vacuum energy in the universe scott dodelson april 5, 2000
TRANSCRIPT
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Vacuum Energy in the UniverseVacuum Energy in the Universe
Scott DodelsonApril 5, 2000
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A long time ago in a
galaxy far, far away...
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Einstein and General RelativityEinstein and General Relativity
Idea: Matter affects the
structure of Space-Time
E.g. A massive starattracts nearby objectsby distorting space
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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
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Energy = Kinetic Energy + Gravitational Energy
0 = (½) m v2 - G m M(r)/ r
Expanding Sphere
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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
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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.
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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
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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
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Edwin Hubble measures expansion in 1929 ...
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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
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After billions of years light from the distant supernova reaches Earth
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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!
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Since M increases with R, universe is driven to expand faster and faster
Since M remainsconstant, expansionslows, like a rocketleaving Earth
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Scale Factor (redshift)
Far Away ->
Fai
nter
->
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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
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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
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Sat
elli
tes
wil
l map
cos
mic
rad
iati
on
Photo of the universe w
hen it was very young
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Proposed satellite will observe thousands of supernovae
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Dark Matter searches continue ...Dark Matter searches continue ...
February 26, 2000
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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?
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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
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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.