Caption: The nearly perfect blackbody spectrum of the cosmic microwave background (CMB) from the Cosmic Background Explorer (COBE, 1989--1993).
Currently, the best result for CMB Temperature T = 2.72548(57) K (Fixsen 2009)
Features:
Wavenumber is inverse wavelength measured in this case in inverse centimeters. It is also frequency divided by the vacuum light speed 2.99792458*10**10 cm/s, and so is actually a frequency. Wavenumber is given by the formula
which for T=2.72548 K gives
As well as yours truly can read the plot, the maximum is at ∼ 5.3 cm**(-1), and so the calculation agrees with the plot as far as yours truly can tell.
Thus, the CMB as aforesaid is strong evidence for Big Bang cosmology.
The complete evidence for Big Bang cosmology is quite convincing.
It would be astonishing if it were just plain wrong.