How did the universe evolve?
If the Universe is expanding, it means that once it was much smaller than
it is now. Arno Panzias and Robert W. Wilson made an important discovery
in 1964, while working for Bell Laboratories. They were trying to understand
the source of background signals which interfered with radio communications.
(Arno Panzias is currently director of ATT Laboratories; Panzias and Wilson
shared the Nobel Prize in Physics for the work mentioned below). During
their work, they found that there was a constant background signal with
a wavelength of 7.35 cm. The intensity of this signal was uniform over
the entire sky.
They measured the "temperature" of this radiation which is supposed
to come from the beginning of the expansion of the universe. This electromagnetic
radiation (cosmic background radiation) has a spectrum
(or pattern of intensity as a function of wavelength) characteristic
of a "black-body" at the temperature of 2.73 K (degree Kelvin, i.e.
2.37 degrees from absolute zero; melting of ice is at 273 degrees in this
scale) or, equivalently, has a characteristic wavelength of 7.3 cm ( black-body
radiation is the electromagnetic radiation that is emitted by a body of
Such measurement is consistent
with the theory of an expanding universe, since, as the universe expanded,
An objection can be raised. If the measured temperature of the universe
Another way to think about it is that at the beginning the universe was extremely dense and hot. As it expanded and cooled, it ceased to be in thermal equilibrium; now there are lumps of matter (stars, galaxies) which are much hotter; however, the signature radiation of the expansion still permeates the universe.
COBE map of the cosmic background radiation; variations with
respect to the average are indicated in colors (red:hotter, blue: cooler).
For more information click this NASA site
Internally related links:
spectra of stars