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The local geometry of the universe is determined by whether the relative density Ω is less than, equal to or greater than 1. From top to bottom: a spherical universe with greater than critical density (Ω>1, k>0); a hyperbolic, underdense universe (Ω<1, k<0); and a flat universe with exactly the critical density (Ω=1, k=0).
Neither the standard model of particle physics nor the theory of general relativity provides a known explanation for why this should be so, and it is a natural assumption that the universe is neutral with all conserved charges. [3] The Big Bang should have produced equal amounts of matter and antimatter. Since this does not seem to have been ...
This imbalance has to be exceptionally small, on the order of 1 in every 1 630 000 000 (≈ 2 × 10 9) particles a small fraction of a second after the Big Bang. [6] After most of the matter and antimatter was annihilated, what remained was all the baryonic matter in the current universe, along with a much greater number of bosons.
All the particles that make up the matter around us, such electrons and protons, have antimatter versions which are nearly identical, but with mirrored properties such as the opposite electric charge.
Why is the distant universe so homogeneous when the Big Bang theory seems to predict larger measurable anisotropies of the night sky than those observed? Cosmological inflation is generally accepted as the solution, but are other possible explanations such as a variable speed of light more appropriate? [31]
In November 2010, the ALPHA collaboration announced that they had trapped 38 antihydrogen atoms for a sixth of a second, [23] the first confinement of neutral antimatter. In June 2011, they trapped 309 antihydrogen atoms, up to 3 simultaneously, for up to 1,000 seconds. [24] They then studied its hyperfine structure, gravity effects, and charge.
The vacuum energy density of the Universe based on 2015 measurements by the Planck collaboration is ρ vac = 5.96 × 10 −27 kg/m 3 ≘ 5.3566 × 10 −10 J/m 3 = 3.35 GeV/m 3 [16] [note 1] or about 2.5 × 10 −47 GeV 4 in geometrized units.
This is equivalent to a mass density of 9.9 × 10 −30 g/cm 3, which is equivalent to only 5.9 protons per cubic meter.” [1] The WMAP data are consistent with a flat geometry, with Ω = 1.02 +/- 0.02.