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I read somewhere that

  • If the expansion rate of the universe were larger or the density of the universe were less , no galaxies would form.
  • If the expansion rate of the universe were smaller or the density of the universe were more, the universe would rapidly collapse.

Is it true that if the expansion rate or the density were slightly different, the universe will not exist as we see it?

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  • $\begingroup$ I am not an expert in this area, but I did read an extremely relevant article about it recently: cosmosmagazine.com/physics/… . So perhaps the comological constant could vary by several orders of magnitude. However, I imagine one would need to know what the probability distribution of possible values is to say if this is still fine-tuned. $\endgroup$ – Rococo May 27 '18 at 19:31
  • $\begingroup$ The answer to your question depends on the cosmological model of your preference. For example, in the Milne model (that makes a lot more sense than the "official" Friedmann model), the universe simply expands wit the speed of light, which is one (as in one light second per second). $\endgroup$ – safesphere May 28 '18 at 5:02

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