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Research done at Nikhef. Gravitational waves. Gideon Koekoek January 10 th 2007. Overview of the talk. What are gravitational waves? Measuring gravitational waves What we @ Nikhef / Vu are doing Conclusions. What are gravitational waves?.

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Gravitational waves

Research done at Nikhef

Gravitational waves

Gideon Koekoek

January 10th 2007

Overview of the talk
Overview of the talk

  • What are gravitational waves?

  • Measuring gravitational waves

  • What we @ Nikhef / Vu are doing

  • Conclusions

What are gravitational waves1

1st Law: motion in straight lines if there is no force.

What are gravitational waves?

Wait, what is gravity in the first place?

Gravity is a force!



Earth’s path is not straight, but bent by a force

What are gravitational waves2

Gravity is not a force; it’s the curvature of space (and time)

What are gravitational waves?

  • Newton does not agree with Relativity,

  • All matter behaves the same under gravity

Einstein disagreed..

Still a straight line, but in curved spacetime!

What are gravitational waves3

This is a very small number! ~ 10-45 (!!)

You need a lot of energy to curve spacetime; gravity is weak!

What are gravitational waves?

Q: What curves spacetime? A: energy does!

Ok, good. Now about those gravitational waves..

What are gravitational waves4

Flat spacetime, plus a little curvature

What are gravitational waves?

Curvature in the vacuum?

A wave equation: a curvature hμυ oscillates through space!

What are gravitational waves5
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


Measuring gravitational waves1

Theory: is General Relativity correct?

Astronomy: what is Dark Matter/Dark Energy made of?

Astronomy: information on interesting systems are carried by GW’s

Cosmology: with GW’s we can see back to the Big Bang!

Measuring gravitational waves

Wait! Why would we do that in the first place?

Measuring gravitational waves2

10-45 (!!)

Measuring gravitational waves

A blessing and a curse: GW’s interact

very weakly

Blessing: once produced, they can’t be disturbed

Curse: very difficult to measure them ourselves!

Measuring gravitational waves3

Note: a million times smaller than a proton!

Measuring gravitational waves

Amplitude and frequency of gravitational waves emitted by a binary system of masses M1 and M2 at separation r

Measuring gravitational waves4

A: with an interferometer!

Fabry-Perot cavities: increase the arm length

Measuring gravitational waves

Q: How to measure gravitational waves?

Idea:if a GW comes by, the length of the arms is disturbed: phase difference between the arms →interference pattern

Measuring gravitational waves5


5 106 km arms

Launch: ~2015

Measuring gravitational waves

These things actually exist!


4 km arms


3 km arms

What we @ nikhef vu are doing1

Theory of gravitational waves

Hardware, data analysis,.…


What we @ Nikhef/Vu are doing

Nikhef has taken and carried out the initiative to start a research group focusing on gravitational waves



  • 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?

Contact Tjeerd Ketel ( or

Jo van den Brand (

The end