Eli5: What makes motor oil shimmer and change colors as you view it from different angles?

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Eli5: What makes motor oil shimmer and change colors as you view it from different angles?

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When it’s in a really thin layer the light will either go through the oil, reflect off the bottom, and go back to the top or just reflect off the top. When the distance between the top and the bottom is a small multiple of the wavelength, then the light that is a full multiple of the wavelength will add together (add the light that bounced off the top to the light that bounced off the bottom), while the light that is a half multiple of the wavelength (the multiple ends in 0.5) will subtract. The result that is some wavelengths are amplified, and the others are reduced, so while white sunlight hit it, most of the reflected light might be green or red, depending on the thickness.