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

2. Overview of the talk What are gravitational waves?
Measuring gravitational waves
What Nikhef / Vu are doing
Conclusions

3. What are gravitational waves?

4. 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

5. 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!

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

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

8. 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

9. Measuring gravitational waves

10. 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?

11. 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!

12. 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!

13. 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

14. 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

15. What we @ Nikhef/Vu are doing

16. 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?

17. Conclusions

18. 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

19. Interested to do a Masters?
Conclusions
Interested to do a Masters?
Contact Tjeerd Ketel ( ) or
Jo van den Brand ( )
The end