11

Dark EnergyDark Energy and the and the

Dynamics of the UniverseDynamics of the Universe

Eric Linder Lawrence Berkeley National Laboratory

22

Uphill to the UniverseUphill to the Universe

Steep hills:Steep hills:

Building up -Building up -

Eroding away - Eroding away -

33

Start Asking Why, and...Start Asking Why, and...

There is no division between the human world and There is no division between the human world and cosmology, between physics and astrophysics. cosmology, between physics and astrophysics.

......

......

Everything is dynamic, all the way to the Everything is dynamic, all the way to the expansion of the universe.expansion of the universe.

44

Our Expanding UniverseOur Expanding Universe

Bertschinger & Ma ; courtesy Ma

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Our Cosmic AddressOur Cosmic Address

Earth 10Earth 1077 meters meters

Solar system 10Solar system 101313 m m

Milky Way galaxy 10Milky Way galaxy 102121 m m

Local Group of galaxies 3x10Local Group of galaxies 3x102222 m m

Local Supercluster of galaxies 10Local Supercluster of galaxies 102424 m m

The Visible Universe 10The Visible Universe 102626 m m

Our SunOur Sun is one of 400 billion stars is one of 400 billion stars in the in the Milky Way galaxyMilky Way galaxy, which is , which is one of more than 100 billion one of more than 100 billion galaxies in galaxies in the visible universethe visible universe. .

66

The Cosmic CalendarThe Cosmic Calendar

InflationInflation 10101616 GeV GeV

Quarks Quarks Hadrons Hadrons 1 GeV1 GeV

Nuclei formNuclei form 1 MeV1 MeV

Atoms formAtoms form 1 eV1 eV

Stars and galaxies Stars and galaxies

first form:first form: 1/40 eV1/40 eV

Today:Today: 1/4000 eV1/4000 eV

[Room temperature 1/40 eV][Room temperature 1/40 eV]

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Mapping Our HistoryMapping Our History

The subtle slowing down and speeding up of the expansion, of distances with time: a(t), maps out cosmic history like tree rings map out the Earth’s climate history.

STScI

88

Discovery! AccelerationDiscovery! Acceleration

Exploding stars – supernovae – are bright beacons that allow us to measure precisely the expansion over the last 10 billion years.

data from Supernova Cosmology Project (LBL)

graphic by Barnett, Linder, Perlmutter & Smoot (for OSTP)

Acceleration and Dark EnergyAcceleration and Dark Energy

Einstein says gravitating mass depends on

energy-momentum tensor:

both energy density and pressure p, as +3p

Negative pressure can give negative “mass”

Newton’s 2nd law: Acceleration = Force / mass

R = - (4/3)G R

Einstein/Friedmann equation:

a = - (4/3)G (+3p) a

Negative pressure can accelerate the expansion

..

..

Negative pressureNegative pressure

Relation between and p (equation of state) is crucial:

w = p /

Acceleration possible for p < -(1/3) or w < -1/3

What does negative pressure mean?

Consider 1st law of thermodynamics:

dU = -p dV

But for a spring dU = +k xdx or a rubber band dU = +T dl

Vacuum EnergyVacuum Energy

Quantum physics predicts that the very structure of the vacuum should act like springs.

Space has a “stretchiness”, or tension, or vacuum energy with negative pressure.

Review -- Einstein: expansion acceleration depends on +3pThermodynamics: pressure p can be negativeQuantum Physics: vacuum energy has negative p

“Tree ring” markers can map the expansion history, measure acceleration, detect vacuum energy.

accelerating

deceleratingaccelerating

decelerating

cf. Tonry et al. (2003)

Cosmic ConcordanceCosmic Concordance

• Supernovae alone

Accelerating expansion

> 0

• CMB (plus LSS)

Flat universe

> 0

• Any two of SN, CMB, LSS

Dark energy ~75%

131395% of the universe is unknown!

Frontiers of CosmologyFrontiers of Cosmology

STScI

Us

Dark Energy Is!!!Dark Energy Is!!!Dark Energy Is...Dark Energy Is...

• 70-75% of the energy density of the universe

• Accelerating the expansion, like inflation at 10-35s

• Determining the fate of the universe

! 70-75% of the energy density of the universe

95% of the universe unknown!

! Accelerating the expansion, like inflation at 10-35s

Repulsive gravity!

! Determining the fate of the universe

Fate of the universe!

Is this mysterious dark energy the original cosmological constant , a quantum zeropoint sea?

1515

What’s the Matter with Energy?What’s the Matter with Energy?

Why not just bring back the cosmological constant ()?

When physicists calculate how big should be, they don’t quite get it right.

Sum of zeropoint energy modes:

/8G = <0> ~ h/2 d3k (k2+m2)

~ kmax4

If Planck energy cutoff, <0> ~ c5/G2h ~ 1076 GeV4

-- If kmax~ QCD cutoff, 10-3 GeV4

-- But need 10-47 GeV4 !

1616

What’s the Matter with Energy?What’s the Matter with Energy?

They are off by a factor of

1,000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000, 000,000,000,000,000,000,000,000,000,000,000.

1717

What’s the Matter with Energy?What’s the Matter with Energy?

But it gets worse: because the cosmological constant is constant, it is the same throughout the history of the universe.

Why didn’t it take over the expansion billions of years ago, before galaxies (and us) had the chance to form?

Or why didn’t it wait until the far future, so today we would never have detected it?

This is called the coincidence problem.

This is modestly called the fine tuning problem.

Matter

Dark energy

Today Size=2 Size=4Size=1/2Size=1/4

Think of the energy in as the level of the quantum “sea”. At most times in history, matter is either drowned or dry.

Cosmic CoincidenceCosmic Coincidence

KeyKey Issue for Physics Today Issue for Physics Today

The universe is not simple:

So maybe neither is the quantum vacuum (or gravitation)?

2020

On Beyond On Beyond !!

On beyond ! It’s high time you were shownThat you really don’t know all there is to be known.

-- à la Dr. Seuss, On Beyond Zebra

We need to explore further frontiers in high energy physics, gravitation, and cosmology.

New quantum physics? Quintessence (atomic particles, light, neutrinos, dark matter, and…), Dynamical vacuum

New gravitational physics? Quantum gravity, supergravity, extra dimensions?

We need new, highly precise data

Type Ia SupernovaeType Ia Supernovae

• Exploding star, briefly as bright as an entire galaxy• Characterized by no Hydrogen, but with Silicon• Gains mass from companion until undergoes thermonuclear runaway

Standard explosion from nuclear physics

Insensitive to initial conditions: “Stellar amnesia”Höflich, Gerardy, Linder, & Marion 2003

SCP

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Standardized CandleStandardized Candle

Time after explosion

Brightness

Brightness tells us distance away (lookback time)

Redshift measured tells us expansion factor (average distance between galaxies)

Images

Spectra

Redshift & SN Properties

Lightcurve & Peak Brightness

data analysis physics

M and

Dark Energy Properties

At every moment in the explosion event, each individual supernova is “sending” us a rich stream of information about its internal physical state.

What makes SN measurement special?What makes SN measurement special? Control of systematic uncertaintiesControl of systematic uncertainties

2424

History & FateHistory & Fate

2525

Weighing the UniverseWeighing the Universe

accelerating

decelerating

2626

Cosmic ConcordanceCosmic Concordance

accelerating

decelerating

cf. Tonry et al. (2003)

2727

Nature of Dark EnergyNature of Dark Energy

“Str

etch

ines

s” (

EO

S)

Matter Density

Today’s state of the art: wconst= -1.05+0.15

-0.200.09 (Knop et al. 2003) [SN+LSS+CMB] wconst= -1.08+0.18

-0.20? (Riess et al. 2004) [SN+LSS+CMB]

What We Know What We Know

“ ‘Most embarrassing observation in physics’ – that’s the only quick thing I can say about dark energy that’s also true.” -- Edward Witten

Dark energy causes acceleration -- “negative gravity” -- through its strongly negative pressure.

Define equation of state ratio by w(z)=pressure/(energy density)

But what about dynamics? Generically expect time variation w

What We (Don’t) Know What We (Don’t) Know

Assuming w is constant can be deceiving, even to test if dark energy is a cosmological constant .

If we don’t look hard for the time variation w then we don’t learn the physics!

We have to do it right.

• Longer “lever arm” (higher redshift, more history)

• Many more supernovae, more precisely

• High accuracy

3030

~2000 SNe Ia

Hubble DiagramHubble Diagram

redshift z

0.2 0.4 0.6 0.8 1.0

10 billion years

3131

Nearby Supernova Factory

Understanding SupernovaeUnderstanding Supernovae

Cleanly understood astrophysics leads to cosmology

Supernova Properties Astrophysics

G. Aldering (LBL)

3232

High Redshift SupernovaeHigh Redshift Supernovae

Riess et al./STScI

Discover Reference Subtract-->SN!

3333

Looking Back 10 Billion YearsLooking Back 10 Billion Years

STScI

3434

Looking Back 10 Billion YearsLooking Back 10 Billion Years

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3535

Looking Back 10 Billion YearsLooking Back 10 Billion Years

To see the most distant supernovae, we must observe from space.

A Hubble Deep Field has scanned 1/25 millionth of the sky.

This is like meeting 10 people and trying to understand the complexity of the entire population of the US!

3636

Dark Energy – The Next GenerationDark Energy – The Next Generation

SNAP: Supernova/Acceleration Probe

Dedicated dark energy probe

3737

Design a Space MissionDesign a Space Mission

colorful

wide

GOODS

HDF

9000 the Hubble Deep Field

plus 1/2 Million HDF

deepdeep• Redshifts z=0-1.7 • Exploring the last 10 billion years • 70% of the age of the universe

Both optical and infrared wavelengths to see thru dust.

3838

Astronomical ImagingAstronomical Imaging

Half billion pixel array

36 optical CCDs

36 near infrared detectors

Larger than any camera yet constructed

Guider

Spectrographport

Visible

NIR

Focus starprojectors

Calibration projectors

JWST Field of View

3939

New Technology CCD’sNew Technology CCD’s

• New kind of CCD detector developed at LBNL • Radiation hard for space ; High efficiency• Able to be combined into large arrays

4040

Astrophysical UncertaintiesAstrophysical Uncertainties

Systematic Control

Host-galaxy dust extinction

Wavelength-dependent absorption identified with high S/N multi-band photometry.

Supernova evolution Supernova subclassified with high S/N light curves and peak-brightness spectrum.

Flux calibration error Program to construct a set of 1% error flux standard stars.

Malmquist bias Supernova discovered early with high S/N multi-band photometry.

K-correction Construction of a library of supernova spectra.

Gravitational lensing Measure the average flux for a large number of supernovae in each redshift bin.

Non-Type Ia contamination

Classification of each event with a peak-brightness spectrum.

For accurate and precision cosmology, need to identify and control systematic uncertainties.

4141

SN Population DriftSN Population Drift

4242

Controlling SystematicsControlling Systematics

4343

Weighing Dark EnergyWeighing Dark Energy

SN Target

4444

Exploring Dark EnergyExploring Dark Energy

Current ground based compared with

Binned simulated data and a sample of

Dark energy models

Da

rk e

ne

rgy

the

ori

es

Needed data quality

4545

The Fate of Our UniverseThe Fate of Our Universe

to look forward 40 billion

Looking back 10 billion years

Size of Universe

History

Fate

0 Future Age of Universe

4646

Frontiers of the UniverseFrontiers of the UniverseWhat is dark energy?

Will the universe expansion accelerate forever?

Does the vacuum decay? Phase transitions?

How many dimensions are there?

How are quantum physics and gravity unified?

What is the fate of the universe?

Uphill to the Universe!

Size of Universe

History

Fate

0 Future Age of Universe

The Next PhysicsThe Next Physics

The Standard Model gives us commanding knowledge about physics -- 5% of the universe (or 50% of its age).

That 5% contains two fundamental forces and 57 elementary particles.

What will we learn from the dark sector?!

How can we not seek to find out?

Frontiers of ScienceFrontiers of Science

Breakthrough of the Year

1919

1998

2003

Let’s find out!

The Next PhysicsThe Next Physics

5050

Cosmic ArchaeologyCosmic Archaeology

CMB: direct probe of quantum fluctuations

Time: 0.003% of the present age of the universe.

(When you were 0.003% of your present age, you were a 2 celled embryo!)

Supernovae: direct probe of cosmic expansion

Time: 30-100% of present age of universe

(When you were 12-40 years old)

Cosmic matter structures: less direct probes of expansion

Pattern of ripples, clumping in space, growing in time.

3D survey of galaxies and clusters.

5151

Cosmic Background RadiationCosmic Background Radiation

Photon density 407±0.4 cm-3

Baryon density bh2=0.023±0.001

nb/n=6 x 10-10 ; consistent with primordial nucleosynthesis

Matter-antimatter asymmetry? Baryogenesis?

Snapshot of universe at 380,000 years old, 1/1100 the size

Planck satellite (2007)

WMAP/ NASA

5252

Gravitational LensingGravitational Lensing

Gravity bends light… - we can detect dark matter through its gravity, - objects are magnified and distorted, - we can view “CAT scans” of growth of structure

5353

Gravitational LensingGravitational Lensing

Lensing measures the mass of clusters of galaxies.

By looking at lensing of sources at different distances (times), we measure the growth of mass.

Clusters grow by swallowing more and more galaxies, more mass.

Acceleration - stretching space - shuts off growth, by keeping galaxies apart.

So by measuring the growth history, lensing can detect the level of acceleration, the amount of dark energy.

Fundamental PhysicsFundamental Physics

Astrophysics Cosmology Field Theory

a(t) Equation of state w(z) V()

V ( ( a(t) ) )SN

CMB

LSS

Map the expansion history of the universe

The subtle slowing and growth of scales with time – a(t) – map out the cosmic history like tree rings map out the Earth’s climate history.

STScI

Cosmic ArchaeologyCosmic Archaeology

Inflation sets seeds of structure, patterning both radiation (CMB) and matter (galaxies)

CMB

Large scale structure,Dark Energy, Acceleration}

NASA GSFC/COBE