h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Soap bubbles are very funky. Not only are they examples of what mathematicians call 'minimal surfaces', meaning that they encompass the greatest possible space they can with the least surface area, but they also boast cool moving patterns due to the interference of light.

The minimal surface thing is demonstrated not only by the basic spherical single bubble, but also by networks and systems of bubbles joined together. Play and see.

The colour patterns happen because the thickness of the bubble's soapy skin is not constant, but has variations due to the air bumping it around. As the thickness of the skin varies, so does the wavelength (colour) of the light that gets reflected most. It's this colour that you see. The science of thin films is complicated, but lots of fun. And you get to play with soap bubbles.

I've also heard that it is possible to make anti-bubbles- hollow spheres of air with water inside and out. Anyone ever been able to make one?

With anti-bubble, do you mean a bubble of water with a film of air separating it from the rest of the water?

Antibubbles..what a curious idea..where did you hear about this?

Antibubbles are structures like a normal bubble, but with water where there would be air, and vice-versa. I read about this somewhere on the 'net, but I can't remember where. I do remember that the site said you need to inject a coloured liquid into another to be able make and to see them. I am not sure of the quality of the physics, but will look into it.

I enjoyed your comments on soap bubbles. I too am a bathtub bubble meditator. You can get anti bubbles in the bath tub in the following manner. You need a clean bath tub, no soapy stuff, and best that you're not in the tub. Let the faucet drip slowly or drip drops of clean water from a good height. The splash will produce tiny drops of water which will skitter across the surface and bounce around the tub for a second or two. Then they dissolve into the surface.(I may be wrong about the complete cleanliness requirement as you may need to introduce a small amount of soap film). I think this is what you're referring to.
I've been fascinated by the attraction of two bubbles when they come in close proximity to each other. If you look carefully you can see that this occurs at the border of the meniscus of each of the bubbles. The meniscus and bubble can be also seen perhaps more cleary in the shadow reflection on the bottom of the tub, but you will need an incandescent light bulb to best cast the immage. Fluorescent or difuse or multiple lights don't work. I've worked out the attraction forces schematically based on the meniscus. It turns out that the bubbles are forced together rather than attracted together. The membrane forces are interrupted at the meniscus interface and the unballanced forces are such that the sides of the bubbles opposite the meniscus interface exert more force. This is a little better explanation than "air bubbles trying to ride up on each other." I can explain better with a diagram but I'm uncertain how to accomplish this on this site, ie how to get the diagram into the text.
I'm trying to apply this information to a theory of gravity which would be akin to it. Perhaps bodies of mass are forced together from the outside rather than attracted to each other from the inside. Any comments?

Changes in the diffraction color of the soap bubble are also driven by fluid flow on the surface of the bubble, say its a free soap bubble drifting in the air, as the fluid flows from the top of the bubble to its bottom, collecting into a drop at the bottom.

As the drop at the bottom begins to fall, the bubble bursts.

Thickness of the bubble membrane determines diffraction color, depending on harmonic resonance of light with the substance of the bubble membrane, longer wavelength red areas forming preferentially at the bottom of the bubble, shorter wavelength blue patches higher.




Negative bubbles can also be observed with formation of proteinoid coacervates* in aqueous media.




*Thought by some to be precursors of cellular life, though I'm personally inclined to doubt that.