Why RED BUBBLES are impossible… or are they?!

- Go look at a picture of a bubble or I guess I could just show you one.

Ha ha, if you don't trust me, 'cause we've never met, go search online for pictures of bubbles and look at what colors are on the surface if you don't have color blindness.

For me it's magenta, yellow, green sometimes, sometimes a little bit of blue, but never red.

In fact, if you search red bubble what do you think you get?

If you search it with two words, then you get red bubbles, but they're all clip art.

They're all fake.

An everyday mystery.

It doesn't seem like red bubbles are possible.

And I wanted to know if that's actually true and if so, why?

Why do they even have a color at all?

But it's a phenomenon that's kind of the opposite of rainbows.

What I mean that is that in bubbles, colors are removed.

They are canceled and it all has to do with thin films, which is something that you learn about if you're taking physics and you get to wave interference.

What's that?

Well, there's this phenomenon that happens sometimes near a seashore.

It's really cool, where a wave comes in and crashes on the shore and it can reflect back and travel backwards.

And then if it hits an incoming wave, you get these monster waves when they collide.

The monster wave happens because of something called wave interference, where you can add up two waves and they combine for a bigger wave and it is pretty cool looking.

So now the same thing can happen with light, because light is a wave.

This makes sense.

If you imagine shining two lights on a spot, they add and they look even brighter than if you have just one of the lights, but you can also shine two lights and get the spot to completely disappear.

You can get destructive interference.

So interference goes both ways.

If you have a crest and a crest, two ups, then you add and you get a bigger up.

I can't do it.

Or if you have a crest and a trough, an up and a down, then they add and they cancel out and you get zero.

So the next step, this wave interference thing that can make light cancel, it's so cool, can create colors from white light.

You have to have a really, really, really thin film.

I'm gonna make one.

So this is my film, but it's not like this; it's this 'cause it's really thin, like on the order of a few dozen molecules.

This is not a few dozen molecules.

This is probably trillions of molecules thick.

But imagine this is a few dozen molecules thick, so thin.

So it could be like a coating of some kind of paint.

It could be a bubble film.

It could be oil.

If you go search an oil spill on a road, it's almost the same colors, right?

It's got that yellow, the magenta, blue, but not red similar to bubbles.

Suspicious huh?

Yeah.

So what you're seeing there is white light and you know what white light is, right?

It's a combo of all of the colors, got white light coming in with all of its colors onto my film.

And then some of it reflects off of the top of the surface like so, and some of it goes into the surface like this.

This is great.

So some of it goes into the film and reflects off of the bottom surface of the film and then comes back out over here.

And now we have to remind ourselves of the fact that light has a wavelength.

Light is a wave.

You can't actually cut light waves in real life but this is gonna have for our purposes.

It looks like this wave, wave, wave, wave, wave.

It's a wave of electromagnetism.

It's not like water or anything.

It's an electromagnetic wave.

A light has these peaks and troughs.

And if you wanna measure how big a light wave is, yeah, you can measure how tall it is.

That's the amplitude.

But another important way, especially for light, is to measure from the up to the down to the up.

So this distance right here is the wavelength or this trough to trough or whatever.

That's one wavelength.

And the reason it's so important to know the wavelength is because the wavelength is different for different colors of light.

So like blue has a shorter wavelength than red, for example.

And I'll tell you when you can recall that little fact later, because it's important.

So when the film is similar in thickness to one of these wavelengths, then you can get interference.

So this is it.

This is almost the end of the explanation.

So you have light coming in and reflecting off the surface, got that?

And then this one that went into this film went farther.

So they were traveling together beforehand.

They were in sync like this and the crests and troughs are matched up.

And then now this one's traveled farther.

So now they're out of sync.

Get it?

So now you can see that this trough is matched up with this crest and those will cancel because they're out of sync.

Now is the time, now you can recall that the different colors of light have different wavelengths.

So depending on what angle this light beam is coming in or depending on the thickness of the film, then you'll get a certain distance traveled by the light that went into the film.

And that tells you how far off these waves are from each other.

And then that will determine which colors get blocked because all the colors have different wavelength.

So for certain thicknesses or certain angles you get red canceled out or you get blue canceled out or yellow.

So we're almost about to see why you never see red in a bubble.

So if you cancel, say blue, if you take blue out of white light, then you end up with something that looks kind of yellow.

If you cancel red, you take red out of white light, you'll end up with kind of a green, blue, turquoise or as they say cyan, and if you take yellow out, then you end up with a magenta color.

So the only colors you can see in a bubble are the result of subtracting out one color.

So you never get red because you would have to cancel out yellow, orange, green, blue, indigo, violet, all of the rest of the visible spectrum in order to see red.

You can't get pure blue either.

You can't get pure anything because you're seeing just this result of color mixing.

So could you ever get a red bubble?

If you take a bubble into the dark and shine just red light on it, you'd be able to get a red bubble.

But what you would see would be stripes, because red light is getting canceled and enhanced and then canceled, enhanced, 'cause you're seeing the thickness of the bubble where the red is getting canceled.

So this tells you something about the thickness of the bubble.

It gets thicker as you go down 'cause of gravity.

The liquid is drooping and then you end up with red, that's one half a wavelength off and then two half wavelengths and then three half wavelengths and so forth.

You can even see the thickness of a bubble in white light.

You just end up getting stripes of color.

It's really pretty.