Gideon Koekoek January 10th 2007 Gravitational waves Research done at Nikhef Gideon Koekoek January 10th 2007

Overview of the talk What are gravitational waves? Measuring gravitational waves What we @ Nikhef / Vu are doing Conclusions

What are gravitational waves?

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

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

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

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

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

Measuring gravitational waves

Measuring gravitational waves Wait! Why would we do that in the first place? Theory: is General Relativity correct? Astronomy: information on interesting systems are carried by GW’s Cosmology: with GW’s we can see back to the Big Bang! Astronomy: what is Dark Matter/Dark Energy made of?

Measuring gravitational waves 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!

Measuring gravitational waves Amplitude and frequency of gravitational waves emitted by a binary system of masses M1 and M2 at separation r Note: a million times smaller than a proton!

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

Measuring gravitational waves These things actually exist! LISA (US + EU) Launch: ~2015 5 106 km arms LIGO (US) 4 km arms VIRGO (EU) 3 km arms

What we @ Nikhef/Vu are doing

What we @ Nikhef/Vu are doing 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 You?

Conclusions

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 as theoretically) on Virgo and LISA

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