# Force from Johnson Noise

A capacitor in parallel with a resistor will have a random noise $$\mathrm{voltage^2}$$ across it of average value $$V^2 = k_{B}T/C$$. If this is a parallel plate capacitor, you can show that the average attractive force between the plates is $$k_{B}T/d$$ where '$$d$$' is the spacing.

Note that this is not the same as the Casimir Effect (which is a quantum effect) -- it is a consequence of the thermal variation in the charges on the plates.

Is this effect significant in the universe between bodies ? Does it have a name ? Is there any practical use or effect ?