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Planck evidence for a closed Universe and a possible crisis for cosmology
My take is that the most likely scenario is that the Planck 2018 power spectrum data do not actually indicate a positively curved universe, because if that is the case then discrepancies between other observations become significantly more severe. In other words, we have more and stronger reasons for concluding that the universe is (essentially) flat than that it is curved to the extent suggested here. Personally I would get more confidence in this result if it made the bulk of other observational discrepancies smaller
In fact, measurements of curvature like this are always problematic, because a wide range of values can be consistent with observations if you allow the densities of matter and energy in the universe to vary. But because we have independent methods of determining those densities, we can pin down the curvature quite well, and they indicate very little curvature if any.
So there are a few possibilities, some more appealing than others depending on your particular philosophy of science, and whatever ends up being correct will still require modifying our understanding of certain measurements, methods, and/or fundamental physics. The most exciting possibility is always that there is new fundamental physics behind any measurement discrepancy, but that's also always the least likely possibility.
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I remember we talked about the value of W and if it was even slightly negative we could have a universe that closes/cycles "at the last moment" when it comes back empty.
The value of w is
negative, with very high confidence. It is approximately -1, which means the dark energy density is constant despite expansion. w=-1 leads to endless exponential expansion with a very boring endstate (heat death) for the universe.
If it is less than -1, then the expansion becomes super-exponential and the universe ends dramatically in a Big Rip. There's still no cyclic behavior there, unless we add in a number of extra assumptions to force such a solution.