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R. Barrett and P. P. Delsanto
(CMB). It displays a typical thermal radiation spectrum, in which the initial
3000 K radiation spectrum of the primordial hot plasma is red-shifted to one
corresponding to a temperature T CMB of just 2.72548 K.
In 1964 Arno Penzias and Robert Wilson, while testing a microwave
antenna at the Bell Telephone Laboratories, accidentally found a “noise”
coming uniformly from every direction in the sky. That “noise” was quickly
recognized as being the cosmic microwave background, a.k.a. the relic radiation, arriving to us after having survived more than thirteen billion years of
travel through space–time. Penzias and Wilson received the Nobel Prize for
their discovery in 1978. Their experimental observation sounded the death
knell for Hoyle’s steady state universe.
Also, now at last Olber’s paradox is explained. The sky is bright at night.
However, it appears black because our eyes sense only a very small portion of
the electromagnetic spectrum, and the white light from the recombination era
has been red-shifted into the microwave region where our eyes see nothing.
For a microwave antenna, the sky is uniformly bright, not as the surface of
a suitably red-shifted star, but as a red-shifted hot plasma transitioning to a
neutral gas.
The uniformity of the CMB, both in intensity and temperature is amazing,
with fluctuations of only 1 part in 100,000. This uniformity raises an interesting question. As we have seen, the first 380,000 years of the universe’s life
are impenetrable to our observations. When we look back in time through
our telescopes, 4 our view is stopped, as if by a curtain, by the recombination taking place at this time, at what is known as the last scattering surface.
However, distant portions of the sky, from which the radiation comes, were
at that time separated by more than 380,000 light years. As no physical
“messenger” can travel faster than light, no causal interconnection can have
taken place between these far-flung regions since the Big Bang. Then how
is it possible that these independent regions can have kept such an amazing
synchrony, arriving at the same average temperature in the same time? We
shall come back to this point in the next section.
Yet differences among various areas of the sky do exist. Evidence of this
inhomogeneity can be seen in Fig. 10.9, where the temperature of the radiation coming from the whole cup of the sky is shown. To be sure, the
unprocessed data from the sky are not as clean as in Fig. 10.9, since there are
also microwave emitters in the foreground, primarily from the Milky Way. In
order to study the primordial radiation field, these nearby sources had to be
4 The light our telescopes receive from distant objects has taken a long time to reach us. What we
see is the situation as it was when the light was emitted, and not as it is now. Our telescopes are
therefore “looking back in time.”
R. Barrett and P. P. Delsanto
(CMB). It displays a typical thermal radiation spectrum, in which the initial
3000 K radiation spectrum of the primordial hot plasma is red-shifted to one
corresponding to a temperature T CMB of just 2.72548 K.
In 1964 Arno Penzias and Robert Wilson, while testing a microwave
antenna at the Bell Telephone Laboratories, accidentally found a “noise”
coming uniformly from every direction in the sky. That “noise” was quickly
recognized as being the cosmic microwave background, a.k.a. the relic radiation, arriving to us after having survived more than thirteen billion years of
travel through space–time. Penzias and Wilson received the Nobel Prize for
their discovery in 1978. Their experimental observation sounded the death
knell for Hoyle’s steady state universe.
Also, now at last Olber’s paradox is explained. The sky is bright at night.
However, it appears black because our eyes sense only a very small portion of
the electromagnetic spectrum, and the white light from the recombination era
has been red-shifted into the microwave region where our eyes see nothing.
For a microwave antenna, the sky is uniformly bright, not as the surface of
a suitably red-shifted star, but as a red-shifted hot plasma transitioning to a
neutral gas.
The uniformity of the CMB, both in intensity and temperature is amazing,
with fluctuations of only 1 part in 100,000. This uniformity raises an interesting question. As we have seen, the first 380,000 years of the universe’s life
are impenetrable to our observations. When we look back in time through
our telescopes, 4 our view is stopped, as if by a curtain, by the recombination taking place at this time, at what is known as the last scattering surface.
However, distant portions of the sky, from which the radiation comes, were
at that time separated by more than 380,000 light years. As no physical
“messenger” can travel faster than light, no causal interconnection can have
taken place between these far-flung regions since the Big Bang. Then how
is it possible that these independent regions can have kept such an amazing
synchrony, arriving at the same average temperature in the same time? We
shall come back to this point in the next section.
Yet differences among various areas of the sky do exist. Evidence of this
inhomogeneity can be seen in Fig. 10.9, where the temperature of the radiation coming from the whole cup of the sky is shown. To be sure, the
unprocessed data from the sky are not as clean as in Fig. 10.9, since there are
also microwave emitters in the foreground, primarily from the Milky Way. In
order to study the primordial radiation field, these nearby sources had to be
4 The light our telescopes receive from distant objects has taken a long time to reach us. What we
see is the situation as it was when the light was emitted, and not as it is now. Our telescopes are
therefore “looking back in time.”