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