COBE (astronomy)

COBE, the Cosmic Background Explorer satellite, was launched on November 18, 1989. COBE was designed and developed to investigate the origins of the universe and succeeded in producing images of the universe as it would have been in its infancy some 13.7 billion years ago.

COBE was the first satellite dedicated exclusively to cosmology.

On May 1, 1992 at a meeting of the American Physical Society, one of COBE’s research leaders, George Smoot, announced that the precise measurements taken with the COBE showed hot and cold regions throughout the universe with temperature differences of a hundred-thousandth of a degree. “At the time captured in our images, the currently observable universe was smaller than the smallest dot on your TV screen and less time had passed than it takes for light to cross that dot.”

The accomplishments of the COBE were so significant that COBE’s originators, John C. Mather (NASA Goddard Space Flight Center) and George F. Smoot (Lawrence Berkeley National Laboratory and the University of California at Berkeley) were awarded the 2006 Nobel Prize for physics.

Instrumentation

COBE was developed by NASA's Goddard Space Flight Center to measure the diffuse infrared and microwave radiation from the early universe. To accomplish this, COBE carried three instruments:

• Diffuse Infrared Background Experiment (DIRBE) to search for the cosmic infrared background radiation;
• Differential Microwave Radiometer (DMR) to map the cosmic radiation and variations in the radiation;
• Far Infrared Absolute Spectrophotometer (FIRAS) to compare the spectrum of the cosmic microwave background radiation with blackbody radiation.

The extent and precision of the data gathered has shifted the entire field of cosmology. So much so, that the Nobel Foundation of the Royal Swedish Academy of Sciences, went so far as to say, "the COBE-project can also be regarded as the starting point for cosmology as a precision science: For the first time cosmological calculations (like those concerning the relationship between dark matter and ordinary, visible matter) could be compared with data from real measurements. This makes modern cosmology a true science (rather than a kind of philosophical speculation, like earlier cosmology)."

Theoretical Rationale for COBE

The initial premise of the COBE research was that the universe had originated in a sudden expansion from a submicroscopically small point, the Big Bang Theory. The competing theory, called the Steady State Theory, maintained that ours was a consistent and unchanging universe which neither grew smaller or bigger and had never come into being—it was timeless with neither end or beginning. The Big Bang theorist maintained that the universe was expanding, it had begun from something else and could conceivably come to an end.

The Big Bang Theory could be supported if there was evidence of background radiation (referred to as cosmic microwave background radiation, CMB radiation) permeating the entire universe—leftover radiation. The leftover radiation would be evidence that the universe had a beginning at which time it had been filled with intense radiation. This state would have been long before the appearance of matter—elements, gases, stars and galaxies. Although CMB radiation was originally predicted in 1948 by Georgiy “George” Antonovich Gamow, it was not until 1964 that Arno A. Penzias and Robert W.Wilson, researchers at AT&T's Bell Laboratory (Holmdel, N. J. USA), discovered that there is CMB radiation evident in all directions from Earth. A clear example is the radiation evident on a TV screen. Much of the black and white static is in fact CMB, photons of energy still cooling after the Big Bang.

Ripples in the space-time fabric

One of the most significant aspects of the COBE data was gathered from the DMR (Differential Microwave Radiomters) which measured difference in radiation. This variation, or anisotropy, in the backgound radiation consists of small temperature fluctuations in the blackbody radiation left over from the Big Bang. The average temperature of CMB radiation radiation is 2.725 degrees Kelvin. The variations in the temperature are very small, thousandths of degrees.

As Smoot has explained, “The tiny temperature variations we discovered are the imprints of tiny ripples in the fabric of space-time put there by the primeval explosion process. Over billions of years, the smaller of these ripples have grown into galaxies, clusters of galaxies, and the great voids in space."