The cosmic microwave background (CMB) radiation has a temperature of 2.73K.
(a) What is the photon energy density in the Universe?
(b) Estimate the number of CMB photons that fall on the outstretched palm of your hand every second.
(c) What is the average energy due to CMB radiation that lands on your outstretched palm every second?
(d) What radiation pressure do you feel from CMB radiation?