This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Why do we believe in a theory as fantastical as the Big Bang, whereby the universe began in a space no bigger than a pin prick and expanded outward in a cataclysmic explosion that beget everything we see (and can’t see) today? It all began in 1964 when two scientists, Robert Wilson and Arnold Penzias, discovered an unrecognizable static noise at the Bell Telephone Laboratory.
After eliminating potential terrestrial sources, such as static interference from New York City, the scientists decided to contact Robert Dicke, a physicist at nearby Princeton who was developing an experiment to study microwaves beaming to Earth from space. With Dicke’s help, the duo went on to discover that the “noise” was actually a signal from the birth of the universe, in the form of cosmic microwave background radiation, or thermal energy traveling to us from the beginning of time.
In 1990, a satellite probe known as the Cosmic Microwave Background Explorer, or COBE, verified this remarkable radiation with unprecedented precision, documenting temperature fluctuations within it—an indication that the universe may have expanded unevenly.
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The radiation is an imprint left on the cosmos as evidence, much like a fossil being evidence of a prehistoric age. The Microwave Background Radiation is uniformly distributed and present in all directions. This shows that the universe is uniform but it cannot be entirely uniform because if it were the stars and galaxies might not have ever formed, there would have to be fluctuations in the temperature. There must be quantum fluctuations in the density and the temperature fluctuations must still be present.
Today the Cosmic Microwave background has cooled to 2.725 degrees above absolute zero from its previous temperature at 273 degrees above absolute zero and therefore the radiation gleams in the microwave portion of the electromagnetic spectrum. It is invisible to the naked eye but if it could be seen it would glow with brightness uniform in all directions.
For the first time in history we can officially answer the question, “how old is the universe?” We can see these fluctuations in the image taken by COBE and as we look at this image, we are viewing the universe a few hundred thousand years after the Big Bang occurred 13.7 billion years. The fact that the universe is expanding has been one of the most profound realizations of the 20th century and demonstrates that the universe was once much smaller and denser. The Cosmic Background Radiation helps us to understand the conditions at very early stages of the universe. You yourself can see the background microwave when tuning between channels on your television and bear witness to the snowy screen while observing the lumpy universe.
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Expanded from The Lumpy Universe and Other Cosmic Mysteries at the World Science Festival blog.