The Science of White

[00:00] This is a type of shower gel called foam burst. It comes out blue, but if you agitate it, it turns into a foam and it changes color from blue to white. Some water that's been stained a dark green, there's some soap in there. If I shake it, it turns white.

[00:14] Clouds are white. Lots of things are white. Why is that? If you take white light, and remember, white light is just all the colors of the spectrum mixed together, and you shine it onto the shower gel, then the shower gel absorbs some of the red

[00:27] and green parts of the spectrum. And the blue parts are scattered in all different directions, some of which ends up in your eyes. Scattering is just reflecting, by the way, except that it's off a rough surface instead of a smooth surface.

[00:41] So it doesn't obey the laws of reflection. But anyway, that's why the shower gel is blue. Because of all those bubbles, you've got all these different surfaces all oriented in different directions. And when light lands on one of these surfaces, some of the light gets reflected, some of it gets transmitted.

[00:55] The transmitted light is refracted, but that's not so important here. The important thing is the light bounces around inside the foam. Some of it getting transmitted, some of it getting reflected. And eventually, after this chaotic bouncing around inside the foam,

[01:09] some of it will bounce back out towards your eyes. And crucially, this scattering of light, as it's called, happens to all the colors of the spectrum. So the light that reaches your eyes is that full spectrum of colors mixed together.

[01:22] It's white. And that's why foam looks white. Well hold on the shower gel still has that blue dye in it So when some of the light is transmitted through those thin layers of the shower gel the red and green parts of the spectrum

[01:36] should get absorbed by that dye and the blue parts scattered. So why doesn't the foam look a little bit blue? Well, yeah, it does. It looks a tiny bit blue. It's just completely overwhelmed by the scattering

[01:48] of all the colors of light. And that makes sense because foam is mostly air. This big thick chunk of shower gel here looks pale blue. So if you spread that out and make it mostly air,

[02:00] then that handful of very thin surfaces that the light passes through in the foam state isn't gonna experience much of that scattering and absorption from the dye itself. I've got some blue liquid here,

[02:13] and if I move the camera, suddenly it turns completely bright white. What foam does is kind of average out these two extremes because the surface of the foam is oriented in all these different directions.

[02:26] There's no one sweet spot where you get glare. You get a little bit of glare from the entire foam surface and the glare of reflection from the light mostly wins out and the foam is white in appearance. So in simple terms, the reason lots of things are white

[02:40] is because of scattering. It's why clouds are white. You've got these droplets of water and they're acting like the surface of the foam or the surfaces within the foam. Otherwise the light is bouncing around off and in

[02:52] and through those droplets of water in all different directions. Eventually that light finds its way to your eyes and you see it as a white cloud.