04 March 2013

Penzias, Wilson and some noise

The universe, Part 5
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Penzias and Wilson discovered an unknown microwave signal that turned out to be evidence for the origin of the universe. The story involves inconvenient pigeon droppings and more than a little serendipity. It ends with a Nobel Prize for physics and fame.

The Holmdel Horn Antenna
In part 4 of the series we saw how the cosmic microwave background radiation (CMBR) provides the earliest visible image of structure in the universe.

This time we're going to follow the curious story of its accidental detection by Penzias and Wilson.

The Holmdel microwave antenna in the image is at Bell Labs in New Jersey and was built in 1959 for early radio experiments with the Echo satellites (reflective balloons in earth orbit).

The horn antenna was being used by Arno Penzias and Bob Wilson in 1964. They were building sensitive, low noise, microwave radio receivers for use with the Echo satellites and had a serious problem with unexplained radio noise. They ruled out several possible causes, including a build-up of pigeon droppings in the horn, but nothing they could think of seemed to reduce the frustrating noise. Eventually they concluded it was not noise, but a genuine signal from an unknown source.

The noise explained - Another physicist, Robert Dicke had been searching for a signal just like the one that had caused Arno and Penzias so much trouble. Dicke had failed in his search but he heard about Penzias and Wilson's results and recognised it as relic light from the early universe, the elusive CMBR! The Penzias and Wilson paper and another by Dicke and three others were published together in July 1965. There's a lot more about this story in the book 'Genesis of the Big Bang' by Ralph A Alpher and Robert Herman who remembered the events well.

This is an interesting example of the way science progresses. Dicke, like George Gamow before him, had predicted the CMBR based on cosmological theory. Now that it had been found, the credibility of the theory was greatly strengthened.

Dicke was soon able to observe the CMBR himself, and later the COBE satellite would observe it in much greater detail, finding small irregularities in temperature. These too had been theoretically predicted.

When experimental results bear out theoretical predictions like this, scientists can be confident the theory is on track and more likely to be reliable.

WMAP, Planck and other instruments have refined the detail still further and strongly support the current Standard Model of Cosmology known as the Lambda-CDM Model..

Penzias and Wilson were awarded the Nobel Prize for physics in 1978 for their discovery.

  • Which interests you the most, the science itself or personal stories like this one?
  • Can you imagine the amount of dedicated effort involved in doing science?
  • Do you sense the determined search for truth in the hearts of dedicated scientists?

See also: 

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