Vacuum Energy in the UniverseVacuum Energy in the Universe

Scott DodelsonApril 5, 2000

A long time ago in a

galaxy far, far away...

Einstein and General RelativityEinstein and General Relativity

Idea: Matter affects the

structure of Space-Time

E.g. A massive starattracts nearby objectsby 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,

1919The Revolution in Science:

Einstein vs. Newton

Energy = Kinetic Energy + Gravitational Energy

0 = (½) m v2 - G m M(r)/ r

Expanding Sphere

Einstein's Static UniverseEinstein's Static Universe

0 = (½) m v2 - 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) ~ r3

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 1929 ...

BUT ...

M(r) r v2 / 2G

Vacuum Energy in the Universe !

Theorists:

``Ignorant Observers’’

Observers:

``Arrogant Theorists''

Galaxies, clusters,Statsof galdistribution

Age

Naturalness, Inflation

Ugly theory

After billions of years light from the distant supernova reaches Earth

Supernovae are standard candlesSupernovae 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 remainsconstant, expansionslows, like a rocketleaving Earth

Scale Factor (redshift)

Far Away ->

Fai

nter

->

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

obse

rvin

gW

e ar

e ob

serv

ing

First light from the Sloan Digital Sky Survey, will mapFirst light from the Sloan Digital Sky Survey, will mapa million galaxies on the skya million galaxies on the sky

Sat

elli

tes

wil

l map

cos

mic

rad

iati

on

Photo of the universe w

hen it was very young

Proposed satellite will observe thousands of supernovae

Dark Matter searches continue ...Dark Matter searches continue ...

February 26, 2000

Deep, profound questions remainDeep, 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

thin

king

..W

e ar

e th

inki

ng ..

Strings?

Quintessence?

Large extra dimensions?

Cosmological constant?

What should we make of Einstein?

The Man of the CenturyThe 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.