Vacuum Energy in the Universe Scott Dodelson April 5, 2000

A long time ago in a galaxy far, far away...

Einstein and General Relativity Idea: Matter affects the structure of Space-Time E.g. A massive star attracts nearby objects by distorting space

In 1919, Eddington led expedition to observe solar eclipse... Leading to confirmation of Einstein's theory... And widespread adulation... London Times Nov 8, 1919 The Revolution in Science: Einstein vs. Newton

Energy = Kinetic Energy + Gravitational Energy 0 = (½) m v 2 - G m M(r)/ r Expanding Sphere

Einstein's Static Universe 0 = (½) m v 2 - G m M(r)/r How did Einstein make the universe static? Changed the energy to be negative Introduced vacuum energy. Ordinary matter: M(r) = constant Vacuum energy: M(r) ~ r 3

Aleksandr Aleksandrovich Friedmann Born: June 1888, St. Petersburgh, Russia Died: September 1925, St. Petersburgh Published paper on Bernoulli Numbers at age 17. WWI: Join volunteer aviation detachment.

Used mathematical tools to improve bombing: I have recently had a chance to verify my ideas during a flight over Przemysl; the bombs turned out to be falling almost the way the theory predicts. To have conclusive proof of the theory I'm going to fly again in a few days. Letter from Friedmann, Feb 28, 1915

June 29, 1922: Friedmann introduces the expanding universe, abandoning the vacuum energy Einstein put in by hand. September 18, 1992: Einstein publishes a comment on Friedmann's paper: result ``seems suspect to me'', ``solutions do not appear compatible'' May 31, 1923: Einstein retracts his criticism: ``My objection rested on a calculational error.'' Expansion of the Universe

Edwin Hubble measures expansion in

BUT... M(r) = r v 2 / 2G Vacuum Energy in the Universe ! Theorists: ``Ignorant Observers’’ Observers: ``Arrogant Theorists'' Galaxies, clusters, Stats of gal distribut ion Age Naturalness, Inflation Ugly theory

After billions of years light from the distant supernova reaches Earth

Supernovae are standard candles The apparent brightness of a supernova is therefore a measure of its distance from us. Can get Hubble relation for very distant objects!

Since M increases with R, universe is driven to expand faster and faster Since M remains constant, expansion slows, like a rocket leaving Earth

Scale Factor (redshift) Far Away -> Fainter ->

What are we up to now? Measuring the distribution of galaxies Measuring anisotropies in the cosmic radiation Sending up satellites to observe more supernovae Searching for exotic, dark matter We are observing

First light from the Sloan Digital Sky Survey, will map a million galaxies on the sky

Satellites will map cosmic radiation Photo of the universe when it was very young

Proposed satellite will observe thousands of supernovae

Dark Matter searches continue... February 26, 2000

Deep, profound questions remain What is the vacuum energy? How is it related to the rest of physics? Is it testable? Could it be useful? What are the ramifications for the future? We are thinking.. Strings? Quintessence? Large extra dimensions? Cosmological constant?

What should we make of Einstein? The Man of the Century The Man of the Century… Missed the expansion Almost suppressed it Blundered into vacuum energy

Even Einstein’s Greatest Blunder... teaches us about the importance of tackling big problems. Even though Einstein was wrong, his audacity laid the groundwork for future work.