Einstein's Legacy: General Relativity Unveiling Universe Mysteries

1. Einstein's Legacy: General Relativity, our Best Description of the UniverseBarry C. BarishCaltechVancouver Institute16-April-05 Crab Pulsar

2. Albert Einstein

4. Annus Mirabilis • In 1905, Albert Einstein wrote five revolutionary scientific papers. • These papers altered our understanding of the nature of light, proved the existence of atoms and molecules, and established the concept of special relativity.

5. LIGHT • Is the behavior of light like a wave or like a particle? "A question so enormously important and difficult that everybody should work on it." ~Albert Einstein Light is also described as being individual particles -- photons. In a solar cells a photon collides with the atoms and generates electricity by knocking an electron out. This is the photoelectric effect. Light is often described as a wave. Sunlight and radio waves are both forms of light, but have different wavelengths. The colors you see in a rainbow demonstrate the wave-like nature of light.

6. ATOMS • How do we know atoms and molecules exist? "My major aim in this was to find facts which would guarantee as much as possible the existence of atoms of definite finite size." ~Albert Einstein Einstein realized that if atoms did exist then they would continually bump into microscopic particles in their paths. He created a mathematical model where accurate measurements of these microscopic motions could be used to determine the actual size of molecules and atoms.

7. RELATIVITY Einstein argued that the laws of physics are the same in all reference frames. A scientist on the ground and a scientist in a fast moving space station will always agree that the laws of physics are the same. He argued that therefore the velocity of light is measured to be the same by all observers in all reference frames. Is there a cosmic speed limit?

8. ENERGY and MASS • For centuries, scientists believed that matter and energy could never be destroyed. • Before 1905, the law of conservation of energy and the law of conservation of mass were two fundamental principles of science that appeared to never be violated. • Einstein showed that these laws were fallible, and that they needed to be reconciled into a single theory unifying mass and energy. E = mc2

9. General Relativitythe essential idea Gmn= 8pTmn • Gravity is not a force, but a property of space & time • Spacetime = 3 spatial dimensions + time • Perception of space or time is relative • Objects follow the shortest path through this warped spacetime; path is the same for all objects • Overthrew the 19th-century concepts of absolute space and time • Concentrations of mass or energy distort (warp) spacetime

10. General Relativity Einstein theorized that a massive object warps the surrounding space

11. General Relativity Smaller objects travel through space that is warped by larger objects

12. Gravity a fundamental force

13. Universal Gravitation • Solved most known problems of astronomy and terrestrial physics • eccentric orbits of comets • cause of tides and their variations • the precession of the earth’s axis • the perturbation of the motion of the moon by gravity of the sun • Unified the work of Galileo, Copernicus and Kepler unified.

14. But, what causes the mysterious force in Newtons theory ? Although the equation explains nature very well, the underlying mechanism creating the force is not explained !

15. After several hundred years, a small crack in Newton’s theory ….. perihelion shifts forward an extra +43”/century compared to Newton’s theory

16. A new prediction of Einstein’s theory … Light from distant stars are bent as they graze the Sun. The exact amount is predicted by Einstein's theory.

17. Confirming Einstein …. bending of light Observation made during the solar eclipse of 1919 by Sir Arthur Eddington, when the Sun was silhouetted against the Hyades star cluster A massive object shifts apparent position of a star

18. Einstein’s Cross The bending of light rays gravitational lensing Quasar image appears around the central glow formed by nearby galaxy. The Einstein Cross is only visible in southern hemisphere.

19. Gravitational Waves ?

20. A Conceptual Problem is solved ! Newton’s Theory “instantaneous action at a distance” Einstein’s Theory information carried by gravitational radiation at the speed of light

21. Russel A. Hulse Joseph H.Taylor Jr The Evidence For Gravitational Waves The Discovered and Studied Pulsar System PSR 1913 + 16 with Radio Telescope Source: www.NSF.gov

22. Neutron Star Radio Pulsar

23. The evidence for gravitational waves • Neutron binary system • separation = 106 miles • m1 = 1.4m • m2 = 1.36m • e = 0.617 Hulse & Taylor 17 / sec · · • Prediction • from • general relativity • spiral in by 3 mm/orbit • rate of change orbital • period period ~ 8 hr PSR 1913 + 16 Timing of pulsars

24. “Indirect”evidence for gravitational waves

25. The Nature of Gravitational Waves Compact Binary Inspiral Merger Ringdown Inspiral

26. The effect of a gravitational wave passing through space …

27. Direct Detection Gravitational Wave Astrophysical Source Terrestrial detectors LIGO, TAMA, Virgo,AIGO Detectors in space LISA

28. LISA The diagram shows the sensitivity bands for LISA and LIGO

29. The frequency range of astronomy • EM waves studied over ~16 orders of magnitude • Ultra Low Frequency radio waves to high energy gamma rays

30. Gravitational Waves in Space LISA Three spacecraft, each with a Y-shaped payload, form an equilateral triangle with sides 5 million km in length.

31. LISA The three LISA spacecraft will be placed in orbits that form a triangular formation with center 20o behind the Earth

32. Leonardo da Vinci’s Vitruvian man stretch and squash in perpendicular directions at the frequency of the gravitational waves

33. Detecting a passing wave …. Free masses

34. Detecting a passing wave …. Interferometer

35. Leonardo da Vinci’s Vitruvian man stretch and squash in perpendicular directions at the frequency of the gravitational waves I have greatly exaggerated the effect!! If the Vitruvian man was 4.5 light years high, he would grow by only a ‘hairs width’

36. Gravitational Wave Detection free masses h = strain amplitude of grav. waves h = DL/L ~ 10-21 L = 4 km DL ~ 10-18 m Laser Interferometer laser

37. As a wave passes, the arm lengths change in different ways…. The Detection Technique • Arms in LIGO are 4km • Measure difference in length to one part in 1021 or 10-18 meters • Laser used to measure relative lengths of two orthogonal arms …causing the interference pattern to change at the photodiode

38. One meter ~ 40 inches Human hair ~ 100 microns Wavelength of light ~ 1 micron Atomic diameter 10-10 m Nuclear diameter 10-15 m LIGO sensitivity 10-18 m How Small is 10-18 Meter?

39. LIGOLaser Interferometer Gravitational-wave Observatory Hanford Observatory MIT Caltech Livingston Observatory

40. 4 km LIGO Livingston, Louisiana

41. Flooding in Louisiana

42. 4 km 2 km LIGO Hanford Washington

43. Also a Few Glitches in Hanford, but Science Moves On …

44. What Limits LIGO Sensitivity? • Seismic noise limits low frequencies • Thermal Noise limits middle frequencies • Quantum nature of light (Shot Noise) limits high frequencies • Technical issues - alignment, electronics, acoustics, etc limit us before we reach these design goals

45. Evolution of LIGO Sensitivity

46. Detecting Earthquakes From electronic logbook 2-Jan-02 An earthquake occurred, starting at UTC 17:38.

47. Detect the Earth Tide from the Sun and Moon

48. Astrophysical Sourcessignatures • Compact binary inspiral: “chirps” • NS-NS waveforms are well described • BH-BH need better waveforms • search technique: matched templates • Supernovae / GRBs: “bursts” • burst signals in coincidence with signals in electromagnetic radiation • prompt alarm (~ one hour) with neutrino detectors • Pulsars in our galaxy: “periodic” • search for observed neutron stars (frequency, doppler shift) • all sky search (computing challenge) • r-modes • Cosmological Signal “stochastic background”

49. Directed Pulsar Search 28 Radio Sources

50. Detection of Periodic Sources • Frequency modulationof signal due to Earth’s motion relative to the Solar System Barycenter, intrinsic frequency changes. • Known Pulsars in our galaxy NEW RESULT 28 known pulsars NO gravitational waves e < 10-5 – 10-6 (no mountains > 10 cm • Amplitude modulationdue to the detector’s antenna pattern. ALL SKY SEARCH enormous computing challenge