Document Type

Course

Journal/Book Title/Conference

Physics 3710 – Intermediate Modern Physics, Spring 2018

Publication Date

1-8-2018

First Page

1

Last Page

6

Abstract

The Cosmic Microwave Background (CMB)

As previously noted, the universe is filled with microwave radiation. The frequency spectrum of this ubiquitous radiation follows a blackbody curve, as shown to the right. (http://map.gsfc.nasa.gov/media/ContentMedia/990015b.jpg) Note that photon energy (proportional to 1/wavelength) increases to the right. You might think the curve shown is the plot of a theoretical equation, but what is shown is actual measured data taken during the flight of the COBE (Cosmic Microwave Explorer) satellite/microwave observatory in 1990. The uncertainties in the measurements are about the thickness of the curve plotted. When compared with a theoretical blackbody curve the disagreement is less than one part in 2000. The CMB isn’t LIKE a blackbody spectrum—it IS a blackbody spectrum! Note that the maximum in the CMB spectrum is at a wavelength of about 2 mm. The energy of a photon of that wavelength is E = hc λ 6.6x10–4 eV.

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