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I was reading this answer where it's explained that the Big Bang is not a theory but a model and that it doesn't say anything about the origins of the Universe.

I was taught in school instead that according to the Big Bang theory, the Universe expanded from an original point concentrating everything. Even a popular TV series is named like that. Why this misinterpretation? Has the "original theory" evolved from its origins and that explains the change, or was instead the popular conception always wrong?

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    Popular ideas about physics are usually wrong in at least one way. – Jon Custer Mar 04 '23 at 15:13
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    Expansion happens at every point in space, so there was no original point of expansion, there is no such thing as the center of the universe where it all expanded from. We know, to the best of my knowledge, nothing about the origin of the universe from a fundamental point of view because that is beyond Planck time, hence we know nothing about gravity at that scale for instance – Vicky Mar 04 '23 at 15:16
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    @JonCuster: I fear that "at least one" is overly optimistic. – Michael Seifert Mar 04 '23 at 15:18
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    @MichaelSeifert There is story where Dirac interrupts a colloquium speaker to point out an extra negative sign in an equation. “I apologize,” says the speaker. “I seem to have made a sign error.” Dirac interrupts him again: “You seem to have made an odd number of sign errors.” – rob Mar 04 '23 at 15:50
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    The Big Bang did not happen at a point. – rob Mar 04 '23 at 15:55

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The physical content of the Big Bang theory is that the Universe was much hotter and denser in the past than it is now. We see this directly in the Cosmic Background Radiation and infer it less directly in the abundance of helium and other light elements in cosmic gas.

But we cannot see or infer conditions all the way back to the beginning (if there was one). Any discussion of a "point" is pure speculation.

John Doty
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