View
216
Download
0
Tags:
Embed Size (px)
Citation preview
LIGO-G020518-01-W
Measuring Ripples in the Geometry of Space
Fred Raab
LIGO Hanford Observatory
LIGO: Portal to Spacetime 2LIGO-G020518-01-W
John Wheeler’s Picture of General Relativity Theory
LIGO: Portal to Spacetime 3LIGO-G020518-01-W
General Relativity: A Picture Worth a Thousand Words
LIGO: Portal to Spacetime 4LIGO-G020518-01-W
The New Wrinkle on Equivalence
Not only the path of matter, but even the path of light is affected by gravity from massive objects
Einstein Cross
Photo credit: NASA and ESA
A massive object shifts apparent position of a star
LIGO: Portal to Spacetime 5LIGO-G020518-01-W
Gravitational Waves
Gravitational waves are ripples in space when it is stirred up by rapid motions of large concentrations of matter or energy
Rendering of space stirred by two orbiting black holes:
LIGO-G020518-01-W
How does LIGO detect spacetime vibrations?
LIGO: Portal to Spacetime 7LIGO-G020518-01-W
Important Signature of Gravitational Waves
Gravitational waves shrink space along one axis perpendicular to the wave direction as they stretch space along another axis perpendicular both to the shrink axis and to the wave direction.
LIGO: Portal to Spacetime 8LIGO-G020518-01-W
Basic Signature of Gravitational Waves for All Detectors
LIGO: Portal to Spacetime 9LIGO-G020518-01-W
Laser
Beam Splitter
End Mirror End Mirror
ScreenViewing
Sketch of a Michelson Interferometer
LIGO: Portal to Spacetime 10LIGO-G020518-01-W
Sensing the Effect of a Gravitational Wave
Laser
signal
Gravitational wave changes arm lengths and amount of light in signal
Change in arm length is 10-18 meters,
or about 2/10,000,000,000,000,000
inches
LIGO: Portal to Spacetime 11LIGO-G020518-01-W
New Generation of “Free-Mass” Detectors Now Online
suspended mirrors markinertial frames
antisymmetric portcarries GW signal
Symmetric port carriescommon-mode info
Intrinsically broad band and size-limited by speed of light.
LIGO: Portal to Spacetime 12LIGO-G020518-01-W
Core Optics Suspension and Control
Local sensors/actuators provide damping and control forces
Mirror is balanced on 1/100th inchdiameter wire to 1/100th degree of arc
Optics suspended as simple pendulums
LIGO: Portal to Spacetime 13LIGO-G020518-01-W
How Small is 10-18 Meter?
Wavelength of light, about 1 micron100
One meter, about 40 inches
Human hair, about 100 microns000,10
LIGO sensitivity, 10-18 meter000,1
Nuclear diameter, 10-15 meter000,100
Atomic diameter, 10-10 meter000,10