by S. Prasad Ganti

The greatest achievement of Cosmology in the last hundred years has been the Big Bang theory. How it was formulated and how it was proved. For most of the time human beings spent on the Earth, our known universe was just our solar system, up to planet Saturn which could be seen with the naked eye. With the advent of telescopes and spectrographs, came the facts that stars are like our own Sun and that they reside outside of our solar system.

What revolutionized the cosmic knowledge was the observation by the great astronomer Edwin Hubble who not only found that Andromeda was a different galaxy than ours, but also the fact that our universe of galaxies and galaxy clusters is expanding. All the galaxies are moving away from each other. The rate of expansion being proportional to the distance between them. The farther a galaxy is, the faster it is moving away.

Extrapolating this observation backwards, if the movie of our universe is played backwards, it should go to a point in time when it was very small. Thus the theory emerged that our universe was formed in a big bang. It was resisted by a rival group of scientists who believed in the steady state theory. Which states that the universe has stayed the same all the time. A universe without any beginning. Religious considerations also played a part in support of the steady state theory.

The Big Bang theory postulated that there should be some radiation left over from the instant of the Big Bang. A prediction made by physicist George Gamow. This radiation should be found uniformly all over the universe and should be in the microwave frequency range. It was aptly titled as Cosmic Background Radiation. Evidence for this came from a totally unexpected source. From two AT&T Bell Labs scientists Robert Wilson and Arno Penzias. They were working on a microwave antenna and had received some noise. They tried to eliminate the noise by cleaning the antenna and turning it in different directions. Nothing worked. The noise seemed to be very consistent and seemed to be coming uniformly from all the directions. As if we were drowned in this ocean of background noise.

Wilson and Penzias mentioned it casually to the scientists at Princeton University who were working on the Big Bang theory. What was noise to Wilson and Penzias was music to the ears of the Princeton scientists ! Thus cosmic background radiation was found and the Big Bang theory got validated ! Wilson and Penzias won the Nobel prize for Physics in 1978 for their serendipitous discovery.

The next question which came up was how did the structures in the universe like the galaxies and stars form when the background radiation is so uniform. There might have been some variation, however tiny in some places in the universe. This tiny variation led to the formation of all the matter and all the structures, thus went the theory. Finding out such minute variations on Earth proved to be immensely challenging. An experiment was devised involving the design and building of very sensitive instruments to measure the temperature of the cosmic background radiation coming from different directions.

These variations known as anisotropy, forms the basis of the story of how the instruments were conceived, constructed and launched on the COBE satellite (Cosmic Background Explorer), is well narrated in 2 books written by 2 of principal investigators on the project. “The Very First Light” written by John Mather and “Wrinkles in Time” by George Smoot. The books contain details on the instruments working under cryogenically cooled conditions in space. And the results produced and the validation of the theory.

John Mather and George Smoot won the Nobel prize for Physics in 2006 for showing the minute variations in the cosmic background radiation which led to the construction of our universe as we see it today. Clearly, each succeeding generation stands on the shoulders of the giants who preceded them. And carry the story forward.