If the observable universe is analogous to a hollow plastic ball, then how thick is the plastic?

Thanks for writing to Ask An Astronomer. Very often some properties of our universe are explained, in layman terms, by comparing it to an expanding balloon, as a visualization aid. However, you should not read too much into that! The balloon analogy is actually a frequent source of misunderstandings, because one tends to asks themselves questions like “where is the center of the universe”, which actually arise from an incorrect understanding of how our universe works. Unfortunately, many properties of our universe clash with common sense; trying to compare how the universe works by using our everyday experience with physics (things fall down, a balloon expanding in space, etc.) is doomed to failure due to the difference in the scales involved.

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Stefano Meschiari - UC Santa Cruz