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overzealous

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- TL;DR Summary
- A question has arisen in my mind about what cosmic inflation actually predicts about flatness-- actual perfect flatness or merely its appearance.

I just read an article by Natalie Wolchover (a smart and knowledgeable writer as far as I can tell) in Quanta about the new analysis supporting a closed universe. In the article she makes this comment, "The leading theory of the universe’s birth, known as cosmic inflation, yields pristine flatness. And various observations since the early 2000s have shown that our universe is very nearly flat and must therefore come within a hair of this critical density — which is calculated to be about 5.7 hydrogen atoms’ worth of stuff per cubic meter of space, much of it invisible."

Prior to reading that comment by Natalie, my understanding was that the idea of cosmic inflation occurred to Alan Guth to account for several characteristics of the universe that we observe today, including its APPARENT flatness, i.e. to have the universe expand so exponentially in the first instant that all the otherwise puzzling features we currently observe could be neatly explained: its homogeneity, its isotropic appearance, as well as its flatness. The idea regarding flatness was simple-- inflate a basketball to unimaginably enormous size and its curvature will no longer be perceptible. But it still will be curved. I thought that's all that inflation was saying about the universe-- not that what Natalie Wolchover calls 'pristine flatness' would be a result. 'Pristine flatness' seems to be indicating that the cosmic inflation theory predicts PRECISE flatness, whereas I thought that it simply accounted for the APPEARANCE of approximate flatness while by no means asserting any sort of ideal, perfect flatness was necessarily the case.

Please clarify whether a theoretical consequence of cosmic inflation is perfect flatness. And if perfect flatness is not a theoretical consequence, and if the universe turns out to be in fact perfectly flat after another thousand years of increasingly accurate measurements, does that mean that we need a new theory in which perfect flatness IS a theoretical consequence?

Prior to reading that comment by Natalie, my understanding was that the idea of cosmic inflation occurred to Alan Guth to account for several characteristics of the universe that we observe today, including its APPARENT flatness, i.e. to have the universe expand so exponentially in the first instant that all the otherwise puzzling features we currently observe could be neatly explained: its homogeneity, its isotropic appearance, as well as its flatness. The idea regarding flatness was simple-- inflate a basketball to unimaginably enormous size and its curvature will no longer be perceptible. But it still will be curved. I thought that's all that inflation was saying about the universe-- not that what Natalie Wolchover calls 'pristine flatness' would be a result. 'Pristine flatness' seems to be indicating that the cosmic inflation theory predicts PRECISE flatness, whereas I thought that it simply accounted for the APPEARANCE of approximate flatness while by no means asserting any sort of ideal, perfect flatness was necessarily the case.

Please clarify whether a theoretical consequence of cosmic inflation is perfect flatness. And if perfect flatness is not a theoretical consequence, and if the universe turns out to be in fact perfectly flat after another thousand years of increasingly accurate measurements, does that mean that we need a new theory in which perfect flatness IS a theoretical consequence?

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