Here is an image I found which illustrates dispersion forces:
One helium has its electron cloud repelled by the other helium's electron cloud, which exposes the nucleus and gives an induced dipole which holds the atoms together weakly. But when two helium atoms approach each other, what determines which atom will have its electron cloud repelled? I would think that both electron clouds would equally repel each other. Also I am guessing that this effect will get stronger as temperature is lowered (since helium is a liquid at very low temperatures), but I am not sure why.