"We don't merely have the Hubble tension to reckon with, or the fact that different methods yield different values for the expansion rate of the Universe today, but a puzzle over whether dark energy is truly a constant in our Universe, as most physicists have assumed since its discovery back in 1998. While "early relic" methods using CMB or baryon acoustic oscillation data favor a lower value of around 67 km/s/Mpc, "distance ladder" methods instead prefer a higher, incompatible value of around 73 km/s/Mpc."
"Now, on top of that, new large-scale structure data seems to throw another wrench into the works: supporting a picture of evolving dark energy, and specifically one where it weakens over cosmic time. Here to guide us through this is Dr. Kate Storey-Fisher, a cosmologist whose expertise is exactly on this topic, and who herself has recently become a member of the very collaboration, DESI, that provides the strongest evidence to date for evolving dark energy."
Concordance cosmology posits a 13.8 billion-year-old Universe dominated by dark energy and dark matter, with ordinary matter comprising roughly 5 percent. A significant discrepancy exists in measurements of the current expansion rate: early-relic probes like the CMB and BAO yield about 67 km/s/Mpc, while distance-ladder methods return about 73 km/s/Mpc. New large-scale structure data, notably from DESI, indicates dark energy may evolve and weaken over cosmic time. Evolving dark energy would conflict with a simple cosmological constant and could require substantial revisions to standard cosmological models. Future observatories will test these tensions and constrain dark energy behavior.
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