Modified Gravity vs. the Dark Sector: Was Einstein Right?

1. Modified Gravity vs. the Dark Sector:Was Einstein Right? Dark Sector Modified Gravity Scott Dodelson

2. Galactic Rotation Curves Kepler: v=[GM/R]1/2 Scott Dodelson

3. Consider the United States in 1790 • Over-densities of order 50 • Concentrated in East • Vast Voids with low density Scott Dodelson

4. Consider the United States Today • Over-densities of order 10,000 • Concentration in coasts • Traces of primordial density (Boston-Washington; East > West) • Vast Voids Scott Dodelson

5. 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 Scott Dodelson

6. The Universe Would Be Too Smooth Without Dark Matter At t=400,000 years, the universe was smooth to one part in 10,000. WMAP General Relativity predicts that perturbations have grown since then by a factor of 1000 Sloan Digital Sky Survey Scott Dodelson

7. Dark Matter Solves Cosmic Structure Problem Dark matter was much clumpier than baryons were at the time of the picture of cosmic microwave background (CMB). Enough time for structure to grow! Clumpiness Large Scales Scott Dodelson

8. Dark Energy Distant supernovae allow us to probe the expansion history of the universe Scott Dodelson

9. The Universe is Accelerating Accelerating Decelerating Brighter Astier et al. 2007 Scott Dodelson

10. Gravity typically produces deceleration Scott Dodelson

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

12. Strange substance (Dark Energy) required to produce acceleration Dark Energy has negative pressure  Total energy within a given region increases as the region expands Scott Dodelson

13. 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 Scott Dodelson

14. Not everyone believed a new planet was responsible Adams informed Airy of his plans, but Airy did not grant observing time. Astronomer Royal, George Airy, believed deviation from 1/r2 force responsible for irregularities Scott Dodelson

15. In June 1845, the French also began the relevant calculations Urbain Le Verrier 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.” Scott Dodelson

16. By June 1846, both Adams and LeVerrier had calculated positions Scott Dodelson

17. This first search (by Challis) was unsuccessful Both Adams and LeVerrier refined their predictions… 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. Scott Dodelson

18. LeVerrier wrote to German astronomer Galle on September 18, 1846 Galle discovered it in 30 minutes on September 23. Scott Dodelson

19. 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. Scott Dodelson

20. We have a similar dilemma today Dark Sector Modified Gravity Scott Dodelson

21. Assumptions For dark matter, we assumed Kepler’s Law, which follows from Newtonian Gravity For dark energy, we assumed General Relativity Weak Gravity Strong Gravity Scott Dodelson

22. Newton’s insight: same force governs motion on earth and in the Heavens Newtonian Gravity Weak Gravity Strong Gravity Scott Dodelson

23. Then Einstein realized Newtonian Gravity was valid only for weak fields Newtonian Gravity Weak Gravity Strong Gravity Scott Dodelson

24. General Relativity was assumed to be the true theory, reducing to Newtonian Gravity in the weak field limit General Relativity Newtonian Gravity Weak Gravity Strong Gravity Scott Dodelson

25. Maybe both need to be replaced in the very weak limit General Relativity Newtonian Gravity Weak Gravity Strong Gravity Scott Dodelson

26. Doing 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). Scott Dodelson

27. Fit 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 Scott Dodelson McGaugh

28. Also makes predictions for galaxy properties Sanders & Veheijen 1998 Luminosity L~v4 Velocity Scott Dodelson

29. On cosmology, MOND is silent WMAP Sloan Digital Sky Survey 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. Scott Dodelson

30. Bekenstein’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 Scott Dodelson

31. 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 Scott Dodelson

32. Inhomogeneities in TeVeS grow faster than in GR Standard Growth TeVeS Dodelson & Liguori Scott Dodelson

33. Cosmic structure explained without dark matter Dec 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). Scott Dodelson

34. Still need to worry about the Shape of the power spectrum Scott Dodelson

35. Workshop 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) Scott Dodelson

36. Sample Slide Scott Dodelson

37. Sample Slide Scott Dodelson

38. Thursday: 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) Scott Dodelson

39. Bright Side: Improved Jewish-Muslim Relations Scott Dodelson

40. 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 Scott Dodelson

41. 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 And that change is ugly! Scott Dodelson

42. Why/how do 2 sets of (rational) people disagree so strongly? Small scale or large scale starting point? Scott Dodelson

43. What about the other component of the dark sector? Scott Dodelson

44. Need to modify gravity in a different way Modify the Einstein-Hilbert Action The acceleration equation generalizes to: Get acceleration if these terms are positive even if pressure is positive Scott Dodelson

45. How will we determine who’s right? Accelerators Indirect Detection Direct Detection LHC Coupp Fermi WIMP’s can be probed in 3 ways … and will be over the coming decade Scott Dodelson

46. How will we determine who’s right? MG vs. DE is harder: measure growth of structure Galaxy Clusters Gravitational Lensing Scott Dodelson

47. We are pondering/probing the modern incarnation of one of the most profound questions in science Dark Sector Modified Gravity Scott Dodelson