Download Einstein's Cosmological Constant: From Ignored Fact to Accelerating Universe and more Lab Reports Physics in PDF only on Docsity! Einstein and the Accelerating Expansion of the Universe Edward L. (Ned) Wright UCLA 13 March 2005 Cosmology is an Observational Science • We can’t do experiments on the Universe. • We can’t change the initial conditions and see what happens. • But we can observe what is the Universe is like. • And we can study what past, present and future conditions of the Universe are compatible with our observations and the same laws of physics that apply in our laboratories. Effect of A term was unexpected
Newtonian Gravity
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Einstein wanted shorter range gravity
Einstein found a long range repulsion
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Source of Cosmological Constant • A vacuum energy density is equivalent to Einstein’s cosmological constant: Λ • Quantum fluctuations could lead to a vacuum energy density. Represent Force by Slope Short range attraction Matter dominated Long Range Repulsion Λ dominated • This is quite a good analogy for cosmological models. Hubble Law: v = HD • Hubble found a recession velocity proportional to the distance. – Einstein static fails, de Sitter & Friedmann pass • Hubble also found that the distribution of galaxies was homogeneous [the same in all places] and isotropic [the same in all directions]. – Einstein static, de Sitter & Friedmann all pass Models vs Olbers Paradox • A static Universe filled with light-emitting stars cannot be static. It will fill up with photons and gradually get brighter. • Einstein’s static model will fill up with light until the night sky is as bright as the surface of a star. • Expanding de Sitter & Friedmann models are consistent with a dark night sky. Λ Was Demoted • Expanding models with or without matter and/or Λ are possible. • But matter is needed – we are here. • Λ was not needed so it was deprecated. Animated View of Inflation • Quantum fluctuations occur uniformly throughout space-time. • Future light cones of fluctuations grow making big circles but new fluctuations continuously replenish the small circles. • Result is Equal Power on All Scales (EPAS). COBE DMR vs EPAS “Chi-by-eye” suggests that the “Equal Power on All Scales” prediction of inflation is correct. A Big Media Splash in 1992: 25 April 1992 Prof. Stephen Hawking of Cambridge University, not usually noted for overstatement, said: “It is the discovery of the century, if not of all time.” We recently learned how to read the “wattage” label on supernovae: As a result, data on velocity vs distance is now much better! 1929 As a result, data on velocity vs distance is now much better! 1995 1929 data fits in here → JDEM in 10 years? NASA needs $$$ Same Laws of Physics? • The cosmological constant Λ is present in space and also in our laboratory. • But its effects in the laboratory are too small to measure. This is not the best situation. • Astrophysicists are very eager to confirm the existence of Λ by every possible method. • Currently there are several independent methods that all agree on the existence of Λ. Λ Confirmed by CMB & IR maps • This late Integrated Sachs-Wolfe effect occurs on our past light cone so the CMB ∆T we see is due to structures we also see. • Correlation between WMAP and large-scale structure seen by: – Boughn & Crittenden at 99.7% confidence with hard X-ray background – Nolta at 98% confidence with the NRAO VLA Sky Survey – Ashfordi at 99.4% with the 2MASS 2 micron all sky survey
