Gravitational
Waves
重力波的
預言
By Andy Cheung
張文康
the waves, which is indispensable in gravitational
wave detection and happens to be at the very
forefront of this discovery.
In an apt analogy, he says “Imagine that
the sur face of a pond represents spacetime
(the combination of space and time). When a
rock is thrown into the pond, we observe ripples
spreading outward from the centre. Similarly,
cataclysmic events in the Universe can distort
spacetime in such a manner that they produce
waves in the fabric of spacetime itself. We call
these gravitational waves”. Similar to water
waves, gravitational waves distort spacetime,
momentarily altering our height and width but
on a minute scale, only detectable with the
most state-of-the-ar t technology. The LIGO
interferometre, a cross-like structure measuring an
arm-length of 4 km, detects gravitational ripples
by measuring the changes in its width. These
changes can be as small as 10
-19
m.
Obser ving these infinitesimal differences
requires researchers to identify and account for
length changes while adjusting for error sources,
such as expansion due to temperature change or
background vibrations. Using special computer
software, much of this involves analysing LIGO
data and searching for bugs and methods to
increase the interferometre’s selectivity at the
correct signal. Such a process requires months
of devoted work, and a substantial amount of
coding and debugging, making the fruits of their
success particularly sweet.
As the final unobserved prediction of Einstein’s
theory of gravity, gravitational wave theory is,
according to Dr. Li, “one of the pillars of modern
physics”. It opens a new avenue of understanding
to the unlit parts of the Universe, shedding light
on the areas where ‘traditional’ astronomy has
trouble reaching. “Instead, gravitational waves
are emitted by all massive things”. Massive would
be an understatement, because what is perhaps
most remarkable about the detection of these
gravitational waves is its source. Generated
by a clash of two black holes almost 1.3 billion
years ago and millions of galaxies away, the
ripple effect was finally identified by LIGO’s two
detectors, the most sensitive measuring devices
ever built.
Perhaps
the most monumental
sci ence event of the yea r so fa r was the
confirmation of the existence of gravitational
waves . These mys ter ious r ippl es were f i r s t
predicted by Albert Einstein exactly a century
ago, but their detection has eluded scientists until
recently. The excitement following this validation
was almost palpable, drawing much attention
from both laypeople and science aficionados
a l i ke. D r. T j onn i e G. F. L i at The Ch i nese
University of Hong Kong has been a member
of the Laser Interferometer Gravitational-Wave
Obser vator y (LIGO) Scientific Collaboration
and has collaborated with other scientists in
this important work. Their team deals primarily
with the imperati ve wor k of di s t i ngui shi ng
background noise from the minuscule signal of
