Gravitational waves are ripples in the fabric
of spacetime, predicted by Einstein’s laws of general relativity, but they are incredibly
difficult to detect. To see them you need a detector that can accurately
measure distances 10,000 times smaller than a proton. Thats crazy! That’s like trying to measure the distance
from our Sun to the nearest star to accuracy of the width human hair. But we have a technology on Earth that can
do that: aLIGO the Advanced Laser Interferometer Gravitational-wave Observatory, and back in
November 2015, on a Monday morning, LIGO detected the first gravitational wave that humans have
ever directly observed. Where they came from and what this means for
space science is nothing short of mind blowing! This is the story. A long long time ago, in a galaxy far far
away. I’m not kidding, 1.3 billion years ago and
1.3 billion light years away, two black holes were stuck in a perilous orbit around one
another getting closer and closer. Black holes are incredible objects, the pull
of their gravity - the amount they bend spacetime - is so strong that no light can escape them. No one knows what exists in the centre of
a black hole as normal physics completely breaks down. What we do know is that they are infinitely
dense. One of these orbiting black holes was 29 times
the mass of the Sun and the other was 36 times the mass of the Sun, but they were only about
200km wide. Which is tiny in comparison to the Sun which
is over a million kilometres wide! And these black holes were orbiting each other
really really fast, about the same frequency as the blade on a blender. Imagine that, such massive objects rotating
so quickly. These orbiting masses created ripples in the
fabric of spacetime called gravitational waves, and the closer they orbited the bigger these
waves got, until the black holes collided at half of the speed of light. And when they merged they formed a new black
hole that rang kind of like a bell, throwing out colossal amounts of energy as gravitational
waves until it settled into a perfect sphere. And all of this happened in 0.2 seconds. And in the collision, they turned a huge amount
of mass into gravitational wave energy. They lost a mass equal to three times the
mass of the Sun which got turned in to gravitational wave energy by Einsteins equation E=mc^2. This created a huge wake of gravitational
waves that ripped out in all directions at the speed of light. And, and this is the thing that gets me, over
that last fifth of a second this collision released more than ten times more energy than
total output of all of the stars in the entire rest of the Universe! It just completely boggles the mind! Meanwhile on Earth… At this exact time our planet was looking
very different to what we see now. It was a barren wasteland, there was no grass
or trees, in fact no plants or animals at all. Life at this stage had only come as far as
microscopic multicellular creatures that lived in the sea. And while the gravitational waves tore through
space towards us all of the complex life on Earth evolved and grew: plants and animals
developed, amphibians crawled on land, there was extinctions, reptiles and dinosaurs and
mammals, more extinctions. Primates evolved into all of human civilization
right up until Saturday 12th November 2015 when the scientists at LIGO turned it on to
begin their initial tests. A mere two days later and … boop … the
gravitational waves flew past us and the first direct detection on Earth was made. And that sound … boop … is actually what
these waves sounded like. Even though gravitational-waves are ripples
in spacetime and not ripples in the air, they vibrate at similar frequencies, so we can
actually turn them into sound waves and listen to them … boop … It might not sound very
impressive, but detection of gravitational waves means a huge amount for science. The results of this detection have already
been profound. This is the very first time that black holes
have been directly detected, in fact gravitational waves are the only way you can directly detect
them! Consider this: all of our knowledge about
the Universe to this date has come to us through telescopes that measure light from the electromagnetic
spectrum like radio waves, visible light, x-rays, or through detectors that measure
subatomic particles. But all of these existing telescopes are completely
blind to gravitational waves. This means that gravitational wave astronomy
is an entirely NEW THING, a whole new way to observe the Universe. And it has already solved some important science
questions: gravitational waves exist, black holes exist, and gravitational waves travel
at the speed of light. Here’s how LIGO detectors work. There are two L shaped buildings, one in Hanford
Washington, and another in Livingstone Louisiana make up LIGO and also there’s another detector
called VIRGO which is in Italy near Pisa. Having several detectors on Earth means that
scientists can verify a signal from space by seeing if it appears at all of the different
detectors, and they are far apart because it means they can see roughly in what direction
the wave is coming from by triangulating the signal. Even with these waves travelling at light
speed there is a delay of a few milliseconds between each of the detectors. Each of these L shaped buildings houses a
thing called a laser interferometer where a laser is produced, then split into two beams
which each fly down a 4km long arm, and then they are reflected off a 40kg pure silicon
test mass which is hung from the ceiling. It is hung from the ceiling on a series of
pendulums to insulate it from any outside disturbances like trucks moving past, or people
sneezing. When you are trying to detect distances with
a sensitivity less than the nucleus of an atom, getting rid of external noise is very
important. Each arm bounces the laser back and forth
400 times to make the arm effectively 1600km long, and each time around the laser is boosted
to make it stronger. Then after its journey the light is collected
and recombined in such a way that if the arms are the same length the light from each arm
cancels out producing no signal. But if a gravitational wave ripples past,
it will stretch or contract each of the arms making the light from each arm arrive at the
detector at slightly different times. That means that when they are recombined,
they will no longer fully cancel out, and a signal will appear. And this is exactly what happened on the 14th
November. It’s crazy to me to imagine that if they
had turned on this detector just two days later, they would have completely missed the
signal that had been travelling towards us for 1.3 billion years. This makes me wonder what other signals from
deep space have we already missed, and what is still out there screaming towards us waiting
to be discovered that we just don’t know about yet. In fact at the time that I made this video
LIGO has detected another even stronger black hole collision, and we can expect a lot more
in the coming months and years. It has already achieved many of its science
goals, there are many more it is aiming for. For example it might be able to give us a
more accurate measure of how fast the universe is expanding, and so how much dark energy
there is. It will hopefully be able to look at what
makes stars go supernova, and might be able to probe the very nature of spacetime and
see if it is made of things called cosmic strings. But the most exciting thing is that we don’t
know what it will find. This is one of the best parts of science,
when you’ve got a new tool to peer into a realm of reality that you’ve never been
able to access before. Who knows what you’ll find? Maybe you’ll discover things that help explain
some of the great mysteries of the Universe, maybe we’ll find things that we can’t
explain at all, and then we have to come up with new physics. In any case I find it super exciting and I
can’t wait to see more results. So there you go, those are the basics of gravitational
wave astronomy. Hey I just want to say thanks for all the
comments on my last video, I wasn’t able to reply to them all, but I did read them
all and the amount of positive feedback was amazing. So it makes me want to carry on and make more
and more of these videos so thanks for that. As for this video, I didn’t get to cover
everything I wanted to. This filed of gravitational wave astronomy
is amazing. In eight minutes you can only cover so much,
so if you are left with any questions please put them in the comments and I’ll try to
reply to them or I’ll collect together the most popular ones and do something later,
a Q&A or something like that. Also I have set up a Patreon account and so
if you want to help support me make these videos go take a look at that, otherwise,
thanks for watching and I’ll see you on the next video.
whoosh!
Though interesting, this seems old. I'm anxiously awaiting new detections, have they started listening for more signals yet? When can we expect news of more mergers?
Awesome. Thank you.
More energy than all the stars huh, that's incredible.
Question, how do we know that the waves we're detecting are coming from the merger of 2 black holes? Do we know the location of the resulting black hole?
they say that the black holes have infinite density yet there's a measurable mass and volume for each one?
Need more info on the gravitons and graviolis.