For long, astronomers have been learning about the universe by studying galaxies and other celestial objects through visible light wavelengths.
Astrophysicists also study the invisible universe, not just the universe that is visible. The invisible universe has electromagnetic wavelengths which are shorter than visible light and are present in the gamma ray, ultraviolet regions and the infrared region. Each range provides scientists with a particular set of data.
However, it was astonishing to find that there is much more information at longer wavelengths.These long wavelengths are waves that are generated within microwave ovens. They also exist naturally in space, where they provide information about the birth and death of celestial objects, black holes etc.
In a project to develop orbiting communications satellites, Arno Penzias and Robert Wilson, from Bell Telephone’s New Jersey laboratories, used a ground-based antenna pointed at the sky. Astonishingly, it picked up a signal of an unknown origin at a wavelength of 7.35 cm. Hence a new discovery was made accidentally. This wavlength remained constant at irrespective of where it’s position, no matter where the antenna pointed.
In 1989, NASA launched the Cosmic Background Explorer (COBE) satelite into space to study this radiation without interference from the Earth’s atmosphere. It was equipped with instruments to measure the strength and wavelength of millimeter and centimeter waves. The results of the study were published in 1993. It showed a distinctive peak at 1.07 mm, a “blackbody curve,” which describes the electromagnetic waves emitted by any object above absolute zero temperature.
The measurement of the Cosmic Microwave Background (CMB), by COBE, combined with the fact that the universe is expanding, provides strong evidence for the Big Bang.
The COBE results also showed that the CMB and the temperature had small irregularities and differed slightly across the sky. This was a crucial piece of information about the state of the universe, while it was forming. The temperature differences in space, account for changes in the density of the hydrogen that filled the universe previously.These density variations gave rise to the birth of galaxies and huge empty voids.