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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Transcript of CA 10.01 Discovery of CMB (Cosmic Microwave Background)