TechStuff Classic: How LIGO Works

What is LIGO and how did it detect gravitational waves? We explain!

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Episode Transcript

Speaker 1 (00:04):
Welcome to Tech Stuff, a production from iHeartRadio. Hey there,
and welcome to tech Stuff. I'm your host Jonathan Strickland.
I'm an executive producer with iHeartRadio and how the tech
are here. It is time for a classic episode. This

(00:25):
one is called How Lego Works. Originally published on February
twenty fourth, twenty sixteen. This was really cool because this
came out shortly after we were learning about how Lego
had detected gravitational waves, which up to that point had
largely been a hypothetical concept. So this was one of

(00:47):
those things where we finally figured out a way to
detect something that had been hypothesized about but previously undetected,
So really cool use of technology. Then the Ligo Observatory
had picked up a gravitational wave, and this was huge
news around the world. And in case you were wondering,

(01:10):
what the heck is this news all about? How did
they pick up that gravitational wave? What exactly is the
technology powering our sensors to detect this stuff? How does
it all work? That's what this episode's all about. So
this was the very first time anyone had been able
to measure a gravitational wave directly So today we're going

(01:32):
to talk all about what that means and how it happened. Now,
to begin with, we need to lay some groundwork and
to really get an understanding of what gravitational waves are.
So gravitational waves ultimately were one of the predictions made
by a certain Albert Einstein with this theory of general relativity.

(01:54):
So in that theory, Einstein presented this idea that our
universe is filled with spacetime. If you're a fan of
science fiction, you have undoubtedly come across that term star
trek is all about the spacetime continuum, and that you've
got to be careful. You could rip a hole in
the fabric of spacetime. As far as we know, that's

(02:15):
not really that possible. I mean, black holes could sort
of be that maybe, But at any rate, spacetime itself
is this calling it stuff is probably the wrong way
of putting it, but it is like a fabric and
mass hangs inside this fabric, And by mass, i'm talking
about stuff like stars or even an entire solar systems

(02:38):
or galaxies that hang in this fabric, and just like
you would see in a two dimensional display, it ends
up curving the fabric around the mass. We often talk
about this in terms of a very simple example that's
easy to imagine. You get some sort of stretching material.

(03:01):
Often you'll just hear someone say, okay, get a trampoline.
You've got a trampoline, and you put a big, heavy
bowling ball on the trampoline. So that bowling ball is
going to deform the trampoline surface. It's no longer going
to be straight. It's going to end up curving around
the bowling ball to some extent, creating kind of a
dmple where the bowling ball has has created this impression

(03:25):
inside the trampoline, and as long as the bowling ball
is there, that impression is going to stay. This is
sort of the like the way spacetime curves around giant
masses like stars and black holes things like that. Of course,
we have to remember that spacetime is actually four dimensional,
not a two dimensional thing like a trampoline. I mean,

(03:46):
I know that trampolines technically have three dimensions, but we're
really looking at a surface, so it's more like a
two dimensional plane. In reality. In spacetime it's four dimensional
because you've got the three spatial dimensions plus time, and
that is a little difficult to get your head around.
But that's why we tend to look at this two
dimensional example. It's a lot easier for us to imagine.

(04:08):
So let's go a little further with that analogy to
kind of talk about gravity. See Einstein proposed that gravity
was a manifestation of this curved space time. And if
we take that trampoline example, Let's say that you have
a regular trampoline. You haven't put the bowling ball on
there yet, so it's a nice flat surface, and you
have a marble, and you roll the marble across the
surface of the trampoline. So if there's nothing else there,

(04:31):
and if the trampoline is level, if the surface is level,
the marble should just roll in the straight line from
one side of the trampoline to the other, no problem.
Now let's say you put that big, heavy bowling ball
on the trampoline. It creates that dimple, and then you
try and roll the marble across the trampoline surface. Well,
now that dimple is going to end up affecting the

(04:51):
pathway of the marble. It's going to start to spiral
inward toward the bowling ball. Ultimately it'll end up making
contact with the bowling ball, and Einstein said, that's essentially
what gravity is. It's that you've got these large masses
that curves spacetime to the extent that smaller masses are

(05:12):
spiraling inward toward the large mass. It's just happening on
a scale that's much much, much larger than any bowling ball,
marble example. But that this isn't essentially what we see
when we see planets orbiting a sun, or we see
a moon orbiting a planet, or we see star systems
orbiting a galaxy, you know, the center of a galaxy,

(05:35):
and it's all because of this curve spacetime. Now, all
of that already is pretty heavy stuff. And keep in mind,
there was not really any way to directly observe this.
It was mostly the the just Einstein using logic to
work all this out and math, logic and math, and

(05:58):
ultimately it fit with what we saw of the universe.
But we weren't able to test a lot of this.
But then it gets even more mind blowing because now
we have to get to gravitational waves. So Einstein said
that if a mass were large enough and either changed
shape rapidly enough or it changed its movement in some way,

(06:21):
really really quickly. It would cause ripples of space time
to move outward from that event at the speed of light.
And those ripples are what we call gravitational waves, which
are different from gravity waves. By the way, I have
been known to accidentally say gravity waves instead of gravitational waves,
but the two are different things. A gravity wave is

(06:41):
a wave that exists because of gravity. In other words,
it's a physical wave of some sort of fluid system,
whether it's atmosphere or water or some other liquid. That's
a gravity wave on a planet's surface. It's not the
same thing as a gravitational wave, which is really a
ripple of space time, and like I said, it moves
outward from that event at the speed of light. And

(07:04):
stuff that could cause significant gravitational waves, things that would
be big enough for us to potentially pick up here
on Earth if we had the right equipment, would include
things like two black holes orbiting or colliding with one another,
which in fact, that was the event that we were
able to pick up with the Ligo facilities. And I'll
talk about those in just a bit. But there could

(07:27):
be other stuff too, like neutron stars orbiting one another
fast enough would generate gravitational waves, or a supernova explosion
would create one as well. And each of these events
give off a huge amount of energy, and some of
that energy gets converted into making these gravitational waves. So
one takeaway from this prediction something that Einstein said would happen,

(07:49):
is that any event that produces gravitational waves is an
event in which energy is being lost, So you would
expect to see less energy within that system afterward than before.
And it would be a hundred years from the time
of publication of the theory of general relativity to the

(08:10):
time when scientists announced that they had detected a gravitational
wave directly. And that's because gravitational waves are devilishly difficult
to detect. And that's some alliteration for you right there.
So gravitational waves are invisible. They don't emit any sort
of electromagnetic radiation, so we can't see them. We can't

(08:31):
detect them with radio detectors, nothing like that, and that
makes it pretty tricky to figure out where they are.
But they do just pass through the universe. They don't
get absorbed or scattered the way electromagnetic radiation does. If
you hold up a mirror and light hits the mirror,
light will bounce off the mirror. That's not the case

(08:51):
with gravitational waves. They pass right through, so it's a
very different thing than electromagnetic radiation. And while they're generated
from enormous events, the gravitational waves aren't very strong. By
the time they get to Earth. They are pretty weak,
so weak that you would need an incredibly sensitive tool

(09:13):
in order to pick them up. And also you have
to be searching at the right time, because if the
event that generated the gravitational waves happened a billion years ago,
but the location is four billion light years from Earth,
then we would have to wait another three billion years
for those gravitational waves to get to us, because again,
they travel at the speed of light. That's their limit.

(09:36):
So you have to be at the right place at
the right time to pick these things up, and in
some cases you might argue that that's incredibly fortuitous. Although
to be fair, it looks like the events that could
generate gravitational waves happen pretty frequently throughout the universe. But
the universe is huge, so if they're happening far away,

(09:58):
far enough away, will take a very long time for
that information to get to us. So before the announcement
on February eleventh, twenty sixteen, scientists had observed phenomena that
supported the existence of gravitational waves, but were not direct
observations of a gravitational wave. Here's an example. A pair
of astronomers in Puerto Rico in the nineteen seventies noticed

(10:20):
that there was a binary pulsar system and they went
back to the theory of general relativity because this was
a sort of system that would be exactly the type
to generate gravitational waves according to the predictions from general relativity,
and because general relativity predicted, hey, if it can create
gravitational waves, it's going to lose energy over time, they

(10:44):
ended up coming up with the hypothesis that, well, over time,
this binary pulsar system should start to slow down because
it's losing energy. It can't keep up at the speed
it's going. So they decided to keep an eye on it.
And by keeping an eye on it, I mean they
continue to observe this pulsar system over the course of

(11:06):
eight years, and by the end of the eight year period,
they were comparing the findings they were observing to the
predictions made by general relativity, and they were matching up.
It was unfolding exactly the way Einstein predicted it should
unfold based upon his theory of general relativity, which is
incredible when you think about it, that the observations are

(11:28):
matching up so neatly against the predictions. You know, it
just shows how how keenly aware Einstein was of how
our universe appears to work. Keeping in mind that general relativity,
while an amazing idea collection of ideas, really it doesn't
encompass everything that we know, right. It doesn't really address

(11:52):
quantum mechanics, for example, at least not in a way
that incorporates it with classical physics. But based upon what
it did cover, it seems like it was an incredibly
accurate theory, all right. So this was really considered strong
but indirect support of gravitational waves, because again the astronomers

(12:15):
didn't observe gravitational waves directly. They couldn't see them or
detect them, but they could see the effects, and again
it was matching up with the predictions made from general relativity.
So it was good indirect evidence that gravitational waves existed.
Then there was an event a couple of years ago
that you might have heard about when a team of

(12:38):
researchers working on the BICEP two telescope, which is an
Antarctica had announced that they thought they might have discovered
evidence of gravitational waves that supported a hypothesis called cosmic inflation.
That's a lot of information right there, So let me
explain what all that means. Cosmic inflation is a hypothesis

(13:02):
that relates to the Big Bang theory. So, with the
Big Bang theory, you've got this event in which the
universe undergoes a period of rapid expansion. Cosmic inflation is
kind of that rapid expansion on steroids. The idea being that, well,
when we look at our universe and we look at

(13:23):
what we can observe, it appears that our observations don't
quite match up with what we would expect if we
had just steady expansion since the Big Bang. In other words,
we look at all the information we have available to us,
and it looks to us that it doesn't quite match up.

(13:44):
Something's got to be wrong. Well, one possible explanation is
that shortly after the Big Bang, and by shortly, I
mean tend to the negative thirty sixth power seconds after
the Big Bang, So you take a ten, you put
a decimal point behind the ten, then you move the
decimal point to the left thirty six times that you

(14:05):
put seconds behind that. We're talking a fraction of a
fraction of a fraction of a second. The universe underwent
massive expansion, and it only lasted from that point to
about ten to the negative thirty third power or thirty
second power seconds. So again an instant. It's completely unimaginable,

(14:28):
at least for myself, how short an amount of time
this was. But that's how quickly the universe expanded significantly,
and then it slowed, but it continued to expand. Now,
if in fact, cosmic inflation is correct, it solves a
lot of the problems we have between the what we

(14:49):
observe today and what we believe happened with the Big Bang,
and reconciles those differences. If cosmic inflation is wrong, then
something else that we believe is wrong. Right. It means
that what we observe either isn't representative of reality somehow
we're not getting a big enough picture to understand it,

(15:09):
or that the Big Bang theory itself is flawed in
some fundamental way. Hey, we'll be back with this heavy
subject of detecting gravitational waves with LEGO after this short break,

(15:30):
so the BIS of two team what they were looking
for was some evidence of gravitational waves that would have
been generated during the Big Bang. This would end up
supporting the cosmic inflation hypothesis. And the way they did
this was they were looking at the cosmic microwave background
or CMBAM. Now, the cosmic microwave background emerged about three

(15:52):
hundred eighty thousand years after the Big Bang. This was
still a period where the universe was so dense that
I could not pass through it. It was dark and dense,
but the cosmic microwave background formed around that time, and
the hypothesis stated, well, gravitational waves would have affected the

(16:14):
cosmic microwave background, polarizing some of those some of those
particles really not particles, but some of that energy polarizing
some of the cosmic microwave background in such a way
that if you were to observe it, you could see
the effect of a gravitational wave passing through the cmb

(16:36):
And then as the universe expand expanded, rather that mark
would also expand. It's kind of like imagine leaving a
fingerprint on some sort of stretchy material and then stretching
that material out, the fingerprint is still there. It's deformed,
but still there. That's what the BICEP two team was
looking for, was this pattern in the CMB that would

(17:00):
indicate that gravitational waves from the Big Bang had passed through,
and if they found that, that would be a huge
support for cosmic inflation. And in the spring of twenty fourteen,
they announced that they believed they had found such evidence,
and they also invited other researchers to take a look
at their data and see if it was verifiable or

(17:21):
maybe they overlooked something. And in the fall of twenty fourteen,
another team said, we're sorry, but it looks to us
like space dust might have created a false positive that
what you thought it was the polarized CMB that you
had been looking for was actually just space dust that's

(17:41):
not actually part of the CMB. And so that ended
up kind of putting a dampener on the whole celebration
of finding gravitational waves to support cosmic inflation. But even
if it was completely verified, even if BICEP two had
irrefutable evidence that they had found the presence of gravitational
waves through a you know, the way it affected the CMB.

(18:07):
Even then that's not direct detection. It's still indirect. You're
looking at the way it's affected something else. So you know,
again we're still not discovering one. And part of that
is that BICEP two is a telescope. It's looking at
through the electromagnetic spectrum, and again, gravitational waves don't show

(18:28):
up that way. So no telescope would help you find
a gravitational wave directly. You might be able to find
how it affected something else, but not the wave itself.
Now that's not the case with the LIGO observatories. Actually
it's technically one observatory, but it has four different facilities,
two detectors and two research facilities that are all part

(18:51):
of the LIGO observatory. LIGO itself is an acronym and
it stands for Laser Interferometer Gravitational Wave Observatory. So it's
a pair of giant detectors built on the surface of
the Earth. One is located in Hanford, Washington, the other
is in Livingstone, Louisiana. Now they're about just a little

(19:14):
under two thousand miles apart, or just over three thousand
kilometers apart from each other, and that's really important. I'll
explain why in a little bit. So to understand how
they work, we also have to talk about something else
that gravitational waves do as they pass through space. They
stretch and compress space itself. So again, if you were

(19:35):
if you were to take a piece of elastic, I'd say,
you've got a rubber band, a nice thick rubber band,
and you cut it so that it's just one strip.
When you pull on that rubber band, it stretches along
the line where you're applying force, So it stretches in
that direction, in the perpendicular direction ninety degrees from where

(19:58):
you're pulling. It compresses, it gets more narrow, and then
when you let it return to its normal shape, it
gets you know, the long part ends up getting shorter
and the narrow part ends up getting wider as a result,
gravitational waves do this to reality. They do this to
actual space. They stretch and compress, and it happens several

(20:22):
times as the wave oscillates through. Really I should just
say as the wave passes through, rather than oscillates. The
distortion oscillates, but the wave passes through, so That means
the actual distance changes between two points as that gravitational
wave passes through that area. So if we were to
magnify this effect, and I mean magnify it to a

(20:47):
ludicrous degree, you would be able to see it. You
would actually be able to witness this. You could stand
ten feet away from someone else and when the gravitational
wave passes through, it would make it look like the
two of you suddenly got further away and then closer
to each other, and then further away and closer to
each other, even though you haven't moved anywhere, because the

(21:08):
distance itself is stretching and compressing. So why don't we
see that? I mean, if these celestial events that produce
gravitational waves happen on the order of something like every
fifteen minutes, why are we all noticing this whibbly wobbly effect. Well,
it's because the actual distortion that happens here on Earth

(21:31):
is much much much smaller in magnitude, so much more
so much smaller that it's difficult to even explain. But
if you were to have a supernova explode in the
Milky Way galaxy, in our galaxy, the gravitational waves generated
by that explosion would maybe be powerful enough to distort

(21:53):
the distance between the Earth and the Sun by about
the diameter of a hydrogen atom, so not noticeable to
any degree, and not at least to human senses. So
if you were to even go on a smaller scale,
let's say that you pick two points that are a
kilometer apart here on the surface of the Earth, the

(22:15):
amount of distortion would be equivalent to a few thousandth
of the diameter of a proton, So you're talking about
a subatomic particle, and just a tiny, tiny, tiny fraction
of that subatomic particles diameter would be the amount of
distortion that would happen across a kilometer worth of distance
here on Earth. Again, that means it's so small that

(22:38):
it's incredibly difficult to detect, so much so that Einstein
himself was pretty sure we would never be able to
directly detect gravitational waves because he could not imagine a
system that would be sensitive enough to pick up such
a minute change, a distortion that's happening so quickly because
it's a fraction of a second, and it's so small

(23:02):
as to be unnoticeable. So the other problem here is
not just that it's such a very tiny effect that
lasts a short amount of time. It's also that a
lot of other stuff could create false positives. You can
have incredibly instrumentation, but if that instrument is really really sensitive,

(23:23):
any sort of interference could set off and you could
end up getting false readings. So a change in air
pressure or temperature, or seismic activity, even a heavy truck
driving nearby could set off false results. So you'd have
to come up with a really clever way to measure distortion,

(23:43):
to limit vibration, and to eliminate the chance that it
was a false positive. And Lego is the answer to
all of that. So the Lego Observatory is actually the
result of decades of collaborative work among different scientific research
centers and internet national bodies and universities, and all started
back in nineteen seventy nine. That's when the National Science

(24:06):
Foundation approved funds for Caltech and MIT to develop laser
interferometer research and development. And a few years later, in
nineteen eighty three, Caltech and MIT submitted a proposal for
a kilometer scale detector. But keep in mind, all right,
so in nineteen seventy nine you get the funding for
R and d nineteen eighty three, there's the submission of

(24:28):
a proposal for a kilometer scale detector. There wouldn't be
approval for a detector until nineteen ninety, so almost a
decade later, and which turns out was probably okay, because
we really didn't have the technological ability to detect things

(24:50):
on a scale small enough to register a gravitational wave
in the first place. But still, you know, a decade's
delay before you even get approval is still pretty rough.
Construction didn't begin until nineteen ninety four. The inauguration of
the Ligo Observatory took place in nineteen ninety nine, but
even then that didn't mean that the observatory was online

(25:14):
collecting data. It didn't do that until two thousand and two.
And here's the kicker. Eventually scientists came to the conclusion
that this Ligo observatory was not sensitive enough to detect
gravitational waves. That despite the fact that it was this
large detector or pair of large detectors, actually because again

(25:36):
one in Louisiana one in Washington, it wasn't sensitive enough
to be effective. So it was not quite back to
the drawing board, but it did mean that they had
to think about how they would upgrade these facilities so
that they could be sensitive enough to pick up a
gravitational wave. So in twenty ten, Ligo went offline to

(25:58):
undergo a big overhaul, and it took four years of
construction and testing to get it into shape and another
year to set it up for new observations, which means
that it wasn't until twenty fifteen that it was ready
to come back online. By now it was called the
Advanced Ligo Observatory and it began collecting data in September

(26:21):
twenty fifteen. Literally days after it had come online, it
picked up a gravitational wave. So that's pretty phenomenal that
just a couple of days, just a few days really
after it had been turned on again in twenty fifteen,
we got a hit. So that was incredibly exciting. So

(26:41):
how did this happen? How does it actually work? Well,
we have to take a look at what interferometers are
all about. An interferometer uses a technique in which electromagnetic
waves are superimposed on one another in order to get information. Now,
Ligo does this with a laser beam because it's a
laser interferometer, and the laser beam gets shot through a

(27:05):
beam splitter, and the beams, the two beams that result
go down two long vacuum tubes. So both of the
Lego detectors are in an L shape. So you've got
these long, long vacuum tubes that extend two and a
half miles or about four kilometers out from the crux
from the angle where they meet up, and each one

(27:31):
is you know, they're both the same length. They have
to be exactly the same length. And the way this
works is that kind of behind the crux, you've got
a laser that shoots out a beam of light to
a beam splitter. The splitter does exactly what it sounds like.
It does. It splits the beam into two separate beams
with alternating canceling wavelengths. I guess I should say, so

(27:56):
the troughs and peaks on one match up with the
peaks and troughs of the other. That's really important when
we get a little further down the line here. So
one of those two beams goes down one branch of
this L shaped detector. The other beam goes down the

(28:18):
other branch. And keep in mind, like I said, both
of these branches are exactly the same length. Two and
a half miles or four kilometers. When the laser gets
to the end, they hit a mirror. Each beam hits
a mirror, they come back to the point of origin,
and because the two laser beams have these counteracting wavelengths,

(28:42):
they cancel each other out, so the peaks on one
cancel out the troughs of the other, and vice versa.
That means that no light gets emitted through this system.
And that's important because there's actually a light detector that's
part of this system as well. It's looking for any
sign of laser light, because a sign of laser light
would say that something has changed somehow the distances between

(29:06):
these or the distances represented by these two vacuum tubes
has changed, and that would be indicative of an event
like a gravitational wave moving through. So if any light
shines through, you know something has happened. Essentially, it says
that there's a mismatch in the lengths of the vacuum
tubes themselves. So when a gravitational wave passes through, one

(29:30):
vacuum tube will get shorter while the other gets longer.
And that's because the two tubes are offset by ninety degrees,
so one is going to be along one side of
the wave and that will lengthen the other will be
along will be perpendicular to that, and will shorten as
a result. And this means that the lasers will have

(29:52):
different distances to travel down, So the laser traveling the
shorter distance takes less time to get back to the crux.
The laser going down the longer distance takes more time.
And even though this is only happening within a fraction
of a second, it's long enough for us to be
able to detect the difference. And it also means that
those wavelengths don't match up anymore, they don't cancel each

(30:15):
other out anymore. So some of that laser light gets
emitted to the light detector, which then indicates what's going on.
It knows which one of the branches was short versus long,
and knows how long it happened. It knows how much
it oscillated back and forth, because obviously this is continuing
as these as the gravitational wave moves through, So you

(30:38):
collect a lot of data in a short amount of time.
And we're talking like teeny tiny slices of a second.
As we're getting all this information, which is pretty incredible.
We're almost done with our discussion about LEGO, but before
we can do that, we need to take one more
quick break. So once you get all that data, you

(31:06):
can then analyze it. Actually, more importantly, before you analyze it,
you have to verify it. Now. This is why it's
important that there are two detectors, and it's also important
that they are so far apart, like three thousand kilometers
apart from each other. That's because if you get a
blip on one of them, if it's a true gravitational wave,

(31:26):
you should also get a blip on the other one.
And because gravitational waves move at the speed of light,
there should be a slight difference in time when both
detectors pick up on this gravitational wave, somewhere right around
ten milliseconds or less. In the case of the one
that was detected back in the fall of twenty fifteen

(31:47):
but not announced until twenty sixteen, it hit the Louisiana
detector first, and seven milliseconds later it hit the Washington detector,
So that is indicative of something like a gravitational wave
as opposed to some local event that would have caused
interference and created a false positive. If an earthquake had

(32:08):
happened in Washington, then the facility may may have picked
something up, but you wouldn't expect to see it in
Louisiana because it was a localized event. Same thing is
true if something had happened in Louisiana. So by seeing
it happen at both within this ten millisecond timeframe meant

(32:28):
that it was a very good candidate for a gravitational
wave passing through. And that's exactly what happened. It was
a home run in the first ending of the game,
or even really the first at bat of the game.
It's like your first player steps up on the first
day of baseball and knocks a home run and that

(32:48):
defines the moment the season. Really, that's that's the equivalent
of what we saw here on a scientific basis. So
the other thing I want to talk about was how
LEGO tries to minimize the possibility of detecting a false
positive in the first place. So, yeah, false positives are

(33:09):
something that they worry about, and the fact that there
are two detectors helps minimize that. But even so, you
want to eliminate the possibility of a false positive so
that you're not constantly sifting through noise looking for a signal.
Do you want to minimize noise as much as possible.
So Lego does this through using combinations of active and

(33:30):
passive vibration reduction systems. One thing that they do is
they remove the air from the tubes. That is why
they're vacuum tubes. They remove the air for two reasons. One,
they don't want any sound passing through the chambers. Sound
could possibly interfere with the measurements. Sound would impact the mirrors,

(33:53):
and even a small impact would be enough to cause
a problem when you're measuring this laser. For one thing,
they're looking at distances when they're measuring the changes between
the two branches. You know, I mentioned that one's getting longer,
one's getting smaller. The distances they're looking at are very
very tiny. We're talking ten to the negative nineteenth power meters.

(34:17):
So again, you take the number ten, you move a
decimal place nineteen times to the left of that, and
you put meters at the end. That's the distance that
these lasers are are measuring the distortion and distance. So
it's very very very tiny, and something as simple as
sound could change that. So you can't have any sound

(34:38):
in these vacuum tubes, you've got to get the air out. Also,
air can absorb and scatter laser light, which would interfere
with the experiment as well, so you've got to get
air out. Now down to the vibration reduction systems. So
the active isolation system is meant to weed out the
majority of vibration, and it's active because it is actively

(35:03):
working against any vibration it encounters. You've got sensors that
detect vibration, they send commands to force actuators that move
in opposition to the vibration. So it's kind of like
noise canceling headphones. If you put on a pair of
noise canceling headphones, what they're supposed to do is pick

(35:23):
up any incoming sound and then generate sound waves that
are in direct opposition of the incoming sound, so that
you get a cancelation effect. That's the same thing that
these active systems are trying to do at LIGO, except
instead of it just being sound, it's really any vibration.
Although I guess you could argue that any vibration really
is sound, so it's kind of a moot point. But anyway,

(35:46):
they're actively trying to counteract that vibration. But then you've
got the passive system. This is the suspension system for
the mirrors, and this is the next step. So you've
eliminated a huge percentage of the vibration at this point,
but that's not good enough. You need to eliminate as
much as close to one hundred percent of the vibration

(36:08):
as you possibly can. So next we look at the
suspension system of Ligo's mirrors, and they are at the
base of a four pendulum system. Meaning imagine you've got
a string and it ends in a pendulum. A weight
a mass of some sort, and it has to be
a mass of significant size so that it will it'll

(36:35):
resist moving. It's the law of inertia. You know, an
object at rest tends to stay at rest, so it
will end up absorbing a lot of vibration and minimizing
it on the other end. So you've got that first pendulum,
that's pendulum number one. From that you suspend pendulum number two.

(36:56):
So already you're getting fewer vibrations because pendulum number one
is picking them up. What vibrations do manage to pass
through start to get picked up by pendulum number two,
and again the law of inertia means that it will
dampen a lot of that vibration. Then you've got pendulum
number three, and then beneath that you finally have the mirror,
which is forty kilograms or about eighty eight pounds worth

(37:19):
of mirror. And hopefully, after the active impassive systems have
all taken care of the vibration, nothing else is getting
to that mirror. By the way, you can actually test
this out yourself, if you like, by getting four strings
that are all equal length, and some washers, some nice
heavy washers. Tie a washer at the end of the

(37:42):
string of the first string. Then tie a washer so
that one end of the string connects to washer number one,
one end of the string connects to washer number two,
and so on and so forth. And if you hold
it up and you start shaking your hand holding the string,
notice that the washer at the top moves more than

(38:03):
the second washer, which moves more than the third, And
by the time you get down to the fourth one,
it's not moving much at all because it's been the
vibrations have been dampened by the previous pendulums. That's the
principle of this passive system. So that helps eliminate a
lot of that vibration. Without those dampening systems in place,

(38:23):
the two LIGO detectors would be picking up a lot
of noise, and since we're still not really sure how
often gravitational waves pass through the Earth, that would be
a problem now. Between two thousand and two and twenty
and ten, with the early version of LEGO, they didn't
pick up any gravitational waves at all, which we think

(38:44):
is because the detectors weren't sensitive enough. We think that's
the reason, but an alternative reason could be that gravitational
waves aren't as frequent as we think they are, that
they don't pass through the Earth as frequently as we
otherwise believe. However, the opposite could be true. We could
have way more gravitational waves passing through Earth than we

(39:09):
had anticipated. Some of them may be so faint that
even this advanced LIGO system cannot pick it up. There
are already plans to upgrade LIGO again, and there are
other LIGO observatory systems that will that are in development
now that will also listen in for gravitational waves. And

(39:30):
listen tends to be the way most people refer to it,
like you're listening for this universal vibration moving through the Earth.
So because it was only a few days after they
came online, a lot of people are thinking that gravitational
waves are probably fairly common. Otherwise, it was just extraordinarily

(39:51):
lucky that we picked it up just days after the
observatory was online. Again, the one that we did pick
up one point three billion light years away, which means
that the event happened one point three billion years ago.
That event being two black holes colliding with one another
to form a solitary black hole mass. In the process,

(40:16):
it vaporized about three solar masses worth of mass I guess,
which is a huge amount to think about being converted
into energy, and the gravitational waves emanated from there at
the speed of light. So one point three billion years later, Earth,
which was one point three billion light years away, picked

(40:37):
them up. So in a way, it was incredibly lucky.
But if this happens more frequently than we originally believed,
we might see that this is not an uncommon event.
It's very possible that there are things we cannot see
in the universe that create gravitational waves. So in other words,

(40:59):
it's off that does not give off electromagnetic radiation at all,
but it does create gravitational waves, meaning that we now
have the capacity to detect things that otherwise would have
remained completely undetectable by us. So one of the many
reasons why this discovery is so exciting, it opens up
brand new science. It creates a new discipline of science,

(41:21):
gravitational astronomy, which can really get going now because it's
not that different from when the telescope was invented. Before
the telescope, astronomy was pretty limited. You could map out
astrological bodies when you were way back in the day
before the science of astronomy had really gotten going. Once

(41:41):
you started figuring out the difference between mythology and science,
then astronomy really takes over. You could map out where
these different bodies go. You could figure out which ones
are must be planets versus stars, but you couldn't really
gather a lot more information than that. You could still
get an impressive amount of data just from observing with

(42:04):
the naked eye, but the telescope opened up a whole
new world of study, and this gravitational wave detector system
has opened up a similar, all new world that was
not accessible by us until this year really late last year,
late twenty fifteen, So we might end up discovering things

(42:28):
that we've never been able to observe before. Will also
likely be able to study all sorts of cool stuff,
like how fast is the universe expanding, how much dark
energy is in our universe. We might learn more about
black holes already. The gravitational wave detected by LIGO has
given us the strongest direct evidence of black holes. I

(42:52):
guess I should say indirect evidence because it's the gravity
waves generated by the black holes. But not that we
ever doubted the existence of black holes, but this is
yet more evidence in support of them. So it's really
an exciting time. We could end up learning all sorts
of stuff, stuff that we can't even anticipate right now,

(43:14):
and that's why it's such a big deal. I also
think that LEGO is just an incredibly elegant way of
detecting something that otherwise is impossible for us to see
or feel or experience, and it's incredibly simple, at least
on the principle of it. The technology itself is very
complicated because it has to be so sensitive to detect

(43:36):
these very tiny changes in distance and time. But the
principle behind it is elegant, and I mean, you don't
get much more simple than a ninety degree angle. That's
pretty bare bones there, but a very clever way of
detecting something that Einstein believed was going to be beyond

(43:56):
our ability to ever experience. So now we have a
revolutionary new way to examine the universe. We have no
way of knowing what sort of stuff we might learn
as a result, which is incredibly exciting. And it's all
due to some lasers, some beam splitters, and some mirrors.

(44:17):
And since we're already looking at lots of different organizations
building their own LIGO observatories and also increasing the capacity
or at least the sensitivity of the current LEGO system,
who knows what we're going to see next. I hope
you enjoyed that classic episode on HOWLEGO works way back

(44:41):
in twenty sixteen. I should definitely do an update on
that and talk more about the sort of things we've
learned since the detection of gravitational waves and how that
has affected science. But if you have suggestions for things
I should cover in future episodes of tech Stuff, I'd
love to hear. There are a couple of different ways
you can do that. You can download the iHeartRadio app.

(45:04):
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(45:26):
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(45:48):
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