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The
2015 Oskar Klein Memorial Lecture
“Gravitational Waves: The Physics and Astrophysics of LIGO”
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Date: |
Download-files: |
Time: |
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Friday, 27. May 2016 |
Audio-only-Recording as MP3-File
(smallest possible size):
- Audio.mp3 (ca.35 Mb) ========================================= Video-Recording for any system with MP4-support:
- Video.mp4 (ca.365 Mb) |
15:15 – 16:30 |
Friday
27. May 2016, from 15:15 to 16:30
Speaker : Kip S. Thorne (California Institute of Technology)
Abstract :
Gravitational waves are so radically different from
electromagnetic waves that they are
likely to revolutionize our understanding of the
universe. LIGO, the Laser Interferometer
Gravitational Wave Observatory, has recently opened up
the first of four gravitational-wave
windows onto the universe (the high-frequency window);
and over the coming two decades,
three more gravitational-wave windows will be opened.
The astrophysical phenomena that LIGO is likely to
explore are remarkable: Already it is
exploring the collision and merger of spinning black
holes and the resulting nonlinear
dynamics of curved, empty spacetime. LIGO is likely
also to detect and explore spinning
neutron stars, collisions of neutron stars, black
holes tearing neutron stars apart, the central
engines of gamma ray bursts, perhaps the cores of
supernova explosions, and perhaps
vibrating cosmic strings (thought to have been
produced by inflation of fundamental strings
in the earliest moments of our universe).
But most wonderful of all will be completely
unexpected phenomena: big surprises.
The physics of LIGO is also remarkable: Gravitational
waves stretch and squeeze the
separations of mirrors that hang from overhead supports
at the ends of 4 kilometer "arms";
and those mirrors' motions are monitored using light
beams and interferometry.
The wavelength of each light beam in LIGO gets
stretched and squeezed by the same
fractional amount as the mirror separations, so how can
LIGO possibly see the waves?
And the stretch and squeeze is 1/100 the diameter of a
proton, or less — which means 10-11
of the wavelength of the light that is used to measure
the stretch and squeeze. How can light
possibly reveal such tiny motions? The atoms of which
the mirrors are made have sizes 10
million times greater than the stretch and squeeze,
and they vibrate, thermally, with amplitudes
that are a million times larger than the stretch and
squeeze; why doesn't this produce noise
that masks the waves' signals? Ambient seismic motions
in the ground beneath LIGO are ten
million times greater than the waves' stretch and
squeeze; why don't these seismic motions
mask the signals? When LIGO reaches its design
sensitivity, several years from now, the
Heisenberg uncertainty principle, applied to LIGO's 40
kilogram mirrors, says that the very
act of measuring the mirror motions will perturb the
mirrors so much that it may mask
the signal. How can this quantum behavior of human
sized mirrors be controlled, so as to
preserve the signals?