Cosmologic philosophy: Big Bang or not? (Introduction)

by David Turell , Saturday, June 04, 2022, 17:07 (903 days ago) @ David Turell

The Big Bang theory involved finding the geometry of space, flat, convex or concurved. This article confirms flat:

https://bigthink.com/starts-with-a-bang/universe-flat/?utm_source=mailchimp&utm_med...

The shape of the Universe didn't have to be flat; it could have been positively curved like a higher-dimensional sphere or negatively curved like a higher-dimensional horse's saddle. The reason space can be curved is that its shape is not absolute, but rather determined by a mix of factors like its mass and energy distribution, as well as its expansion rate. Nevertheless, when we measure it, we find that our Universe really is flat. Here's what we can learn from that, and why, from a cosmic perspective, it matters so much.

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The fact that our Universe exists with the properties we observe tells us that, very early on, the Universe had to be at least very close to flat. A Universe with too much matter-and-energy for its expansion rate will have positive curvature, while one with too little will have negative curvature. Only the perfectly balanced case will be flat.

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The fact that we see a null result, particularly if we combine it with the cosmic microwave background results, gives us an even more stringent constraint: the Universe is flat to within ~99.75% precision.

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All of that tells us how we know the Universe is flat. But to understand why it’s flat, we have to look to the theory of our cosmic origins that set up the Big Bang: cosmic inflation. Inflation took the Universe, however it may have been previously, and stretched it to enormous scales. By the time that inflation ended, it was much, much larger: so large that whatever part of it remains is indistinguishable from flat on the scales we can observe it.

The only exception to the flatness is caused by the sum of all the quantum fluctuations that can get stretched across the cosmos during inflation itself. Based on our understanding of how these fluctuations work, it leads to a novel prediction that has yet to be tested to sufficient precision: our observable Universe should actually depart from perfect flatness at a level that’s between 1-part-in-10,000 and 1-part-in-1,000,000.

Right now, we’ve only measured the curvature to a level of 1-part-in-400, and find that it’s indistinguishable from flat. But if we could get down to these ultra-sensitive precisions, we would have the opportunity to confirm or refute the predictions of leading theory of our cosmic origins as never before. We cannot know what its true shape is, but we can both measure and predict its curvature.

This is one of the major goals of a series of upcoming missions and observational goals, with the new generation of Cosmic Microwave Background measurements poised to measure the spatial curvature down to 1-part-in-1000 or better, and with the Roman Telescope, the EUCLID mission, and Rubin Observatory all planned to come online and measure the baryon acoustic oscillation signature better and more precisely than ever before.

Comment: what flat means is the universe will expand forever until it becomes totally cold, frigid, with very low energy and finally tears apart in ending. No contraction, no Big Bounce. From my viewpoint, I doubt one and done, if there is a God. He'll do it over and over.