It was the year 1964, a few years before the first human landed on the Moon and when US and Russia were in the thick of their space race… Arno Penzias and Robert Wilson were searching the space for neutral Hydrogen using a sensitive radio telescope in Bell’s lab (New Jersey). But during their observations, they realized that they were consistently getting a strange signal from every direction the telescope was pointed to. Such uniform signal could have meant an error in the telescope, after all we are talking about technology in 1964! But Penzias and Wilson wanted to dig out the root of this signal and hence accounted every type of error. Everything from pigeons in the antenna to faulty wirings was rectified. But despite all this, a part of that strange signal persisted. This was when they realized they might have stumbled upon something big…
Theory Meets Observation
This discovery of the strange signal was well and good. But the problem was – what the heck was that signal? It was akin to having an egg in your hand and not knowing what species that egg belongs to. So, these clueless researchers went on a hunt to solve the mystery of this signal. This was when Penzias crossed path with a fellow radio astronomer named Bernard Burke, who tagged them with Bob Dicke. The interesting thing was Dicke, along with his team which consisted of scientists such as James Peebles, Peter Roll and Donald Wilkinson, was looking for Cosmic Microwave Background (CMB). This group had also done extensive study on its theoretical models. But they were far away from making any observations when Penzias and Wilson contacted him. So serendipitously, theory met observation!
Understanding what the signal was about, Penzias and Wilson then published a paper in 1965 with the most understated title in the history of titles – ‘A measurement of excess antenna temperature at 4080 Mc/s’. Hmmph am just dying to read the paper (note the sarcasm)! In the same issue of Astrophysical Journal, Bob Dicke’s team’s research was published too.
But here came the plot twist. Neither Bob Dicke’s team nor Penzias and Wilson were the first to know about cosmic microwave background! Almost two decades before them (between 1948-1953), Ralph Alpher and Robert Herman had already stated the existence of cosmic microwave background in their many publications. Strangely, for a long time, George Gamow was credited for this theoretical confirmation while ironically, he rejected the validity of their work for years! Then in 1978, only Penzias and Wilson were awarded the Nobel Prize in Physics for their work.
This was all about the discovery of CMB. The real story lies in the history of understanding the CMB.
The Story Behind
The period during which CMB was discovered was rife with a tussle between two main theories about the origin of the universe. One group was a firm believer in an explosive ‘Big Bang’ that birthed the universe and the other group believed that the universe had always been there i.e. a ‘steady state universe’. So, the discovery of CMB was monumental! You see, the cosmic microwave background is actually the thermal signature of the Big Bang. It was proof that the universe was born as an explosion.
Well, technically, when the universe was born till around 380,000 years after its birth, it was optically opaque. Which means that we won’t be able to see the universe in that time range. And CMB is actually the earliest visible light from the time when the photons gained freedom to move about freely. So, it gives us a picture of the earliest visible universe!
But coming back to the story, the discovery of CMB solidified the idea of the Big Bang. The researchers had observed the signal to be consistent everywhere they pointed their telescopes. So naturally, they believed that the CMB was homogenous. But a few years later (1970s), James Peebles and simultaneously Yakov Zel’dovich and Rashid Sunyaev came to the conclusion that the CMB should not be homogeneous.
They thought that it should contain what they called ‘anisotropies’, which are basically detected as tiny fluctuations in the temperature in the CMB radiation. But given the technology in those years, it was extremely difficult to get a high-resolution image to catch these tiny fluctuations.
Then years later, in 1992, NASA’s Cosmic Background Explorer (COBE) backed the theory by detecting the anisotropies in CMB. Since then, technological advancement hasn’t stopped and neither have the findings. For instance, after COBE, the telescope named BOOMERANG confirmed that the geometry of the universe is actually Euclidean meaning that the space is flat! Later, NASA’s WMAP satellite confirmed it and also helped get an accurate age of the universe.
The fact is, even after more than 50 years since its discovery, we are still learning about CMB and will continue to do so for years to come.
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