The Big Bang no longer means what it used to - by StartsWithABang
If there’s one hallmark inherent to science, it’s that our understanding of how the Universe works is always open to revision in the face of new evidence. Whenever our prevailing picture of reality — including the rules it plays by, the physical contents of a system, and how it evolved from its initial conditions to the present time — gets challenged by new experimental or observational data, we must open our minds to changing our conceptual picture of the cosmos.
But the idea, in its original form, wasn’t simply that all of the Universe’s matter was created in one moment in the finite past. That notion, derided by Hoyle, had already evolved from its original meaning. Originally, the idea was that the Universe, not just the matter within it, had emerged from a state of non-being in the finite past.
If you begin with a bound, stationary configuration of mass, and there are no non-gravitational forces or effects present , that mass will always inevitably collapse down to a black hole. It’s one of the main reasons why a static, non-expanding Universe is inconsistent with Einstein’s General Relativity.
Edwin Hubble’s original plot of galaxy distances versus redshift , establishing the expanding Universe, versus a more modern counterpart from approximately 70 years later . In agreement with both observation and theory, the Universe is expanding, and the slope of the line relating distance to recession speed is a constant.
In 1927, Georges Lemaître became the very first person to put these pieces of information together, recognizing that the Universe today is expanding, and that if things are getting farther apart and less dense today, then they must have been closer together and denser in the past.
However, the next great development in formulating what we know of as the Big Bang wouldn’t come until the 1940s, when George Gamow — perhaps not so coincidentally, an advisee of Alexander Friedmann — came along. In a remarkable leap forward, he recognized that the Universe was not only full of matter, but also radiation, and that radiation evolved somewhat differently from matter in an expanding Universe.
But in the past, when the Universe was smaller, the opposite would have been true. If we were to extrapolate backward in time, the Universe would have been in a hotter, denser, more radiation-dominated state. Gamow leveraged this fact to make three great, generic predictions about the young Universe.
Schematic diagram of the Universe’s history, highlighting reionization. Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms that formed back when the Universe was ~380,000 years old. Most of the Universe doesn’t become reionized until 550 million years afterwards, with some regions achieving full reionization earlier and others later.
The measured abundances of the light elements throughout the Universe verified the predictions of Big Bang nucleosynthesis, while also demonstrating the need for fusion in stars to provide the heavy elements in our cosmos. A visual history of the expanding Universe includes the hot, dense state known as the Big Bang and the growth and formation of structure subsequently. The full suite of data, including the observations of the light elements and the cosmic microwave background, leaves only the Big Bang as a valid explanation for all we see. As the Universe expands, it also cools, enabling ions, neutral atoms, and eventually molecules, gas clouds, stars, and finally galaxies to form.
Equal temperatures and properties for the Universe even in causally disconnected regions; a Universe with a singular beginning made no such prediction.
France Dernières Nouvelles, France Actualités
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