Question

What formula is used to find the fluctuatoin of the shape of a body

Answer 1

The wave-interaction noise term of Einstein's formula for the fluctuations in the number of quanta received from a black-body radiator

varn=n̄1+1ehvkT−1

is verified by splitting the beam and cross correlating the photodetector noise currents. This technique eliminates the shot noise and measures the wave-interaction noise directly. Good agreement between theory and experiment is obtained when the effects of optical losses and the wavelength dependence of the optical filter are taken into account.