Black Holes, Part 1: Phantom

Nothing can escape the pull of a black hole, not even Stuff to Blow Your Mind. Join Robert Lamb and Joe McCormick for a three-part exploration of these incredible, invisible regions of the cosmos where ponderous mass warps the very fabric of space and time. Up first, learn how the idea of black holes emerged as a mere ghost in the math. 

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Episode Transcript

Speaker 1 (00:00):
My World. Welcome to Stuff to Blow your Mind from
how Stuff Works dot com. Hey, welcome to Stuff to
Blow your Mind. My name is Robert Lamb and I'm
Joe McCormick, and today is going to be part one
of a multi part episode on on a topic that

(00:23):
I know you came back from New York with a fever.
For Robert, We're gonna be talking about black holes, that's right. Yeah,
I attended, Uh, I attended a talk at the World
Science Festival that I believe I mentioned in our previous
sort of World Science Festival roundup episode that I just
thought did a great job of providing an overview of
black holes and uh help straighten out a few of

(00:44):
the details for me. Yeah, I realized we have talked
about black holes on the podcast before, but you haven't
really I felt given it, given them proper, do We haven't.
We haven't really uh looked at black holes with the
attention that they deserve. Yeah, And of course, even in
doing a multi part series, we're not gonna be able
to cover every interesting thing about black holes. So this

(01:06):
is gonna be kind of a grab bag of things
that seemed interesting to us. So in this first episode,
we're gonna be talking mainly about the history of the idea,
where it came from, how we arrived at this bizarre
conclusion about the cosmos that we live in. In the
second episode, we're going to be focusing mainly on like
how we get a look at these things. And in

(01:26):
the third episode, I think we're gonna explore some of
the strangest avenues of thought that you can contemplate with
regard to black holes, like what's it like to fall
into one? Or what happens when a black hole collapses?
Does it does it create something on the inside? Yeah,
And I want to acknowledge that black holes, I feel
are kind of a challenging topic to tackle some people.

(01:48):
I mean, certainly from a like a physics standpoint, yes,
but but also just in terms of becoming engaged with
the idea, because I know there are plenty of you
out there like, yeah, black holes, let's do this. I
love I love science I love science fiction. I think
King of of all my favorite black hole related movies.
But I know other people are a little hesitant because ultimately,
black holes are a concept that have very little impact

(02:10):
on our personal lives and the scope of the universe.
That we observe and interact in. Well, they don't have
any people in them, right. I mean a lot of times,
I think when people look up to space and they say,
you know, I want to be interested in it, but
there's if there's no people up there, it's hard to
feel like I'm following a story or narrative. Or can

(02:31):
I even imagine a person there, because obviously there are
no people on Mars. But I can, But I can
imagine a future in which there are people on Mars.
I can. I can imagine multiple different sci fi scenarios,
many of which match up reasonably well with scientific expectations,
and and that can allow me to engage myself in

(02:51):
Mars more. But unfortunately, if you know anything about black holes,
you know that it's not even possible to say colonies
a black hole. You can't have singular and knots going
in there to see what's on the inside. Or you could,
but it just wouldn't be very useful for us on
the outside, or I guess very useful for those getting
ripped apart on the inside. Right. And I think another

(03:13):
challenge with black holes is that when they have played
a key role in science fiction and been made ultimately
kind of relatable concepts. Uh, the films don't really do
much with the science. They don't really do a great
job about really conveying what a black hole is. For instance,

(03:33):
I have to admit that my first introduction to black
holes was the nineteen seventy nine Walt Disney sci fi
movie The black Hole. Oh, Robert, I've never seen this one,
but I'm excited. I'm excited for you to tell me
about it. Tell me about it, fill my brain. All right,
we'll just briefly. I'll try not to go on too
long about this, because this is a film I loved

(03:53):
as a child and I still look back on finally today.
But it lands in a weird spot for a science
fiction film because it's it's not as fun and original
as nineteen seventy seven Star Wars, and of course it's
nowhere near as high minded and scientifically savvy as ninety
eight two thousand and one of Space Odyssey. But then again,
you know what is Instead, it's kind of an old

(04:15):
fashioned Jules Verne esque tale of space explorers who wind
up on a space station that's circling a black hole,
and the station's run by a mad scientist whose only
attendance are robots and lowbottomized androids. There's ultimately some fairly
horrific and and kind of ambitious stuff mixed in there,
but you're also faced with just kind of a maximum

(04:37):
dosage of of of of late seventies big budget cinema.
Like all the actors you would expect to show up
do show up. Ernest borg nine, Anthony Perkins, great, Maximilian
Shell shows up as the villain. How about Harry Dean Stanton?
Uh no, no, Dean Stanton, as I recall, And you

(04:57):
also have one of the Bottoms brothers, timoth Bottoms, No, no,
no one one of the other ones. Not not last
picture was it last picture show? Yeah, less picture show, Yeah,
not last picture shows bottoms, but but but one of
the other ones some other bottoms yes, okay. And also
slim pickings, slim pickings. Yeah, he's the voice of a
robhid just busted up robot it had It is really
cool robots in it. I gotta see this. The trailer

(05:19):
is pretty great for it. H In fact, if we
if we can play it, I would like to just
throw in just a clip from this trailer. There is
an inexorable force in the cosmos, where time and space converge,
a place beyond men's vision but not to his reach.

(05:42):
It is the most misdious and awesome point in the universe,
whether here and now maybe forever. The black hole in
this film, the actual black hole that we're presented with,
it's it's it's presented like a vortex. It's it's more

(06:02):
in keeping with the charybdis whirlpool of Greek myth. You know, this,
this terrible thing that you're on the verge of falling into.
It's ultimately treated with more religious reverence than scientific, which
of course is pretty much what happens later on in
the film Event Horizon, which I also love, but it's

(06:23):
hardly a scientific tour to force. Were you watching Event
Horizon recently, Robert, Yes, I was. I started watching it
again last night, but only made it about ten minutes
in before my ambient kicked in, because that's a horrible idea.
It's it's not really not ten minutes end, because you
get past the scary stuff and then you're just done

(06:43):
a spaceship, and then you realize it's time to go
to bed. I realized that the spaceship in that movie
it's like the only leather punk spaceship I've ever seen
in science fiction. It's like, you know, those like black
leather wrist bands with the metal studs on them. It's
that as a spaceship, it is very industrious, especially the uh,
the core that you end up exploring. But but hopefully

(07:04):
we'll get to talk about event Arizon a little bit
more in one of the future episodes. But basically the
idea is it's got a black hole and that's how
you get to Hell. I think, yeah, which again is
kind of the idea that has explored in Disney's a
black Hole as well. So there's people in it, well,
there are things in it, humanoids that you end up
with characters traveling through it. It's ultimately the confusing part

(07:26):
is that both films kind of treat a black hole
more like a wormhole, which is a separate thing altogether,
but that is ultimately more relatable I think to us
the idea of like a magic tunnel that goes somewhere.
But of course, actual black holes don't exist on a
scale that that directly influences individual human life for life
on Earth, except in our study of them. But the

(07:49):
bottom line is that they're They're just a physical reality
of our universe. They're not some sort of evil, malignant force.
They are just a physical part of the universe. At
the same time, though, I would say they are astounding
and one of the most interesting things in the universe
because they are the absolute extremists of of what we

(08:10):
know about physics. They're sort of like the test cases.
They're the exceptions. They break things that and that. For
that reason, they're interesting to scientists because we can look
at them and say, okay, what happens in these extreme
cases where you know, where we can't necessarily see inside
to know the answer. So at this point some of
you might be asking, well, well, what is a black hole?
Just lay lay out the basic definition. If it's not

(08:33):
a wormhole, it's not a gateway to Hell, then then
what are we talking about here? Well, in short, we're
talking about regions of space where the gravity is so
intense that light cannot escape the poll and the gravity
is that intense because matter is compressed to a very
small space and they range in size. For instance, primordial

(08:54):
black holes are no larger than a single atom, but
they contain the mass of a terrestrial Mount him So
Mount everest crunched down to the side of an atom.
It's pretty dense. A stellar black hole might be ten
kilometers in diameter, but would boast the mass of twenty suns,
for instance. And then finally you have the supermassive black hole. Uh,

(09:18):
the types of black holes that that that that live
at the centers of galaxies. Uh. And these would have
the mass of millions of suns compressed to a sphere
the size of a single solar system. That's extreme compression. Yeah,
a little harder to even think about it. Like I
find that the mountain atom uh comparison is maybe a
little more impactful for the human imagination. But still we're

(09:41):
talking about considerable, considerable consolidation of mass. Now we call
them black holes because light cannot escape them. Optically, they
appear as an absence. We can't see inside them, but
we can observe the effect of say, of of this
intense gravity on the surrounding environment. And despite the fact
that we can't see inside them, as we'll talk about

(10:02):
a couple of times as we go along, that doesn't
necessarily mean we don't see anything around them. In fact,
they can often put on quite a show. Yeah, I
hate to lean into the horror movie implications here, but
it's kind of like imagine the uh, the house from
the Texas Chainsaw Mask. Here, you can't see any of
the teenagers dying inside it from the outside, but you
see them like moving towards the house. You see a

(10:25):
lot of of random hippie activity on the outside, and
it gives you an idea of what might be going
on in the inside. Actually came up with an analogy
I was going to use in the next episode, but
maybe I'll go ahead and say it. So this is
a little less grizzly than what you said, but kind
of similar. So, uh, imagine you've got like a haunted
house ride in an amusement park, and the ride, the

(10:46):
part of the ride that you ride in is the
soundproof box where nobody can hear anything on the outside.
So you've got everybody in line to get in the ride,
to get in the soundproof box and go through the
haunted house. And as you're hurting tourists towards this soundproof box,
even though you can't hear any of the screams inside
the box, you will hear more and more sort of
nervous chatter and laughter and shrieks as people are approaching

(11:09):
the door, but then once you shut the door, bye bye.
I like that we both independently came up with haunted
house explanations for black holes. Personally, I seriously doubt that
the Texas Chainsaw House is haunted or contains a black hole. Now,
now it's important to note in all of this that
I really think we should try and get away from
thinking of black holes as essentially galactus or or some

(11:30):
sort of other unstoppable, insatiable cosmic devour that just destroys
and consumes everything, which is kind of hard because, as
we've discussed before in the show, like that's a classic
mythic trope, like the idea of some entity that will
consume the Sun. I mean, it's key to these various
eclipse mythologies that we've discussed in the past. But a
black hole is not, uh, this thing is just going

(11:54):
to eat the entire universe. They're bound by physics, so stars, planets,
whole galaxies may orbit around them. And I've seen it
pointed out before by NASA that if our Sun were
a black hole of equal mass, the Earth would not
fall in. Yeah, that's a point I've read many times before.
So what would happen to the Earth if the Sun

(12:14):
turned into a black hole? The Earth would keep orbiting. Yeah,
So again, to come back to the Texas Chainsaw mascure House,
it's it's not like the Texas Chainsaw Masscure House is
just going to suck in everybody in the surrounding area
and collapse the town. Now, the town continues to thrive. Yeah,
the next door neighbors, they just keep going to work,
they saying, keep selling barbecue. Everything's fine. And I also
think again, the whole aspect of this is a stumbling

(12:36):
block because it tends to encourage us to think of
black holes less as what they presumably are and more
like wormholes. Okay, so it's like it's like a tunnel
you can go through. Yeah, yeah, But ultimately, a singularity
is not a gateway. It doesn't go anywhere other than
to the center of its gravity. Their celestial objects that

(12:57):
just happened to be massive on a scale that's really
harder to square with human experience. Well, I can tell already,
Robert that you're running into issues with the language that
we have to use to describe things, because there is
no language, I mean, the only language we have is
like normal terrestrial vocabulary, and then the metaphors we build

(13:18):
out of that normal terrestrial vocabulary, so inevitably our language
will ultimately fail to have words that, at a fundamental
level really communicate the nature of celestial objects, you know,
powerful objects, huge objects like black holes. So we we
just have to use metaphors, right, and the idea of

(13:38):
a black hole is a metaphor. Yeah, and it's it's
a challenge for science communication for sure. A lot of
great black hole studies come out, and then you look
at the headlines that that are used right to to
relate these findings, and it's it's I often get a
laugh out of it because the world leader model is
so often employed and you end up hearing reading about

(14:00):
hannibal black holes, gobbling black holes, eating black holes, barfing
black holes. Yeah, it's so anthropomorphised in a really visceral way.
I mean you almost want to imagine that there are
articles about dating black holes, swipe right black holes. But
it's it's kind of a your damned if you do,
your damned if you don't situation. It's kind of like
when you when when we even anthropomorphize evolution to some extent,

(14:23):
we treat it like a person, right, And I mean,
on one hand, I acknowledge, yes, one should not do that.
You fall into, you know, potential traps by doing it.
But at the same time, you ultimately are trying to
put some fairly complex ideas into a form that people
can really consume. Well, you can talk about evolution without

(14:45):
anthropomorphizing it or you know, treating it like a person
with intentions. It's possible to do that. It can just
get really tedious to constantly be talking that way. So
we and we inevitably in these discussions, if we're just
trying to move things long and you know, move at
a brisk pace, we end up using the shorthand. And
the same thing happens for black holes. Black holes, we

(15:07):
end up using these colloquial shorthands to describe them that
are based on Earth metaphors that don't really get at
the truth of what it's like to have the geometry
of space time warped by this gravitational anomaly. Now, one
of the really fascinating things about black holes, though, is
that we we simply we didn't simply look into the
sky and observe them. Uh. It all began with the math.

(15:29):
It began with with with some some very bright individuals
crunching the numbers and seeing them as a possibility. Yeah,
and that's one of the things that makes black holes
so interesting. They weren't like stars. They weren't you know, stars.
We could look up and know something was there, and
then over time gradually make observations to refine our knowledge

(15:50):
of what stars are. Right, black holes weren't like that.
We had to work them out from first principles and
then say, okay, is there a way we could observe them?
It worked actually the opposite way. Yeah, that's the beautiful
part we see because we see it paying off. We
we we we we end up looking out into the
cosmos and observing the very things that we have simulated

(16:11):
with math and physics. The great astrophysicists Supermania and Chandra
Sheker had in a prologue to his book The Mathematical
Theory of black Holes, he wrote, quote, the black holes
of nature are the most perfect macroscopic objects there are
in the universe. The only elements in their construction are
our concepts of space and time. All right, Well, on

(16:32):
that note, we're gonna take a quick break, and when
we come back. We are going to jump into the
history of black holes. Thank you, thank alright, we're back.
So previously we were just talking about how black holes
began as an idea before they were observed in nature.
They started as something that people worked out from principles
they had established through other means, rather than something we

(16:53):
looked up into the heavens and saw. And there's there's
a really great book about this actually that I want
to for two because it's one of the sources I
used in working on this episode. But it's called black
Hole by Marcia Bartoustiac, and it's a it's a book
just about the history of the idea of the black hole,
how it went from the idea of gravity to something
that we now do experiments on with with cosmological detection equipment.

(17:18):
So the story of the black hole can really be connected,
I think, to the broader story of the discovery of gravity. Uh.
You know, we often don't even bother to think anymore,
why do objects fall down and not up? But I, oh,
I sometimes wonder like do kids still have this thought?
Do kids ask this sometimes or are they exposed to

(17:38):
the theories we have of gravity before they even have
the chance to ask that question naturally, you know, that's
that's a great question, because I they certainly grasp the
idea and the reality of gravity is just one of
the realities of the natural world that they've evolved to
thrive him. Of course we understand how it works, but
why yeah, yeah, you know my own personal experience, I

(18:00):
don't know that I've ever had a conversation with my
son about gravity um or at least not when he
was old enough to to appreciate it. I'm gonna have
to make a mission of explaining it to him. But
he also he may know already because he listens to
to educational podcasts, so he when I mentioned black holes,
he was like, oh, yeah, black holes. I was listening
to a while in the world about black holes, so

(18:22):
he already had a already had a leg up on
the concept. Well, I mean, it's one of those things
where most of us, I think, even people who are
aware of general relativity, we sort of have the idea
that we understand how gravity works, but then sit down
and try to put into words like explain it, and
then you start going, oh, wait a minute. But yeah,
So it's one of those things that once you've heard
it you think you've got to grasp on it, but

(18:44):
even then it can prove tricky to try to explain yourself.
But so you know, thousands or maybe millions of people
must have stopped to wonder this all the time before
we had a real answer why did things fall down
instead of up? And for a long time I think
humans were led astray by this intuitive, false cosmology of geocentrism.
So if you believe, like Aristotle, that the Earth is

(19:06):
the center of the universe, it makes a kind of
intuitive sense that everything would fall toward the center, right
And then again I sometimes wonder, like, why is that
even intuitive? Why doesn't everything fall away from the center
out to the edges. It just feels right enough that
you can stop thinking about the question basically. But then
once you introduce the Copernican model, the you know, the

(19:26):
heliocentric model of the Solar system, and the idea that
the Earth is not the center of the universe and
in fact is no kind of privileged place at all.
It's just another object floating around in space, Suddenly we
really need an explanation for why objects fall to the
ground rather than fly off in the opposite direction. And
the bigger question. Is the force that causes objects to

(19:48):
fall to the ground the same force that guides planets
in their orbits around the Sun. I like what you
said about the geocentric view because I think the geocentric
view also kind of lines up with our aasic egoic
experience of the world, Like everything in the world ultimately
breaks down to what I feel about it, because I
am the only the only experience, the only worldview you

(20:11):
know that I that I have control of and one
percent vision through. And uh. But then if someone would say, actually,
you're not the most important person in the world. Is
uh this person over here is that throws everything out
of out of whack. Well, it makes you realize that
your egoic view is not even necessarily a coherent view,
is just something that you can do without having to

(20:32):
think about. And I would argue the same is largely
true for geocentric physics. Uh though actually, in a funny way,
a lot of really intense thinking did go into constructing
geocentric cosmologies and they look kind of beautiful. But anyway,
coming back to gravity, so so we know that for example,
Johannes Kepler suggested that the sun exerted a magnetic force

(20:54):
that guided the orbits of the planets. Weird to think
back to a time when they were thinking, Okay, how
are the planets controlled in there? Or maybe it's magnetism.
We know magnets exist, that's an attractive force. Maybe that's
what controls it. And in the sixteen thirties, Descartes proposed
that the orbits of the planets were guided by swirlings
in the ether, which was this substance that was believed

(21:17):
to occupy space. The ether would have been kind of
like air water, this fluid that occupied empty space, and
you could have whirlpools or cyclones guiding objects in a
circular pattern around a center of motion, and that would
be what would guide orbits in the ether. But then,
of course we got to Newton. And so in sixteen
seven Isaac Newton struck gold with the philosophy naturalists Principia Mathematica,

(21:40):
or the Principia as people usually call it these days,
and it established the mathematical principles that correctly describe gravity
and planetary motion, which in effect turn out to be
the same thing. The motion of the planets dis guided
by momentum and gravity, and Newton calculated the inverse square
law of gravity, meaning that as you move away from
an object, it's gravitational influence is diminished by the square

(22:04):
of the distance. So what does that mean. That means
if you double the distance between two objects, the gravitational
force between them is reduced to a fourth and if
you quadruple the distance, the gravitational force between them is
decreased to one sixteen. It's a square of the distance.
So this indicates that the force of gravity is a
constant force, spreading out equally in all three dimensions. And

(22:27):
so a key insight that that Newton has that gravity
is universal. It applies equally to the objects we drop
and throw here on Earth, end of the objects we
see in the night sky. Though it's worth pointing out
at this stage that we still didn't know what gravity
actually was other than this mutually attractive force between objects
with mass. Newton wrote, actually, quote, I have not as
yet been able to deduce from phenomena the reason for

(22:50):
these properties of gravity, and I do not feign hypotheses.
And so Newton's laws were widely accepted, especially after they
were used to correctly predict the reappearing of Halley's comment
and this leads us to an English natural philosopher, geologist, astronomer, mathematician,
dabbler in mini domains named John Michelle. That's right, armed

(23:13):
only with a Newtonian and obviously pre Einsteiny and understanding
of gravity. Um. John Michelle and Henry Cavendish, Uh, contemplated
some pretty big cosmological questions, including the scale of the
universe and the cycle of stars. Yeah, they were really
ahead of their time in a way. John Michelle for
a long time was not necessarily recognized as one of

(23:33):
the earliest people to think about black holes. But but
he did some interesting work. Yeah. And and to put
him in within a you know, you have the right
time scale here. Uh. John Mitchell literally of seventeen and
Cavendish lived seventeen through eighteen ten. Okay, so what was
the deal? What? How did they touch on black holes? All? Right? So,

(23:54):
even in their day, it was known that stars flared up,
they subsided, and even vanished from the heavens. A popular
theory of the day was that they had dark spots
on them, you know, much like the spots that could
be observed on our own sun, and that this would
affect visibility. Though theories varied on what those dark spots

(24:14):
were actually going to be. They might be dark valleys
or ripples or peaks at a darker core underlying you know,
outer fluid or gases, um scum, or rock like bodies.
Even uh, there was all the star scum, yes, your
star scum. And then there was this cool idea that
that was also thrown around that you might have flattened stars.

(24:39):
So these would have been I guess kind of like
kind of like lenses rotating disks. Yeah, And so if it,
depending on what how it was facing you, it would
affect luminosity. So if it turned its edge to you,
there would obviously be a lot less illumination. So it's
not exactly the same principle, but I can see that
being an interesting inside preceding the discovery of things like pulsars.

(25:04):
So they pondered the structure of the cosmos and the
nature of stars and eventually hit upon a rather i
would say, haunting idea. And this was in Sight three.
What if a star was was massive enough, large enough
that it attracted back upon itself all the light it admitted,
in other words, so massive that light itself could not

(25:24):
achieve escape velocity. This was the idea of the dark star. WHOA,
Now we should give a little more context and explanation
to what they're thinking was here. But I have to
say the name of this paper because it's crazy. The
paper by John michelle In, presented at the Royal Society
of London in seven in seventeen eighty three and eighty

(25:47):
four was quote on the means of discovering the distance, magnitude,
etcetera of the fixed stars in consequence of the diminution
of the velocity of their light. In case such a
diminution should be found to take play sent any of them,
and such other data should be procured from observations as
would be farther necessary for that purpose. That's a pretty

(26:07):
good one. It's got a ring to it. He needs
like a social media editor working with him. And you
get that title down. Yeah, So what's what's the clickbait
title of this paper? Oh you gotta you gotta some
help fit um. You know a gobbling star in there.
Let's see, I tried to measure the massive binary stars.
You can't You won't believe what happened next by the

(26:28):
way that they figured that. Uh that if you have
a dark star like this. This would be the case
if you had a star as dense as our sun,
but with a radius four nineties seven times larger, and
it's such it would be difficult to optically observe such
a star. Yeah, so what what was Michelle doing in
this paper? As I just alluded to, his main goal,

(26:48):
the more banal goal was to measure the mass of
binary stars. So he was armed with, as you said,
Newton's gravitational laws. People were excited about Newton at the time.
What you could learn by using Newton so, uh, the
laws guiding planetary orbits, and he had those in hand,
and with those you could calculate the masses of two
stars in a binary system by observing the way they

(27:10):
orbit one another over the years. If you know how
wide their orbit is and how long it takes them
to orbit, you can estimate their mass. But Michell also
explored the limits of light, so he was working on
this assumption that light was composed of what was known
at the time as corpuscles. That makes the light sound
very romantic, I know, and kind of organic as well. Yeah.

(27:31):
So the corepuscles of light collections of particles, which, given
what we know about light today is sort of partially
correct and partially incorrect, right like we know we know
it's now given that light can be measured in particle
units known as photons, but can also behave like a wave.
But operating on this earlier assumption that light was composed
of these corpuscles these particles, Michell noted that light, like

(27:54):
anything else, must have an escape velocity. So the normal
illustration of this is you stand on the evace of
the Earth, you throw a baseball straight up in the
air at a hundred kilometers an hour, it'll fall back
down to the ground. And if you throw it at
two hundred kilometers an hour, it will travel up farther,
but it will still fall back down. If you just
keep throwing it up at greater and greater velocities each time,

(28:16):
eventually it's going to reach a velocity where, if it's
at the right angle, it doesn't fall straight back down
to the ground, but instead can go into orbit around
the planet. And if you keep throwing it straight up
at a great enough velocity, eventually it will actually escape
the planet's gravity and fly off into space and not
fall back down to Earth. And specifically, how fast an
object needs to be traveling to leave Earth's gravity is

(28:39):
eleven point two kilometers per second. If you can go
that fast, you can leave. If not, you're stuck here
with the rest of us. Uh. And a funny side
here is that you ever think about the idea of
a terrestrial alien planet with so much mass essentially that
it prohibits the aliens who live there from practicing space
exploration when also to just so so stocky they had

(29:02):
trouble with it. Yeah, I mean, who knows how that
would change their culture and all that. But uh, but yeah,
I mean you could imagine a more massive planet that
had a greater escape velocity might just make it the
case that you could never come up with a technology
that could get you out of the planet's gravity. Well,
this is my entire read on the the the horror
film phantasm, by the way, is that they have that

(29:24):
portal that goes to another world. Well, how did they
get here in the first place? Yeah, I guess they
sent the tall man. And the tall man is tall
because he's supposed to be on a high gravity planet,
and it like you know, straightens them out and makes
them taller on our planet. And then they have to
crunch those corpses down into dwarves so that they can
labor on the on the high gravity world. You know,

(29:45):
it's it's a really smart concept. It it really gets
at things that make you think, uh phantasm, Yeah, yeah,
I mean, it's just mysterious enough to get your brain working,
you know. Oh you know when Silicon Valley saw that ball,
they were all like, I could to design one of those.
I can make that ball. Yeah I Pentagon, come on, yeah,

(30:06):
I one day, we'll see him. Now. So coming back
to John Michelle, So what he believed was that you
got these core pustles of light and they they've got
an escape velocity as well, and what they have to
do to shine away from a star is escape the
stars gravity. And fortunately, as Michelle, light travels very very fast,
so this doesn't normally happen. But he realized as we

(30:28):
were saying, that if a star have has enough mass,
even according to this new Tonian model of physics, before
we had relativity, before we had Einstein, even on Newtonian mechanics,
you could imagine a star so big with so much
gravity that even light could not escape it and would
always get pulled back down. And like you said Robert.

(30:48):
The number he came up with was that a star
four hundred and ninety seven times the escape velocity of
our sun would prevent all light from leaving. And to
read a quote from Michelle's work, the existence of bodies
under these circumstances, we could have no information from sight.
Yet if other luminous bodies should happen to revolve about them,

(31:10):
we might still perhaps from the motions of those revolving bodies,
infer the existence of the central ones with some degree
of probability, as this might afford a clue to some
of the apparent irregularities of revolving bodies, which would not
be easily explicable on any other hypothesis. So Michelle's planting
a clue there for how we could detect black holes

(31:32):
or objects that did not allow light to escape before
we've even discovered relativity. And I wanted to drive home
again that this was the eighteenth century. Yeah, this is so,
this is this is pretty out their thought from the
time by by far. And I should point out that
Sir William Herschel also argued on the basis of the
particulate theory of light the corpuscles that nebulae could be

(31:56):
made of agglomerations of particles of light captured by gravity,
is sort of sort of held in place by gravity.
So essentially that we have the groundwork here for what
would eventually become the concept of a black hole, even
though they certainly were not calling it a black hole. No,
and uh one more thinker, we should mention somebody who
often gets credited, maybe more often than Michelle, or at

(32:18):
least used to get credited more often than John Michelle
is Pierre Simon de Laplace. So, in seventeen ninety six,
with the upheaval of the French Revolution still in effect,
the French astronomer and general scholar kind of Renaissance Guy
Pierre Simon de Laplace published Exposition du System dumont or
the System of the World, And in this book he

(32:40):
hypothesized the existence of cores, obscures, or hidden bodies or
dark bodies of those dark bodies out there. So so
he wrote, quote, a luminous star of the same density
as the Earth, and whose diameter should be two hundred
and fifty times larger than that of the Sun, would not,
in consequence of its attraction and allow any of its

(33:01):
rays to arrive at us. It is therefore possible that
the largest luminous bodies in the universe may, through this cause,
be invisible. Now, notice that Laplace estimated a different required
size to prevent the escape of light. This is because
he expected stars to have a different density than Michelle did.
But either way, I love that idea. So he's saying,
it's possible that the biggest things out there in the

(33:24):
universe are completely invisible to us. We we wouldn't even
know they were there. Now, rounding up from this, we
know that Michelle and Laplace were certainly ahead of their time,
but they were also wrong about a lot of stuff,
just owing to the time that they lived. Like that,
they didn't know lots of things about physics and about
astronomy that we did. When they imagine stars getting so
big that no light could escape their gravity, they imagine,

(33:46):
for one thing, stars scaling up simply by getting bigger
at a constant density. And then they also imagined light
being a projection of particles that would be slowed down
by gravity. So let's complicate the picture with some Einstein.
Let's do it. We're into the twentieth century now, during
the opening decades of the twentieth century German theoretical physicist

(34:06):
Albert Einstein in is the picture. He was born eighteen
seventy nine died ninety and he gave us a new
theory of gravitation, the general theory of relativity, and it
entails the idea that massive objects distort space time. And
we experienced this as gravity. Okay, So this is a
change in the idea of gravity. Instead of being a
force that that objects exert on each other, general relativity

(34:31):
imagines gravity as indentations in the geometry of the space
time we inhabit. That's right. Now, there's a there's a
wonderful experiment that I always like to fall back on
to kind of explain this, And in fact, there's a
video of this on stuff to Blow your Mind dot com,
and i'll i'll try and put a link to it
on the landing page for this episode. But basically it
involves taking a plastic sheet, having it stretched out generally

(34:52):
like if you stretch it over a hula hoop, okay,
and then you apply weighted balls onto the sheet, so
you know, you might have something that's the size of
a baseball up until up up scaling up to things
about the size of say a bowling ball, all right,
and when you place those on the sheet, it distorts
the sheet. It distorts the space time that is the

(35:13):
surface of that sheet. Right, So normal planets and stars
might be things on the sheets sort of like baseballs
or golf balls or something causing these small indentations where
generally things can move around them and not cause there
wouldn't really be much of an issue until you got
very close, and then you'd start to kind of circle
around or have your path diverted as you passed by

(35:33):
one of them, owing to the indentations they make in
the topography of the sheet. But imagine you've got, say,
like a big hunk of depleted uranium, and you put
that on the sheet like the densest thing you can
come across, and it's gonna bend the sheet down in
this crazy kind of suction that will for a certain
radius around it pull all kinds of stuff in. Yeah,

(35:55):
you try and roll a marble then across the sheet,
and it doesn't stand a chance it's going to be
sucked in. Can't it can't say roll past and just
get its path diverted. Suddenly things will just get sucked
all the way in and never come out. And so this,
in essence is the general theory of relativity. And again
it differs from the Newtonian model in which gravity wasn't
innate force, right, which Newton didn't know how to explain,

(36:17):
and I respect he didn't try to explain. He just said,
this is how it is. I'll write equations showing you
how to solve for it and how to predict how
it works. But I'm not going to say what it is.
Now We've got a pretty idea what it actually is,
and it's these these distortions in the geometry of space time.
The funny thing about that is, I think how often
we still talk about gravity as a force, as if

(36:39):
it were some kind of like magnetism attracting matter. I mean,
I honestly think about it that way most of the time. Yeah.
I mean again, we have to fall back on on
our experience, and that ends up coloring what we think
we know about the cosmos. Yeah. And so Einstein definitely
put he put together the theory radical framework for how

(37:01):
general relativity works. But one thing you might wonder is, like, Okay, well,
let's say we're really into Einstein's theory of general relativity.
How would you ever test whether such a thing were true?
You know, if you could do all of your Newtonian
experiments just using Newtonian physics and get the right answers
on Earth, how would you test to see whether Einstein's

(37:21):
theory was actually better? So there did come along some demonstrations,
and one of them, one that proved very decisive for
public opinion, was in nineteen nineteen when the English astrophysicist
Arthur Eddington carried out an experiment to test the predictions
of Einstein's theory. And I think we've talked about this
experiment on the show before, but one of the predictions
of general relativity is that light passing directly by a

(37:43):
massive object like a star should actually be bent by
a specific predictable amount, depending on how massive the object
is and how close the light passes. And so a
pretty easy way to test this would be by say,
taking a picture of the star field at night and
noting where all of the stars are, getting the locations
of those stars, and then watching what happens when the

(38:05):
Sun passes between the Earth and those stars. It should
be if Einstein's theory is right, that the light coming
to us from the star behind the Sun should get
bent as it's coming right past the Sun. So when
it's right beside the edge of the Sun, our view
of it should be displaced and distorted by a very predictable,
certain small but certain amount. But part of the problem is, well,

(38:28):
how do you test that, Like, can you usually look
at the stars if you're looking also at the sun. Yes,
you need something, you need something special to happen, something
that that that blocks out the sign. If only there
were some other object in the sky that was just
the right size to do that. And for we're very
fortunate to live in that laboratory by accident. So Earth's

(38:50):
Earth is very privileged. And here's one way that the
Copernican principle seems to fail. Earth is very privileged, and
that our moon is just about the same size as
the Sun, apparently from our perspective. So the Moon can
block out the Sun's light during a solar eclipse. And
if you wait for a solar eclipse, you actually could
look at the stars that are shooting light at you

(39:10):
from right beside the Sun from your perspective. So the
Eddington experiment waited for a solar eclipse when the moon
passed in front of the Sun, and that eclipse came
in May nineteen nineteen, passing over Eddington's experimental station on
prin Cape Island off the western coast of Africa, and
also over some uh some other astronomers working in the
Amazon rainforest. And so the eclipse dimmed the light from

(39:33):
the Sun enough for Ddington and colleagues to take photos
of the starfield in the background, and they found that
the Sun did indeed bend the light from the stars
right around it, and the light was bent by the
amount predicted by Einstein's general relativity. So this experiment was
a huge international sensation. It was in all the newspapers,
and it made Einstein a celebrity. Kind of makes me wonder,

(39:54):
like what sort of scientific experiment would make headlines in
major newspapers like front page headlines in major newspapers today. Well, uh,
skipping ahead a little bit here, but I believe gravitational
waves uh made some some headlines. They made some I mean, like,
can you imagine them as like top banner, like beating

(40:16):
out all the politics and everything like that. Yeah, it
is it is difficult to imagine it, but yeah, I
want to say we still have some some hits on
the way maybe maybe. So now we know that even
those stars can't slow down light. One of the key
features of Einstein's work is that the principle of the
speed of light and a vacuum never changes. Right. We

(40:38):
do know that very massive objects bend light as the
light travels along its trajectory through spacetime very near them.
And this is where we are going to introduce somebody
who changed the game when it comes to black holes,
and that is Carl Schwartzhield. We will discuss him when
we come back from a break. Than alright, we're back,

(41:00):
So Robert, take us into the mind of Karl schwartz Shield.
All right, So Karl schwartz Field was a German physicist
and astronomer. He lived only eighteen seventy three through nineteen sixteen.
He died in the war. Yeah, now he and I
should say they should point he did. He died of illness,
but he did still very much die during the First

(41:20):
World World War. Uh. And he calculated the possibility of
an Einsteiny and dark star. Um. He like did this
while he was in the in the service, I believe. Yeah. Yeah,
Often it's described as him like being in the trenches.
I think that, well, we like the room. The room.
It's a romantic idea, right, the idea that we have

(41:40):
someone that's in a literal pit and they're in a
it's a time in in world history that is that
feels like a pity and a time of just total war, uh,
encompassing the Earth, and it's seeming like we not, we
might not be able to climb back out of it.
And here this, uh, this gentleman is contemp lighting the
black hole. Yeah. As World War one is changing the

(42:03):
social fabric of Europe and much of the world, short
Shield here is changing the fabric of spacetime. Yeah. And
as a he shorts shorts Field was a very impressive dude,
though he was again he only lived to be forty
two years of age. Uh. But during his short life
he made practical and theoretical contributions to astronomy, and he

(42:25):
used general relativity equations to demonstrate celestial bodies within enough
mass would have an escape velocity beyond the speed of light.
I should also point out that again, even though he
died at the age of forty two, he had his
first theoretical physics paper published at the age of sixteen. Yeah.
He you get the impression that, like you're when you
read about him, you're sort of in the presence of

(42:46):
one of those brains. Uh so. Yeah. He he was
experimenting with different types of geometry for understanding the behavior
of massive objects like stars, and part of what he
was doing was trying to work out rigorous solution sans
to Einstein's equations. Einstein had sort of done the simplified
version of general relativity, and he's like, surely it'll be

(43:08):
really hard to work out all of the rigorous, you know,
precise solutions of my equations. But but swart Shield did,
and he did this by using a system of spherical coordinates.
Short Shield discovered that if you imagine the mass of
a star compressed down to a great density around it
in all directions reaching out to a specific radius later
known as the swart Shield radius, would form this gravitational

(43:32):
dead zone. Anything that went into the dead zone, whether
it was matter, light, whatever, would never come out again.
And this spherical dead zone came to be known at
the time as the schwart Shield sphere. Now we call
the boundary leading over into this zone today the event horizon,
and that's where you get the movie title. Of course,

(43:53):
that's sort of the outer boundary of the zone of
total influence of the black hole. Because inside this radius,
inside the event horizon, swart Shield concluded that all radiation
and matter passing into the sphere would become stuck. And
of course, under general relativity, if you were flying into
this sphere, outside, observers would notice your time slowing down

(44:15):
as you approached the sphere, and to those observers out there,
you would appear to sort of stop as you crossed over.
So do the people imagining this object, like, what would
they picture? Maybe according to this conception, anything entering the
sphere of the short Shield radius would seem to appear
frozen forever in time at the moment it was about
to cross over into the dead zone. Speaking, this made

(44:38):
me think about one of the videos we watched from
the World You were there at the event, but one
that I watched from the World Science Festival this year
had a astrophysicist Chep Doleman talking about black holes and
he said, quote, what happens in the black hole stays
in the black hole. Yeah. I like that. That that
that oftentimes you see the especially the more modern physicists

(44:58):
who who have written about black holes that they tend
to have a sense of humor regarding their nature. Yeah, yeah,
I think that's generally true, like they don't get all well.
I mean, so here's what you can contrast that lighthearted
approach with. Apparently some French speaking astrophysicists took to calling
the short shield sphere the sphere catastrophe, the sphere that's

(45:23):
a hard thing to say, sphere catastrophe. I like the
idea of this, of this is being the avant garde
French version of the event Arizon. Oh I'd pay to
see that. I hope it's still have sam Neil. Now
we go with the instead. Oh yeah, okay, it would be.
It would be a great version of event Horizon where
every scene they have fresh baked bread. Now, one thing

(45:45):
that's worth noting about the sphere of doom, the schwart
shield sphere or the sphere catastrophe, it's not actually the
same as the central object, the black hole itself. An
example given in Marcia Bartosik's black Hole, our son is
about one point four million kilometers wide. If a star
the mass of our Sun were compressed down to a point,

(46:08):
the sphere catastropheke surrounding it would be less than six
kilometers across. If the mass of ten sons were reduced
to a point like volume, its sphere catastrophe would be
about sixty kilometers wide. And as we mentioned earlier, if
our son were to suddenly shrink down to that size,
objects far outside the sphere would not suddenly be like

(46:28):
sucked in or torn apart. The planets would continue orbiting
just like they orbit the Sun, only it's only much
closer that things would really go crazy. But here's a
really important point that we need to drive home. At
this stage, even after short Shield had done these these calculations,
most physicists and astronomers did not believe a black hole

(46:48):
could exist in nature. Uh. Einstein just thought that short
Shield sphere sphere of doom thing was a sign there
was still some things to work out in the theory,
and Einstein did not think that black holes would be
found in the actual universe. So at the time, the
idea that it might have just been a mirror ghost
in the math kind of a remainder that had to
be figured out later on. Yeah, so you do the

(47:10):
math and you say, oh, this is a strange finding.
But people, I think, just assumed, Well, so we'll find
out something in the future that will make sense of
all this, you know, we will have some kind of observation,
some update to the theory, something that will eventually let
us know, oh, okay, there's not actually such a thing
as a black hole. They weren't calling it a black
hole at the time, but there's not actually one of

(47:32):
these to be found in nature. Something prevents this from happening.
So remember Arthur Eddington, the English astro physicist who did
the eclipse experiment about general relativity. In his nineteen book
The Internal Constitution of the Stars, he wrote, I think,
kind of dryly, invoking some awesome imagery, I might add quote,
a star of two d and fifty million kilometers radius

(47:54):
could not possibly have so high a density as the Sun. Firstly,
the force of gravitation would so great that light would
be unable to escape it, the rays falling back to
the star like a stone to the Earth. Secondly, the
red shift of the spectral lines would be so great
that the spectrum would be shifted out of existence. Thirdly,
the mass would produce so much curvature of the space

(48:17):
time metric that space would close up around the star,
leaving us outside i e. Nowhere. So the idea is
that it would can suddenly contain all of space, and
then we couldn't be in space anymore. Well, when you
put it like that, it does sound like a like
a mathematical problem that has to be worked out later on.

(48:38):
But of course Eddington was wrong about that, and even
Schwartzfield himself didn't think you would find these mathematical objects
in nature. He thought that sort of the outward pressure
of stars would prevent them from collapsing down to a
volume smaller than that sphere catastrophe. And remember he was
not setting out to posit the existence of black holes.
That wasn't his goal. That they just simply pop up

(49:00):
as this weird byproduct of him using general relativity to
calculate the gravitational fields generated by different kinds of massive
bodies in space. Now we have to stress here that
sword Shield didn't call it a black hole. He called
it a discontinuity. Yeah, what did Eddington call it? Oh?
He called it a magic circle. Oh that's really good.

(49:21):
I kind of wish we'd stuck with that. Yeah, though
that of course has its own baggage. You expect like
elves to come flying out of it, right. Uh No,
But the term black hole was coined later still by
American theoretical physicist John Archibald Wheeler, who lived nineteen eleven
through two thousand and eight. Did he coin it or
was he just the first one to start using it? Well?

(49:42):
He has. So the story that I read is that
he was in a conference in New York City in
nineteen sixty seven and he apparently seized on a suggestion
shouted from the audience. I'm a I'm as I could.
I couldn't find out what the exact shout was, but
I'm assuming it was something like call it a black hole, John,
or that's a black hole, something of that effect, or

(50:03):
just maybe a chant black hole black hole. So he
was like trying to work the audience. He's like, throw
out some names, come on, give me some ideas, and
people are like magic circle and he's like, nah, no,
no magic circles here. Yeah, it's like improv alright, somebody
give me a theme and we'll we'll construct some sort
of theoretical physics structure out of it. How about dark Star?

(50:25):
So in his autobiography Sphere Catastrophe, I would like to
see an improv sketch around the sphere catastrophe. Uh So.
In his autobiography, Wheeler wrote that the black hole quote
teaches us that space can be crumpled like a piece
of paper into an infanticible dot, that time can be

(50:45):
extinguished like a blown out flame, and that the laws
of physics that we regard as sacred, as immutable or anything,
but which I think sums it up rather nicely. Yeah,
I like that. Well, I mean it also Wheeler, there
he speaking, Einstein is ms right, Like the whole idea
of general relativity is that we used to think, oh,
space and time, those are the things that are constant

(51:08):
and immutable, and other stuff can can get moved around,
and we found out through relativity. No, well, the speed
of light and a vacuum might be constant, but space
and time you mess all. You mess with them a
lot and Wheeler Wheeler is carrying that torch. So maybe
that's going to be where we have to wrap up today.
But the big question left lingering for us to explore

(51:28):
next time is how did this mathematical curiosity this sort
of like weird artifact of people trying to solve problems
on paper become a feature that scientists actually think exists
out in the physical world, and how do we detect
them if they do exist? You will find out next time.
In the meantime, however, be sure to head on over
to stuff to Blow your Mind dot com. That is

(51:50):
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(52:10):
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