If a star explodes in a distant galaxy and no one’s around to hear it, does it make
a sound?
No!
But it DOES generate a truckload of gravitational waves!
(We think.)
Hi!
I’m Ian O’Neill, space producer for Discovery News, and I wanted to take you on a brief
voyage into what links some of the craziest cosmic events we know about.
I’m talking about supernovas, black hole mergers, neutron star collisions, orbiting
white dwarfs and even the biggest bang of them all… the Big Bang!
So what exactly connects them all?
That’d be gravitational waves; and if you’ve been paying attention these last few months,
you’ll know that these wiggles in spacetime have been insanely hard to find.
Astronomers using the BICEP2 telescope located in the South Pole THOUGHT they’d identified
primordial gravitational waves embedded in the Cosmic Microwave Background radiation
last year.
Unfortunately, it seems that these signals may have just been noise.
But that doesn’t mean it’s curtains for the search for gravitational waves and gravitational
wave detectors, not by a long shot.
Rather than seeking out ancient gravitational waves created by the Big Bang, the Laser Interferometer
Gravitational-Wave Observatory -- or LIGO -- is ACTIVELY looking for gravitational waves
passing through Earth right this second!
These waves were predicted by Einstein and are a product of his famous theory of general
relativity.
In a nutshell, Einstein’s equations predicted that should a massive object like a black
hole or neutron star suddenly accelerate, decelerate or collide, energy will be lost.
But in these cosmic scenarios, energy is lost through powerful ripples in spacetime -- much
like the ripples that race across the surface of a pond after a pebble hits the water.
Although there is strong indirect evidence of their existence, we have yet to spot them
directly.
This is where LIGO comes in.
LIGO consists of two stations on opposite sides of the United States, and it uses a
highly sensitive method called interferometry to detect the TINY effect a propagating gravitational
wave will have on spacetime.
As gravitational waves wash THROUGH the Earth -- yes, I said THROUGH, as in through US!
-- there is the tiniest of tiny shrinkage or expansion in local spacetime.
But for LIGO, which has recently undergone an upgrade, such a minuscule spacetime warping
SHOULD be detectable and, since 2002, the project has been on the lookout.
This thing is so sensitive that it is probing distances on the smallest scales thought to
exist in spacetime -- it should be able to detect a distance change of 10,000th the width
of a proton.
Although LIGO has yet to see a definitive signal, it is using a process of elimination,
ruling out where these waves AREN’T and physicists are confident they are closing
in on the first detection in the coming years.
By firing a split laser down LIGO’s two perpendicular 4 kilometer-long L-shaped tunnels
and bouncing those beams many times, an interferometer can compare the two beams and detect any slight
shifts in frequency.
This tiny shift could represent the passage of a gravitational wave.
Should that wave be detected by both LIGO locations, the source of the wave could be
derived and we could see the beginning of a new era of gravitational wave astronomy.
Although the LIGO instrumentation uses a complex system of shock absorbers, magnetic fields
and sophisticated filters to drown out any outside interference, the detector is so sensitive
that it can still pick up false signals from strong winds or passing vehicles, only making
this search for a gravitational wave in the proverbial haystack of noise even harder.
Fortunately this epic quest on the frontier of scientific discovery isn’t short of some
great physics minds.
Students from Caltech recently created a colorful visualization to connect known interference
events with their corresponding signal detected by LIGO, thus eliminating terrestrial noise
from the continuing search for extraterrestrial sources of gravitational waves.
But will this be enough to finally tease this tiny wobble out of the tangled, noisy mess
of spacetime?
Let us know what you think in the comments below, and if you’re interested in other
cosmic peculiarities, check out my video about a weird cold spot
in the universe and what it might mean