Detecting Dark Energy
Michael Levi
Lawrence Berkeley National Laboratory
Detecting Dark Energy
or,
Is Larry a Cosmological Constant?
The Mystery:
Where does he get his energy from?
Why is he still so youthful?
The Postulate:
Underlying energetic scalar field with strong “LS” couplings.
Scalar field is dynamical so we feel it differently from Larry.
The Cosmological Constant
The Cosmological
Constant is back!!!
L
L
• Einstein 1917
– Field equations show contracting or expanding
universe, but the universe was thought to be
static.
– Einstein postulated a cosmological constant, L
“energy” (with negative pressure), to maintain a
static universe.
Einstein’s field equations (1917)
The Cosmological
Constant is back!!!
L
L
• Danger! Runaway solution if L is large and positive!
Edwin Hubble
• To measure the expansion rate of
the universe Hubble needed to
measure astronomical distances
• Apparent brightness of an object
depends on its distance
• If a set of identical objects could
be found (“standard candles”)
then brightness could be used to
determine their distances
The Universe, its Expanding!
Hubble’s 1929 evidence that the universe is not static.
The Cosmological Constant is unnecessary
-- Einstein’s proclaimed his “Biggest Blunder.”
The Fate of the Universe
Average distance
between galaxies
Slowing
Forever
Time
The Fate of the Universe
Average distance
between galaxies
Slowing
Forever
Big Crunch
Time
“Standard” Candles
•Nearby supernovae used to study
SNe light curve (z<0.1)
•Brightness not quite standard
•Intrinsically brighter SNe last
longer
•Correction factor needed
Peakmagnitude
dispersion of
0.25 – 0.3
magnitudes
~0.15
magnitude
dispersion
“Brookline is expanding!”
The Accelerating Universe
What is causing this
accelerating expansion?
– Some kind of ‘dark energy’
that counteracts gravity?
L
L
A Revolution in Cosmology
Big Bang
Nucleosynthesis
Inflation
Flat universe
total= 1.02+/-0.02
Baryon Density
B= 0.044+/-0.004
DE= 0.7, M= 0.3
for a flat universe
 Weak lensing mass census
 Large scale structure
measurements
M= 0.3
WMAP
New
Standard Cosmology:
73±4% Dark Energy
27±4% Matter
0.5% Bright Stars
Matter:
22% CDM, 4.4% Baryons,
0.3% ’s
Energy budget of Universe
Dark
Energy:
65%
Dark
Matter:
30%
Fundamental Physics Questions
• What is the Nature of the dark energy?
—The dominant component of our universe.
—Dark energy does not fit in current physics theory.
—Theory proposes a number of alternative new physics
explanations, each with different properties we can measure.
• Two key contrasting theories of dark energy.
— vacuum energy, constant over time:
Deep philosophical implications, why are the matter (M) and
energy densities (L) nearly the same today, they have totally
different time evolution. Why now? Why is L so small?
— or, time dependent possibly a dynamical scalar field:
Might explain M @ L and so small, we’ve seen these fields
elsewhere in particle physics and in the theory of inflation.
Points to new physics.
The Expansion History of the Universe
Need lots of
precision
data to study
this region
Need Lots more Data!
Turn Dozens of Supernovae  Thousands Supernovae
Space
Ground
Z=0.8
Z=1.0
Z=1.2
Z=1.4
Z=1.6
Supernova / Acceleration Probe
SNAP is “Dog Simple”:
Innovation in Simplicity
•
Innovative 2m aperture telescope design
does IR imaging with room temperature
optics
•
Built in end-to-end optical test capability
simplifies Integration and testing
•
The fixed antenna, fixed solar panels
eliminates a major mission risk.
•
Fixed filters, passive cooling, eliminates
instrument risk.
•
No onboard data analysis: all images are
downlinked to Earth
D=56.6 cm (13.0 mrad)
0.7 square degrees!
Focal plane
Fixed filters atop the sensors
Guider
NIR
Visible
Integral Field Spectrograph
Spectrograph port
SNAP Surveys
Survey
Deep/SNe
Wide
Area(sq.deg) Depth(AB mag) ngal(arcmin-2)
Ngal
15
30.3
250
107
1000
28.0
100
108.5
26.7
40-50
Panoramic 7000-10000
Hubble Deep Field
109
Base SNAP survey:
15 square degrees near
ecliptic poles
~9,000  as large as
Hubble Deep Field,
same resolution but
deeper (and in nine
visible and NIR bands)
GOODS Survey area
SNAP Collaboration
LBNL
G. Aldering, S. Bailey, C. Bebek, W. Carithers, L. Cominsky†, T. Davis†, K. Dawson,
S. Deustua†, D. Groom, M. Hoff, S. Holland, D. Huterer†, A. Karcher,
A. Kim, W. Kolbe, B. Krieger, G. Kushner, N. Kuznetsova, R. Lafever,
M. Levi, S. Loken, B. McGinnis, R. Miquel, P. Nugent, H. Oluseyi†, P. Platt†,
N. Palaio, S. Perlmutter, N. Roe, H. Shukla, A. Spadafora, H. Von Der Lippe,
J-P. Walder, G. Wang
Berkeley
M. Bester, E. Commins, G. Goldhaber, H. Heetderks, P. Jelinsky, M. Lampton,
E. Linder, D. Pankow, M. Sholl, G. Smoot, C. Vale, M. White
Caltech
R. Ellis, R. Massey†, A. Refregier†, R. Smith, K. Taylor, A. Weinstein
Fermi National
Laboratory
J. Annis, F. DeJongh, S. Dodelson, T. Diehl, J. Frieman, D. Holz†, L. Hui, S. Kent,
P. Limon, J. Marriner, H. Lin, J. Peoples, V. Scarpine, A. Stebbins, C. Stoughton,
D. Tucker, W. Wester
Indiana U.
C. Bower, N. Mostek, J. Musser, S. Mufson
IN2P3-Paris
-Marseille
P. Astier, E. Barrelet, R. Pain, G. Smadja†, D. Vincent
A. Bonissent, A. Ealet, D. Fouchez, A. Tilquin
JPL
D. Cole, M. Frerking, J. Rhodes, M. Seiffert
LAM (France)
S. Basa, R. Malina, A. Mazure, E. Prieto
University of
Michigan
B. Bigelow, M. Brown, M. Campbell, D. Gerdes, W. Lorenzon, T. McKay, S. McKee,
M. Schubnell, G. Tarle, A. Tomasch
University of
Pennsylvania
G. Bernstein, L. Gladney, B. Jain, D. Rusin
University of
Stockholm
R. Amanullah, L. Bergström, A. Goobar, E. Mörtsell
SLAC
W. Althouse, R. Blandford, W. Craig, S. Kahn, M. Huffer, P. Marshall
STScI
R. Bohlin, D. Figer, A. Fruchter, B. Mobasher
Yale U.
C. Baltay, W. Emmet, J. Snyder, A. Szymkowiak, D. Rabinowitz, N. Morgan
†
Institutional affiliation
Optical Sensors
Infra-Red Sensors
Electronics
Space Optics
Spectrograph
Earth
Orbit
L2
Telescope
National Academy of Sciences
Department of Energy
NASA
OSTP
JDEM
Expansion
History
of the
Universe
We live in a special time
when:
- we can ask questions
about the history and
fate of the universe
- and expect to get an
answer!
“Brookline is expanding!”