The universe is thought to be flat: $\Omega = 1 \pm 1\%$. As I understand it we can determine this by measuring triangles against the CMB.

Yet during inflation dark energy made the universe grew much larger than the radiation universe, of which the CMB is the limit. Isn't it possible then that at the "smaller" scale of our visible universe it appears flat, but at the universe's full size it's curved? A bit like a square of 1 meter sides on the surface of the earth also looks flat, while at larger scale the earth is curved.

What are the chances that the 1% uncertainty could lead us to a universe with $\Omega \ne 1$?

  • $\begingroup$ Inflation wasn't caused by dark energy. In truth, we don't know for certain what caused it, although the inflaton field idea is one possible reason. By the way, what do you mean by "chances"? 1% already brings probability into it. $\endgroup$
    – HDE 226868
    Sep 19, 2014 at 15:07
  • $\begingroup$ What I meant was: can we account the 1% as completely observational error, or are there voices for a curved universe, when we can reduce the error? Suppose we now see +1/-1 %, but in the future +1/-0.5 % and even further in the future +1/-0.2 %. Doesn't this hint to a curved universe, when looked at at larger scales (than we can observe)? $\endgroup$
    – stevenvh
    Sep 19, 2014 at 15:16
  • $\begingroup$ As far as I know, it is purely the range of observational error. $\endgroup$
    – HDE 226868
    Sep 19, 2014 at 15:23
  • $\begingroup$ Actually, the observational error from WMAP was 0.4%. Do you know if the 1% figure is from somewhere else? $\endgroup$
    – HDE 226868
    Sep 20, 2014 at 20:13

1 Answer 1


It's entirely possible that our seemingly flat observable universe sits inside a much larger and very curved universe. Since there is, by definition, no way to ever measure anything beyond the observable universe, such possibilities are essentially non-scientific musings.


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