Lot's Wife Edition 2 2016

A wiggle in
space-time:
detecting
gravitational
waves
SCIENCE
become gravitational waves. In the same way that there are
troughs and peaks in the water waves, there are compressions
and expansions of space-time as a gravitational wave travels.
Any mass moving through space-time will produce waves as
it does so, just like a boat in the ocean. These waves are space
itself compressing and expanding.
That should be pretty easy to detect, right? People should
be getting noticeably shorter and fatter when a star goes supernova
half a million light years away? Wrong. Because the effects
of gravitational waves are so incredibly, unimaginably small.
The change in height of a person is on the scale of tiny fractions
of a proton. It seems almost impossible to even feasibly be able
to measure such a distance; this is where LIGO comes in.
LIGO stands for Laser Interferometer Gravitational wave
Observatory. It features two perpendicular lasers bouncing
By Isaac Reichman
back and forth within the 4km-long arms of the detector.
Illustration by Sigrid Lange
Initially the beams are perfectly in sync, but if a gravitational
wave passes through the detector the beams become out-ofsync,
as it compresses one of the 4km arms and expands the
other. If the beams become out of sync, there is a variation in
Over 100 years after its first publication in 1915,
the light output.
Einstein’s
General
theory
Relativity
of general
and Gravitational
relativity has
Waves
finally been
– Isaac Reichman The output signal is then compared against theoretical
completely verified by experimental evidence. But what was signals calculated using Einstein’s equations. Analysing the raw
Over 100 years after its first publication in 1915, Einstein’s
the final piece of the puzzle, why did his theory take so long to output
theory
signal
of
itself
general
would
relativity
be a nightmare
has finally
as
been
a tremor on the
completely verified by experimental evidence. But what
verify, and why should you care?
other was side the final of the piece world of is the ‘loud’ puzzle, enough why to did be detected his theory by LIGO.
take so long to verify, and why should you care?
General relativity is Einstein’s interpretation of gravity.
What was the smoking gun that proved gravitational
To date, it is the most accurate and elegant way to describe the waves?
General relativity is Einstein’s interpretation of gravity. To date, it is the most accurate and elegant way to
complexity of the universe at astronomical and cosmological
When two black holes are orbiting around one another,
describe the complexity of the universe at astronomical and cosmological scales, and it does so in relatively
scales, and it does so relatively (pun intended) simple terms. it is called a binary black hole system. After millions of years,
(pun intended) simple terms. All of the burning balls of plasma and massive clouds of cosmic dust are
All of the burning balls of plasma and massive clouds of cosmic this orbit can deteriorate, and when the two black holes get
described in perfect detail by 12 – or rather 16 – equations that represent the dynamics of existence.
dust are described in perfect detail by 12 – or rather 16 – equations
that represent the dynamics of existence.
close enough to one another, something interesting happens.
They begin to orbit each other tightly, speeding up and warping
space-time as they do. As their orbital distance contracts, the
black holes emit massive amounts of their mass as energy in
RR μμμμ − 1 2 RRgg μμμμ + ΛΛgg μμμμ = 8ππππ
cc 4 TT μμμμ
the form of gravitational waves. In the moment of merging, the
At first glance, this would be absolutely terrifying to black holes are orbiting one another at the unimaginably fast
At first glance, this would be absolutely terrifying to most people: all those subscripts and Greek letters
most people: all those subscripts and Greek letters replacing speed of half the speed of light.
replacing the more pedestrian FF⃗ = mmaa⃗ of high-school physics.
the more pedestrian F=ma of high-school physics. But upon
Once But they upon merge, closer a inspection, mass equivalent it reveals to about a rather three times
beautiful simplicity. The left side of this equation describes
closer inspection, it reveals a rather beautiful simplicity. The that the of our geometry sun is converted of the fabric into gravitational of the universe energy. and It’s how
it ‘bends’ or ‘warps’. The right side describes how the matter
left side of this equation describes the geometry of the fabric fitting that and energy it would within be the the first universe event to moves. produce This gravitational
of the universe
beautiful
and
equation
how it ‘bends’
allows
or ‘warps’.
us to understand
The right side
many
describes
how forming the matter nebulae, and energy the orbits within of the planets, universe and moves. even cataclysmic evidence of events such a like binary the black merging hole of system, black which holes. would Space have
of the waves wondrous that we events could that detect, occur as it within is so ‘loud’. our universe: It’s also our star-
first
This beautiful and equation time are allows described us to as understand one the many same; of the components been of unable Einstein’s to detect fabric: using space-time. light astronomy Space-time as this is is made a ‘dark’
wondrous of events the three that occur dimensions within our of space universe: – up star-forming
and down, left and event. right, forward and back –and a fourth dimension of
nebulae, the time. orbits What of the my planets, main man and Einstein even cataclysmic explained events with the above equation Einstein, using is that no gravity more than is simply a pen a and manifestation
paper, was able
like the merging of matter of black warping holes. space-time. Space and time are described to use mathematics to derive the secrets of the universe. His
as one and the same – components of Einstein’s fabric: spacetime.
Space-time
ideas have not only had profound impacts on physics and the
The merging
is made
of
of
two
the
black
three
holes
dimensions
is a perfect
of space
example of philosophy a cosmic event of science, that releases but have so enabled much humanity energy that to it grasp far
– up and down,
produces
left and
periodic
right,
ripples
forward
in
and
space-time,
back –and
i.e.
a fourth
gravitational further waves: than the we last ever unverified could have prediction without them. of general No theory is as
dimension relativity. of time. What As of my February main man 2016 Einstein however, explained these waves with have well-known been discovered. or as accurate. It is now completely and unequivocally
supported by experimental evidence. Where do we go
the above equation is that gravity is simply a manifestation of
What is a gravitational wave?
matter warping space-time.
from here? There are still plenty of unknowns in the universe:
The merging of two black holes is a perfect example of from dark matter to dark energy. We may need a new theory in
Imagine throwing a stone into a pond. The ripples travel across the surface of the pond transferring energy as
a cosmic event that releases so much energy that produces order to understand them, but regardless, Einstein will always
they go. Now we replace the water with space-time and the ripples become gravitational waves. In the same
periodic ripples in space-time, i.e. gravitational waves: the last be among the likes of Newton: the giants, on whose shoulders
way that there are troughs and peaks in the water waves, there are compressions and expansions of spacetime
as a gravitational wave travels. Any mass moving through space-time will produce waves as it does so,
unverified prediction of general relativity. As of February 2016 we stand to see further.
however, these just like waves a boat have in been the ocean. discovered. These waves are space itself compressing and expanding.
Imagine throwing a stone into a pond. The ripples travel
across the That surface should of the be pond pretty transferring easy to detect, energy right? as they People should
See
be
over
getting
for
noticeably
an interview
shorter and
with
fatter
Eric
when
Thrane,
a star
Monash’s own gravitational waves expert.
go. Now we goes replace supernova the water half with a million space-time light and years the away? ripples Wrong. Because the effects of gravitational waves are so
Lot’s Wife | 35
incredibly, unimaginably small. The change in height of a person is on the scale of tiny fractions of a proton. It
seems almost impossible to even feasibly be able to measure such a distance; this is where LIGO comes in.