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
Lawrence Berkeley National Laboratory
Building up -
Eroding away -
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.
Bertschinger & Ma ; courtesy Ma
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
Quarks Hadrons1 GeV
Nuclei form1 MeV
Atoms form1 eV
[Room temperature 1/40 eV]
Stars and galaxies first form:1/40 eV
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.
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.
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
a = - (4/3)G (+3p) a
Negative pressure can accelerate the expansion
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
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.
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.
95% of the universe is unknown!
Dark Energy Is!!!
! 70-75% of the energy density of the universe
95% of the universe unknown!
! Accelerating the expansion, like inflation at 10-35s
! Determining the fate of the universe
Fate of the universe!
Is this mysterious dark energy the original cosmological constant , a quantum zeropoint sea?
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)
If Planck energy cutoff, <0> ~ c5/G2h ~ 1076 GeV4
-- If kmax~ QCD cutoff, 10-3 GeV4
-- But need 10-47 GeV4 !
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.
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.
Think of the energy in as the level of the quantum “sea”. At most times in history, matter is either drowned or dry.
The universe is not simple:
So maybe neither is the quantum vacuum (or gravitation)?
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
Insensitive to initial conditions:
Höflich, Gerardy, Linder, & Marion2003
Time after explosion
Brightness tells us distance away (lookback time)
Redshift measured tells us expansion factor (average distance between galaxies)
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
cf. Tonry et al. (2003)
“ ‘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+0.15-0.200.09(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
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.
~2000 SNe Ia
10 billion years
Nearby Supernova Factory
G. Aldering (LBL)
Cleanly understood astrophysics leads to cosmology
Riess et al./STScI
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!
Dedicated dark energy probe
SNAP: Supernova/Acceleration Probe
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.
Half billion pixel array
36 optical CCDs
36 near infrared detectors
JWST Field of View
Larger than any camera yet constructed
For accurate and precision cosmology, need to identify and control systematic uncertainties.
Needed data quality
Dark energy theories
Current ground based compared with
Binned simulated data and a sample of
Dark energy models
Size of Universe
Future Age of Universe
Looking back 10 billion years
to look forward 40 billion
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 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?
Let’s find out!
Breakthrough of the Year
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!)
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)
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
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.
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
Inflation sets seeds of structure, patterning both radiation (CMB) and matter (galaxies)
Large scale structure,
Dark Energy, Acceleration