Gravitational waves Gravitational waves

Gravitational waves Gravitational waves

Gideon Koekoek Gideon Koekoek January 10

January 10^thth 2007 2007

Research done at Nikhef

Research done at Nikhef

Overview of the talk Overview of the talk

 What are gravitational waves?What are gravitational waves?

 Measuring gravitational wavesMeasuring gravitational waves

 What we @ Nikhef / Vu are doingWhat we @ Nikhef / Vu are doing

 ConclusionsConclusions

What are What are

gravitational waves?

gravitational waves?

What are gravitational waves?

What are gravitational waves?

Wait, what is

Wait, what is gravitygravity in the first place? in the first place?

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

force force

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

FF

vv

r2

G mM F  

Gravity is a force!

What are gravitational waves?

What are gravitational waves?

Einstein disagreed..

Einstein disagreed..

Still a straight line, but in

Still a straight line, but in curvedcurved spacetime! spacetime!

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

 Newton does not agree Newton does not agree with Relativity,

with Relativity,

 All matter All matter behaves the behaves the samesame under gravity under gravity

What are gravitational waves?

What are gravitational waves?

Q:Q: What curves spacetime? What curves spacetime? A:A: energy does! energy does!







 T c

R G g

R 8 ₄

2

1  



Ok, good. Now about those gravitational Ok, good. Now about those gravitational

waves..

waves..

You need a lot of energy to curve You need a lot of energy to curve

spacetime;

spacetime; gravity is weak! gravity is weak!



This is a very small number! ~

This is a very small number! ~ 1010^-45-45 (!!) (!!)

What are gravitational waves?

What are gravitational waves?







 h

g  

Flat spacetime, plus a little curvature Flat spacetime, plus a little curvature

2 0

1 

 g R R_{ }

A wave equation:

A wave equation: a curvature a curvature hh_μυμυ oscillates oscillates through space!

through space!

1 0

2 2 2

2

2 _  h_ 

dt d h c

dx d

Curvature in the vacuum?

Curvature in the vacuum?

What are gravitational waves?

What are gravitational waves?

An example:

An example: gravitational waves gravitational waves produced by a binary star system produced by a binary star system

We want to measure these

waves!

UsUs Binary stars: source of GW’s

Binary stars: source of GW’s

Measuring Measuring

gravitational waves

gravitational waves

Measuring gravitational waves Measuring gravitational waves

Wait!

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

Theory:

Theory: is General is General Relativity correct?

Relativity correct?

Astronomy:

Astronomy: information on information on interesting systems are interesting systems are

carried by GW’s carried by GW’s Cosmology:

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

Bang!

Bang!

Astronomy:

Astronomy: what is Dark what is Dark

Matter/Dark Energy made Matter/Dark Energy made of? of?

Measuring gravitational waves Measuring gravitational waves

A blessing and a curse: GW’s interact A blessing and a curse: GW’s interact veryvery weakly weakly







 T c

R G g

R 8 ₄

2

1  

 1010^-45-45 (!!) (!!) Blessing:

Blessing: once produced, they can’t be disturbed once produced, they can’t be disturbed Curse:

Curse: very difficult to measure them ourselves! very difficult to measure them ourselves!

10 21

~ ^ L

L



Measuring gravitational waves 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 Measuring gravitational waves

Q:Q: How to measure gravitational waves? How to measure gravitational waves?

A: A: with an interferometer! with an interferometer!

Idea:

Idea:

if a GW comes by, the if a GW comes by, the

length of the arms is length of the arms is

disturbed: phase disturbed: phase

difference between the difference between the

arms arms →→

interference pattern interference pattern

Fabry-Perot cavities: increase the arm length Fabry-Perot cavities: increase the arm length

Measuring gravitational waves Measuring gravitational waves

These things actually exist!

These things actually exist!

LIGO LIGO

(US)(US)

VIRGO VIRGO

(EU)(EU)

4 km arms 4 km arms

3 km arms 3 km arms

LISALISA

(US + EU) (US + EU)

Launch: ~2015 Launch: ~2015

5 105 10⁶⁶ km arms km arms

What we @ What we @

Nikhef/Vu are doing

Nikhef/Vu are doing

What we @ Nikhef/Vu are doing What we @ Nikhef/Vu are doing

Nikhef has taken and carried out the initiative to start a Nikhef has taken and carried out the initiative to start a

research group focusing on gravitational waves research group focusing on gravitational waves Management

Management

Hardware, data Hardware, data

analysis,.…

analysis,.…

Theory of Theory of gravitational gravitational

waves waves You?You?

Conclusions

Conclusions

Conclusions Conclusions

 Gravitational waves are ripples in spacetime that travel with velocity Gravitational waves are ripples in spacetime that travel with velocity c;c;

 They can teach us a lot about binary star systems, Dark They can teach us a lot about binary star systems, Dark Matter/Dark Energy, the Big Bang.. etc etc;

Matter/Dark Energy, the Big Bang.. etc etc;

 Measuring GW’s is difficult; it can be done by using interferometers;Measuring GW’s is difficult; it can be done by using interferometers;

 Nikhef is working (both experimentally as theoretically) on Virgo and Nikhef is working (both experimentally as theoretically) on Virgo and LISALISA

Conclusions Conclusions

Interested to do a Masters?

Interested to do a Masters?

Contact Contact

Tjeerd Ketel

Tjeerd Ketel ( ( TJ.Ketel@few.vu.nlTJ.Ketel@few.vu.nl ) )

or or

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

The end

The end