Evidence for accelerated expansion Interpretation – “phenomenology” Explanation – “theory”

The Accelerating Universe: A Challenge to Fundamental Physics

אוניברסיטת בן-גוריון

Ram BrusteinIrit maor(BGU Cambridge)P. Steinhardt (Princeton)

PRL 86 (2001), PRD 65 (2002),PRD 67 (2003)

Et pourtant il accélère ! L'expansion de l'Univers, loin de ralentir comme on le pensait depuis soixante-dix ans, est en train de s'accélérer sous la pression d'une mystérieuse énergie noire. Les astrophysiciens tentent de comprendre la nature de ce constituant majeur de l'Univers.

01/02/2003 La Recherche

La concordance de toutes ces expériences a fait sursauter plus d'un cosmologiste. À l'aube du XXIe siècle, il devient clair que 95 % de l'Univers nous est totalement étranger ! Les astrophysiciens s'aperçoivent que toutes leurs théories ne se fondent que sur l'observation des cinq petits pour cent visibles de l'énergie totale [fig. 4]. De quoi rendre sceptique le commun des mortels, mais pas les scientifiques, qui continuent à bâtir leur édifice théorique contre vents et marées. Leur plus grand défi est aujourd'hui de dévoiler la nature de cette énergie noire,

מפץ גדול חם : המודל הסטנדרטי

0)(3

)(4

83 2

pH

pGH

GH

N

N

Geometry

GR: a(t), 1+ z =a(now)/a(t),

Matter (z), p(z), w(z) = p/

aaH /

2222 )( drtadtds

C- critical density (Euclidean space)X - X / C

3/1

030

/ 2

w

pa

HHaa

0)(3

)(4

83 2

pH

pGH

GH

N

N

Accelerated expansion ?!Radiation = 3p, w = 1/3

Matter (normal and dark)

p=0, w = 0

Attractive gravity + “normal” matter decelerated expansion

Mapping the Universe

Luminosity – energy/time emitted by source Flux – energy /time/area absorbed by detector

Due to expansion:Energy/time(1+z)2 (1+z) – red shift of energy(1+z) – increased timeNeed “standard candles”

For light

2a

dadz

dt

da

aH

1

0222 dradt

Luminosity distance dL vs. redshift z: Hubble Diagram

Example:SNIa

Proper diameter - dObserved angular diameter – d/(a r)

rtad

d A )( 1

Example:Peaks in CMB spectrum

Angular distance dA vs. redshift z

Need “standard feature”

Evidence for Accelerated ExpansionDirect and Indirect

• Cosmic Microwave Background : inhomogeneities in radiation

• Large Scale Structure :

inhomogeneities in matter

object counts: galaxies, clusters, weak lensing, strong lensing, …

• SuperNovae Ia – most direct

SNIaהתפוצצות גרעינית של ננסים לבנים

מתאם בין בהירות שיא, צורה וספקטרום של עקומת

פיזור ~% 10האור בבהירות שיא

di

mmer

more distantz

m

AC/DC

pure matter

L

L

d

dm

10ln

5

L

Lm

Key issue:systematic errors

Current SNIa Data

preferred

fiducial models:m= 0.3

wQ= const.

Previous version: Sci. Am. 1/2001

)1( mQ

QQQm

Qm

T

TT

w

wpp

pw

0 20 40 60 80 100

0

20

40

60

80

Current Data

m vs. wQ

(assume flat U.

wQ

-2.5

-1.5

0.50.3

-.5

-3.5

0.7 m

CMB data : WMAP

February 2003

Cosmic variance!

One more point on the Hubble diagram

)z ~ 1,000(8.01.2201

~ Flat U.

Cosmic variance!

4- 6%

20- 40%

60- 80%

Baryons

Dark matter

Dark energy

astro-ph/0302209

Combined results

Interim report I•flat universe• acceleration • consistent• reasonable ?!

small

The end of the universe is cancelledBy Robert Matthews, Science Correspondent(Filed: 09/02/2003) Professor Hawking, we have a problem. Nasa, the American space agency, is expected to announce this week that it has proved the existence of "dark energy", a cosmic force that counteracts gravity and will keep the universe expanding forever.

The announcement will effectively demolish the theory that life will be wiped out in a "Big Crunch" when the universe collapses, and should end decades of academic dispute over the forces at work on the universe

Interpretation: theoretical expectations

• Dark energy is not just • Dynamical field (s):

Kinetic & potential energies Interactions with other particles Cosmic friction Very small mass

time-dependence

Dark Energy EOS• Parametrization in terms of (time-dependent)

Energy density Q(z)

Pressure pQ(z)

EOS wQ(z)=pQ(z)/Q(z)

• previously : wQ = -1

wQ = 0 cold matter

oscillations, “sudden start”, “decay to a constant”

Luminosity distance dL vs. redshift z

Maor et al.g= m /(1- m)

Current SnIA data: some acceleration inthe last 8 billion years (0 < z < 1)

l'avenir: SNAP (F)

SNAP proposal:1000’s de SNIa, surtout 0 < z < 1.2, quelques-uns1.2 < z < 1.7

snap.lbl.gov

Also:ESSENCECFHLS (F)GOODS,SNFactory (F)

fiducial models:m= 0.3wQ= const.

wQ = -1

wQ = -1/3

wQ = 0

See: Sci. Am. 1/2001

Degeneracy!

a) DLb) DL/DLc) wQ (z)

For 9 different EOS

Maor et al.

• Dark energy expected to “disappear” for z > 2

• CMB photons propagate most of the way through matter dominated U.

No gain compared to “low z” probes

• Best accuracy for dL from CMB ~ 1%

CMB comparable to other probes

CMB cannot help much …Maor & Brustein

Interim report II

• recent acceleration (0 < z < 1, today < t < 8 billion years)• evidence from many sources, consistent.• qualitative information only (on

fundamental physics) from most accurate planned experiments

Dark sector &

the standard model of particle physics

4- 6%

20- 40%

60- 80%

Baryons

Dark matter

Dark energy

Dark sector &

gravity and quantum mechanics

N

Vacuum

GG 800

21

Does not make sense as a normal source

4- 6%

20- 40%

60- 80%

Baryons

Dark matter

Dark energy

(R.B.) : Cloud No. IV: Black Hole Entropy

:

"We live where we can live," NYT: 2 Sept. 2003

• Quantum mechanics• More space dimensions• Cherished principles: causality, …

Something has to give

N

Vacuum

GG 800

21

• Gravity

• Matter – additional fields, light, extremely weakly coupled – “quintessence”

and the ugliest(?) of them all: the Anthropic principle

The “boring” option: Quintessence

•“Tracker” fields•Many other possibilities

Degeneracies

m ~ H = 10 –33 eVV ~ crit ~ (10

-3eV)

4

Steinhardt + …Rhatra+PeeblesWetterich …

Maor & Brustein

The Anthropic PrincipleR. Dicke (1961): “ carbon-based life can only arise when the Dirac large numbers hypothesis is true because this is when burning stars exist”

B. Carter (Early 1970’s): “what we can expect to observe must be restricted by the conditions necessary for our presence as observers” (Leslie ed. 1990). The word "anthropic" was intended as applying to intelligent beings.

A possible argument for preferring the God hypothesis: think in terms of many possible fundamental theories, God selecting a theory which permitted life's requirements to be fulfilled without contradictions.

Conclusions

• Excellent measurements are not good enough as clues for fundamental physics !

• A large source of error: theory• Need:

–either a new “local” test -what is it?–or radically new theoretical input -what is it ?

• Theory situation in a nut-shell

“we don’t have a clue”• Personal hope: revolutionary resolution