A century ago, the hot topic of the 1920's was the structure of the universe. Was the universe a single Galaxy or was the Milky Way just one of many galaxies? This was resolved by the late 20's and the general expansion was discovered. With the recognition that the galaxies were separate island universes, studies of their groupings (late 30's) quickly led to a dilemma. Where was all the mass? In the late 70s the dilemma was extended to individual galaxies that could be well observed. Was the mass hidden as very hot or very cold gas? Was it in clumps (machos)? Was gravity itself different at large scales? Step by step the mundane solutions were eliminated, and the composition of the big bang itself argued that this mass was not ordinary (Baryonic) matter. Worse, the missing (dark) matter was insufficient to create the flat universe that was observed (CMB). Cosmologists started reviving Einstein's greatest blunder, Λ, the cosmological constant. Then came dark energy! Today we are sorting through an understanding of known particles (neutrino masses), theorized particles with motivation from physics (axions, ...), and without (Wimps of various properties). With LIGO, matter bound up in primordial black holes formed before the era of nucleosynthesis is being studied. We do not yet have final answers on the nature of the dark/missing matter, or dark energy, but we come closer each year. Join TVS for a discussion on the effort to learn about the dark/missing matter.
Speaker: David Dearborn, Lawrence Livermore National Labs
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