Gravitational wavesGravitational waves

Gideon KoekoekGideon KoekoekJanuary 10January 10thth 2007 2007

Research done at NikhefResearch done at Nikhef

Overview of the talkOverview 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 forceforce

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

FF

vv

2r

mMGF

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

GRgR

4

8

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?

hg

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

02

1 RgR

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

01

2

2

22

2

hdt

d

ch

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 systemproduced by a binary star system

We want to measure these

waves!

UsUsBinary stars: source of GW’sBinary stars: source of GW’s

Measuring Measuring gravitational wavesgravitational waves

Measuring gravitational wavesMeasuring gravitational wavesWait!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’scarried 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 wavesMeasuring gravitational wavesA blessing and a curse: GW’s interact A blessing and a curse: GW’s interact

veryvery weakly weakly

T

c

GRgR

4

8

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!

2110~

L

L

Measuring gravitational wavesMeasuring 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 wavesMeasuring gravitational wavesQ: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 patterninterference pattern

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

Measuring gravitational wavesMeasuring gravitational wavesThese things actually exist! These things actually exist!

LIGO LIGO (US)(US)

VIRGO VIRGO (EU)(EU)

4 km arms4 km arms

3 km arms3 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 doingNikhef/Vu are doing

What we @ Nikhef/Vu are doingWhat 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

ManagementManagement

Hardware, data Hardware, data analysis,.…analysis,.…

Theory of Theory of gravitational gravitational waveswaves

You?You?

ConclusionsConclusions

ConclusionsConclusions

Gravitational waves are ripples in spacetime that travel with Gravitational waves are ripples in spacetime that travel with velocity 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 Measuring GW’s is difficult; it can be done by using interferometers;interferometers;

Nikhef is working (both experimentally as theoretically) on Virgo Nikhef is working (both experimentally as theoretically) on Virgo and LISAand LISA

ConclusionsConclusionsInterested to do a Masters?Interested to do a Masters?

Contact Contact

Tjeerd KetelTjeerd 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 ))

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