dark energy and the dynamics of the universe
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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Dark EnergyDark Energy and the and the
Dynamics of the UniverseDynamics of the Universe
Eric Linder Lawrence Berkeley National Laboratory
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Uphill to the UniverseUphill to the Universe
Steep hills:Steep hills:
Building up -Building up -
Eroding away - Eroding away -
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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.
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Everything is dynamic, all the way to the Everything is dynamic, all the way to the expansion of the universe.expansion of the universe.
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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. .
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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
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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?
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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 !
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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.
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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
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History & FateHistory & Fate
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Weighing the UniverseWeighing the Universe
accelerating
decelerating
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Cosmic ConcordanceCosmic Concordance
accelerating
decelerating
cf. Tonry et al. (2003)
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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
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~2000 SNe Ia
Hubble DiagramHubble Diagram
redshift z
0.2 0.4 0.6 0.8 1.0
10 billion years
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Nearby Supernova Factory
Understanding SupernovaeUnderstanding Supernovae
Cleanly understood astrophysics leads to cosmology
Supernova Properties Astrophysics
G. Aldering (LBL)
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High Redshift SupernovaeHigh Redshift Supernovae
Riess et al./STScI
Discover Reference Subtract-->SN!
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Looking Back 10 Billion YearsLooking Back 10 Billion Years
STScI
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Looking Back 10 Billion YearsLooking Back 10 Billion Years
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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!
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Dark Energy – The Next GenerationDark Energy – The Next Generation
SNAP: Supernova/Acceleration Probe
Dedicated dark energy probe
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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.
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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
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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
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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.
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SN Population DriftSN Population Drift
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Controlling SystematicsControlling Systematics
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Weighing Dark EnergyWeighing Dark Energy
SN Target
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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
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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
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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
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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.
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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
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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
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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