modified gravity vs. the dark sector: was einstein right?

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


SCOTT DODELSON

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

SCOTT DODELSON

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


This intuition carries over into Einstein’s theory … with a twist

This intuition carries over into Einstein’s theory … with a twist

SCOTT DODELSON

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


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.


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


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…


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.


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.


We have a similar dilemma todayWe have a similar dilemma today


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


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



Newtonian Gravity

Then Einstein realized Newtonian Gravity was valid only for weak fields

Then Einstein realized Newtonian Gravity was valid only for weak fields



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



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



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).


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


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.


WMAP Sloan Digital Sky Survey

Bekenstein’s TheoryBekenstein’s Theory


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


•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


Dodelson & Liguori


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


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)


Sample SlideSample Slide


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)


Bright Side: Improved Jewish-Muslim Relations

Bright Side: Improved Jewish-Muslim Relations


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




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


And that change is ugly!



Small scale or large scale starting point?Small scale or large scale starting point?


What about the other component of the dark sector?

What about the other component of the dark sector?


Need to modify gravity in a different wayNeed to modify gravity in a different way


)(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?


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?


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


DARK SECTOR

MODIFIED GRAVITY

modified gravity vs. the dark sector: was einstein right?

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