Nobelmen: Cosmic microwave radiation and the Big Bang

The Prize:

The 2006 Nobel Prize in Physics to John C. Mather and George F. Smoot “for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation” which was a pivotal turn in cosmology evolving into a precise science.

The Science:

In 1964, Arno Penzias and Robert Wilson uncovered a strange phenomenon: cosmic background radiation. This radiation is the same phenomenon that can be picked up by your television: the “snow” you see on channels that your television doesn’t receive. Penzias and Wilson first thought that this effect was mere “noise” from their radio receivers, but later discovered it to be far more significant. Their discovery led to the 1978 Nobel Prize in Physics.

The Big Bang model proposed by Georges Lemaître describes the birth of our universe as an expansion from an intensely hot and dense point. Cosmic microwave radiation had been predicted by others as a by-product of the Big Bang. The theory states that the “body” that started our universe emitted intense radiation called blackbody radiation (the electromagnetic radiation emitted from an opaque object). The higher the object’s temperature, the shorter it’s emitted wavelength. This radiation cools as time passes and the universe expands. If the Big Bang model is correct, we should be able to measure the wavelength of the radiation and check it against a model of blackbody radiation behaviour. Proving that the radiation fits a blackbody radiation model would lend significant support to the Big Bang theory.

In 1989, NASA launched the Cosmic Background Explorer (COBE) satellite into orbit with a mission to measure the spectrum of the cosmic background radiation. John Mather led the project, which involved over 1,000 collaborators. George Smoot worked on determining if there was any difference between the temperatures of the radiation coming from different directions towards Earth. Differences in temperature could indicate how matter and energy accumulated in the early days of our universe.

After only nine minutes of recording time, the COBE satellite found that the wavelength distribution of the background radiation corresponded to a perfect blackbody spectrum and recorded an average background temperature of only 2.7 degrees above absolute zero. The results agreed with previous ground-based and balloon-borne instruments and offered very convincing proof of the Big Bang theory.

The COBE satellite also detected minute temperature differences (changes of less than a hundred-thousandth of a degree!) and drew a “sky-map” of the temperature fluctuations. The map is lovingly referred to by NASA as the universe’s “baby picture.” This map helped astronomers understand how matter may have aggregated in the early days of our universe in order to develop into galaxies and stars, rather than being spread out evenly throughout the universe.

The Significance:

The results of the COBE satellite project were so revolutionary and exciting that world-renowned physicist Stephen Hawking (author of bestseller A Brief History of Time) called it “the greatest discovery of the century, if not all time.”

By far the most significant achievement of the COBE project was to turn modern day cosmology into an exact science. For the first time, scientists could experimentally if indirectly probe the skies for the density of visible matter and dark matter by measuring their temperature.

Since the original COBE observations, other higher-resolution projects have built on COBE results, including the Wilkinson Microwave Anisotropy Probe, launched in 2001, and most recently, the Planck spacecraft, launched in May of 2009. Although alternative explanations for the cosmic microwave background have been put forward, to date, the most convincing theories support the Big Bang theory.

What you may not know:

Like many ground-breaking discoveries, COBE posed as many questions about the universe as it answered. An unexpected result from the COBE project is the uniformity of the sky-map. This is surprising because although the universe should have eventually reached an equilibrium, it appears to have reached equilibrium too quickly. Estimates put the equilibrium point at age 380,000 years—requiring energy to move at the seemingly impossible rate of 100 times the speed of light.

One explanation for the homogeneity of the temperature of the universe is an “inflation” event. It is possible that shortly after the Big Bang, the universe experienced a dramatic burst that expanded and filled it with an unknown form of “primordial energy.” The jury is still out on this and other mysteries spawned by COBE. Future missions to understand the beginnings of the universe and determine the validity of the inflation model, by measuring gravity, for instance (missions LISA, and the Big Bang Observer), may be launched shortly.