The Universe began with a bang, but that discovery was a complete accident. In the 1940s, George Gamow and his collaborators put forth a radical idea: that the Universe that was expanding and cooling today was not only hotter and denser in the past, but arbitrarily so. If you extrapolated back far enough, you'd have a Universe hot enough to ionize all the matter in it, while even farther back you'd break apart atomic nuclei. The idea became known as the Big Bang, with two major predictions arising:
- The Universe we began with wouldn't have only matter made of mere protons and electrons, but would consist of a mix of the light elements, fused together in the high-energy, early Universe.
- When the Universe cooled enough to form neutral atoms, that high-energy radiation would be released, and would travel in a straight line for all eternity until it collided with something, red shifting and losing energy as the Universe expanded.
This "cosmic microwave background" was predicted to be just a few degrees above absolute zero.
In 1964, Arno Penzias and Bob Wilson accidentally discovered the Big Bang's leftover glow. Working with a radio antenna at Bell Labs to study radar, they found uniform noise everywhere they looked on the sky. It wasn't the Sun, or the galaxy, or Earth's atmosphere... but they didn't know what it was. So they cleaned out the inside of the antenna with mops, removing pigeons in the process, but still the noise persisted. It was only when the results were shown to a physicist familiar with the Princeton group's (Dicke, Peebles, Wilkinson, etc.) detailed predictions, and with the radiometer they were building to detect exactly this type of signal, that they recognized the significance of what they found. For the first time, the origin of our Universe was known.
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