Mathematics – Logic
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20920701f&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #207.01; Bulletin of the American Astronomical Society,
Mathematics
Logic
Scientific paper
The measured luminosity distances of hydrogen-deficient Type Ia (white-dwarf) supernovae as a function of redshift (z) have shown that the expansion of the Universe is currently accelerating, probably due to the presence of "dark energy" (X) having a negative pressure, such as Einstein's infamous cosmological constant (Λ). Combining all of the data with existing results from large-scale structure surveys, we find a best fit for ΩM and ΩX of 0.28 and 0.72 (respectively), in excellent agreement with the values derived independently from WMAP measurements of the characteristic angular scale of fluctuations in the cosmic microwave background radiation. A number of possible systematic effects (e.g., dust, supernova evolution) thus far do not seem to eliminate the need for ΩX > 0. Recently, analyses of supernovae at z = 1.0-1.7 reveal an early epoch of deceleration ending at z ≈ 0.5, followed by acceleration as dark energy began to dominate over dark matter. Several research groups are now in the process of measuring hundreds of Type Ia supernovae in the range z = 0.2-0.8 to determine the equation-of-state parameter of the dark energy, wX = P/(ρc2), where P is the pressure and ρ is the energy density. Thus far, the best-fit value is wX = -1, and dw/dz is consistent with 0, suggesting that the dark energy may indeed be the cosmological constant Λ or something quite similar. The true nature of the dark energy is one of the major unsolved problems in fundamental physics, with far-reaching implications beyond the standard model.
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