Why are bubbles perfect spheres?

Question

I've even seen smoke bubbles that do this.

Answer 1

Equal pressure from the inside and at the total circumfrence.

Answer 2

They're essentially perfect spheres because of surface tension.  Surface tension is the amount of energy it takes to make surface per unit surface area.  A sphere minimizes the surface area for a given volume and therefore minimizes the energy required to make surface.

Answer 3

I don't know... They do look perfect and pretty.

Answer 4

They're not, really. The air pressure at the top of the bubble is always less than the air pressure at the bottom. But the difference is so small that you can't see the difference.