Transcript BCB Vancouver Inst T..

Einstein's Legacy:
General Relativity, our Best
Description of the Universe
Barry C. Barish
Caltech
Crab Pulsar
Vancouver Institute
16-April-05
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Albert
Einstein
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Annus Mirabilis
 In 1905, Albert Einstein
wrote five revolutionary
scientific papers.
 These papers altered our
understanding of the
nature of light, proved the
existence of atoms and
molecules, and established
the concept of special
relativity.
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LIGHT
 Is the behavior of light like a
wave or like a particle?
"A question so enormously
important and difficult that
everybody should work on it."
~Albert Einstein
Light is often described as a
wave.
Light is also described as being
individual particles -- photons.
Sunlight and radio waves are
both forms of light, but have
different wavelengths.
In a solar cells a photon collides
with the atoms and generates
electricity by knocking an
electron out.
The colors you see in a
rainbow demonstrate the
wave-like nature of light.
This is the photoelectric effect.
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ATOMS
 How do we know atoms and molecules exist?
"My major aim in this was to find facts which would
guarantee as much as possible the existence of
atoms of definite finite size."
~Albert Einstein
Einstein realized that if atoms did
exist then they would continually
bump into microscopic particles in
their paths.
He created a mathematical model
where accurate measurements of
these microscopic motions could
be used to determine the actual
size of molecules and atoms.
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RELATIVITY
Is there a cosmic speed limit?
Einstein argued that the laws
of physics are the same in all
reference frames.
A scientist on the ground and
a scientist in a fast moving
space station will always
agree that the laws of physics
are the same.
He argued that therefore the
velocity of light is measured
to be the same by all
observers in all reference
frames.
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ENERGY and MASS
 For centuries, scientists
believed that matter and
energy could never be
destroyed.
 Before 1905, the law of
conservation of energy and
the law of conservation of
mass were two fundamental
principles of science that
appeared to never be violated.
 Einstein showed that these
laws were fallible, and that
they needed to be reconciled
into a single theory unifying
mass and energy.
E=
2
mc
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General Relativity
the essential idea
Gmn= 8pTmn
 Gravity is not a force, but a property of
space
& time
 Objects
Overthrew
follow
thethe
19thshortest
-centurypath
concepts
through
of
 Concentrations of mass or energy distort
»this
Spacetime
= 3 spatial
dimensions
+ timefor
absolute
warped
space
spacetime;
and
time
path
is
the
same
(warp) spacetime
objects of space or time is relative
»all
Perception
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General Relativity
Einstein theorized that a massive object
warps the surrounding space
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General Relativity
Smaller objects travel through space
that is warped by larger objects
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Gravity a fundamental force
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Universal Gravitation
 Solved most known
problems of astronomy and
terrestrial physics
» eccentric orbits of comets
» cause of tides and their
variations
» the precession of the earth’s
axis
» the perturbation of the motion
of the moon by gravity of the
sun
 Unified the work of Galileo,
Copernicus and Kepler
unified.
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But, what causes the mysterious force in
Newtons theory ?
Although the equation explains nature very
well, the underlying mechanism creating
the force is not explained !
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After several hundred years, a
small crack in Newton’s theory …..
perihelion shifts forward an extra
+43”/century
compared to Newton’s theory
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A new prediction of
Einstein’s theory …
Light from distant stars are bent as they graze
the Sun. The exact amount is predicted by
Einstein's theory.
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Confirming Einstein ….
bending of light
A massive object shifts
apparent position of a star
Observation made
during the solar
eclipse of 1919 by
Sir Arthur Eddington,
when the Sun was
silhouetted against
the Hyades star
cluster
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Einstein’s Cross
The bending of light rays
gravitational lensing
Quasar image appears around the central glow
formed by nearby galaxy. The Einstein Cross is
only visible in southern hemisphere.
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Gravitational
Waves ?
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A Conceptual Problem is solved !
Newton’s Theory
“instantaneous action
at a distance”
Einstein’s Theory
information carried
by gravitational
radiation at the
speed of light
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T
The
Evidence
h
e
For
Gravitational Waves
Russel A. Hulse
Discovered and Studied
Pulsar System
PSR 1913 + 16
with
Radio Telescope
Source: www.NSF.gov
Joseph H.Taylor Jr
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Neutron Star
Radio Pulsar
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The evidence for
gravitational waves
Hulse & Taylor
•
•
•
•
separation = 106 miles
m1 = 1.4m
m2 = 1.36m
e = 0.617
period ~ 8 hr
Prediction
from
general relativity
17 / sec


•
Neutron binary
system
PSR 1913 + 16
Timing of pulsars
• spiral in by 3 mm/orbit
• rate of change orbital
period
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“Indirect”
evidence
for
gravitational
waves
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The Nature of Gravitational Waves
Compact
Binary Inspiral
Merger
Inspiral
Ringdown
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The effect of a gravitational
wave passing through space …
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Direct Detection
Gravitational Wave
Astrophysical
Source
Terrestrial detectors
LIGO, TAMA, Virgo,AIGO
Detectors
in space
LISA
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LISA
The diagram shows the sensitivity bands for
LISA and LIGO
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The frequency range of astronomy
 EM waves studied
over ~16 orders of
magnitude
» Ultra Low Frequency
radio waves to high
energy gamma rays
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Gravitational Waves in Space
LISA
Three spacecraft, each with a Y-shaped
payload, form an equilateral triangle with sides
5 million km in length.
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LISA
The three LISA spacecraft will be placed in orbits
that form a triangular formation with center 20o
behind the Earth
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Leonardo da Vinci’s Vitruvian man
stretch and squash in perpendicular directions
at the frequency of the gravitational waves
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Detecting a passing wave ….
Free masses
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Detecting a passing wave ….
Interferometer
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Leonardo da Vinci’s Vitruvian man
stretch and squash in perpendicular directions
at the frequency of the gravitational waves
I have greatly exaggerated the effect!!
If the Vitruvian man was 4.5 light years
high, he would grow by only a ‘hairs width’
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Gravitational Wave Detection
free masses
h = strain amplitude of grav. waves
h = DL/L ~ 10-21
L = 4 km
DL ~ 10-18 m
Laser
Interferometer
laser
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The Detection Technique
 Laser used to
measure relative
lengths of two
orthogonal arms
…causing the
interference
pattern to change
at the photodiode
 Arms in LIGO are 4km
 Measure difference in
length to one part in
1021 or 10-18 meters
As a wave
passes, the
arm lengths
change in
different
ways….
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How Small is 10-18 Meter?
One meter ~ 40 inches
 10,000
100
Human hair ~ 100 microns
Wavelength of light ~ 1 micron
 10,000
Atomic diameter 10-10 m
 100,000
Nuclear diameter 10-15 m
 1,000
LIGO sensitivity 10-18 m
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LIGO
Laser Interferometer
Gravitational-wave Observatory
Hanford
Observatory
MIT
Caltech
Livingston
Observatory
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LIGO
Livingston,
Louisiana
4 km
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Flooding in Louisiana
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LIGO
Hanford Washington
4 km
2 km
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Also a Few Glitches in Hanford,
but Science Moves On …
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What Limits LIGO Sensitivity?

Seismic noise limits low
frequencies

Thermal Noise limits
middle frequencies

Quantum nature of light
(Shot Noise) limits high
frequencies

Technical issues alignment, electronics,
acoustics, etc limit us
before we reach these
design goals
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Evolution of LIGO Sensitivity
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Detecting Earthquakes
From electronic logbook
2-Jan-02
An earthquake occurred,
starting at UTC 17:38.
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Detect the Earth Tide from
the Sun and Moon
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Astrophysical Sources
signatures
 Compact binary inspiral: “chirps”
» NS-NS waveforms are well described
» BH-BH need better waveforms
» search technique: matched templates
 Supernovae / GRBs:
“bursts”
» burst signals in coincidence with signals in
electromagnetic radiation
» prompt alarm (~ one hour) with neutrino
detectors
 Pulsars in our galaxy:
“periodic”
» search for observed neutron stars (frequency,
doppler shift)
» all sky search (computing challenge)
» r-modes
 Cosmological Signal “stochastic background”
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Directed Pulsar Search
28 Radio Sources
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Detection of Periodic Sources
 Known Pulsars in our galaxy
 Frequency modulation of
signal due to Earth’s motion
relative to the Solar System
Barycenter, intrinsic
frequency changes.
 Amplitude modulation due
NEW RESULT
28 known pulsars
NO gravitational waves
to the detector’s antenna
pattern.
e < 10-5 – 10-6
(no mountains > 10 cm
ALL SKY SEARCH
enormous computing challenge
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Einstein@Home
 A maximum-sensitivity all-sky search for
pulsars in LIGO data requires more
computer resources than exist on the
planet.
 The world’s largest supercomputer is
arguably SETI@home
» A $599 computer from Radio Shack is a very
powerful computational engine.
» Currently runs on a half-million machines at any
given time.
 With help from the SETI@home developers,
LIGO scientists have created a distributed
public all-sky pulsar search.
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Einstein@Home Usage
Already have about 35K Users
20x LIGO computing capacity
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Einstein@Home Users
 I'm from Germany and was
interested in the mysteries of
the universe since I was a
little boy. I read lots of
magazines about astrophysics
and astronomy. When I heard
about the Einstein@Home
project it was no question for
me to participate.
 My job is to make originalsized design models of new
Mercedes-Benz cars,
especially the interieur. When
I don't work I often play
keyboards and percussions
and sing some backing vocals
in my cover-rock-band "GilgaMesh"
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Einstein@Home Users
 Hi, my name's John Slattery. I'm
a 62 year old English teacher,
originally from Boston, MA,
currently living in Santa Fe, New
Mexico where I'm tutoring, and
teaching ESL.
 My hobbies: fitness, camping,
hiking, reading, writing, surfing
the Net
 I'm so very new at this; I'm not
even sure what's going on. But it
seemed, from the little I could
understand, to be a worthwhile
project.
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Einstein@Home Users
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Einstein@Home
LIGO Pulsar Search using
home pc’s
BRUCE ALLEN
Project Leader
Univ of Wisconsin
Milwaukee
LIGO, UWM, AEI, APS
http://einstein.phys.uwm.edu
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