CA 10.01 Discovery of CMB (Cosmic Microwave Background)

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THE DISCOVERY OF CMB
Cosmic Adventure 10.01

The Hidden Light
Besides the light emitted by
stars, there is a kind of radiation
that is fleeting around and filling
the universe. They cannot be
seen by the human eyes. So they
remain hidden for thousands of
years - no, for billions of years,
until some human beings started
to listen to the great emptiness
with very precise machines not
devised for the purpose.

The Horn Antenna
It started in the early
1960s, when Bell Labs
constructed a horn
antenna system at
Holmdeln, New Jersey,
USA. It was designed
to capture radio
signals bounced off
from satellites and was
used with an early
satellite system called
Echo.

Arno Penzias & Robert Wilson
Arno Penzias (1933-) is an
American physicist and
Robert Wilson (1936-) is an
American astronomer.
Bell Labs hired them to
carry out checking and
evaluating the antenna.

Decommissioned Instrument
But after a few years, another
satellite was launched and Echo
became obsolete. Since the
antenna was no longer tied to
commercial applications,
Penzias and Wilson got the
permission to use it to analyse
radio signals from the space
between galaxies.
Physics History, June 1963: Discovery of the
Cosmic Microwave Background," APS News,
July 2002.

Nightmarish Whispers
However in 1964, they detected a small but persistent “noise” in the microwave
range was coming from every direction. These noise was not from any radio site on
earth either. They could not explain or get rid of it from their radio antenna signals,
no matter how hard they tried.

Similar to TV Noise
This external disturbance is
similar to the noise (TV
‘snow’) we found in our TV. It
only contributes up to about
1% of the incoming signals.
But if they were to conduct
precise experiments with the
antenna, they would have to
find a way to remove the
static.

Could not Find Problem. Pigeons?
.
At first we thought it
was due to dirt such as
pigeon deposits on the
antennae. But after
cleaning them up, the
noise persisted.
We utterly had no idea
of what the “problem”
with our experiment
was. We became
depressed as this
unexplained radio noise
would make our
measurement a failure.

Trouble from outside
Milky Way
Throughout the struggles to get
rid of the noise, they learned
that these noises were coming
from all directions uniformly in
the sky. The noise was there
whether they pointed the
antenna toward the Sun or the
Milky Way or other empty parts
of the sky. This could only mean
that the signal might have come
from far beyond our Galaxy.

Very Old Radiations
The evenness of distribution told them that the signal might have originated in places
very far away, or equivalently, very early in time. It might have been some system of
background radiation that had diffused through space a long, long time ago.

Noise had been Predicted
At the period around the 1940s,
the American scientists George
Gamow (1904-1968) and his
students Robert Herman (1914-
1997) and Ralph Alpher (1921-
2007), were working on the
assumption that if the universe
was once a hot and dense fireball,
in the intervening years it should
have cooled down considerably. It
should then be possible to find
remnants of the original energy by
examining the cosmos.

Fruitful Enquiries
Penzias and Wilson started asking
people for ideas and they learned
about Robert Dicke and Jim
Peebles of Princeton University.
At that time in the 1960s in Princeton
University, physicist Robert Dicke
(1916-1997) was also working on the
details of the left over radiation.
Dicke was about to design an
experiment to test this hypothesis
when he was contacted by Penzias.
Upon hearing of Penzias’ and
Wilson’s discovery, Dicke immediately
recognized that this radiation was
what they were looking for.

What a Discovery!
In view of the similarities, Penzias and Wilson began to realize what they
had encountered. The noise that had been perplexing them was actually
the cosmic background radiation (CMB).

Nobel Prize 1965
In 1965, Penzias and Wilson published an article in Astrophysical Journal on
their discovery of the radio signal remaining supposedly from the beginning of
the universe. In 1978, Penzias and Wilson were honoured with the Nobel Prize.

A Wonderful Story
This discovery of the CMB by Penzias
and Wilson was serendipitous. But it
was indeed a wonderful story.

The Hidden Treasure
The things that render it so
much fun was that Penzias and
Wilson were not actually looking
for the CMB; they only stumbled
upon it while they were working
on something else.
They started with trying to find
the source of a problem that
might have jeopardized their
experiments and ended in
finding one of the most prized
trophy in astrophysics.

The Significance of CMB
“The CMB is a cosmic background radiation that is fundamental to
observational cosmology because it is the oldest light in the universe.”
Wikipedia
“The cosmic microwave background is the most ancient image we have of
the universe and therefore it's one of the most valuable tools to
understand the universe’s origins.” Marcos Cruz of the Instituto de Fisica de Cantabria,
in Santander, Spain.
The discovery of CMB is regarded as one of the foremost cosmological
deed next to the discovery of an expanding Universe by Hubble and that
of Planck’s constant by Max Planck.

National Historic LandmarkThe horn antenna was
designated a National Historic
Landmark in 1990. Its
significance in fostering a new
appreciation for the field of
cosmology and a better
understanding of our origins
can be summed up by the
following statement:
“Scientists have labelled the
discovery [of the CMB] the
greatest scientific discovery of
the 20th century.”
Schoenstein, Ralph, "The Big Bang's
Echo," All Things Considered, NPR, May
17, 2005.

MAPPING THE CMB
To be continued on: Cosmic Adventure 10.02

CA 10.01 Discovery of CMB (Cosmic Microwave Background)

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CA 10.01 Discovery of CMB (Cosmic Microwave Background)