1. Gravitational waves Gideon Koekoek January 9 th 2008 Research done at Nikhef

2. Overview of the talk  Graviational waves: a revolution  What are gravitational waves?  Measuring gravitational waves  What we @ Nikhef / Vu are doing  Conclusions

3. Why gravitational waves?

4. What is so interesting about them? We already have telescopes, neutrino detectors and stuff like that to study the Universe, right? So why do we want to measure gravitational waves as well?

5. Why gravitational waves? Theory: how correct is General Relativity? Astronomy: what processes occur in exotic objects? Cosmology: what happened after the Big Bang? Astronomy: what is the nature of Dark Matter and/or Dark Energy? We need gravitational waves!! There are questions we cannot answer without GWs:

6. Why gravitational waves? What is the nature of Dark Matter/Dark Energy? Most of the Universe, we don’t know anything about! We need gravitational waves! This is us

7. Why gravitational waves? How about the Big Bang? Light can only see up to here..but gravitational waves can see up to here! We need gravitational waves!..neutrino’s can only see up to here..

8. What are gravitational waves?

9. Wait, what is gravity in the first place? Earth’s path is not straight, but bent by a force 1 st Law: motion in straight lines if there is no force. F v Gravity is a force!

10. What are gravitational waves? Einstein disagreed.. Still a straight line, but in curved spacetime! Gravity is not a force; it’s the curvature of space (and time)  Newton does not agree with Relativity,  All matter behaves the same under gravity

11. What are gravitational waves? Q: What curves spacetime? A: energy does! Ok, good. Now about those gravitational waves.. You need a lot of energy to curve spacetime; gravity is weak! This is a very small number! ~ 10 -45 (!!)

12. What are gravitational waves? Flat spacetime, plus a little curvature A wave equation: a curvature h μ υ oscillates through space! Curvature in the vacuum?

13. What are gravitational waves? An example: gravitational waves produced by a binary star system We want to measure these waves! Us Binary stars: source of GW’s

14. Measuring gravitational waves

15. A blessing and a curse: GW’s interact very weakly 10 -45 (!!) Blessing: once produced, they can’t be disturbed Curse: very difficult to measure them ourselves!

16. Measuring gravitational waves Amplitude and frequency of gravitational waves emitted by a binary system of masses M 1 and M 2 at separation r Note: a million times smaller than a proton!

17. Measuring gravitational waves Q: How to measure gravitational waves? A: with an interferometer! Idea: if a GW comes by, the length of the arms is disturbed: phase difference between the arms → interference pattern Fabry-Perot cavities: increase the arm length

18. Measuring gravitational waves These things actually exist! LIGO (US) VIRGO (EU) 4 km arms 3 km arms LISA (US + EU) Launch: ~2015(?) 5 10 6 km arms

19. What we @ Nikhef/Vu are doing

20. Nikhef has taken and carried out the initiative to start a research group focusing on gravitational waves Management Hardware, data analysis,.… Theory of gravitational waves Theory of gravitational waves You?

21. Conclusions

22. Conclusions  Gravitational waves are ripples in spacetime that travel with velocity c;  They can teach us a lot about binary star systems, Dark Matter/Dark Energy, the Big Bang.. etc etc;  Measuring GW’s is difficult; it can be done by using interferometers;  Nikhef is working (both experimentally and theoretically) on Virgo and LISA

23. Conclusions Interested to do a Masters? Contact Tjeerd Ketel ( TJ.Ketel@few.vu.nl ) or Jo van den Brand ( jo@nat.vu.nl ) Jo van den Brand ( jo@nat.vu.nl ) The end