modified gravity vs. the dark sector: was einstein right?
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Modified Gravity vs. the Dark Sector:Was Einstein Right?
Modified Gravity vs. the Dark Sector:Was Einstein Right?
SEPTEMBER 26. 2010 SCOTT DODELSON 1
DARK SECTOR
MODIFIED GRAVITY
Galactic Rotation CurvesGalactic Rotation Curves
Kepler: v=[GM/R]1/2
SEPTEMBER 26. 2010 SCOTT DODELSON 2
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Consider the United States in 1790Consider the United States in 1790
•Over-densities of order 50
•Concentrated in East
•Vast Voids with low density
3SEPTEMBER 26. 2010
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Consider the United States TodayConsider the United States Today
Over-densities of order 10,000
Concentration in coasts
Traces of primordial density (Boston-Washington; East > West)
Vast Voids
Over-densities of order 10,000
Concentration in coasts
Traces of primordial density (Boston-Washington; East > West)
Vast Voids
4SEPTEMBER 26. 2010
SCOTT DODELSON
The story of this evolution is the story of the United States
The story of this evolution is the story of the United States
When we understand the evolution from one map to another, we can understand the sociological, economic, and political forces acting on the US the people, or the constituents, of the US
5SEPTEMBER 26. 2010
The Universe Would Be Too Smooth Without Dark Matter
The Universe Would Be Too Smooth Without Dark Matter
SEPTEMBER 26. 2010 SCOTT DODELSON
WMAP
Sloan Digital Sky Survey
At t=400,000 years, the universe was smooth to one part in 10,000.
General Relativity predicts that perturbations have grown since then by a factor of 1000
6
Dark Matter Solves Cosmic Structure Problem
Dark Matter Solves Cosmic Structure Problem
ClumpinessDark matter was much clumpier than baryons were at the time of the picture of cosmic microwave background (CMB). Enough time for structure to grow!
Large Scales
SCOTT DODELSON SEPTEMBER 26. 2010 7
Dark EnergyDark Energy
SEPTEMBER 26, 2010 SCOTT DODELSON
Distant supernovae allow us to probe the expansion history of the universe
8
The Universe is AcceleratingThe Universe is Accelerating
Accelerating
B
rig
hte
r
SCOTT DODELSON SEPTEMBER 26, 2010
Decelerating
Astier et al. 2007
9
Gravity typically produces decelerationGravity typically produces deceleration
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This intuition carries over into Einstein’s theory … with a twist
This intuition carries over into Einstein’s theory … with a twist
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Pc
G
a
a3
3
42
SEPTEMBER 26, 2010 11
ACCELERATION = - [CONSTANT] X [ENERGY DENSITY + 3 X PRESSURE]
As long as the energy density and the pressure are positive, the Universe should be decelerating.
SCOTT DODELSON
Strange substance (Dark Energy) required to produce acceleration
Dark Energy has negative pressure Total energy within a given region increases as the region expands
SEPTEMBER 26, 2010 12
Dark Sector has been invoked previously in astronomy
Dark Sector has been invoked previously in astronomy
Formed a design in the beginning of this week, of investigating, as soon as possible after taking my
degree, the irregularities of the motion of Uranus, which are yet unaccounted for; in order
to find out whether they may be attributed to the action of an undiscovered planet beyond it;
and if possible thence to determine the elements of its orbit, etc.. approximately, which would
probably lead to its discovery. John Adams
Undergraduate Notebook, July 1841
SEPTEMBER 26. 2010 SCOTT DODELSON 13
Not everyone believed a new planet was responsible
Not everyone believed a new planet was responsible
Astronomer Royal, George Airy, believed deviation from 1/r2 force responsible for irregularities
Adams informed Airy of his plans, but Airy did not grant observing time.
SEPTEMBER 26. 2010 SCOTT DODELSON 14
In June 1845, the French also began the relevant calculations
In June 1845, the French also began the relevant calculations
Contemporary: “I do not know whether M. Le Verrier is actually the most detestable man in France, but I am quite certain that he is the most
detested.” SEPTEMBER 26. 2010 SCOTT DODELSON 15
Urbain Le Verrier
By June 1846, both Adams and LeVerrier had calculated positions
By June 1846, both Adams and LeVerrier had calculated positions
SEPTEMBER 26. 2010 SCOTT DODELSON 16
This first search (by Challis) was unsuccessfulThis first search (by Challis) was unsuccessful
In September 1846, Dawes’ friend William Lassell, an amateur astronomer and a brewer by trade, had just completed building a large telescope that would be able to record the disk of the planet. He wrote to Lassell giving him Adams’ predicted position. However Lassell had sprained his ankle and was confined to bed. He read the letter which he gave to his maid who then promptly lost it. His ankle was sufficiently recovered on the next night and he looked in vain for the letter with the predicted position.
In September 1846, Dawes’ friend William Lassell, an amateur astronomer and a brewer by trade, had just completed building a large telescope that would be able to record the disk of the planet. He wrote to Lassell giving him Adams’ predicted position. However Lassell had sprained his ankle and was confined to bed. He read the letter which he gave to his maid who then promptly lost it. His ankle was sufficiently recovered on the next night and he looked in vain for the letter with the predicted position.
Both Adams and LeVerrier refined their predictions…
SEPTEMBER 26. 2010 SCOTT DODELSON 17
LeVerrier wrote to German astronomer Galle on September 18, 1846
LeVerrier wrote to German astronomer Galle on September 18, 1846
Galle discovered it in 30 minutes on September 23.
SEPTEMBER 26. 2010 SCOTT DODELSON 18
Anomalous precession of Mercury’s perihelion went the other way
Anomalous precession of Mercury’s perihelion went the other way
LeVerrier assumed it was due to a small planet near the Sun and searched (in vain) for such a planet (Vulcan).
We now know that this anomaly is due to a whole new theory of gravity.
SEPTEMBER 26. 2010 SCOTT DODELSON 19
We have a similar dilemma todayWe have a similar dilemma today
SEPTEMBER 26. 2010 SCOTT DODELSON 20
DARK SECTOR
MODIFIED GRAVITY
AssumptionsAssumptionsFor dark matter, we assumed Kepler’s Law, which follows
from Newtonian GravityFor dark energy, we assumed General Relativity
For dark matter, we assumed Kepler’s Law, which follows from Newtonian Gravity
For dark energy, we assumed General Relativity
SEPTEMBER 26. 2010 SCOTT DODELSON 21
STRONG GRAVITYWEAK GRAVITY
Newton’s insight: same force governs motion on earth and
in the Heavens
Newton’s insight: same force governs motion on earth and
in the Heavens
SEPTEMBER 26. 2010 SCOTT DODELSON 22
STRONG GRAVITYWEAK GRAVITY
Newtonian Gravity
Then Einstein realized Newtonian Gravity was valid only for weak fields
Then Einstein realized Newtonian Gravity was valid only for weak fields
SEPTEMBER 26. 2010 SCOTT DODELSON 23
STRONG GRAVITYWEAK GRAVITY
Newtonian Gravity
General Relativity was assumed to be the true theory, reducing to Newtonian
Gravity in the weak field limit
General Relativity was assumed to be the true theory, reducing to Newtonian
Gravity in the weak field limit
SEPTEMBER 26. 2010 SCOTT DODELSON 24
STRONG GRAVITYWEAK GRAVITY
Newtonian Gravity
General Relativity
Maybe both need to be replaced in the very weak limit
Maybe both need to be replaced in the very weak limit
SEPTEMBER 26. 2010 SCOTT DODELSON 25
STRONG GRAVITYWEAK GRAVITY
Newtonian Gravity
General Relativity
Doing away with Dark MatterDoing away with Dark Matter
In 1983, Mordecai Milgrom proposed Modified Newtonian Dynamics (MOND). In very weak fields (edges of galaxies) the force from gravity changes from (1/r2) to (1/r).
In 1983, Mordecai Milgrom proposed Modified Newtonian Dynamics (MOND). In very weak fields (edges of galaxies) the force from gravity changes from (1/r2) to (1/r).
SEPTEMBER 26. 2010 SCOTT DODELSON 26
Fit Rotation CurvesFit Rotation Curves
•Fit Rotation Curves of many galaxies w/ only one free parameter.
•Compare to fitting CDM: http://burro.astr.cwru.edu/JavaLab/RotcurveWeb/main.html
SEPTEMBER 26. 2010 SCOTT DODELSON 27McGaugh
Also makes predictions for galaxy properties
Also makes predictions for galaxy properties
L~v4
Sanders & Veheijen 1998
SEPTEMBER 26. 2010 SCOTT DODELSON 28
Lum
inosi
ty
Velocity
On cosmology, MOND is silentOn cosmology, MOND is silent
Not a comprehensive theory of gravity so cannot be applied to an almost homogeneous universe. We don’t even know if the underlying theory – which reduces to MOND in some limit – is consistent with an expanding universe.
SEPTEMBER 26. 2010 SCOTT DODELSON 29
WMAP Sloan Digital Sky Survey
Bekenstein’s TheoryBekenstein’s Theory
SEPTEMBER 26. 2010 SCOTT DODELSON 30
Questions a basic assumption of General Relativity: the metric which
determines geometry is the same one which dictates how particles move
TeVeS (Tensor Vector Scalar) reduces to MOND on Galactic scales. Enables us to do cosmology
Many groups have now applied TeVeS to cosmology
Many groups have now applied TeVeS to cosmology
SEPTEMBER 26. 2010 SCOTT DODELSON 31
•The picture of a smooth, expanding universe is almost identical to that obtained with General Relativity. •Key Question: How do inhomogeneities grow? Is there enough time for structure to grow even without dark matter?
WMAP
Sloan Digital Sky Survey
Inhomogeneities in TeVeS grow faster than in GR
Inhomogeneities in TeVeS grow faster than in GR
TeVeS
Standard Growth
SEPTEMBER 26. 2010 SCOTT DODELSON 32
Dodelson & Liguori
SEPTEMBER 26. 2010 SCOTT DODELSON 33
Cosmic structure explained without dark
matterDec 18, 2006
An alternative to Einstein's theory of general relativity
called "TeVeS" could describe the formation of cosmic structure without requiring the existence of
dark matter, say physicists in the US (Phys. Rev. Lett.
97 2006).
Still need to worry about the Shape of the power spectrum
Still need to worry about the Shape of the power spectrum
SEPTEMBER 26. 2010 SCOTT DODELSON 34
Workshop June, 2010Workshop June, 2010 PROGRAM Monday 28/06 10h00-10h05: Welcome (H. Wozniak) 10h05-10h30: Outlook of the meeting (B.
Famaey) 10h30-11h30: Modified Newtonian Dynamics for
practicioners (M. Milgrom) 11h30-12h30: Dark energy and modified gravity
(P. Brax) 14h30-15h30: Empirical tests of MOND in
galaxies (S. McGaugh) 15h30-16h00: Bulge-dominated galaxies, a
challenge for MOND? (F. Fraternali) 16h30-17h00: THINGS about MOND (G. Gentile)
Tuesday 29/06
09h00-09h30: What are the best constraints on theories from galaxy dynamics (F. Combes)
09h30-10h00: Dynamical friction, galaxy merging, and radial-orbit instability in MOND (C. Nipoti)
10h00-10h30: Testing gravity with galaxy mergers and polar rings (O. Tiret)
10h30-10h45: MOND in the Milky Way (O. Bienaymé)
PROGRAM Monday 28/06 10h00-10h05: Welcome (H. Wozniak) 10h05-10h30: Outlook of the meeting (B.
Famaey) 10h30-11h30: Modified Newtonian Dynamics for
practicioners (M. Milgrom) 11h30-12h30: Dark energy and modified gravity
(P. Brax) 14h30-15h30: Empirical tests of MOND in
galaxies (S. McGaugh) 15h30-16h00: Bulge-dominated galaxies, a
challenge for MOND? (F. Fraternali) 16h30-17h00: THINGS about MOND (G. Gentile)
Tuesday 29/06
09h00-09h30: What are the best constraints on theories from galaxy dynamics (F. Combes)
09h30-10h00: Dynamical friction, galaxy merging, and radial-orbit instability in MOND (C. Nipoti)
10h00-10h30: Testing gravity with galaxy mergers and polar rings (O. Tiret)
10h30-10h45: MOND in the Milky Way (O. Bienaymé)
SEPTEMBER 26. 2010 SCOTT DODELSON 35
Sample SlideSample Slide
SEPTEMBER 26. 2010 SCOTT DODELSON 36
Sample SlideSample Slide
SEPTEMBER 26. 2010 SCOTT DODELSON 37
Thursday: Final DayThursday: Final Day
09h00-09h30: Structure formation in the presence of dark interactions (M. Baldi) 09h30-10h00: A dark fluid to explain MOND, dark matter, and dark energy? (H.S. Zhao) 10h00-10h30: N-body simulations for coupled scalar field theories (B. Li) 11h00-12h00: Modified gravity as an alternative to dark energy (L. Amendola) 12h00-12h30: The dilaton and modified gravity (C. Van de Bruck) 12h30-13h00: Asymptotically safe gravity from a bimetric perspective (F. Saueressig)
13h00-14h00: LUNCH
14h00-14h30: Cosmography and clusters of galaxies from f(R)-gravity (S. Capozziello) 14h30-15h00: Testing f(R) theories with elliptical galaxies (N. Napolitano) 15h00-15h30: MOND and dark matter in ellipticals (T. Richtler) 15h30-16h00: Dark matter and MOND in NGC 1399 (Y. Schuberth) 16h30-16h50: The MOND fundamental Plane (V. Cardone) 16h50-17h10: Interloper removal in dwarf spheroidals (A.-L. Serra) 17h10-17h30: Dark matter and MOND in ulra-compact dwarf galaxies (J. Dabringhausen) 17h30-18h00: The disk of satellites and other small-scalle issues (P. Kroupa)
18h00-18h30: Meeting Summary and final discussion (led by S. McGaugh & S. Dodelson)
09h00-09h30: Structure formation in the presence of dark interactions (M. Baldi) 09h30-10h00: A dark fluid to explain MOND, dark matter, and dark energy? (H.S. Zhao) 10h00-10h30: N-body simulations for coupled scalar field theories (B. Li) 11h00-12h00: Modified gravity as an alternative to dark energy (L. Amendola) 12h00-12h30: The dilaton and modified gravity (C. Van de Bruck) 12h30-13h00: Asymptotically safe gravity from a bimetric perspective (F. Saueressig)
13h00-14h00: LUNCH
14h00-14h30: Cosmography and clusters of galaxies from f(R)-gravity (S. Capozziello) 14h30-15h00: Testing f(R) theories with elliptical galaxies (N. Napolitano) 15h00-15h30: MOND and dark matter in ellipticals (T. Richtler) 15h30-16h00: Dark matter and MOND in NGC 1399 (Y. Schuberth) 16h30-16h50: The MOND fundamental Plane (V. Cardone) 16h50-17h10: Interloper removal in dwarf spheroidals (A.-L. Serra) 17h10-17h30: Dark matter and MOND in ulra-compact dwarf galaxies (J. Dabringhausen) 17h30-18h00: The disk of satellites and other small-scalle issues (P. Kroupa)
18h00-18h30: Meeting Summary and final discussion (led by S. McGaugh & S. Dodelson)
SEPTEMBER 26. 2010 SCOTT DODELSON 38
Bright Side: Improved Jewish-Muslim Relations
Bright Side: Improved Jewish-Muslim Relations
SEPTEMBER 26. 2010 SCOTT DODELSON 39
Why/how do 2 sets of (rational) people disagree so strongly?
Why/how do 2 sets of (rational) people disagree so strongly?
MG proponents argue against DM/DE because they say it assumes substances that do not necessarily exist
MG proponents argue against DM/DE because they say it assumes substances that do not necessarily exist
SEPTEMBER 26. 2010 SCOTT DODELSON 40
Why/how do 2 sets of (rational) people disagree so strongly?
Why/how do 2 sets of (rational) people disagree so strongly?
Well yes, but … supersymmetry was introduced for other reasons
MG also represents a change to the action, the quantity that encapsulates all laws of nature
Well yes, but … supersymmetry was introduced for other reasons
MG also represents a change to the action, the quantity that encapsulates all laws of nature
SEPTEMBER 26. 2010 SCOTT DODELSON 41
And that change is ugly!
Why/how do 2 sets of (rational) people disagree so strongly?
Why/how do 2 sets of (rational) people disagree so strongly?
Small scale or large scale starting point?Small scale or large scale starting point?
SEPTEMBER 26. 2010 SCOTT DODELSON 42
What about the other component of the dark sector?
What about the other component of the dark sector?
SEPTEMBER 26. 2010 SCOTT DODELSON 43
Need to modify gravity in a different wayNeed to modify gravity in a different way
SEPTEMBER 26. 2010 SCOTT DODELSON 44
)(16
1 4 RfRgxdG
S )(
16
1 4 RfRgxdG
S
26
33
4 2 RR
ffHfP
G
a
a
Modify the Einstein-Hilbert Action
The acceleration equation generalizes to:
Get acceleration if these terms are positive even if
pressure is positive
How will we determine who’s right?How will we determine who’s right?
SEPTEMBER 26. 2010 SCOTT DODELSON 45
Accelerators Indirect Detection Direct Detection
LHC Fermi Coupp
WIMP’s can be probed in 3 ways … and will be over the coming decade
How will we determine who’s right?How will we determine who’s right?
SEPTEMBER 26. 2010 SCOTT DODELSON 46
MG vs. DE is harder: measure growth of structure
GRAVITATIONAL LENSING
GALAXY CLUSTERS
We are pondering/probing the modern incarnation of one of the most profound
questions in science
We are pondering/probing the modern incarnation of one of the most profound
questions in science
SEPTEMBER 26. 2010 SCOTT DODELSON 47
DARK SECTOR
MODIFIED GRAVITY
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