What actually causes the bursting of a spherical air bubble? Is it because of the random collisions of air molecules with the bubble? But if that's the case, shouldn't the collision effects be symmetrical? I mean, if air molecules are colliding at one point of the spherical bubble, it's diametrically opposite point also experiences collision effects from air molecules, so as to cancel any imbalance. Or is the bubble collapse due to the drying of the water layer? But I've seen bubbles lasting weeks, if not months!