for staying concealed, and sometimes for reasons
we don't understand. But iridescence is uniquely mind-blowing because the colors that we
see aren't really there. They come from a weird trick of physics. To figure out how it works, I asked a beetle expert, a bird expert, and a rock expert to show us some of nature's most incredible
examples of iridescence. It turns out if you go
to a huge awesome museum like the National Museum
of Natural History in Washington D.C., they have entire rooms full of awesome colorful
stuff to show you. We started in the bird wing. (crickets chirp) Get it? (crickets chirp) Bird wing. (crickets chirp) Okay, sure. So peacocks get all the attention when it comes to iridescent plumage, but I think that the
fanciest rainbow feathers belong to the smallest members of the living dinosaur
family, hummingbirds. - They're gorgeous, unbelievable. Our biggest wow factor is
probably this crimson topaz here. - That's not real. Hold on a second. - Gives you a flash at the camera. - Did you see that? That looks fake. It looks like somebody made a hummingbird in a lab and said, "This would be cool." Why do hummingbirds have
these amazing colors? - So hummingbirds, we think, it's always a we think in science, right? We think that hummingbirds
have these amazing colors because largely they're
using them to attract mates, picking who they might
wanna have offspring with based on who is the prettiest because pretty might indicate best genes, best ability to find food, best ability to care for offspring and so- - You don't have a lot
parasites crawling all over you, which I know-
- Exactly. - is a big problem in dating. These look really cool. There's like purple and
green and everything. - These are beautiful. The different body parts of these birds have different iridescent colors on them. You get these brilliant greens on the body and these really beautiful
roses and violets on the tails. - I mean, I can see how
this would get attention in the hummingbird dating community. What is happening inside of these feathers that helps create these colors? - It's just a little bit
of a trick of physics. There are three things
that make up the basics of this iridescent color
in these hummingbirds. Melanin, which is the same
pigment that colors your hair, keratin, which is what
makes up the feather, and also similar to your
fingernails and air. - The way that light
dances off of hummingbirds doesn't come from the color of the pigment in those feathers. It comes from how the feathers are built. Now, if we could shrink ourselves down to the nano scale and
look at them up close, what we'd see is millions of
these pancake shaped structures in these orderly little pancake stacks all packed with tiny air bubbles. When waves of light enter the feather, they bounce off of those layers. Now, when light waves
overlap, they can interfere with each other in different ways, depending on the wavelength of light, the angle that it enters, the crests and valleys
might cancel each other out to dim the color or make
it disappear altogether. But at certain angles for
certain colors of light, sometimes those waves line up and are added together to
make the reflected color even more vibrant. All of the light enters, but only some light is
allowed to come out. So when you look at the
feather from different angles, different waves of light line up as they're bounced back to your eye. That is what creates the sensation of shimmering, changing color. - Yeah, that's the fundamental
definition of iridescence is that the color changes depending on the direction
that you are looking at it. - Wow, that's pretty fancy. Not bad for some little dinosaurs. Okay, so hummingbirds are cool, but they aren't the iridescent royalty of the animal kingdom. That title probably belongs to beetles. Biologist J.B.S. Haldane once said that if nature did in fact have a creator, he has an inordinate fondness for beetles because beetles make up a quarter of all known animal species, and beetles themselves seem to have a particular fondness for iridescence. Not every beetle is iridescent, but the thousands that are, they have some of the most
unbelievable colors in nature. I mean, honestly, if you didn't know that some of these were real, you'd be forgiven for thinking
that they were painted by an artist or a YouTuber
trying to trick you. But they are real. The outer layer of a beetle's body is made of this super stiff
polymer called chitin. And when light hits these layers, it bends through a
process called refraction. Just like when we look
through a glass of water, the light waves seem to
bend and not quite line up. Same thing happens to light
in this beetle's outer shell. If those layers are spaced out just right, we're talking a couple hundred
billionth of a meter apart, certain colors of reflected
light waves will interfere and only certain colors of
light escape at certain angles. Sometimes, those refraction reflectors are in the farthest outer
layer of the beetle's body, or they can be buried a
little bit deeper inside. That's what creates the huge range of iridescence that we see in beetles. For instance, this one looks like a greenish reddish rainbow, but this one here, you hold it to light, it looks like a hologram. But being shiny and
iridescent may look cool, but one of the most important
questions we have to ask in biology is why
something is the way it is. Turns out, these flashy suits of armor may have some surprising functions. - You're probably thinking, "Oh, how could this possibly be useful as a defense or camouflage or something?" We're pretty sure that
nature doesn't bring about any kind of a change
that doesn't have a purpose. And in most cases, you know, the really bright metallic greens or living places with lush green forests with a lot of residual water, so being shiny and reflective
in just the right habitat and just the right ecosystem
can actually be beneficial. So the same beetle, if
you are six feet from it may be really visible, but if
you move back just 10 feet, it will start to fade into the background because of the way that the
light is playing with it and the position you're in observing it. It's also easy for us
to sort of look at this from the standpoint of human color vision which is actually pretty good, versus say, birds, which are
the most common predators of insects, including beetles. And so their perception
of what that looks like may be quite different than
what our perception is. There's also lots of other
things that being shiny might actually help you find mates. Depending on the color patterns, indicate that, you know, maybe
you don't taste very good so a bird would leave you alone. And in some cases, it may actually be about a non-visual thing altogether. Something like thermal
regulation is super important in insects because they can't
control their temperature. They are impacted by the
temperature around them. So having an ability to
reflect some of that UV back so that you don't overheat,
is probably a good thing. So there's lots of speculated reasons, but we still don't have definitive answers as to for one particular species of beetle why it's this way versus another species. But it obviously serves them, or it would have dropped
out of the population. - Now, what I think is the
coolest thing about iridescence is how completely
distantly related animals can sort of stumble on the
same physics for making color. This is a piece of abalone
seashell that I keep on my desk. It's made of layers and layers of a different hard material called nacre. Light is bending and
reflecting and interfering in almost the same way
as in the beetle's shell, using a totally different material. And since the seashell
stuff is basically rock, the iridescence can even be seen after these shells fossilized. This is a fossilized ammonite, and it's at least tens
of millions of years old, and it's still iridescent. That is incredible. But I've been saving my favorite kind of iridescence for last. The beetle that I'm about to show you, I have to admit, I didn't
believe it was real, but it is. (curious music) Come closer. It's really small. This is an actual earthling. It's a type of beetle called a weevil, and this particular one looks
like it was dipped in glitter, but this is also a form of iridescence. But to understand how this
kind of iridescence works, we're gonna have to go
to an unexpected place. The rare minerals vault at the Smithsonian in Washington D.C. The rocks and crystals
inside of this vault are some of the rarest and most
priceless minerals on earth. To get in, we had to go
through an armored door with an actual laser palm scanner like something out of a spy movie which I was not allowed to film
because of security reasons. - So this is an opal from Australia which is where a lot of
the great opals come from. This is actually a whale bone from Australia that in
fact has been opalized. (Joe laughs) - Every part of what you
just said is ridiculous. It's a whale bone from Australia that's- - I know.
- in the earth that is not just a bone anymore, but it's been turned into opal. - Yeah, and basically the bone was there. It gets saturated with water
that has silicon in it. That porous material that was the bone got filled in with little
spheres, opal, basically. - That's probably the coolest
fossil I've ever seen. (Joe laughs)
- Isn't that pretty? I mean, it's one of the
most beautiful, right? - Yeah, that is incredible. - It is. - Every day I walk in here and I go, "Something about the earth just amazed me in a different way." This is one of the most amazing opals (Joe laughs)
I've ever seen in my life. - [Joe] This grew in the earth. - [Jeffrey] This grew in the earth. Have you ever seen an
opal like that before? - [Joe] No, it's, I mean, it's coming from every direction.
- [Jeffrey] It is. - [Joe] And they're big chunks. - You'd swear that somebody
put a little battery inside of there, right? - Yeah.
- I mean, isn't that the most amazing? - It looks like an LED toy. - [Jeffrey] Look at this one. This is also an Ethiopian opal. - [Joe] This doesn't look real. - So you've got, opals are made up with these
little spheres of silica. These are spheres of
silica, silica and oxygen. They're probably formed out
of a silica rich solution. These little spheres of
silica are, you know, here, you know, very tiny. - Wow.
- Point five microns are stacked together very perfectly. I mean, it's kinda like, you know, we always stack oranges
in a grocery store, right? - Yeah.
- They're just all stacked together. And so-
- Wow. - when the light hits
those, they go hurrah, and you get these great flashes of color that we love in opals. - They are amazingly orderly. - Oh.
- Like it looks like somebody went in-
- Nature is- - with little tiny tweezers and was placing these-
- Well. - one by one. - Basically these little spaces in here, these are about the right separation size to cause refraction to take place. And you get the flashes of color. - Sure.
- Well, light comes in but what happens is light gets reflected off of different layers.
- Mhm. - [Jeffrey] And then in some
places, as the light combines, it combines constructively and
other places destructively. - So some colors are taken out, some are accentuated.
- Some, some, that's right. - Okay.
- And as you change the angle, that can change. Light coming in at different angles, different colors come
off at different angles. - As you're getting different parts of it, you know.
- [Joe] Wow. - The orientation hits your eye. I mean, those flashes are
just unreal, aren't they? Isn't that neat? - That is incredible. - Yeah. - The ordered structures
that cause iridescence in opals are called photonic crystals, a kind of crystal where the bending and reflecting of light is happening in three dimensions in a
periodic or repeated pattern. Photonic crystals are also
what make these weevils look like they were dipped in glitter. They're like walking opals. They are nano-sized,
three-dimensional, repeating structures in the beetle's outer shell. Some of them are built like honeycombs with orderly spaced pockets of air. Others are sort of the opposite of that with stacks of evenly spaced
spheres with air in between. And just like in an opal, light is bent, waves combine constructively
or destructively, and different flashes of color appear. All of these iridescent
colors are the result of physical structures that bend light, not pigments or fluorescence or any of the other ways that
color is created in nature. Just the strange and beautiful result of light waves interfering
with each other. What I love most about these things, isn't that they're beautiful. It's that we can look at rocks and shells and bubbles and birds and even beetles, and despite how different they all are, they're all tied together by
this colorful bit of physics. Kind of makes the universe feel a bit less and a bit more mysterious. (curious music)
Stay curious. That's right, Paul. I think we should call
ourselves The Beatles. Oh, you made yourself, you made it to the end screen. Thanks. By the way, if you haven't
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