1. Gravitational Waves Earth expands and contracts by the diameter of an atomic nucleus: 10 -12 cm A world-shaking discovery

2. James Clerk Maxwell Professor at King’s College London: 1860 – 1865 Unified theory of electricity and magnetism Predicted electromagnetic waves Identified light as due to these waves Calculated the velocity of light … One scientific epoch ended and another began with James Clerk Maxwell - Albert Einstein

3. Electromagnetic Waves Proposed by Maxwell Discovered by Hertz A lot to answer for …. Nobody knows where fundamental physics may lead

4. Gravitational Waves General relativity proposed by Einstein 1915 He predicted gravitational waves in 1916

5. First Attempts at Detection 1970s: Metal bars (Joseph Weber) Also Explorer experiment at CERN

6. Indirect Detection Binary pulsar discovered 1974 (Hulse & Taylor) Emits gravitational waves Change in orbit measured for years Perfect agreement with Einstein Nobel Prize 1993

7. Binary Pulsar Measurements

8. Discovery of Gravitational Waves Measured by the LIGO experiment in 2 locations State of WashingtonState of Louisiana

9. LIGO experiment Inteference between 2 laser beams measures the expansion and contraction of space

10. Principle of Laser Interferometer Inteference between 2 laser beams measures the expansion and contraction of space

11. LIGO Layout & Sensitivity

12. What was observed Very similar signals in the 2 detectors In agreement with gravitational-wave predictions

13. Significance of Detection Based on coincidences between detectors: > 5σ Second most significant coincidence ~ 2σ Could also be BH merger

14. Fusion of two massive black holes Masses ~ 36, 29 solar masses Radiated energy ~ 3 solar masses

15. Fusion of two massive black holes Einstein was right A new horizon in the study of the Universe

16. The Gravitational Chirp … … heard around the world Frequency increases with time during inspiral Followed by ringdown of combined black hole Gravitino mass < 1.2 × 10 -22 eV Waves of different frequencies have same speed JE, Mavromatos & Nanopoulos, arXiv:1602.04764

18. Direction in Sky (LIGO)

19. Follow-up Campaign Many experiments looked for electromagnetic counterpart (light, radio, γ rays, X rays, … All results negative except for Fermi satellite γ rays > 50 keV Astrophysical puzzle Tells us speeds of light and gravitational waves same to 10 -17 JE, Mavromatos & Nanopoulos, arXiv:1602.04764

20. Direction in Sky (Fermi)

21. Ground-Based GW Detectors

22. Gravitational Wave Spectrum

23. Future Step: Interferometer in Space

25. Excellent Video Explanation http://motls.blogspot.ch/2016/02/bria n-greenes-ligo-colbert-lecture- was.html