Transcript gravity - Nikhef

Gravitational waves
Research done at Nikhef
Gideon Koekoek
January 9th 2008
Overview of the talk
 Graviational waves: a revolution
 What are gravitational waves?
 Measuring gravitational waves
 What we @ Nikhef / Vu are doing
 Conclusions
Why gravitational
waves?
Why gravitational waves?
What is so interesting about them?
We already have telescopes, neutrino
detectors and stuff like that to study the
Universe, right?
So why do we want to measure
gravitational waves as well?
Why gravitational waves?
We need gravitational waves!!
There are questions we cannot answer
without GWs:
Theory: how correct is General Relativity?
Astronomy: what is the nature of Dark Matter
and/or Dark Energy?
Astronomy: what processes occur in exotic
objects?
Cosmology: what happened after the Big
Bang?
Why gravitational waves?
What is the nature of Dark Matter/Dark Energy?
This is us
Most of the Universe, we
don’t know anything
about!
We need gravitational waves!
Why gravitational waves?
How about the Big Bang?
Light can only
see up to here
..neutrino’s can only
see up to here..
..but gravitational
waves can see up
to here!
We need gravitational waves!
What are
gravitational waves?
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
mM
F  G 2
r
F
Earth’s path is not straight, but bent by a force
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!
What are gravitational waves?
Q: What curves spacetime? A: energy does!
R
1
8G
 g  R   4 T
2
c
This is a very small number! ~ 10-45 (!!)

You need a lot of energy to curve
spacetime; gravity is weak!
Ok, good. Now about those gravitational
waves..
What are gravitational waves?
R
1
 g  R  0
2
Curvature in the vacuum?
Flat spacetime, plus a little curvature
g      h
d2
1 d2
h  2 2 h  0
2 
dx
c dt
A wave equation: a curvature hμυ oscillates
through space!
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
Measuring
gravitational waves
Measuring gravitational waves
A blessing and a curse: GW’s interact
very weakly
1
8G
R  g  R   4 T
2
10-45 (!!)
c
Blessing: once produced, they can’t be disturbed
Curse: very difficult to measure them ourselves!

L
L
~ 10
 21
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
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
Measuring gravitational waves
These things actually exist!
LISA
(US + EU)
LIGO
(US)
4 km arms
VIRGO
(EU)
3 km arms
5 106 km arms
Launch:
~2015(?)
What we @
Nikhef/Vu are doing
What we @ Nikhef/Vu are doing
Nikhef has taken and carried out the initiative to start a
research group focusing on gravitational waves
Management
Theory of
gravitational
waves
Hardware, data
analysis,.…
You?
Conclusions
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 and
theoretically) on Virgo and LISA
Conclusions
Interested to do a Masters?
Contact
Tjeerd Ketel
or
( [email protected] )
Jo van den Brand ( [email protected] )
The end