1. Gravitational Waves

2. The Basics According to Newton the force of gravity is instantaneous
Einstein says nothing can travel faster than light
Remember from General Relativity: gravity is space-time which has been warped by matter
More mass = More warping
So how does gravity travel ‘through’ space?

3. Mechanics of These Waves
Like light Gravity travels as a wave
As electro-magnetic waves propagate they affect the two planes perpendicular to their line of motion
The electric and magnetic fields
gravity propagates does the same thing
Compression and expansions
Moving charge - light
Moving mass - gravity
Gravitational waves also exhibit a particle nature
Light has the photon
Gravity has the graviton
Neither particle has mass
Therefore gravitational waves can travel at the speed of light
They travel the same speed through any medium

4. "Electromagnetic waves are oscillations of the electromagnetic field that propagate through spacetime; gravitational waves are oscillations of the 'fabric' of spacetime itself." (Kip Thorne)

5. Indirect Evidence
According to General Relativity a binary system of stars should lose energy to gravitational radiation
This means the stars should slow down
In 1993 the Nobel Prize was awarded to Hulse and Taylor for proving this
In 1974 they found a neutron star binary
Over twenty years of observations they found a shift in the in the orbits which was consistent with the predictions of General Relativity

6. Strength of These Waves
If every moving mass causes a gravitational wave why aren’t we all stretching and contracting now?
Compared to the other 3 forces gravity is very weak.
A black hole binary, each with the mass of 10 suns, 1 billion light years away, would displace the oceans by only 10 times the diameter of an atomic nucleus
What can we use to detect such a small affect

7. INTERFEROMETRY
Capable of detecting a path difference smaller than the diameter of the nucleus of an atom
Light passed through beam splitter
Travels down either arm and is reflected back and out for observation
If both paths are the same there should be constructive interference
If the path difference changes the interference pattern will shift which can be detected
This is used to detect abnormalities in a surface, find the refractive index of an optical material, the change in refractive index etc.

8. Interferometers to Detect Gravitational Waves
LIGO - Laser Interferometer Gravitational-wave Observatory
LISA – Laser Interferometer Space Antenna

9. LIGO In operation since 2002
Two active observatories in Livingston, Louisiana and Richland, Washington
Have not detected anything significant
Each arm is 4000m, these are the largest interferometers ever built to detect gravitational waves
LIGO uses two interferometers to rule out any discrepancies
LlGO detects movements as small as one thousandth the diameter of a proton

10. LIGO – more specs
The vacuum tubes housing the interferometer have a volume of nearly 300,000 cubic feet
They are evacuated to a pressure one-trillionth of an atmosphere
The suspended mirrors are even shielded from vibrations occurring due to the random motion of the atoms within the mirrors
Over 30 control systems are used to hold the lasers and mirrors in place
VIRGO is another ground based interferometer

11. LISA If approved development will begin in 2004
Launch set in 2011 for a duration of five years
Will consist of three unconnected spacecraft five million km apart, in an equilateral triangle
50 million kilometers above Earth
Each spacecraft will contain two test masses floating freely space craft will follow the masses with an accuracy of 10^-9 m
Noise due to:
Solar pressure
Solar magnetic field
Earths gravity
Micro-thrusters will attempt to move LISA out of such noise if detected
Separation between spacecraft will be maintained with an accuracy of 10^-12 m
Main craft fires laser to second which fires laser in phase to third which fires laser in phase back the main craft
This goes in both directions
Each can craft calculates the path deviation
By measuring the relative positions of the test masses
LISA will not be ‘better’ than LIGO or VIRGO but will be able to detect different frequencies of waves
LIGO detects high frequencies
LISA will detect low frequencies

12. Promising Sources Binary Systems Non-Spherical Rotating Objects
Stars
Neutron Stars
Black Holes
Non-Spherical Rotating Objects
Super nova
Vibrating Black Holes
Galaxy Formation
Dark Matter
Big Bang ???

13. MOVIE TIME Low Frequency waves due to a rotating binary system
High Frequency waves due to a rotating binary system

14. Types of Signals Chirps Burps Periodic Stochastic Binary Systems
Collapse of Supernova
Black Hole eating a star
Periodic
Non-Spherical Objects rotating
Stochastic
Big Bang
Need much improvement i.e. another observatory

15. Summary Gravitational waves warp spacetime as they travel
Indirect Evidence exists
Direct evidence places its hope mostly on interferometers
Since they can travel through anything gravitational waves offer a new and exciting view of the universe
Comparable to the first use of x-ray etc. astronomy

16. My sources LIGO Laboratory Homepage Laser Interferometer Space Antenna
Laser Interferometer Space Antenna
lisa.jpl.nasa.gov/
Jillian’s Guide to Gravitational Waves
Ripples in Space Time
List of Gravitational Wave Detectors
Gravitational Wave Sources
Propagation of Gravity Waves