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Of all the great mysteries out there in the Universe, perhaps the greatest one of all is the question of our cosmic origin, “where did all this come from?” For countless millennia, we told one another stories: of a fiery birth, of the separation of light from dark, of order emerging from chaos, of a dark, empty, formless state from which we emerged, or even of an existence that was eternal and unchanging. Some stories involved an active creator; others needed no intervention from anything other than nature itself. But despite our propensity to believe in one of these stories or another, in science, we don’t settle for belief: we want to know.
Today, we talk about the Big Bang as though it’s foundational and taken for granted. But that wasn’t always the case. So how did we get to this point? What critical scientific steps occurred to promote the Big Bang from just one among many ideas to a scientific certainty? That’s what Muhammed Ayatullah wants to know, as he writes in and asks, simply and straightforwardly:
“How was it proven that the Big Bang actually took place?”
It’s a story that started long before it was proven. Let’s go back to when the idea was first conceived: nearly a full 100 years ago.
Back in 1915, Einstein shook up our understanding of the Universe by publishing his theory of General Relativity: a radically new conception of gravity. Previously, Newton’s law of universal gravitation was how we conceived of gravity, where space and time were absolute quantities, that masses occupied certain positions in space at certain moments in time, and that every mass exerted a force on every other mass, inversely proportional to their distances. This explained most observed phenomena very well, but fell short under a few physical circumstances: at speeds that began to approach the speed of light, and in very strong gravitational fields, where you were only a short distance away from a large mass.
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At any epoch in our cosmic history, any observer will experience a uniform “bath” of omnidirectional radiation that originated back at the Big Bang. Today, from our perspective, it’s just 2.725 K above absolute zero and hence is observed as the cosmic microwave background, peaking in microwave frequencies. At great cosmic distances, as we look back in time, that temperature was hotter dependent on the redshift of the observed, distant object. As each new year passes, the CMB cools down further by about 0.2 nanokelvin, and in several billion years, will become so redshifted that it will possess radio, rather than microwave, frequencies. (Credit: Earth: NASA/BlueEarth; Milky Way: ESO/S. Brunier; CMB: NASA/WMAP)
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Click the link below for the article:
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