When you hear the word wave you might
think of this. Waves have an everyday
meaning but also a specific meaning in
science. Even so water waves can tell us
a lot about the science of waves. A light
breeze ripples the surface of the water,
a pebble thrown into a lake creates
ripples, in each example there is
something disturbing the water and it is
the energy from that disturbance that
creates the recognizable pattern as it
moves through the water. If we bounce a
rubber ball into the surface of a pond
we can set up a regular pattern of waves
and the pattern can be represented
mathematically. Using a graph we could
represent the wave height on the
vertical axis and distance on the
horizontal axis. We can graph this
pattern from another perspective too. If we
pick a point along the surface of the
water we can plot the height of the wave
on the vertical axis in relation to time.
To make that clear imagine we place a
tiny rubber ducky on the water and watch
it closely. We see the duck bobbing in
place its height moving up and down as
time passes. In this wave model we're
charting the displacement of the water.
Once we have this mathematical model we
can explain and predict more complicated
waves. For instance when two waves
interact in the water the result is a
more complex pattern. By superimposing a
chart of each wave and adding together
their displacements over the same time
intervals you can graph the more complex
wave pattern.
Waves like the ones we see in water are
a fundamental pattern seen everywhere in
nature.
For instance music is created by complex
waves traveling through air, earthquakes
and tremors are caused by disturbances
that propagate through the Earth's crust
and electromagnetic energy moves through
space as waves. In fact waves are
universal. We can even find them
traveling through the fabric of
space-time we call these gravitational
waves and in some ways they are quite
similar to water waves or sound waves.
In water if you talk underwater you know
somebody else can hear you because the
sound gets transmitted through the water.
So a gravitational wave is literally the
same kind of wave it's a sound wave of
space itself so that as it travels
through space it shrinks space in one
direction and stretches it in the
perpendicular direction as it's moving
in the other direction. When Albert
Einstein predicted gravitational waves
over a hundred years ago he pointed out
that these waves would be so faint that
we could only dream of building a
detector sensitive enough to detect them.
The calculations Einstein did
indicated that no matter how good an
experiment we did we would never ever
see these waves they were just so weak.
Although it took nearly 100 years
researchers have now built detectors
just sensitive enough to hear the
largest of the gravitational waves
moving through space. The detectors rely
on laser beams reflecting back and forth
down 2 perpendicular tunnels 4
kilometers long. A passing gravitational
wave alters the length of the tunnels
very slightly and that change is
detected by the laser beams. So if I'm
sitting here and here are the two LIGO arms
as the wave goes past this arm will
shrink while that one is stretching and
then this one will stretch while that one
is shrinking and these will oscillate.
So you have to see this combined signal
that tells you you have a gravitational
wave. Even though any accelerating mass
creates gravitational waves current
detectors can only sense waves caused by
large masses undergoing huge
accelerations. So not only did they detect
gravitational waves if you ask what
caused them it was two black holes and
these two black holes were orbiting each
other and as they orbited they were
emitting gravitational waves and energy
and as they spiral inwards they
eventually merged and the last gasp of
that spiral emitted the brightest pulse
of gravitational waves which then
traveled through space for 1.3 billion
years -
this was 1.3 billion light years away
from us this happened - and then travelled
right through the LIGO detector and we
saw the signal just after the detector
was switched on. A completely unambiguous
confirmation of Einstein's theory. The ability to
detect gravitational waves has opened up
a whole new way to explore the night sky.
Events that would otherwise be invisible
to us we can now detect through the faint
whispers of their gravitational waves.
[Music]