1. Dynamics of the Universe Lawrence Berkeley National Laboratory
Dark Energy and the
Dynamics of the Universe
Eric Linder
Lawrence Berkeley National Laboratory

2. Uphill to the Universe
Steep hills:
Building up -
Eroding away -

3. 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.

4. Our Expanding Universe
Bertschinger & Ma ; courtesy Ma

5. Our Cosmic Address Earth 107 meters Solar system 1013 m
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

6. The Cosmic Calendar Inflation 1016 GeV Quarks  Hadrons 1 GeV
Nuclei form 1 MeV
Atoms form 1 eV
[Room temperature 1/40 eV]
Stars and galaxies first form: 1/40 eV
Today: 1/4000 eV

7. 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.
STScI

8. 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.

9. Acceleration 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 ..

10. 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

11. 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.

12. Cosmic Concordance Supernovae alone  Accelerating expansion  > 0
decelerating
cf. Tonry et al. (2003)
accelerating
decelerating
Supernovae alone  Accelerating expansion
 > 0
CMB (plus LSS)
 Flat universe
  > 0
Any two of SN, CMB, LSS
 Dark energy ~75%

13. Frontiers of CosmologyUs
What a frontier!
STScI
95% of the universe is unknown!

14. 95% of the universe unknown!
Dark Energy Is...
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
Repulsive gravity!
! Determining the fate of the universe
Fate of the universe!
70-75% of the energy density of the universe
Accelerating the expansion, like inflation at 10-35s
Determining the fate of the universe
Is this mysterious dark energy the original cosmological constant , a quantum zeropoint sea?

15. 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 GeV4 !

16. 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.

17. 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.

18. 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.
Size=1/4
Size=1/2
Size=2
Size=4
Dark energy
Matter
Today

19. Key Issue for Physics Today
The universe is not simple:
So maybe neither is the quantum vacuum (or gravitation)?

20. We need new, highly precise data
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

21. Standard explosion from nuclear physics
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
SCP
Insensitive to initial conditions:
“Stellar amnesia”
Höflich, Gerardy, Linder, & Marion 2003

22. Standardized Candle Brightness tells us distance away (lookback time)
Time after explosion
Brightness tells us distance away (lookback time)
Redshift measured tells us expansion factor (average distance between galaxies)

23. 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
Images
M and L
Dark Energy Properties
Redshift & SN Properties
Spectra
data
analysis
physics

24. History & Fate

25. Weighing the Universe
accelerating
decelerating

26. Cosmic Concordance
accelerating
decelerating
cf. Tonry et al. (2003)

27. Nature of Dark Energy
“Stretchiness” (EOS)
Matter Density

28. 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= 0.09 (Knop et al. 2003) [SN+LSS+CMB]
wconst= ? (Riess et al. 2004) [SN+LSS+CMB]
But what about dynamics? Generically expect time variation w

29. What We (Don’t) Know We have to do it right.
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

30. Hubble Diagram 10 billion years ~2000 SNe Ia redshift z 0.2 0.4 0.6
0.8
1.0

31. Supernova Properties Astrophysics
Understanding Supernovae
Supernova Properties Astrophysics
Nearby Supernova Factory
G. Aldering (LBL)
Cleanly understood astrophysics leads to cosmology

32. High Redshift Supernovae
Discover
Reference
Subtract-->SN!
Riess et al./STScI

33. Looking Back 10 Billion Years
STScI

34. Looking Back 10 Billion Years

35. 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!

36. Dark Energy – The Next Generation
Dedicated dark energy probe
SNAP: Supernova/Acceleration Probe

37. Design a Space Mission wide deep colorful 9000 the Hubble Deep Field
GOODS
HDF
wide
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
deep
colorful
Both optical and infrared wavelengths to see thru dust.

38. Astronomical Imaging Guider Spectrograph port Visible NIR Focus star
projectors
Calibration projectors
Half billion pixel array
36 optical CCDs
36 near infrared detectors
JWST Field of View
Larger than any camera yet constructed

39. 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

40. Astrophysical Uncertainties
For accurate and precision cosmology, need to identify and control systematic 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.

41. SN Population Drift

42. Controlling Systematics

43. Weighing Dark Energy
SN Target

44. Exploring Dark Energy Needed data quality Dark energy theories
Current ground based compared with
Binned simulated data and a sample of
Dark energy models

45. The Fate of Our Universe
Size of Universe
History
Fate
Future Age of Universe
Looking back billion years
to look forward 40 billion

46. Frontiers of the 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?
Size of Universe
History
Fate
Future Age of Universe
Uphill to the Universe!

47. The Next Physics
The Standard Model gives us commanding knowledge about physics % 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?

48. Frontiers of Science Let’s find out! 1919 1998
Breakthrough of the Year
2003

49. The Next Physics

50. Cosmic Archaeology CMB: direct probe of quantum fluctuations
Cosmic matter structures: less direct probes of expansion
Pattern of ripples, clumping in space, growing in time.
3D survey of galaxies and clusters.
Supernovae: direct probe of cosmic expansion
Time: % of present age of universe
(When you were years old)
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!)

51. Cosmic Background Radiation
WMAP/ NASA
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 ; consistent with primordial nucleosynthesis
Matter-antimatter asymmetry? Baryogenesis?
Planck satellite (2007)

52. 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

53. 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.

54. Fundamental Physics Map the expansion history of the universe
Astrophysics  Cosmology  Field Theory
a(t)  Equation of state w(z)  V()
V ( ( a(t) ) ) SN
CMB
LSS
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
Map the expansion history of the universe

55. Cosmic Archaeology
Inflation sets seeds of structure, patterning both radiation (CMB) and matter (galaxies)
CMB }
Large scale structure,
Dark Energy, Acceleration
NASA GSFC/COBE