In 1964, 2 American astronomers named Robert Wilson and Arno Penzias made a really profound accidental discovery. It shaped our understanding of the universe and of cosmology.
Wilson and Penzias were creating a really sensitive antenna to detect microwave radiation at Bell Labratories. They noticed something unusual. There was a constant background noise interference with the antenna. They thought there was something wrong with the instrument so they proceeded to apply many fixes. They cooled the instruments to very low temperatures. There was still background noise. They found bird feces on the antenna and they cleaned that up too. There was still background noise.
They decided to point their antenna at the sky to see if it was coming from space. They got the same interference they usually had. They pointed it to another point in space. They got the same result.
Until, they stumbled across a research paper published by a research group from Princeton. That research group had predicted that there is going to be a unifrom microwave radiation left over from the Big Bang. The microwave radiation that was interfering with the antenna created Wilson and Penzias was actually the microwave radiation left over from the Big Bang. Wilson and Penzias had confirmed the prediction of cosmic microwave background radiation (CMB) and promptly won the Nobel Prize for their discovery.
CMB was created 300000 years after the big bang during the recombination phase of the universe. The recombination phase happened when the universe got cool and dense enough to allow free electrons to bind themselves to the nuclei of elements such as Hydrogen, Helium and other elements available at that time. Previously, those electrons were impeding the path of photons so photons couldn’t travel far without colliding with an electron. When the electrons became bound the nuclei, it freed up space and photons could finally travel without being obstructed. The universe became “transparent”. Since light (photons) was actually able to travel, this is the earliest phase we can see the universe in.
The electromagnetic radiation that was initally created was very high energy but due to red-shift it is now observed in the microwave portion of the spectrum. Red-shift is when the electromagnetic waves of an object emitting radiation increase in wavelength when the object is moving farther away from the observer. Since the universe is expanding the high energy light(electromagnetic radiation) travelling during the recombination phase red-shifted to microwave radiation.
How do we observe CMB? Well scientists use satellites such as WMAP to look really far into space to observe CMB. Since light travels at a constant rate, the light that reaches your eyes from distant objects e.x.stars is actually the light that left that object millions of years ago. So when you look at a star your seeing what it looked like in the past. Same thing applies to the CMB. When satellites peer far into space they actually see in the past. WMAP is a really powerful telescope that was able to look so far into space that it is able to detect CMB.
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