Detecting Gravitational Waves

What are gravitational waves and how did LIGO detect them? We take a close look at space-time to find out.

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Episode Transcript

Speaker 1 (00:00):
Brought to you by Toyota. Let's go places. Welcome to
Forward Thinking. Hey there, and welcome to Forward Thinking, the
podcast that looks at the future and says white about
I'm Jonathan Strickland, I'm Lauren voc Obama, and I'm Joe McCormick.

(00:23):
And today, you guys aren't going to be able to
depend on me to be my normal plucky self because
I've got kind of a bad cold. So I'm sorry
that I'm even talking in your general direction right now,
but I suppose the show must go on. Well yeah,
and Joe, it's it's kind of it's kind of fitting
that that you are a little out of play here,
right because we're going to revisit a topic that Lauren

(00:46):
and I talked about, gravitational waves, and you weren't here
for that episode. God, just act like I'm not here.
So yeah, so mentally you're you're again not in the room.
You're on vacation. You're always wonderful and find an excellent Yeah,
I'm sure that you'll be a joy as always. But hey,
gravitational waves, this was some big this month. Yeah, huge news.

(01:07):
And actually it's funny because the discovery happened in two
thousand and fifteen. But as is the case with any
really you know, careful, responsible scientific inquiry, it took some
time for scientists to verify the information the data they
had gathered before they actually announced what they had found.
You know, it did, but I don't know if you

(01:28):
all noticed it, if you follow the the I don't know,
science writers on Twitter or or the science press in general.
There were several rounds of rumors flaring up where some
prominent physicists or cosmologists would sort of like drop a
hint saying like, I think they found gravity waves. Yeah,

(01:49):
I know, you're gonna you're gonna get out of your
red pin about that a little bit. Yeah, And and
so somebody would print a story about that, and the
rumor mill would flare up, and then it would all
end with well, I guess we'll just have to wait
until they announced their findings and see what happened. But
it turned out that the rumors were in this case true, right.
There was a very very strong, very well established piece

(02:10):
of evidence for gravitational waves in the universe. Yes, a
a detection that appears to be pretty much air tight.
So uh, And that was announced on February eleven. We
were all eagerly waiting for the announcement. In fact, many
of us were following it live as it was happening. Joe,
you were tweeting about it live as it was happening.

(02:32):
As I recall, I think I just I retweeted. Some
people got you. I wasn't. I wasn't live tweeting, and
you were tweeting. You weren't undead? Are you undead? Is
this what this called? Isomie a little bit undead? I
hope you all both brought across well at any rate.

(02:52):
The last zombies. Okay, go ahead if you if you're
really cross with a zombie, they take note. So we
originally talked about gravitational waves back in September two thousand
and fourteen, and in that conversation we were talking specifically
about BICEP two, which is a telescope that's in the Antarctic. Yeah,
and if you remember some time vaguely in the past,

(03:14):
either this podcast or just other general news announcements a
few years ago, and you're saying, like, wait, I thought
they already discovered gravitational waves. There is a reason you're
remembering that. Yeah. Yeah, Well they said, hey, guys, I
think that we we we think that we discovered gravitational waves.
This is so great. And what they actually discovered was
spacedest yeah, or at least space dust was enough of
a factor to throw the results into serious doubt. But

(03:38):
we'll talk about that a little bit more later in
the podcast. This time, we're going to really be focusing
on what Lego found. Uh Ligo is a pair of observatories,
and we'll talk more about those in a minute. But
before we get into any of that, perhaps it's best
to actually take some time to talk about what gravitational
waves are in the first place, and to understand that

(03:59):
you've gotta look back in history, all the way back
to nineteen sixteen, which is when Albert Einstein published his
his theory of general relativity, had been working on it
since nineteen o five. Right, So, Alfred B. Iimstein was
out on a train one day, hurling axes out the
window at passing herds of buffalo and he never give

(04:20):
you cold medication before a podcast. And he noticed that
as he tossed each ax, it arcd towards the ground
instead of flying off in an infinite direction in which
he threw it. So why does that happen. Alright, ignoring
everything that Joe just said, Here's here's what Einstein was
was considering. He had been really thinking hard about the

(04:42):
nature of the universe. Uh. This was part mathematics, part philosophy,
part just uh just using logic to its inevitable conclusion.
And it was incredible. The theory he came up with,
it was it was phenomenal, and not just phenomenal. But
over the years, so much of that theory has proven

(05:04):
to be accurate to what we see in reality. That
you know, we we just keep on supporting the various
predictions that were made, and gravitational waves were one of
the predictions made in the theory of general relativity. Uh.
He he had argued that that the universe is made
up of uh space time continuum. You've probably heard that

(05:27):
if you've ever watched any Star Trek, you've heard about
the space time continuum. But the spacetime continuum is is
sort of this idea of space and time together forming
kind of a fabric of the universe and matter or
to be really just just to to talk it in
the terms he used, mass can change, can can warp spacetime.

(05:48):
In fact, it does warp spacetime. The presence of matter
warps spacetime. So the most common analogy that you tend
to see is that imagine you've got a trampoline and
you put a bowling ball on the trampoline. It ends
up making a dimple in the trampoline. It sinks down
where the bowling ball is resting that here here, the

(06:09):
trampoline being spacetime and the bowling ball being say a star,
yeah exactly, let's let's a star, black hole, anything that's
got a lot of mass, and uh you that would
show you how the trampoline warps around the bowling ball,
like spacetime warps around an object of great mass. Keeping
in mind, of course, that we're using more or less
a two dimensional representation to talk about three dimensional concept.

(06:32):
But it's really hard to imagine a three dimensional concept. Really, Yeah,
that's true, because you're talking about time. It is true.
But then if you were to take a marble, let's say,
and roll it across the trampoline. Now, if it were
if there were no bowling ball on it, the marble
would just roll from one side to the other, assuming
that you're on level ground and all that. But with
the bowling ball. There, it's gonna start spiraling inward towards

(06:53):
the bowling ball. And Einstein argued that what we see
with gravity, with with gravitational pull between like a star
and a planet, or even the center of a galaxy
and all of the star systems, that's how they behave
they move in that same spiral. And uh So, now

(07:15):
one difference you might observe is that you think, hey,
well if I did that on a trampoline, and probably
marble would probably only spiral around the bowling ball three
or four times before it crashed into it. There, I
would guess the difference is going to be in this
example friction between the marble and the trampoline. We also
speak and orbits in space being you know, almost negligible
amounts of friction. Yeah, that's definitely, that's definitely the case.

(07:38):
It helps. So what we see here is that spacetime
curves around objects and then be building upon that. Uh
Einstein said, if you have a large mass undergo a
violent change, either it changes shape or it changes its
motion in some way in a dramatic way, it creates

(08:00):
these ripples in space time that propagate outward at the
speed of light. And these are gravitational waves. Um. So
it's actual ripples in space time itself, and it's kind
of like an electromagnetic wave, and that it moves at
that speed of light, but unlike electromagnetic waves, it can't
be absorbed and it can't be scattered. Yeah, it behaves

(08:22):
in that way, more like a sound wave. Yeah, exactly.
So if you think of sound waves, where when you
hear a sound, what you're actually hearing is the motion
of air molecules. Those air molecules are being compressed by
an oncoming wave and then they expand again afterward. It's
very similar to that, except we're talking about the fabric
of reality itself. Now, let me play Jonathan for a

(08:46):
second and be pedantic. It wouldn't necessarily have to be
air molecules, would it be whatever medium that the sound
is traveling through. That's true. Yeah, it could be solid
wood and it's still has um and we should we
should put in that Einstein himself wasn't entirely sure about
this gravitational wave stuff. He kind of flip flopped on

(09:07):
it a few times, but always came back around to
support it. So I think that he himself would be
sort of tickled that we a came up with a
way to detect them and be have actually detected Yeah.
I think he would be flabber guested because I the
impression I get is that Einstein was fairly certain because
the nature of gravitational waves, they would be undetectable. There

(09:28):
there'll be no way to directly observe them because they
are invisible, there's nothing. They're not like electromagnetic radiation, where
you've got an actual visible spectrum. Um. So I think
that would have really shocked him that we had come
up with a really clever way of detecting the presence
of gravitational waves. Now, Jonathan, why is it that you

(09:49):
have a bone to pick with anybody who calls this
most recent discovery the discovery of gravity waves? Well, because
it's wrong. So gravity waves you told me all about
the wrongness. Gravity and gravitational are two different things. With
a gravitational wave, you are talking about this ripple through
space time that travels outward at the speed of light.
With gravity waves, you're talking about a wave that exists

(10:12):
due to gravity. It's something that you would find on
a planet, either in some sort of fluid system, whether
it's an atmosphere or like a body of water. So, um,
let's say you've got an ocean and you've got wind
blowing across the surface of that ocean, it starts to
disturb the water. Gravity is pulling down on the surface

(10:33):
of that water, and uh, waters buoyancy is acting in
opposition to gravity, and that combined with the wind, creates
a wind driven um wave. That would be a gravity wave.
It's a wave that exists because gravity is there. If
there were no gravity through would even be a body
of water there. Uh. That is a gravity wave totally

(10:57):
different from a gravitational wave, just a physical wave that
you can observe through some form of fluidic system. And
so if you ever hear someone say gravity waves of
gravitational wave as a matter of shorthand they're technically being incorrect,
you should probably find a polite way to say, maybe
you meant gravitational wave, or you could be like me,

(11:19):
and there's no polite way to say that. Yeah, I
gave up on being polite years ago, so I just
tried to caution other people not to make the same
choices I made. Um. But yeah, there's some some other
interesting things about gravitational waves. They pass through stuff. So
like we said, yeah, yeah, they don't act like electromagnetic waves. Yeah,

(11:40):
they don't get absorbed or reflected, so they just poop
keep on going. So if you've got, for example, a
planet between you and electromagnetic radiation such as light from
the Sun, you will experience in eclipse because the planet
blocks it. But it will not block these gravity waves exactly, won't.
It won't eclipse the the movement of waves toward you.

(12:01):
The waves will get weaker as they propagate out over
distance though, yes, and uh So if you're talking about
a gravitational wave that has you know, has happened because
of some massive event that's a billion light years away,
they are very very faint by the time they get
to Earth. Uh And that also leads to why they've

(12:23):
been so tricky to detect. Not only are they invisible,
but they're not very strong. So we have to look
for gravitational waves that have been caused by really really
big events, like in the case of the one that
Ligo detected in September two thousand fifteen, it was the
collision of two black holes. It's a pretty big event.

(12:43):
Others could be two neutron stars that are orbiting one
another rapidly, which would create kind of an oscillating and
continuous a series of gravitational waves. Um or it could
be like a supernova exploding that to do it. A
big bang that would do it too. In fact, that
was what my step two was looking for, was the

(13:04):
evidence of gravity waves from the era of the Big Bang.
I just caught you in it. What, oh man, I
I I stand correct, I sit corrected here in to eat,
Thank you well, and as soon as I get the
foot out of my mouth, I will start chewing upon
the hat. Yes, gravitational wave not gravity wave. No, it's

(13:27):
true that they have been so difficult to detect and
that we've had to come up with very interesting methods
of trying to detect them, involving laser interferometry. Yeah. So
here's here's something that's really cool about a gravitational wave
because it's this ripple in space time. It actually is
a small you can think of it like a small

(13:48):
fold in spacetime, right, and that means it can actually
change the distance between two points by compressing that distance
or expanding it like a rubber band. So you've got
like a piece of elastic h or if you prefer,
you know, just just imagine that, Um, Joe, you and
I are standing across a football field from one another.

(14:11):
You're on one end zone. I'm in the other end zone.
Their en zones in football, right, I'm just looking for
There's no help from the one with the oblong spheroid, right, Yes,
that's it. Or you know, a soccer field if you prefer,
But then you know where at either end gravitational wave
passes through. Let's say it's a massive gravitational wave, something
way bigger than we would ever actually observe here on Earth.

(14:34):
What would appear to happen is that Joe and I
from our perspectives, it would look like we got closer
and then further apart, and then closer and then further apart,
without ever taking a step in either direction. That the are,
the world itself has compressed and expanded around us because
of this fold in spacetime that's passing through, which sounds

(14:56):
like some serious like matrix style stuff. But either fortunately
or unfortunately, depending on how you know, stable you like
your reality, that's that's that kind of dramatic change is
not what we observe from gravitational waves, right, Not at all,
not even remotely in the same football field as it were.

(15:17):
Uh No, Instead, if you were to have something like
a supernova explosion, and I should say an asymmetric supernova
explosion for reasons I don't understand, a symmetrical supernova does
not a supernova explosion does not generate gravitational waves. I
don't know why I was reading it trying to find
more information, but it got to a point where the

(15:37):
astrophysics got way too complicated for me to understand. However,
what I do understand is that if there were a
supernova explosion in our galaxy in the Milky Way, the
gravitational waves generated from that would only be powerful enough
to change the distance between Earth and the Sun by
the diameter of one hydrogen atom. That's how much it

(15:58):
would oscillate. Oh yeah, okay, you probably would notice. So
this is like a princess and the p kind of thing,
isn't it. Yeah, definitely, definitely on that level. Obviously, we
need to build a more sensitive princess. That's that's the
you know, that's entirely the plot. Yeah, yeah, we're about

(16:20):
a mattress. You know, it's all musical about that. Oh
I didn't build a robot princess, any number of mattress.
They just they just uh collued to make her uncomfortable
so that she she complains about the the lumpiness of
the mattress, and it turns out that there's not just

(16:41):
a p under there. There's also a suit of armor
and a shield. Spoiler alert for any of you who
are really looking forward to what's upon a mattress. Yeah.
But but but I suppose they did kind of create
like a laser princess. So yeah, but we'll get into that.
So anyway, So so I just mentioned that if you're
looking at the Earth and the Sun, you're talking about
the differ prints of the diameter of an hydrogen atom

(17:02):
in the distance, which is incredible to think about. But
that that change, that difference in distance gets smaller as
you get two smaller scales. So let's talk about if
you were on Earth and trying to measure this, because
this gets to why it has been so challenging to
detect gravitational waves here on Earth. Okay, don't use a

(17:23):
football field analogy. What about the need to how about
the beginning and end of the line for space Mountain.
That's a queue that goes like, yeah, that one already
loops around back on itself in weird ways. Yeah, it's
not really gonna work. No, I don't need to make
that comparison. I was just to to establish the weirdness
of what happens. But no, I wanted to just talk

(17:45):
about the scale. So if you were talking about here
on Earth and you're trying to measure that that change
in reality, that change in distance because the spacetime continuum
is being folded in this ripple. Uh. If you had
two objects that are about a column butt are apart,
the change in distance they would experience due to that
gravitational wave would be thousands of the diameter of a proton.

(18:09):
So take a sub atomic particle and go a teeny
tiny fraction of the diameter of that subotomic particle, and
that's how much difference in distance it would experience. Get
out your your proton knife and your proton measuring set,
and it turns out your ruler is not going to
be terribly helpful in that case. So that is one

(18:30):
of the reasons why it's been so incredibly challenging to
detect the presence of a gravitational wave. And and we
we've had a few leads, or if you prefer, a
few false starts in detecting them throughout history. Back in
nineteen sixty nine, University of Maryland physicist Joseph Weber created
this this six foot aluminum cylinder that he claimed would

(18:51):
act like an antenna for gravitational waves. He said that
when such a wave hit the cylinder, it would ring
like a tuning fork, but nobody else could replicate his results.
It was a kind of neat looking device, though. There's
actual video of this, and it look kind of like
a mirrored two inside another tube, like there was like
some sort of crazy physics disco going on inside there. Uh,

(19:14):
or at least that's what I like to think. Back
in nineteen seventy four, there are a pair of scientists
in Puerto Rico who saw a binary pulsar system and
they looked at the theory of general relativity, which predicted
that such a system would gradually lose energy due to
the too emitting gravitational waves. Some of its energy would

(19:36):
go into creating these gravitational waves, and because you have
a system losing energy, it would start to lose speed.
And so they said, well, based upon this prediction, we
should observe this change in speed as long as we
keep an eye on this binary pulsar system. So they
tracked it for eight years. At the end of the

(19:58):
eight year period, they said the behavior of the binary
pulsar system was completely in line with the predictions from
general relativity. He said, it is behaving precisely the way
it would if, in fact, gravitational waves are reality. Therefore,
this is in support of gravitational waves. And even since then,

(20:19):
over the forty years of observations that have happened with
this binary pulsar system, those predictions continued to be supported.
So that was great, you know, indirect evidence of gravitational waves, saying, well,
if they don't exist, something else must be happening for
this system to slow down the way it is. But

(20:39):
the thing that makes most sense is that Einstein was right.
Then we move ahead quite a bit. Let's talk about
BICEP two. Now, BICEP two was going a different way
about looking for gravitational waves. They were specifically looking for
evidence of UH that would support a hypothesis called cosmic inflation,
and inflation is a big deal in physical cosmology today.

(21:02):
This is I think most physical cosmologists look at inflation
is very promising theory. Yeah, And the whole reason why
we have this this idea in the first place is
to explain why the universe appears the way it does,
while also trying to reconcile that with the Big Bang theory.
Because I'm not going to get too far into the

(21:25):
weeds here, but the basically the hypothesis says that about
ten to the negative thirty six seconds. So take a
ten and then take a decimal point and move that
thirty six places to the left. Get get that proton
knife out again, did up a second, right, That's that's

(21:47):
where you get down to the teeny tiny, tiny tiny
fraction of a second to about ten to the negative
thirty three or thirty second power seconds. So so in
an instant, as far as we're concerned, into an instant, Yeah,
that at that moment, that's when the universe underwent rapid expansion,

(22:07):
far greater than the rate of expansion it currently is
going through. And it's expanding fast today. Yeah. Actually, then
it's picking up speed, which is a little uh, at
least according to our measurements, it is picking up speed.
But that's that's something that we hope gravitational waves will
help us learn more about in the future at any rate.
A scientist named Alan Gooth proposed a hypothesis to explain

(22:31):
why the universe looks the way it does and stay
in line with the Big Bang theory. It was kind
of like, well, in order for us to be where
we are now based upon the observations of the universe
we have made so far, and in order for the
Big Bang theory to make any sense whatsoever, there had
to be this period of cosmic inflation or else. It

(22:51):
just doesn't work out. The math doesn't work out. And
in a way you could argue, all this is almost
like a placeholder, except again, it's kind of like Einstein.
It's using logic saying, well, we we know about this,
we're pretty sure about this other thing. But in order
for those two things to reconcile, this other, this third
thing must have happened at some point. Yeah. Yeah, it's

(23:11):
theoretically solving for X in this equation. Yeah, and if
you fast forward three thousand years after the Big Bang,
you then have the emergence of the cosmic microwave background
or c MB. Now, this is a radiation that's sort
of a fingerprint left over from the from the era
after the Big Bang. It's from it's when the universe

(23:33):
was still seeing birdies. Like in the cartoon, universe really
wasn't seeing anything. It was so dense that even light
couldn't pass through it at this point. Um, but it is.
It's sort of the remnant of that era, and we
can we can detect the cosmic microwave background. So BICEP
two I didn't mention to se either. BICEP actually stands
for background imaging of cosmic extra galactic polarization. Was looking

(23:57):
for polarized cosmic microwave background radiation. The idea being that
gravitational waves should have aligned certain segments of the CMB,
so if you could detect that, then that would be
indirect evidence of gravitational waves and therefore also indirect evidence
of this cosmic inflation idea, because something as dramatic as

(24:19):
cosmic inflation would have generated gravitational waves and they would
have left their mark on something like the CNB, and
they the team thought they found it. They actually thought
they found it a couple of years before the news broke.
They spent years trying to verify the information they found
to make sure that they eliminated other possibilities. They went

(24:41):
public with the UH the announcement I think March of
two thousand fourteen, and it was September two thousand fourteen
when other teams came out and said, we think it
might be the presence of space dust that has at
least complicated your findings, if not discredit it. Did them, Yeah,
well yeah, and that's you know, they had opened up

(25:03):
their research to that kind of scientific scrutiny. They were
basically saying, hey, y'all, would you please check this for us?
And so that's and that's the process of science. And
that's really what Jonathan and I talked about in our
previous episode about BICEP. Let's be responsible scientists, folks, And
that's exactly what was going on here, which sometimes leads
to disappointing outcomes, but it's better than UH being wrong

(25:25):
and just sticking to being wrong, and and even even
disproving an outcome can be fascinating and in terms of
research progress moving forward. Right, So, in the case of
BICEP two, we're talking about using telescopes to try and
detect UH the presence of gravitational waves through its effects
on other stuff. But what about just trying to detect
the presence of gravitational waves themselves, not look at how

(25:48):
it's affecting something else, but somehow detecting their presence here
on earth. So let me guess you get two things,
and you put them a kilometer apart, and you watch
them real close to see if they vary by the
width of a thousandth of a proton very close. You
actually have to get at least three things. Uh, and

(26:09):
then you have to watch them very close with lasers.
So this was an idea that was proposed by Ray
weiss Um. He suggested creating a laser interferometer system to
detect any sort of distortion in spacetime. And uh, it's
a really brilliant and elegant solution to a difficult problem. Yeah,

(26:31):
and and he started working on this along with one
of the other people who would become a lead on
the project, Kip Thorne. Kip Thorne, by the way, good name,
good good job. Kip Thorne's parents. Anyway, So they got
their start way back in five when the two of
them happened to share a hotel room at a conference
and wound up just staying up all night chattering about

(26:51):
gravitational waves and feel that's not what's going to happen
to me at south By Southwest, I know anyway, So
so Thorn wound up pulling in Ronald Drever, who's whose
original idea I think it was to use lasers for this,
And the work was originally out of cal Tech because Weiss,
who was at m I T at the time, couldn't

(27:12):
convince M I T the black holes were cool enough
to study sat draw bone. Yeah, he says, by the way,
that M I T has since gotten better. So LEGO
is the pair of observatories that was responsible for detecting
this particular gravitational wave. Have you seen a picture of
one of the LEGO facilities. Yes, they're really cool. Yeah,

(27:33):
they look like giant V or an L. Yeah, depends
on your perspective. I suppose, I guess. I guess so.
I always thought it L not V shaped, But I
understand entirely. Um. The so LEGO, the Laser Interferometer Gravitational
Wave Observatory. Its purpose wasn't to look for gravitational waves

(27:55):
that were responsible during or were a result oather of
cosmic inflation. Uh, they're looking for things that happened after
the Big Bang, things like black holes colliding or these
neutron stars that are in orbit around one another. That's
sort of stuff. Those those sort of gravitational waves. The
presence of gravitational waves that are actively passing through Earth,

(28:18):
that's what these are looking for. And so they're not telescopes.
So the discovery that was announced in February is though
they're both involving gravitational waves, they were sort of fundamentally
different discoveries between that and the one from Yes. So, uh,
some interesting stuff about LEGO. It originally went online in

(28:39):
two thousand two UM and it was the largest project
to ever be funded by the National Science Foundation at
that time. They've spent over the past forty years about
one point one billion dollars in pursuit of this. YEP.
And like I mentioned before, there are two observing stations.
One is in Louisiana and the other is in Washington.
There almost two thousand miles apart. Part I'll talk more

(29:01):
about exactly how far they are a little bit later,
but uh uh, the two stations are necessary to confirm
the presence of gravitational waves. You want that same observation
to be picked up by both facilities within like ten
milliseconds of one another for it to be considered a
potential gravitational wave. Hit right, because otherwise, you know, like

(29:21):
a really big truck passing by could possibly set off
one of the monitors. It could be a seismic activity,
could be anything that would uh jitter the system, if
you will. And if one of them picks it up
and the other one doesn't, then that tells you it
was probably a localized event that gave a false positive
at one observatory. If both of them pick it up

(29:42):
again within ten milliseconds of each other and it's clearly
the same frequency wave, we know it's not a giant
crayfish attack in the Louisiana location. That's right. It's probably
we're probably not John Balaya related at that point unless
they've unless they've colluded, colluding crawfish Washington, right, crawfish collusion.

(30:05):
I gotta find your stash of though medication, because I
want whatever you're on, So you don't let's talk about
so I don't want the cold, that's true. Let's talk
about the the actual facility. So I think of them
as being L shaped because there they are the two
branches or two arms of this facility are at a

(30:27):
ninety degree angle from one another. And maybe because Lego
starts with a nail, that also a bit of priming there. Yeah,
that probably probably helps. You're right, they are at ninety
degree angle, but it's this giant nine degree angle with
arms stretching way out into the into the fields. Yeah.
So there's one that goes under a little road. Did
you see that one? Because like there's like a they

(30:48):
built a little tunnel that the arm goes through and
a road passes over it. And by road, I mean
like a dirt road. I'm not talking like a highway
or something. So each branch of the l each arm
of the is two and a half miles or four
kilometers long, and it's actually a vacuum tube. They pump
out all the air uh in the facility in order
to avoid any kind of absorption, refraction or anything like that,

(31:12):
any any interference that atmosphere could create while you're firing
a laser down this tube. And they actually have a
beam splitter, So they have a single laser that generates
a laser beam hits a beam splitter. The beam splitter
splits the beam as the name would indicate into two.
One goes down one branch, the other one goes down
the other branch. Remember they're perpendicular to each other. H

(31:34):
branch has a series of mirrors in it, so the
lasers bounce off the mirrors and return back to the
crux of the l and there, because they're both from
the same laser, they have the same wavelength, they cancel
one another out. That's where the interferometry comes in. Yes,
so they interfere with one another. They end up creating uh. Well,

(31:57):
because they cancel out, there's no more light that's admitted
through the the that area. And they have a light detector,
so the light detector would detect if any laser light
came through. But as long as everything is going perfectly well,
they cancel each other out. But what if somebody were
to come along and shorten one of those long arms

(32:18):
a little bit, Well, then one laser would travel a
shorter distance than the other laser, and those wavelengths would
be out of alignment, and then you would get some
laser light coming out from that, and the light detector
would pick it up and say, hey, uh, things are hinky.
So when a gravitational wave moves through. What happens is

(32:40):
one arm will start to get longer while another arm
will start to get shorter, and then they alternate because
they're perpendicular to one another, and that's the way the
wave propagates across the facility. That's why you have an
l shape in the first place, because of that ninety
degree perpendicular alignment means one side is going to always
be getting shorter while the the one is getting longer

(33:00):
as a gravitational wave passes through. So that means that
while the wave is passing through, the laser on one
side is traveling a shorter distance than the laser on
the other side, and that ends up creating this mismatch
of wavelengths, and you get the light leaking through. The
light detector picks it up and and and then you've

(33:20):
got data to analyze and you can say, all right,
we've got a hit. Let's find out if our counterparts
at the other observatory also picked this up. And if
they did, then that's a potential gravitational wave. And it's
really elegant approach to detecting something like this, and it's
incredibly precise. So I was watching a video where one

(33:43):
of the engineers was talking about the measurements that are
made by this, and they said, when we talk about
differences in distance, we're talking about the distance of ten
to the minus nineteen power meters small. So again, you
take a take the number ten, take a decimal place,
moveing to the left nineteen times put meter behind it.

(34:05):
That's the distance we're talking about for uh. You know
that has to be measured when one of these gravitational
waves passes through, and they're passing through at a fraction
of a second, so it's incredibly precise, very fast measurement
that has to take place in order for even one
of the observatories to say we got a hit. But

(34:27):
as we mentioned earlier, if only one of them has
a hit, we know that that's probably a false positive.
It's probably a localized event in Louisiana or possibly Washington,
in which case it will make the news. In Louisiana
it's old hat, but in Washington that would be unusual.
Uh So, yeah, because they are so far apart by

(34:51):
specifically it's one thousand between the two or three thousand
two kilometers, that light does take a little longer to
it to one versus the other. It all depends on
what what direction the gravitational wave is coming from. But
there will be a delay. It's a tiny delay again,
less than ten milliseconds, but it's enough of a delay

(35:11):
that if there is that amount of time between the
two and they're picking up the same frequency wave or
same frequency in in this interference, then that suggests that
they found a gravitational wave. And now this kind of
precision means that they had to go through a little
bit of a growth period before they could really get

(35:34):
these things working. Yeah, so here's here's the bad news
they had to give. The facility came online in two
thousand two, by it was clear that the instrumentation they
were using was not going to be precise enough to
pick up gravitational waves. It didn't matter how long they
left it on, it was just not precise enough. And

(35:55):
they had to go back to the drawing board and say,
we're gonna need to upgrade these facilities in order for
them to be capable of detecting this. If in fact,
gravitational waves are a thing, then we're going and we
know that they are, but in order for us to
detect them, we're gonna have to get more precise. So
in twousen LIGO goes offline and there was an international

(36:16):
collaboration that took five years of work to overhaul and
upgrade LIGO until they got advanced LEGO or a. Yeah.
The observatories came back online in September two thou fifteen,
and literally days after turning on, they detected a gravitational wave.

(36:39):
So think about this for a second. The gravitational wave
they detected was from a pair of black holes colliding.
That pair of black holes collided one point three billion
years ago, and that means that the black holes were
by definition one point three billion light years away from Earth,
because again, gravitational waves travel at speed of light. So

(37:02):
one point three billion years ago, one point three billion
light years away, two black holes collided, and the facility
came online just days earlier at you know, on Earth
one point three billion years later. To catch it. That's
like the biggest dartboard you can imagine with the tiniest

(37:25):
bull's eye, and you are miles away and you just
happened to throw it perfectly well, so that catches the
air and flies over and hits that bull's eye. Now granted,
that is pretty amazing, but it's also it's a big universe.
Is a big universe, and people have said that things
like the black holes colliding events of that nature happened
in the universe on the order of about every fifteen minutes,

(37:45):
but it all depends on when and where they happened,
right like if it happened a billion years ago, but
it's four billion light years away, it will be three
billion more years before those gravitational waves make it to Earth.
So because the universe is big, yes, these things happen
all the time, but they don't hit Earth all the time. Yeah,

(38:06):
it was still pretty cool. Yeah, it's really really cool,
so cool that I remember on the day it was
announced one of the people working at Lego said, Yeah,
at first we thought that they might have been testing
the system again, and then we checked and no one
was testing the system and we were like, whoa, it works.
And so that was just one of those like great

(38:29):
fortuitous moments um and yeah, it was very exciting. Of course,
they wanted to take time to confirm it, to validate
the information, which is why we did not hear about
it till February eleven, twenty sixteen, so it was some
time later before we got a chance to find out
what the big discovery was. You know. One of the

(38:50):
cool things to me about this, uh, this observation, they
called it a chirp. Yeah, the thing that they detected
of the gravitational waves. And because it's a wave with
a certain number of number of oscillations per second represented
as hurts, you can actually represent this chirp as sound,
which people have done there. I watched one YouTube video

(39:12):
that was a compilation of different scientists and people who
were involved with the project doing doing little chirps, doing
their little gravitational wave of chirps with their mouths and
devices and stuff. I'm so glad I didn't make one
of those videos, would be so tempted just to do
the whole stupid Rick Roll thing. So the Louisiana Observatory
detected that gravitational wave first, and seven milliseconds later the

(39:35):
Washington Observatory detected it. So that's what when they were
able to say, yes, this does appear to be a
gravitational wave. And they used triangulation to determine where did
this come from, and they determined that it was coming
from the Southern hemisphere skies um and that's what led
them to the conclusion of hey, you know, we this

(39:55):
this is working. We understand where this is coming from
and even what's causing it, which was really cool, But
that wasn't all they were able to tell about it
from the data collected. In fact, they were able to
look at the data they had and say what they
think happened to cause these gravitational waves? Yeah, yeah, Like so,
let's it's hard to explain how huge a moment this is.

(40:20):
It's it's very difficult to kind of put that into words.
But keep in mind that black holes, while we understand
they are a thing, it's not something that we directly observe, right,
But you can't see a black hole, because that's rather
the point. Yeah, they really, you really can't. You can
see the effects off of them and nothing escapes from them.

(40:40):
So yeah, you can. You can see how gas clouds
behave in vicinity of you know, like in the Kessel run,
you see gravitational lensing. Yes, you can see gravitational lensing.
But you know, this is about as strong evidence for
the existence of black holes as you can get without
sending Matthew McConaughey through one um, and certainly the strongest

(41:02):
evidence for binary black holes where you have to colliding
with one another, and the data picked up matched the
calculations that that people had made based upon the knowledge
of general relativity in physics about what would happen with
these two black holes so well that it was phenomenal.
So reality and math were actually agreeing with one another,

(41:24):
which is fantastic. They determined the black holes in question
were pretty pretty big, not like super massive black holes.
We're not talking about the kind that would be at
the center of a galaxy or anything. But one had
twenty nine times the mass of our Sun and the
other thirty six times the Sun's mass, and right before
they collided, they were circling each other two and fifty

(41:44):
times a second UM. During the actual collision, which took
place over about a fifth of a second, they blogged
together and then coalesced into like a smooth sphere in
a process that's called ring down and ring down and
it's and it's this process in which three solar masses

(42:04):
worth of energy was vaporized that that caused the gravitational
waves that we observed um. The resulting black hole, by
the way, is therefore only sixty two times the mass
of the Sun, being that three masses just went. Yeah,
and when you think about energy equals mass times the
speed of light squared, and you think three solar masses vaporized,

(42:29):
that's that's an unimaginably huge amount of energy, right, Like
it's so enormous that I can't even begin to think
about it, so I won't. Yeah, yeah that but but yeah,
if you're wondering how something that was that far away
propagated all the way to Earth, that's why. So again
remarkable that this facility even picked up the signal in

(42:50):
the first place, considering that, you know, it all has
to be timed out where this thing that happened one
point three billion years ago, one point three billion light
years away. Uh, just the observatory coming online when it did,
like all of that is pretty phenomenal stuff. Yeah, and
they almost didn't do the engineering run during which the
signal was found. Uh, just three days prior, the Livingstone

(43:14):
antenna was getting some radio interference and White actually recommended
that they put off the run. But his colleagues they're
were like, Nah, let's let's go ahead. We think it's ready,
so don't worry about it. The nice thing is that
we know eventually this would have worked anyway, but it
was still just just one of those cool stories about
how much came into alignment to allow it to happen

(43:36):
so early. When it came back online, it's a great
story for science. Well. One of the things that I
have definitely heard reported from some of the people involved
in the project is that the signal was much stronger
than they expected it to be. Like they they were
able to see the signal clearly in the data with
the naked eye just looking at the data. They're like, oh,

(43:58):
there it is. When what they thought they we're gonna
have to do was like run a you know, computational
analysis across all the data and compare it to uh
to random noise generated as a sort of cross reference,
and see if it maybe was a gravitational wave. But no,
it was just obvious, which is amazing. And so this

(44:19):
is kind of wrapping up our initial discussion about gravitational waves.
In our next episode, we're gonna talk a little bit
more about the specifics of what Lego found. I'm gonna
talk a little bit about some angular momentum. In that episode,
we'll also talk about what does this mean and the
rise of a new type of astronomy, gravitational astronomy, which
is literally in its infancy right now. Uh and what

(44:43):
could this possibly mean for the future? That will be
in our next episode. Guys, if you have suggestions for
future episodes of Forward Thinking, I recommend you write us
and tell us because if you've been putting messages and
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Stop it and they're not getting to us. So right,
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(45:07):
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(45:34):
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