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Dark Energy and the Dynamics of the Universe. Eric Linder Lawrence Berkeley National Laboratory. Uphill to the Universe. Steep hills: Building up - Eroding away - . Start Asking Why, and. There is no division between the human world and cosmology, between physics and astrophysics. .

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Dark Energy and the

Dynamics of the Universe

Eric Linder

Lawrence Berkeley National Laboratory


Uphill to the Universe

Steep hills:

Building up -

Eroding away -


Start Asking Why, and...

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



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


Our Expanding Universe

Bertschinger & Ma ; courtesy Ma


Our Cosmic Address

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

Earth 107 meters

Solar system 1013 m

Milky Way galaxy 1021 m

Local Group of galaxies 3x1022 m

Local Supercluster of galaxies 1024 m

The Visible Universe 1026 m


The Cosmic Calendar

Inflation1016 GeV

Quarks  Hadrons1 GeV

Nuclei form1 MeV

Atoms form1 eV

[Room temperature 1/40 eV]

Stars and galaxies first form:1/40 eV

Today:1/4000 eV


Mapping 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.



Discovery! Acceleration

data from Supernova Cosmology Project (LBL)

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

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

acceleration and dark energy
Acceleration and Dark Energy

Einstein says gravitating mass depends on energy-momentum tensor: both energy density and pressurep,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 pressure
Negative 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 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 +3p

Thermodynamics: pressure p can be negative

Quantum Physics: vacuum energy has negative p

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


cf. Tonry et al. (2003)





Cosmic Concordance

  • Supernovae aloneAccelerating expansion
  •  > 0
  • CMB (plus LSS)
  •  Flat universe
  •   > 0
  • Any two of SN, CMB, LSS
  •  Dark energy ~75%

Frontiers of Cosmology



95% of the universe is unknown!

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?

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:

/8G = <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 !

what s the matter with energy16
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.

what s the matter with energy17
What’s the Matter with Energy?

This is modestly called the fine tuning problem.

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.

cosmic coincidence
Cosmic Coincidence





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

Dark energy



key issue for physics today
Key Issue for Physics Today

The universe is not simple:

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

on beyond
On Beyond !

On beyond ! It’s high time you were shown

That 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 supernovae
Type 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, & Marion2003

standardized candle
Standardized Candle


Time after explosion

Brightness tells us distance away (lookback time)

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

what makes sn measurement special control of systematic uncertainties
What makes SN measurement special? Control of systematic uncertainties

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

Lightcurve & Peak Brightness


M and L

Dark Energy Properties

Redshift & SN Properties





weighing the universe
Weighing the Universe



cosmic concordance
Cosmic Concordance

cf. Tonry et al. (2003)



nature of dark energy
Nature of Dark Energy

“Stretchiness” (EOS)

Matter Density


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)

Today’s state of the art:

wconst= -1.05+0.15-0.200.09(Knop et al. 2003)[SN+LSS+CMB]

wconst= -1.08+0.18-0.20?(Riess et al. 2004)[SN+LSS+CMB]

But what about dynamics? Generically expect time variation w


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
hubble diagram
Hubble Diagram

~2000 SNe Ia






redshift z

10 billion years


Supernova Properties Astrophysics

Understanding Supernovae

Nearby Supernova Factory

G. Aldering (LBL)

Cleanly understood astrophysics leads to cosmology

high redshift supernovae
High Redshift Supernovae




Riess et al./STScI

looking back 10 billion years35
Looking 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!

dark energy the next generation
Dark Energy – The Next Generation

Dedicated dark energy probe

SNAP: Supernova/Acceleration Probe

design a space mission
Design a Space Mission




9000 the Hubble Deep Field

plus 1/2 Million  HDF

• 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.

astronomical imaging
Astronomical Imaging

Focus star







Calibration projectors

Half billion pixel array

36 optical CCDs

36 near infrared detectors

JWST Field of View

Larger than any camera yet constructed

new technology ccd s
New Technology CCD’s
  • New kind of CCD detector developed at LBNL
  • Radiation hard for space ; High efficiency
  • Able to be combined into large arrays
astrophysical uncertainties
Astrophysical Uncertainties

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

exploring dark energy
Exploring Dark Energy

Needed data quality

Dark energy theories

Current ground based compared with

Binned simulated data and a sample of

Dark energy models

the fate of our universe
The Fate of Our Universe

Size of Universe




Future Age of Universe

Looking back 10 billion years

to look forward 40 billion

frontiers of the universe
Frontiers of the Universe

Size of Universe




Future Age of Universe

What 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!


The 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 science
Frontiers of Science

Let’s find out!



Breakthrough of the Year


cosmic archaeology
Cosmic Archaeology

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.

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!)

cosmic background radiation
Cosmic Background Radiation

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


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?

Planck satellite (2007)

gravitational lensing
Gravitational 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

gravitational lensing53
Gravitational 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 physics
Fundamental Physics

Astrophysics  Cosmology  Field Theory

a(t)  Equation of state w(z)  V()

V ( ( a(t) ) )




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.


Map the expansion history of the universe


Cosmic Archaeology

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



Large scale structure,

Dark Energy, Acceleration