Daniel and Kelly’s Extraordinary Universe - Can a gravitational wave pass through a black hole?
Episode Date: August 16, 2022Daniel and Jorge talk about what happens when one superstar of physics slams into another.See omnystudio.com/listener for privacy information....
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hey horay which superhero throws the hardest hunch
that's a hard one it's uh maybe either the hulk or superman all right and then which superhero is
the best at taking a punch.
Either the Hulk or Superman.
I thought you might say the guy made at rubber.
But then the obvious question is, what happens when Superman punches the Hulk?
Oh, man, you're making my comic book fan brain burst in delight right now.
I think mostly Hulk just gets mad.
You know, that's what he does.
A shower of bricks.
It doesn't blow up the multiverse.
Yeah, it does.
but it bursts into a shower of money for Marvel and DC.
Money flowing from our wallets to theirs.
And the light going into my brain.
Hi, I'm Jorge. I'm a cartoonist and the co-author of Frequently Asked Questions about the universe.
Hi, I'm Daniel. I'm a particle physicist.
and a professor at UC Irvine, and I always fast forward through the punching scenes in superhero
movies. Always? Really? What if you're at the theater? What do you do? Take a quick nap?
Then I run upstairs to the projection booth, force my way in and fast forward those scenes.
I see. You get arrested. It's basically what you do. No, I tune them out because in the end,
none of it really matters, you know, A punches B, B punches A. In the end, they're still around.
There's no consequences to the punching.
Right, right. Yeah.
It's kind of a cliche, I guess, in superhero movies and sci-fi movies.
It always ends in a mono-a-mano, right?
Exactly.
More houses get destroyed.
Some cars get flipped, but nobody really gets hurt.
Well, sometimes.
Sometimes the hero dies.
Sometimes a hero dies, but is it ever because of punching?
And usually they come back in the sequel, so.
But anyways, welcome to our podcast, Daniel and Jorge,
Explain the Universe, a production of IHeard Radio.
In which we try to punch through your confusion about the nature of our universe.
We try to knock down the walls that prevent you from understanding how this incredible cosmos has come together,
how it's woven at the very smallest scale, how it works at the very largest scales,
and how the amazing emergent properties that are me and you and our curiosity come together to make this a wonderful universe to explore.
That's right, because there is something about human nature that makes us mad when we don't understand how things work out there in the cosmos,
and it makes us turn green to think about that maybe there are aliens out there who do.
do understand what's going on or maybe just future humans will understand and here we are trapped
in antiquity trapped in the ancient past where humans are so clueless about the nature of our
universe we don't know the answer to basic questions about how it's put together how old is the
universe how long will the universe survive what's it made out of in the end and how do all the
pieces of it work after all why are we so ignorant oh man you're jealous of future physicists
that's that's interesting do you put little notes for them in your papers
Like, I hope this helps you, eye roll.
Every paper is just a note to future physicists, right?
That's exactly what it is.
But yes, I am jealous of future physicists.
I wish that I could live forever so that I could understand what they figure out.
Sometimes I dream about taking a time machine and going forward just to steal like a child's astronomy book from the year 3,000 or 10,000.
So I could figure out what it is that humanity has unraveled in the future.
I think you're assuming they're going to get it right.
What if they think of a, you know, a cost.
mathematically wrong. And those children's books are all, you know, made up.
I think that science always gets it wrong, but it sort of gently drifts towards more and more
right. So I don't know that the future humanity will have final answers, but I think they will
have unraveled more mysteries that will have deeper questions, at least than the ones that we have.
I see. The long arc of science bends towards being annoyingly right.
It naps towards the truth, yes.
but it is a wonderful universe full of amazing and incredible things
things that seem unstoppable sometimes
and things that seem to travel across billions of light years
to get where they will always get to go
and it's a universe filled with things that we want to understand
we can't go out and visit all of these incredible things in the universe
i'm not going to take a trip to orbit a black hole i'm not going to surf along a gravitational
wave i'm not going to walk along the surface of a neutron star but we can still do thought experiments
we can imagine what might happen in crazy combinations of these events.
What happens if you bank a neutron star off another one and into a black hole?
These are fun games to play in your mind and they can also teach us things about the universe.
Right.
And if you're deluded enough, the mind games are just as good as the real thing, right?
Surfing a neutron star in your head is in your daydream.
It could be just as good as doing it.
Well, as an experimentalist, I have to say that actually collecting data has no substitute
because the universe is filled with surprises.
And often we think we know what will happen in these situations.
And the universe says, oops, sorry, silly human, we're going with secret option C.
But to prepare for those things, just to sort of like test our understanding of concepts,
we can try to bring together crazy, intense ideas that we have in our minds and wonder, like,
what would happen if they bounced off each other?
What would happen if I sent A against B?
What would happen in these various scenarios?
It's like tests our understanding.
Wait, is this whole episode about the Hulk punching Superman?
Are we actually doing this?
We're talking about the physics Hulk punching the physics Superman.
I thought you were going to say the math Superman.
That would be a matchup for the ages.
But it's sort of similar.
Like if you ask questions about what happens when Hulk fights Superman,
then it makes you think carefully about those extremes you never imagined before.
Like who really is stronger?
Like how hard of a punch can the Hulk really take?
Does he have bones that can get broken?
I mean, is it really impossible for Superman to break Hulk?
I think these are deep questions that, you know, the writers of that universe then have to figure
out. In our universe, it makes us wonder about the mathematics of extreme situations. And those
are places where we can really learn about the fundamental nature. These objects were tossing
against each other. Yeah, because I guess thinking about the extremes really kind of pushes your
thinking about these things and really kind of pushes your theories to maybe the breaking point,
right? Because there are some questions you can ask that maybe don't have an answer. Exactly. And
they can reveal inconsistencies. And we hear our listeners doing this kind of
of stuff all the time. You know, they're wondering about like, what if I throw this into a black hole?
What if I throw that into a black hole? What do I throw another black hole into another black hole?
Right? And these are the games they're playing in their minds when they're just seeking to understand.
What are the rules? And the way to figure out what the rules are, are to push them, are to break them.
Every parent knows that's true. And so today on the podcast, we'll be tackling the question.
Can a gravitational wave pass through a black hole?
Now, Daniel, I'm disappointed.
I would have preferred the question to be,
can a gravitational wave punch a black hole?
That might get us more clicks.
Well, I guess you can ask the question
is, can a gravitational wave punch a black hole
without getting slurped in?
Oh, well.
No, I want to see him fight.
I want to see him go mono-a-mano for 20 minutes
at the end of the movie.
But it is a question that's fun to think about
because black holes are famously impenchables,
can survive anything.
You can even throw another black hole into it.
And gravitational waves are sort of famous
for being able to pass through almost anything
because there are ripples in space and time itself.
And so it's our version of Hulk versus Superman.
Yeah.
It's almost like this, that famous question,
what happens when an unstoppable force meets an unmovable object?
Does this one of these like questions
that just go to infinity, sort of?
Well, you know, in philosophy, you can make up any kind of thing you want and pit it against something else.
And you're making up the rules also, so it doesn't matter.
But here in our universe, we think there are real rules and experiments should have outcomes.
Like, this is something which we think happens in the universe.
You know, gravitational waves do hit black holes.
And so there is an answer.
Either they make it out the other side or they get slurped in.
And so then the question is like, what do we think is going to happen?
Does our understanding of these things allow us to predict the result and then could we eventually go out and measure it?
Yeah, because actually this thing is happening right like right now all the time, probably, right?
I mean, there are, you know, as far as we know, millions of black holes out there probably.
And there are definitely gravitational waves going around all the time, all around this.
Yeah, we are bathed in very, very gentle gravitational waves all the time.
And so this in principle should be happening constantly.
So it's something we should figure out eventually.
Yeah.
And also, can a black hole surf a gravitational wave?
Or is that the next episode?
That's the sequel, yes, black hole surfer.
Yeah, one of them dies, but then they come back in the sequel.
Well, as usual, we were wondering how many people had thought about this impossible
or maybe incredible question of what happens when a gravitational wave meets a black hole?
And so as usual, Daniel went out there to ask people on the internet.
And so if you'd like to hear questions that might blow your mind or at least blow up your
understanding of physics. Please don't be shy. Write to me to questions at danielandhorpe.com,
and we can all enjoy hearing your answers on the podcast. Think about it for a second. Do you think
a gravitational wave can pass through a black hole? Here's what people had to say. I don't think so
because a black hole can suck in pretty much anything. Okay, but a gravitational wave is just the change
in the curvature of space
as it propagates
with distance from a
source of gravity
at the speed of light
I guess they could pass around
a black hole
yeah
maybe
and no and through a black hole
because you would be
really the world
the universe is trapdoor
yeah because the gravity
that you are
Feeling in a gravitational wave is based off the distance of the yourself from that object.
So if there was a black hole in between, yeah, it shouldn't affect it at all.
I would say that gravitational waves do because there is some form holding it all together.
So I would say, well, I mean, assuming that Hawking's radiation can see,
split. Particles can split and enter it. Yeah, maybe gravity can. I don't know. Prove me wrong.
Yes, I believe gravitational waves would pass through a black hole. More specifically, I think
they would pass around a black hole. I think a black hole would fundamentally change the
gravitational wave in the same way that an object would change a radar signal. Maybe the gravitational
wave would be able to give us an intimate look at the structure, shape, other factors,
that we are unaware of, of a black hole?
I'm not sure because, well, a black hole is as infinite gravity.
And I'm not sure if they can pass through a black hole.
I think they will be sucked in.
That would be my answer for that question.
Now, I want to say, no, they can't,
because surely nothing can pass through a black hole.
Nothing can go through the event horizon
and through the singularity and then come out the other end.
back into space. So no. No, I'm going to say no, they can't do. Surely they would be swallowed up
within the black hole and, you know, kind of due to the massive curvature of space itself
and gravitational waves are, you know, kind of integrated with the very fabric of space. Then they would be
directed only in one direction like light is and all information that is to the singularity.
So no, gravitational waves can't pass through a black hole.
I believe gravitational waves can pass through black holes, although I'm convinced
that they will be distorted as they go through.
They will also distort the black hole while they are passing through, because gravitational
waves distort space and time, and the black hole is part of the space and time,
although almost it is on universe, but the gravitational wave
will also be distorted by the black hole.
Black holes attract each other, so I guess not.
First of all, gravitational waves, they are these ripples in space and time fabric.
And also a black hole distorts space and time.
And when these two interact, most likely these waves,
won't get to affect the object, the black hole itself, its core.
I don't know if gravitational waves will pass through a black hole, but I do think that they do
because we are able to know where there are black holes and when they shock with one
another because of the gravitational waves. So I'm guessing that they do pass through it.
They don't go inside it, but they go around it, yes.
I think any part of the wave that interacts with the event horizon is going to get trapped inside
because all directions point towards the singularity once you're inside the event horizon.
But I think any wave is outside of that might get bent around the black hole around the event horizon
and actually get like gravitationally focused like gravitational lensing.
All right.
It seems like people are cheering for Superman here in this case for the black hole.
Nobody thinks the Hulk will survive.
No, there's some people there that say it'll pass through it or at least around.
it, you know, in the end, these things are both curvatures in space.
So it's tricky stuff to think about.
All right.
Well, let's jump in and let's maybe tackle one of these combatants one at a time.
And let's start with a black hole.
Daniel, what's a good way to define a black hole?
So you might think of a black hole is something really weird, very strange in our universe,
something that's hard to grapple with.
But what a black hole looks like depends a lot on sort of how close you are to it.
And from far away, a black hole just looks like anything else that has mass, right?
Black hole is a massive object in space, which means that it bends space.
And so that curved space then causes gravity.
So you can be in an orbit around a black hole, the same way you can be in the orbit around the sun or an orbit around the Earth.
Far away from any object, its gravity is the same as like a point particle placed at the center of mass.
And that's true for a black hole or for the sun or for any weird, like huge unicorn-shaped rock, for example.
And so far away from a black hole, there's no difference.
The difference is that a black hole is very, very dense.
So now take all the mass that's in the sun, for example, compact it down to a very, very small space.
Now you can get much closer to the center of mass than you could before.
When it comes to the sun, you can only get to the surface of the sun, right?
If you dig into the sun, then the gravity from the sun actually starts to decrease.
But with a black hole, you can get closer and closer and closer to that point mass because general relativity,
tells us that that's exactly what's there, a point mass with all of that stuff wrapped into a
tiny little volume. So the gravitational curvature becomes really, really strong, so powerful
that there's an event horizon beyond which nothing can escape. No information can leak out past
the event horizon. Right. That's something that I think is kind of interesting about black holes.
It's that, as you said, it's just a lot of mass compacted really tightly. And it's not like as you're
squeezing this mass and suddenly something explodes or something pops or a hole is punched.
through the space stem of the universe.
It's almost like a gradual process.
There's nothing exciting happens as you squeeze down this mass.
Yeah, that's a really interesting question to imagine, like,
taking a star and compacting it down gradually,
when does the black hole actually form?
And so a black hole is defined by the presence of the event horizon,
this region past which you cannot escape.
And remember, the event horizon is not like, you know,
there's no flashing lights or firewalls or anything crazy there.
It's just sort of like a location.
It's a distance from this center of mass beyond which every future ends up at the center.
And to actually know where the event horizon is, you have to know the whole future history of this object.
It's the place past which no test particles ever escape.
So you have to know sort of like the future history of every test particle you shoot at this thing to know where the event horizon actually is.
But we can calculate it.
We can say if you have a certain mass within a certain radius, then you get an event horizon.
So now take the sun and start squeezing it down smaller and smaller and smaller.
At some point, it's going to pass that threshold where you have enough mass within a radius and then you get that event horizon.
Right.
Like as I'm squeezing the sun, it's going to look like a sun that's just getting smaller and smaller and smaller, maybe brighter.
But then at some point, it's just going to blink turn black, right?
It's not like it's going to send out shockways or the universe is going to shake.
It'll just like blink, turn black.
Yeah.
And actually, it's going to gradually fade to black because as it gets more,
more gravitational curvature, the light that's coming off of that sun is going to get more
more gravitationally redshifted. So if you squeeze this object down, it gets redder and
redder and redder and eventually black. So it's a gradual process. There's no like crazy
fireworks. Interesting. Yeah. Pretty cool. And the other thing about black holes is that they're
hungry. They can, anything you throw into them into this event horizon supposedly can never come out.
Yeah. It's the most fascinating aspect of these black holes that they eat anything. Right. Anything with
energy that enters the black hole just grows its energy, just makes it stronger, right?
So people ask me like, what happens to be throwing nuclear weapon into a black hole, as if a
black hole is like some structure that you could explode, if you like push on it internally with
enough force. And if you let this nuclear bomb go inside and then blow up, you could somehow
explode the event horizon from the inside. Remember, the event horizon is just there because
of the strength of gravity. And as you add more energy, even an explode,
nuclear bomb, you are just curving space more, which makes it stronger gravitationally,
right? So there's nothing you can do to a black hole to weaken it. Anything you do that
adds energy makes it stronger. Right. And we talked about last time what happens, even if you
put in a white hole into a black hole, right? The black hole sort of wins. Yeah, we don't know
that white holes are real, but theoretically, a black hole will turn that white hole into another
black hole and then gobble it and you get some big black hole. And we talked to
the program recently also about exactly what happens when two black holes merge how their event
horizons come together you get for a moment this weird peanut shaped event horizon and then it turns
into a new larger black hole with a spherical event horizon but it's super fascinating another thing
that people ask about in terms of like growing black holes is how you actually see it happen like
if you throw a banana into a black hole it sort of like falls towards the black hole but then
time slows down because there's gravitational time dilation near the surface. So you never actually
see the banana fall into the black hole. And people wonder about like, well, how do we actually
see black holes growing if things freeze before they fall into them? And so the answer is to think
again about the gravitational energy of the black hole. Right. As you throw this banana into the black
hole, it's not like it needs to pass the event horizon some magical marker before the black hole
officially has eaten it. You have the banana in the black hole and they're now part of a larger
gravitational system. So the banana is contributing to the gravitational energy of the black hole
before it crosses the event horizon. Another way to think about that is that the event horizon is growing
outwards to meet the banana. They never actually meet. You have to wait till time equals infinity
for them to meet. But this event horizon is getting pulled out by the banana's mass. So they never
actually cross. And if the banana was the last thing anybody ever threw into this black hole,
You're right, it wouldn't actually fall in.
But then if somebody else comes along and throws a donut towards the black hole,
that donut pulls the event horizon out also past the banana.
So now the banana has fallen in.
So the last thing anybody ever throws into a black hole never actually falls in.
But everything else that was thrown in before does pass the event horizon.
So that's a useful way to think about like how the energy of the black hole is growing.
Right.
It's almost like the black hole grows and eats the banana, which is always a good idea,
I mean, it doesn't have any choice, right?
The black holes just eat whatever you throw at it.
It might not like bananas.
It might be really grumpy that somebody keeps throwing bananas in there,
but it's got no options.
I guess it's not going to let it slide.
Well, what about the idea that, you know,
sometimes black holes might be connected through a wormhole to a white hole, right?
Which would be spewing out energy instead of sucking in energy.
And that energy is coming from the black holes.
Is it possible for a black hole to kind of leak out?
or, you know, shrink because it's leaking through a white hole somewhere else?
Yeah, there are ways that black holes can shrink.
One of them that's on sort of stronger theoretical footing that we've never seen
it before is hawking radiation.
We know that quantum effects near the edge of the black hole,
and the black hole having a non-zero temperature suggests that it should be radiating away
energy, which shrinks the mass of the black hole.
So the key concept there again is the size of the black hole,
the radius of the event horizon depends on the total energy there.
So if you take away energy, the black hole shrinks.
And another option, though even on much worse footing theoretically, is this question of white holes.
It is possible that black holes and white holes sort of share a singularity.
They're connected by a wormhole.
But this is like speculation upon speculation.
But yes, absolutely, mass could then move through that wormhole, come out the other side of the
white hole and shrink the size of that black hole.
And what would happen to the banana that was at the border that got absorbed?
Would it then have a chance to escape the black hole?
Once it's inside the event horizon, I think.
I think the only way for it to get out would be through the wormhole and out the white hole.
But what if the, you know, Event Horizon shrinks?
I guess the banana would fall in a little bit too, right?
Exactly, yeah.
Banana would fall in with it.
So the moral of the story is if you drop your banana into a black hole, let it go, because man, it's gone.
Well, you could go to the nearest white hole and maybe it'll come out.
That's right.
One particle at a time or something.
That's right.
Go near a white hole and open your mouth and see if it tastes like banana.
Or donuts, if you're lucky.
Maybe banana donuts.
There you go.
It's the ultimate smoothie maker.
Just throw all of your ingredients into the black hole and go stand by the white hole and see what comes out.
No, Danny.
What happens if I take a banana and put it through a donut?
I think you just invented the latest pop food craze.
A bono nut.
A bono nut.
All right.
Well, that's a black hole.
It's full of interesting mysteries and amazing effects and physics that are going on and that we are starting to understand.
But then there's another fundamental and monumental thing in the universe called a gravitational wave.
And so let's get into what that is and what's going to happen when the two meet at the same place.
But first, let's take a quick break.
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We're talking about fun fan fiction, I guess.
You know, we're conjuring imaginary meetups in the universe.
Physics fan fiction, exactly.
It's not quite fan fiction because this thing is happening.
This question is happening all over the universe, probably.
Gravitational waves are passing through all of space and time,
and there are black holes in the universe.
So somewhere out there right now, there's probably a gravitational wave hitting a black hole.
Almost certainly.
And the universe has to decide what happens.
happens, right? That's the amazing thing about experiments. You set something up and the universe
has to have an outcome. It can't be like, I don't know, you figure it out, right? It's always
an answer to experiments. The universe can't pass the buck. Exactly. Can't go pass. I'm not
sure about this one. They wrote themselves into a corner and now they got to figure out how the movie
ends, right? Exactly. Maybe that's when the universe invents time travel so it can retcon
its own history. Yeah, yeah. Or maybe that's when it invents event horizon. So you
you can never know what's going on.
Yeah.
Maybe that's just the plot hole fixer for the universe.
It is the ultimate plot hole.
Plot hole's nice.
But, you know, it's sort of an interesting statement in philosophy, this assumption that the
universe is in the end following laws, that the laws are predictable, that we can figure
them out, and that the universe is bound by them, right?
That every physical effect has a physical cause.
And that means that any physical situation you set up must be predictable by those physical
laws and so something's got to happen right something's got to happen is that the mantra for physics
something's got to happen what happens if i collide a bazillion particles together something's
going to happen yeah in physics it goes by the name of unitarity it says that the wave function when you
integrate it has to be one which means something has got to happen the probability distribution has
to go somewhere it can't be like you do this experiment and nothing happens or the particles just
disappear right quantum information flows through the universe it
can't be deleted, which means that it's got to go somewhere. That's the theory at least,
or you think that's what's going to happen or it has to happen, right? It could be that maybe
there are places where things break down, right? It certainly could be. We definitely don't
understand quantum mechanics that deeply. And we could also be philosophically wrong about the
universe. This assumption that every experiment has an outcome that makes sense and is reproducible,
you know, that's just an assumption. It's been working really well so far, but we don't really
know why even that is. So yeah, if you want to question the foundations, then we can go all the way
down. Yeah. I mean, we used to think that energy is always conserved, but it turns out that energy
is not always conserved in the whole universe. Yeah, exactly. Physics has been upending the apple card
for hundreds of years. All right. Well, we talked about black holes for a while, and now the
question is what happens when it hits a gravitational wave, which is something that's pretty
cool. So let's step through it and talk about what is a gravitational wave. A gravitational
wave is a combination of something that's very familiar to us, a wave, an update in information,
and something that's very weird, right, which is gravity.
So you can think about gravitational waves
is sort of like a way to communicate gravitational information.
You know, like you are in space and there's gravity around you.
There's a gravitational field around you.
Imagine for a moment that that's not changing.
It's the same.
You know, whatever's creating that gravitational field is fixed in place and not changing.
So then there's no gravitational information.
There's no updates, right?
Every moment, your gravitational force is the same.
But what if that does change?
What if somebody, for example, deletes the sun, which is the source of your gravity?
Then how does that information propagate through the universe?
Newton said that it was instantaneous, that if you deleted the sun, gravity far away from the sun would instantly change, right?
It would go to zero instantly.
Einstein told us that that's not true, that gravitational information is information,
and the gravitational field takes time to update.
And that update, the change in the gravitational field propagating through space,
because the source of the gravitational field has changed,
that is a gravitational wave.
It's an update to the gravitational field.
Right.
It's kind of like if he asks,
like, what happens if someone shakes the sun or the sun like wiggles?
Like, do you feel those wiggles right away?
Or do you have to wait a while for those wiggles to get to you?
And I guess, you know, the idea is also that if you're closer to the sun,
you're going to feel those wiggles first.
So there's sort of like a propagation, like a ripple of those wiggles that comes out of the sun.
Exactly. And those ripples travel at the speed of light.
So these gravitational waves, this information that propagates through the gravitational field,
which really are in the end ripples in the curvature of space time.
Because gravity, remember, not really a force.
It's just the effect of the curvature of space time,
which is invisible to us except for this weird effect that it has on the path of particles.
And so, as you say, if you wiggle the sun, for example,
that should change the curvature of space.
And that causes a gravitational wave.
with frequency proportional to the wiggling,
which is totally analogous to like how you create electromagnetic waves.
You take an electron, which has an electric field all through space,
and you wiggle it in an antenna, for example, at a certain frequency,
then it shakes the electromagnetic field.
It changes that field, which is emanating out from the electron.
And that shake in the electromagnetic field is a photon.
It's a wiggle in the electromagnetic field.
And so in the same way, if you wiggle the source of gravity like the sun,
then you get wiggles in the gravitational field.
And that's a gravitational wave.
Right.
Well, I wonder if you can get into a little bit of a rabbit hole here,
thinking about what simultaneity is and whether or not you can actually measure a wave moving
or to claim that it didn't happen at the same time because, you know, as we talked about
in the last episode, it's kind of hard to synchronize clocks and make sure that the wave,
you didn't feel that gravitational wave at the same time that it was generated.
I mean, simultaneously is complicated.
And it's not trivial or intuitive.
We can't think about a clock all the way through space and imagine that everybody agrees on the
order of events.
But that doesn't mean that we can't talk about it from our frame and say like, what do we
think happen first?
What do we see?
And in the case of gravitational waves, we can actually measure their propagation through
space.
So we've seen gravitational waves because we have detectors on Earth that are sensitive to these
things.
And we have multiple detectors.
And we can see them propagating through space because they hit one detector before
another detector. And this is the way we can actually get directional information about gravitational
waves. We can say, oh, look, it hit in New Orleans before it hit in Washington and in Italy. Therefore,
it must have been going in that direction. And so that helps us triangulate the source of the
gravitational wave because we can actually see it arriving at different places at different times,
which shows you that it really is flowing through space at a certain speed.
Cool. Yeah, I guess if you measure it first in one place and then later in the
other one then it's moving it's moving through space yeah and we can see the same wiggle right
it's like each of these things have a very characteristic wiggle usually formed by the black hole merger
or neutron star murder that formed it so we can tell that it's the same gravitational wave now as you
said earlier gravitational waves are everywhere in space because every acceleration generates them
when you run to the kitchen to get a banana and you've accelerated then you are creating little
gravitational waves but remember that gravity is super duper weak and so the gravity from your body or from
your banana is really, really weak.
So while it does generate gravitational waves anytime anything
accelerates, those are basically impossible to see.
That's why when we look for gravitational waves,
we usually look for ones generated by incredibly massive objects,
like huge stars or like black holes with tens of times the mass of the sun,
because you need a lot of gravity to generate gravitational waves that we can actually see.
Right.
Well, it sort of depends how many bananas you eat too, right, though, right?
Like if you eat enough bananas, you will technically,
generate a big gravitational wave. Exactly. If you just throw everything in your fridge into the black hole and then
eat it as a smoothie out the other side on the white hole, it's going to taste pretty funny and you're going to get
pretty heavy. Now I'm confused. But it's kind of interesting to think that everything does generate a
gravitational wave, right? Like, as you said, if I jump up and down or move my arm, I am generating
gravitational wave. And in fact, that gravitational wave that I'm generating with my arm, even though
it's really small and weak, it is sort of propagating to the universe. And technically it is going to, you know,
go out to the edge of the universe, right?
It will in the same way that if you, like, you know, stand at night and shine your
flashlight up at the sky and turn it on and off, you're sending photons which could travel
forever, right, billions or trillions of years until they hit some alien eyeball on some other
planet or never, right?
They could just go forever.
In that same way, everything that we throw out into space could go forever.
Remember, though, that your gravitational waves, they start off really weak and they get weaker
with distance because the energy that's in the gravitational waves gets spread.
spread out over a larger and larger sphere as they get further and further from you.
So the strength of these gravitational waves goes like one over the distance squared,
just like all other kinds of radiation.
So they start off already weak and then twice as far away,
they are four times weaker and 10 times as far away.
They are 100 times weaker and that gets pretty stiff pretty quick.
Right.
But I guess as far as we know, gravitational waves are not sort of quantum, right?
So there's no minimum size to these waves.
Is there right?
So technically the waves I'm making with my arm right now are going to travel throughout the entire universe.
Well, we don't know. It's a great question. People might be wondering, because we compared earlier gravitational waves to photons.
And gravitational waves are classical objects, meaning that we don't know if they are made at the small scale out of some quantum unit.
So a better analogy is probably not the photon, but like a big pulse of light, which might be made out of many photons.
So gravitational waves might be classical objects, meaning it might be smooth.
than continuous and as you say, they could get as small as you like. Or they might be made out
of gravitons, like the quantum unit of gravity. But we just don't know because we don't have a
quantum theory of gravity. So we can see gravitational waves without knowing whether or not there
are even are gravitons. Gravitons, if they exist, would be like tiny little pieces of a gravitational
wave. Each one might have like 10 to the 16 gravitons. Yeah. You know, I think this sort of gets down to
the question of the episode, because
you know, when you shoot a flashlight out into the
sky, you're sending out photons and technically
those photons could go to the
ends of the universe and keep going, but
more likely they're going to, you know, hit a
dust particle and bounce or get
absorbed or
something happens to them when they hit something
else. And also, if you think about the analogy
of like a ripple in a lake, that
wave, that water wave, loses energy
as it goes from the friction of the
molecules, but gravitation
ways are different, right? They sort of
don't actually hit things when they hit things.
Yeah, gravitational waves are incredible because they, in principle, pass right through stuff.
You know, you have some like huge gas cloud.
Photons might not be able to penetrate it because they've got to interact with all the stuff
in the gas cloud.
They get absorbed by it or they get reflected by it, whatever.
Gravitational waves are ripples in the underlying substrate of space itself, right?
So they pass right through these gas clouds.
They can go basically through anything.
They can go through neutrons.
stars, right? Some of the densest non-black hole material in the universe. And so in that sense,
they're an incredible way to see the universe because they can pass through stuff that is
otherwise totally opaque to us. So they're incredible, like new kind of eyeball that like,
you know, excuse the analogy, but x-rays everything in the universe. One thing we're really excited
about is using them to see even further back in time. You know, the earliest light that we can see
from the universe comes from the cosmic microwave background radiation, which is from the first
moment when the universe was transparent to photons, like 380,000 years after the Big Bang,
the universe went from opaque plasma to transparent gas so the photons could fly free.
We can't see before that with photons, but we might be able to see before that with gravitational
waves. People are looking for gravitational waves created during the Big Bang that we might even be
able to see. Yeah, that's pretty amazing. And so I guess what happens then if a gravitational wave
hits something solid like a planet? Like it just totally goes through it or does it lose a little
bit of energy? Does some of the gravitational wave get absorbed or does it really, you know,
nothing happens to the wave? It's a great question. So what happens to the stuff that's in space
when a gravitational wave passes through it? You're right. This is critical to understand when we get
into the question of what happens when it hits a black hole. So,
one sense, things do happen, right? Like, we can see gravitational waves because they do have an
effect on our physical systems. Like, the way that we detect them is that we measure distances changing.
Remember, gravitational wave is a change in the curvature of space. The curvature of space
really is another way of saying, like, how far apart are different parts of space to each other?
You know, you bend space by changing the intrinsic curvature of space by saying, like, this piece
of space is now closer than that one. And so the natural path for a photon is what looks
like a curve. It's really a straight line through this bent space. And so the way we detect them
is by having these laser beams, which are shooting back and forth between mirrors, constantly
measuring the distance between those mirrors. And so we see the gravitational wave because it
changes the distance between those mirrors because it actually shrinks the space between them.
We can measure that because we know the speed of light and it's bouncing back. We can time
essentially the distance between the speed of light. It's a bit more complicated because the measurement
has to be very precise. So they use interferometry. We have a whole episode and video.
about that. But basically, it does shrink the stuff in space so you can measure those distances.
But then it shrinks it back, right? So it squeezes it and then it comes back. So from that sense,
no energy is lost, right? Space is rippled, but then the gravitational wave just passes on.
Right. It's sort of like I was thinking, it's sort of like a slinky. If you take a slinky and you
stretch it out and then you sort of pinch one bit of it and then let go, it's going to, that
pinching is sort of going to propagate, right? It's going to squeeze the little bit of slinky next to
it, but then it's going to stretch out and then that's going to squeeze the little bit of slinky
next to that one. And so like space, you see this kind of squeezing and stretching of space.
But as you say, I think that's really kind of the question is like, is any energy going into
moving and squeezing the stuff that's in this space, right? Because you're technically sort of
accelerating it, right? Like if a gravitation waste passes through the earth, you're squeezing all of
the earth molecules together a little bit and then spreading them out a little bit. Doesn't it take
energy to squeeze them and also to unsqueathes them.
So this is a topic of great debate in the 1950s about whether gravitational waves can actually
deposit energy into matter or whether they just sort of like pass through taking their energy
with them.
And Feynman came up with a great way of thinking about this.
It's called the sticky bead example.
And so imagine like some rod and this rod is like really tightly held together with atomic
forces.
And then you have beads on that rod that can slide up and down.
And so as the gravitational wave comes through, the rod is sort of like held to a
fixed length by the atomic forces and the beads will be slid back and forth by the gravitational
wave because the relative distances between the beads will change but they'll slide back and forth and
they'll end up in the same position because there's no friction but then if you add friction to it
then what happens as they slide back and forth on the rod is that they do heat up the rod and that
takes some of the energy from the gravitational wave the answer from this thought experiment is that the
gravitational wave can deposit some energy in this matter as it's passing through if it generates
friction between stuff. If some stuff resist the motion of the gravitational wave and other stuff
doesn't, so you get friction sliding between them. Right. But I guess wouldn't everything have
friction to them, right? Like nothing is quite held together by perfect spring. Exactly. So there's
nothing that's really frictionless. So everything has some internal friction. Even those mirrors in
LIGO, right, where they're measuring these gravitational waves, they're held up on the
wall and the wall is part of a larger cavity and his internal friction in that whole setup.
And so the answer in the end is that gravitational waves do deposit energy and stuff as they
pass through. And so they do get fainter and fainter as they propagate out through the
universe. They do get it sort of absorbed a little bit. But I guess I'm thinking, you know,
kind of like a wave in the ocean or at the beach, you know, a wave is not just like in one
spot. It's a long piece of the coast, right? Like a wave is really long. And if it goes through
me, I might block a little bit of it where I am, but the whole wave is still going to keep
going. And in fact, it sort of almost reassembles itself after it hits me. A wave is a very
long object. And in this case, a gravitational wave is more like a sphere, right? From a black
hole merger, gravitational waves emit in every direction. And so if you put Jorge just in one
direction, he will get heated up by the gravitational wave, but the rest of it won't be impacted
at all. And you can calculate what would happen after it hits you, right? The wave sort of reforms,
but it's a little bit distorted on the other side.
Well, that's a gravitational wave.
They're pretty interesting.
They are not quite unstoppable, right?
You can't stop them if you have enough mass, although they're so large that maybe they might ignore an obstacle that is in their path.
And so let's get into the ultimate question of what happens when a gravitational wave meets a black hole, which one will get matter?
But far as, let's take a quick break.
LaGuardia Airport.
The holiday rush.
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Then, at 6.33 p.m., everything changed.
There's been a bombing at the TWA terminal.
Apparently, the explosion actually impelled metal glass.
The injured were being loaded into ambulances.
Just a chaotic, chaotic scene.
In its wake, a new kind of enemy emerge.
And it was here to stay.
Terrorism.
Law and order criminal justice system is back.
In season two, we're turning our focus to a threat that hides in plain sight.
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Listen to the new season of Law and Order Criminal Justice System on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.
Have you ever wished for a change but weren't sure how to make it?
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I'm Emily Tish Sussman, and on she pivots, I dive into the inspiring pivots of women who have taken big leaps in their lives and careers.
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And that's when I was like, I got to go.
I don't know how, but that kicked off the pivot of how to make the trend.
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I don't write songs. God write songs. I take dictation.
I didn't even know you've been a pastor.
for over 10 years.
I think culture is any space that you live in that develops you.
On a recent episode of Culture Raises Us podcast,
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Grammy-winning producer, pastor, and music executive
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This is like watching Michael Jackson talk about Thurley before it happened.
Was there a particular moment where you realized
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From Mary Mary to Jennifer Hudson, we get into the soul of the music and the purpose that drives it.
Listen to Culture raises us on the iHeart Radio app, Apple Podcasts, or wherever you get your podcasts.
All right, we're talking about...
about the ultimate meetup of what happens when a gravitational wave meets a black hole.
And I guess, first of all, Daniel, is it a friendly meeting?
Like, are they looking forward to seeing hanging out?
Or is this a fight to be had?
I think black holes in gravitational waves are just sort of like screaming through the universe.
So I think they're just going to get matter and matter about the matter.
And I guess are they going to turn red or green?
And are there gamma rays involved?
Because, right, black holes are full of gamma rays?
Yeah. Well, I think that as they curve space, they tend to redshift things. So they're going to get redder and redder, right? Which is the color of anger in comic books, isn't it?
All right. Well, that's the ultimate comic book question here. What happens when a gravitational wave meets a black hole? And what happens, Daniel? Does it crack the black hole? Does the gravitational wave get sucked in or split in half?
So once again, black holes win, right? Black holes seem to win every single time. You throw something at them. Another black hole, a neutron star, a banana, even a gravity.
wave. You know, if you throw anything with energy at a black hole, it will just gobble it up. And that
includes gravitational waves. And you know, in the end, gravitational waves, there are ripples in
space and time, and they can be affected by the curvature of space. The same way they're like
photons can't, right? Photons don't have any mass, but they are affected by the curvature of space.
They are redshifted by gravitational expansion. They are distorted by gravitational lensing. They are
captured by black holes, all the same things also apply to gravitational waves.
Right. Well, I guess the question is, you know, what might be confusing is that, you know,
a black hole is a distortion in space time, right? It's like space sort of curves towards the
center of the black hole. And a gravitational wave is a ripple in that space time. So does it even
make sense for a gravitational wave to hit a black hole, right? It's sort of like,
You know, if it's a ripple and a rope, but the rope is just going down the drain, nothing really collides.
It just ripples down the rope into the hole.
Be careful about how we think about black holes, right?
There may be some mass concentrated at the center, but really when we're talking about the black hole, we're talking about the event horizon.
The event horizon is not a surface in the way that you can stand on.
It's just a location past which nothing can emerge.
And so a gravitational wave, you should think about it as energy, the same way you think about it like a banana as energy.
banana's made of particles, they're just ripples in those quantum fields.
And so a gravitational wave is ripples in space itself.
But in the end, that's just energy.
When that energy enters into the region around this dense mass inside the event horizon,
then that energy is affected by the curvature of space itself,
even though that energy is in the curvature of space itself.
Right.
I guess I'm thinking, you know, it's sort of like the wave, the energy doesn't really go anywhere
or disappears or gets absorbed,
it just sort of falls into the hole, like everything else.
It falls into the hole and eventually ends up at the singularity,
if you believe in classical general relativity,
that there are singularities at the hearts of black holes.
Remember, singularities are like endpoints, right?
You throw a particle into singularity.
There's no direction for it to go.
It just sort of like ends there.
That's one reason why we think maybe general relativity is wrong
because it seems like information is being deleted from the universe
when it goes into the singularity.
But according to classical general relativity, then yeah, the gravitational wave just gets like slurped up into the singularity and ends there.
It just adds its energy to the singularity.
Doesn't matter what form of energy you're in.
Photon, banana, gravitational wave.
Anything that enters in the event horizon just contributes to the mass of that black hole.
Right.
But we talked about earlier how like if you throw a banana into a black hole, never actually falls in because, you know, time slows down and it just looks frozen at the surface of a black hole.
Does the same thing happen to a gravitational wave?
Like you'll see the ripple, sort of ripple in and then stop at the surface?
Yeah, the same thing happens.
But remember, there's more gravitational wave coming behind it, usually like, unless you have a single burst of gravitational waves,
then there's a train of these gravitational ripples coming through the universe.
And so each one is growing the black hole a little bit, helping the one that came before it actually fall past the event horizon.
So it's more like a long chain of bananas than an individual banana.
Sounds delicious.
But you were also asking earlier about like the whole wave front of the gravitational wave.
Because gravitational waves are affected by black holes, they can also be like lensed by black holes.
So you can have like gravitational lensing of gravitational waves as they pass around a black hole.
So the ones that like actually hit the event horizon are slurped in, but the ones that go nearby,
they can get like bent around the black hole.
Right.
And even get sort of like bent back, right, reflected back towards the source of the gravitation
wave. Yeah, they absolutely could. The same way if you look near a black hole, you're seeing all
sorts of weird distortions. Like you can see the other side of the event horizon. You can see stuff
that whizzed around the black hole and came back at you. Then you can get the same effects with
gravitational waves. And so, for example, if you have the bright source of gravitational waves
and then between you and that bright source is a black hole, what would you see? You would see a little
shadow. You would see gravitational waves coming in all directions, except you would see this little
shadow just the same way we saw a picture of a black hole recently right that was in the x-ray
and we saw an accretion disk around a little shadow so you would see a gravitational wave
shadow that's gobbling up some of the black holes but around it you would see these other
gravitational waves that are like lensed and distorted by the black hole interesting and
would the gravitational wave also contribute to making the black hole bigger it would right
absolutely because it's got energy but you know there's an important caveat here which is that
we're assuming that the gravitational wave itself is pretty small, that like relative to the mass of the black hole, it's not that big a deal because black holes typically have very large masses and gravitational waves typically don't have that much energy.
So we're assuming basically like the black hole is fundamentally unchanged.
Maybe it grows a tiny bit, but it's not like really changing the structure of space time around the black hole.
And then we're using that setup to like solve the wave equation for the gravitational wave.
In the presence of an unchanged black hole, what would happen to a gravity?
gravitational wave. If, however, the gravitational wave is like enormous, it's like really big. It's
monster. Two supermassive black holes have merged. Then the calculation gets more complicated
because you can't assume that the gravitational wave is going to not fundamentally change the black hole.
And then it's trickier to say exactly what happens. You need to like fully solve the Einstein equations.
You might get some weird distortion to the black hole. But in the end, all that energy is going to go into
a bigger black hole. Well, it's weird to think that a gravitational wave has energy.
in the traditional sense, because as we talked about before in the podcast, anything with energy also bends space and attracts other things.
So it's almost like this ripple in space is also rippling in space or, you know, attracting things.
Yeah, and the energy we're talking about is enormous.
You know, when two black holes merge, maybe they start out each having like 50 times the mass of our sun, they don't form a black hole that has 100 times the mass of the sun.
And it ends up with something like 80 times the mass of the sun.
And the rest of it goes into gravitational waves.
Just stop for a moment and think about how much energy we're talking about.
We're talking about all of the energy that's stored in 20 times the mass of our sun.
Remember that like a single raisin, a gram of matter, has as much energy as a nuclear bomb.
Right.
So now imagine how much energy is stored in the sun.
And now 20 of those.
So we're not talking about a small amount of energy here.
We're talking about incredible cosmic quantities of energy radiated out through the universe.
Right.
But is the black hole at all affected by the gravitational wave?
Like does it get even like squeezed a little bit or, you know, does it kind of like move a little bit at all?
Or does black hole literally totally ignore the gravitational wave and just sucks in it?
It definitely is affected by it.
And as the gravitational wave gets larger and larger, you start to approach the case we talked about recently,
which is like two black holes merging.
Remember, when two black holes merge, then you don't just have like a big spherical event horizon.
You get this weird blob that forms as they merge and it becomes a peanut and eventually becomes a sphere.
So something similar would happen.
If you had a super powerful gravitational wave that was approaching a black hole, it would distort the shape of the event horizon.
It would like grow it out in one direction before another direction.
Eventually, a black hole would like stabilize and thermalize and get into equilibrium and become a sphere again.
but momentarily it would look really weird
and to figure out exactly how that would look,
you'd have to solve the Einstein equations
for that particular setup, which is really hairy.
Well, you sort of make it sound like the black hole wins
over the gravitational wave,
but I sort of feel kind of the opposite
because gravitational wave is not just huge,
it's sort of like it's the size of basically
almost the entire universe, right?
Like when two black holes collide
or a black hole collides with a neutron star,
it generates a sphere of a ripple, right?
Right? Like it's propagating in all directions at the same time. And if you're billions of light years away from the source, then literally the size of that sphere is billions of light years wide. Whereas a black hole is really just like a tiny little blip that it passes through.
You know, sort of like if you dig a hole in the sand at the beach and a huge long wave passes through, like, you know, some of the waves is going to fall into the hole, but the rest of the waves is just going to keep going as if nothing happened, right?
Yeah, that's true. Gravitational waves are bigger than black holes.
some part of them will survive.
The part that hits the black hole, it's gone.
But the rest of it will wiggle on through the universe.
Yeah, that's true.
Yeah.
And in fact, a black hole might even sort of feel insignificant to that gravitational wave, right?
It's like, oh, here's a little hole.
Whoops.
I'll just step over it.
It really is about the friends that the gravitational wave made along the way.
You're right.
Right.
But do you know what I mean?
Like it's just a little blib.
It's like putting a little obstacle in a huge, long, you know, break at the beach in a wave.
And in fact, at the beach, that when the wave goes through an obstacle, it sort of almost like reforms itself after the obstacle.
The same thing happened here with a black hole.
Like with the wave that immediately hits the black hole, it'll get sucked in.
But will the rest of the, you know, waves sort of like patch up that hole eventually?
Yeah, absolutely.
As the wave passes by the black hole, then the bits of the gravitational wave that are like just barely making it past, they will continue to disperse.
So eventually they will fan out and sort of fill in that gap.
It won't be totally unaffected.
You could tell that that had happened.
You'll see lensing effects on the gravitational wave from the black hole.
But yeah, there is no way that one black hole can completely squash a gravitational wave.
So if you imagine, for example, a billion supermans all running out in different directions,
then Hulk can only stop one of them.
From that point of view, the billion Superman win.
The infinite sequels of Superman beats out the one movie of the Hulk they've made.
Yeah, exactly.
All right.
So it's sort of a toss-up, I guess.
You know, like at the local level, a black hole will win over the gravitational wave.
But in the long term, you know, the gravitational wave is going to have a better life.
Don't they say that's the best revenge to have a good life?
Yeah, I suppose so.
And remember that the universe is filled with these gravitational waves.
They're passing through you right now.
Even if you're not the Hulk, even if you're not Superman, you are getting squeezed and tugged by gravitational waves,
probably generated by ancient black holes
gobbling each other billions of years ago.
It's everywhere.
We have a whole episode about the cosmic gravitational background
if you'd like to learn more about efforts
to discover and measure these very gentle gravitational waves.
Yeah, even though you're the size that you are
compared to a giant black hole,
you still affect that gravitational wave, right?
It's passing through you, but you are sort of absorbing
a little bit of it each time, right?
Part of the energy you have for your life today
It comes from those gravitational waves.
Well, I just have one more question, Daniel.
If I'm at the surface of a black hole and I slip on a banana peel, do I still generate a gravitational wave?
You do, and then the black hole eats it.
And you.
Exactly.
You eat it when you slip on the banana and then the black hole eats your waves.
Right.
Lots of eating here in the universe.
Time to take a break for lunch.
All right.
Well, we hoped you enjoyed that and maybe made you think a little bit about all of the amazing things that are happening out there right now.
are gravitational waves hitting black holes and black holes crashing into each other and making
gravitational waves? It's a pretty busy universe. It is. And those black holes continue to
hide all of the plot holes from us. We can't even figure out what's going on in there by passing
gravitational waves through them. If gravitational waves did pass through black holes, then they
would be affected by what's inside. And we can use that as a way to see inside those black hole
event horizons. But unfortunately, we can't. And they remain black. Uh-oh.
is Daniel getting mad?
Are you turning green or red?
I'm just frustrated by our inability to see the cosmic secrets hidden inside black holes.
Well, you can always ask the billion supermans that are out there.
Or future humanity.
All right. Well, thanks for joining us.
See you next time.
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has gotten to be a very wonderfully experiential sporting event.
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Culture eats strategy for breakfast, right?
On a recent episode of Culture Raises Us,
I was joined by Belisha Butterfield, media founder, political strategist, and tech powerhouse.
for a powerful conversation on storytelling,
impact, and the intersections of culture
and leadership. I am a free
black woman. From the
Obama White House to Google to the Grammys,
Valicia's journey is a masterclass
in shifting culture and using your voice to spark change.
Listen to Culture raises us on the
IHeart Radio app, Apple Podcasts, or wherever you
get your podcasts. Hey, I'm
Kurt Brown-Oller. And I am Scotty Landis
and we host Bananas, the podcast
where we share the weirdest, funniest,
real news stories from all around
the world. And sometimes from our guest
personal lives, too.
Like when Whitney Cummings recently revealed her origin story on the show.
There's no way I don't already have rabies.
This is probably just why my personality is like this.
I've been surviving rabies for the past 20 years.
New episodes of bananas drop every Tuesday in the exactly right network.
Listen to bananas on the IHeart Radio app, Apple Podcasts, or wherever you get your podcasts.
This is an IHeart podcast.
