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Gravitational waves

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Research done at Nikhef

Gravitational waves

Gideon Koekoek

January 10th 2007

- What are gravitational waves?
- Measuring gravitational waves
- What we @ Nikhef / Vu are doing
- Conclusions

What are gravitational waves?

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

Wait, what is gravity in the first place?

Gravity is a force!

v

F

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

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

Einstein disagreed..

Still a straight line, but in curved spacetime!

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

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

Q: What curves spacetime? A: energy does!

Ok, good. Now about those gravitational waves..

Flat spacetime, plus a little curvature

Curvature in the vacuum?

A wave equation: a curvature hμυ oscillates through space!

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

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!

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

10-45 (!!)

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!

Note: a million times smaller than a proton!

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

A: with an interferometer!

Fabry-Perot cavities: increase the arm length

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

LISA(US + EU)

5 106 km arms

Launch: ~2015

These things actually exist!

LIGO (US)

4 km arms

VIRGO (EU)

3 km arms

What we @ Nikhef/Vu are doing

Theory of gravitational waves

Hardware, data analysis,.…

You?

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

Management

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?

Contact Tjeerd Ketel ( TJ.Ketel@few.vu.nl) or

Jo van den Brand ( jo@nat.vu.nl)

The end