Except for an extremely small number of lucky
astronauts or the billionaire customers of
Elon Musk, most of us won't get the chance
to escape Earth.
But even though we're stuck down here, everyone
knows there are certain things you want to
avoid up there.
Don't get blown out of an airlock, never vomit
inside your helmet and avoid going into a
black hole, because once you’re in you're
not getting back out again.
It's impossible for anything to escape one
of those things.
Even light.
They’re essentially the universe's ultimate
prison.
In fact, black holes are probably one of the
most weird and brain melting things in existence.
The physicist who invented the term black
hole, John A. Wheeler, said they teach us…
"THAT SPACE CAN BE CRUMPLED LIKE A PIECE OF
PAPER INTO AN INFINITESIMAL DOT, THAT TIME
CAN BE EXTINGUISHED LIKE A BLOWN-OUT FLAME,
AND THAT THE LAWS OF PHYSICS THAT WE REGARD
AS 'SACRED', AS IMMUTABLE, ARE ANYTHING BUT".
JOHN A. WHEELER | THEORETICAL PHYSICIST
So while black holes might make us question
everything we’ve ever believed in and give
the biggest brains on the planet something
of a headache, there’s one thing everyone
agrees on, you can’t get out of one.
Neil deGrasse Tyson put it pretty simply,
“LIGHT DOESN’T COME OUT, NOTHING COMES
OUT.
IF YOU FALL IN, YOU DON’T COME OUT.”
NEIL DEGRASSE TYSON | ASTROPHYSICIST
But is this really true, can nothing, absolutely
nothing, escape from a black hole?
I’m Stu, this is Debunked, where we sort
the truths from the myths and the facts from
the misconceptions.
This video is made possible with the support
of ‘Brilliant.org’!
A problem solving site and app that aims to
develop your scientific thinking.
Before we can truly understand whether anything
can escape the clutches of a black hole, we
need to understand what these monsters are
and how they work.
Well, to put it simply, a black hole is basically
a point in space that can seemingly devour
everything in its path.
And, once they’ve gobbled something up,
their gravitational pull is so strong that
there’s no chance of that intergalactic
meal ever being seen again.
And, while we're on the subject of hungry
black holes, a lot of you might have heard
that black holes just suck everything up,
like a massive vacuum cleaner.
Well that’s not what happens, Black holes
aren't sucking at all.
What actually occurs, is that things fall
into the black hole as a result of its gravity.
Think of it this way.
You've got a really old satellite, well past
its sell by date, let's call it Sputnik.
It's time for Sputnik to retire and come back
down to Earth.
Now, you wouldn't describe the Earth as sucking
that satellite down, rather the satellite
is falling to Earth, because of gravity.
It's the same for a black hole, if an object
gets close enough to it, then gravity will
cause it to fall in.
If you're still not convinced, let's swap
out the sun with a black hole of the same
mass.
If anyone was expecting a quick death and
some crushing apocalypse, I've got some good
news, that’s not what would happen.
The black hole would exert the same gravity
as the Sun, so the planets keep orbiting as
normal.
There’s no huge suck in the solar system
pulling everything in.
If anything, you can expect a slow death and
a freezing apocalypse instead, because no
Sun, means no heat, means no humans.
But just how powerful can a black hole’s
gravity be?
Well, light, travelling at a whopping 1.07
billion kilometres per hour, can't get away
from these gargantuan gravitational forces
once its got too close..
And as we all know, you can’t travel faster
than the speed of light, so once something
is in a black hole, it’s staying there.
That all sounds pretty scary but not as scary
as the fact that, technically, anyone of us
watching this video could become a black hole
ourselves.
All you’d have to do is compress yourself
into a really tiny space… really tiny.
Take an average human, compress them down
to a size much smaller than an atom's nucleus
(10-23 cm) and they’ll be dead.
Sure.
But their mass would now be dense enough to
produce gravity so strong that light wouldn’t
be able to escape – in other words you’ve
got yourself... a black hole.
Every object has something known as a Schwarzschild
radius.
This is the space that, should you manage
to compress the object's mass into it, then
you’d create a gravity so strong that light
can’t escape.
Collapse the Earth down so its got an 8.7
millimetre radius, making it roughly the size
of a peanut, and you’ve guessed it, you’ve
created a black hole.
Fortunately, black holes aren’t created
by collapsing planets or people, usually they’re
formed by collapsing stars.
Big stars too, ones that start out with a
mass around 25 times that of our own Sun.
When one of these larger stars runs out of
fuel, it collapses in on itself, forming a
black hole.
This type of black hole is not only incredibly
dense, they’re also incredibly common.
According to the Harvard-Smithsonian Center
for Astrophysics, our galaxy, the Milky Way,
contains a few hundred million of them.
And right at the centre of the Milky Way,
is thought to be another type of black hole
altogether, a supermassive black hole.
Scientists aren’t exactly sure how these
black holes form, but they’re confident
that these behemoths sit in the centre of
pretty much every galaxy, not just our own.
And they keep gaining mass from the nearby
dust and gas found in the heart of most galaxies.
Now, you’re probably wondering what supermassive
even means.
Okay, so if the mass of our sun is 2 nonillion
kilograms – that’s a lot of zeros.
Well, a supermassive black hole can be billions
of times more massive than that, meaning we’re
talking about billions of nonillions of kilograms.
Let’s take the supermassive black hole that’s
closest to home, Sagittarius A* (Sagittarius
A-Star), slap bang in the middle of the Milky
Way.
Its mass is the equivalent of 4 million suns
but its diameter is just 17 times larger - in
other words, these supermassive black holes
are super dense.
Now it might seem reasonable to assume that
all that mass is evenly distributed throughout
the black sphere, but those billions of nonillions
of kilograms are squeezed into a point that
is so small, it is actually impossible to
measure, and is known as the singularity.
Now this obviously doesn’t show us much,
so if we take a cross section and flip it
around... the Singularity would look like
this.
This point sits deep inside the black hole,
leading to infinite density and gravity.
Understandably gravity that strong can stop
everything from escaping its clutches, even
if the object is travelling at the universe’s
top speed, the speed of light.
So, if you were able to look directly at a
black hole, what would you see?
Well, you wouldn’t be viewing the singularity
that makes the black hole, instead you’d
be looking at the black hole’s event horizon.
This is the boundary or edge of the black
hole, and once something has crossed that
line and gone past the event horizon, into
the black hole, then it’s game over.
There’s no getting out, because you’d
need to travel at or above the speed of light
to do so, which I’m afraid is just impossible.
Even if you got close to a black hole’s
event horizon, it’s important to remember
that you couldn’t see anything going on
inside because literally nothing can escape
out through that barrier.
For people on the outside trying to look in,
you'd just see a black void, which, depending
on how close you were, could be a tiny black
ball or a huge void filling your field of
vision.
However, that doesn’t mean there isn’t
a load of other cool stuff going on outside
the black hole.
What you’d see here is a swirling ring of
gas and dust that’s gathered there because
of the hole’s incredible gravity.
This so-called accretion disc circles the
black hole and is slowly consumed by it, a
bit like water circling a drain, but because
of the incredible friction generated by the
unfathomable speeds, those bits of material
are heated to billions of degrees, releasing
radiation and glowing incredibly brightly.
This process can lead to something known as
a quasar.
For example, a supermassive black hole with
a mass two billion times that of the Sun,
led to a quasar which gave off an extreme
amount of light.
How extreme?
60 trillion times more light than our Sun.
So, while the black hole itself is completely
devoid of light, their existence can help
produce some of the brightest objects in the
entire universe.
And while we’re on the subject of black
holes and light, because they’re so massive
their gravity can warp space-time.
What this means in practice, is that light
coming from objects behind a black hole would
be bent, distorted or magnified.
This phenomenon is called gravitational lensing
and is a bit like looking at the universe
using a funhouse mirror.
Let’s say you were on Earth, doing a bit
of star gazing and you spot a bright light
source somewhere on the other side of the
universe.
It just looks like a white dot in the sky,
but if a black hole were to somehow pass between
the Earth and the dot, you’d see something
like this.
When the black hole was directly in front
of the dot, the small but solid dot would
appear to become a larger hollow circle.
In truth, nothing has changed, it’s still
a bright spot but the black holes gravity
has distorted light so much that it looks
completely different to us.
But enough of what’s going on outside the
black hole, what everyone wants to know is
what would happen if you booked a one-way
ticket and went inside?
Essentially... you’d die, but how you’d
die is still up for debate.
Let’s look at scenario 1.
You’ve jumped into the black hole feet first,
which means your feet are closer to the singularity
than your head.
In other words, the bottom part of your body
will be subject to stronger gravitational
forces than the top part, and the difference
between those forces will become even greater
the closer you get to the singularity.
Scientists refer to these differences in force
as tidal forces, and the result of them on
the human body isn’t good.
You’d slowly be stretched from toe to head
and squished inward at the sides, basically
creating a human-flavoured piece of spaghetti.
Hence why this process is called spaghettification.
Put more simply, the tidal forces will rip
you apart, breaking down every molecule of
your existence.
Weirdly though, smaller black holes would
kill you faster than a supermassive one.
This might seem counterintuitive, but with
a small black hole you’re a lot closer to
the singularity, so those tidal forces start
to have an effect much earlier.
In fact, they could kill you before you’d
even crossed the event horizon.
Oddly, with a supermassive black hole you
could cross the event horizon and survive
for a while before being turned into a noodle.
But that’s just one theory about death by
black hole.
Time for scenario 2, first put forward in
2012 by physicists Ahmed Almheiri, Donald
Marolf, Joe Polchinski and James Scully.
According to them, someone falling into a
black hole would be incinerated by a huge
firewall made up of ultra-high energy particles
as they made their way across the event horizon.
This relatively new idea isn’t exactly popular
in the scientific community.
Raphael Bousso, a physicist at the University
of California, Berkeley, said
“A FIREWALL SIMPLY CAN’T APPEAR IN EMPTY
SPACE, ANY MORE THAN A BRICK CAN SUDDENLY
APPEAR IN AN EMPTY FIELD AND SMACK YOU IN
THE FACE”.
RAPHAEL BOUSSO | PHYSICIST | UNIVERSITY OF
CALIFORNIA, BERKELEY
However, despite some reservations about this
new theory, scientists have yet to disprove
the idea.
One thing is clear however, you are going
to die.
And it’s not going to be pretty.
So, crossing the event horizon wasn’t the
best idea.
Let’s rewind and this time, maybe you trick
an enemy, let’s call them Darth, into taking
a journey to a black hole.
What would you see as he unsuspectingly got
closer and closer to his final destination?
As we’ve learnt, black holes can warp light,
but they can also do some pretty strange things
to time as well.
As you watched Darth fall ever closer to the
black hole he’d appear to be moving increasingly
slowly and his watch would tick more slowly
than yours.
Also, you’d never actually see him cross
over the event horizon, instead he’d just
grind to a stop, in a kind of suspended animation,
right on the edge of the black hole.
Because of the extreme gravity, any light
coming from Darth would be shifted to the
red end of the spectrum, making him seem red
as he got closer to the black hole.
Eventually he’d just get dimmer and dimmer
and fade away, and according to you, he never
actually makes it across the event horizon.
But he does make it, and then he’s either
turned into spaghetti or barbecued by radiation.
Thankfully Darth is never coming back, well
unless Disney come up with a really convoluted
plot device.
But, it doesn’t matter who you are, you
can't escape a black hole.
Renowned physicist Kip Thorne, who helped
consult on the film Interstellar, sums up
black holes as:
“A HOLE IN SPACE WITH A DEFINITE EDGE OVER
WHICH ANYTHING CAN FALL AND NOTHING CAN ESCAPE”
KIP THORNE - THEORETICAL PHYSICIST
But, here's the thing, this isn't strictly
true.
Okay, bear with me, because we're going to
have to leap very briefly into some quantum
theory.
According to this, empty space isn't totally
empty.
Here virtual particles can pop in and out
of existence in extremely short time frames.
These particle-antiparticle pairs usually
just annihilate each other.
For example, a positron, a particle of antimatter,
will annihilate an electron.
This is happening all the time, but something
weird can happen when these virtual particles
pop into existence around a black hole.
We already know that nothing can escape from
inside the event horizon, and that’s true
when these particles spawn inside a black
hole.
They’re stuck there for a moment before
annihilating each other as usual.
However, sometimes, outside of the hole, one
half of these particle pairs can pop into
existence and then fall into the event horizon,
while the other half escapes off into the
universe.
This process is called Hawking radiation and
slowly causes the black hole to evaporate,
since it is losing energy.
I’m talking seriously slowly though, for
Sagittarius A*, our neighbouring supermassive
black hole, it would take 10^87 years before
it evaporated away.
That’s 1 octovigintillion years, and no,
that’s not a made up number!
IT’S 87 ZEROS!
Although we should point out that Hawking
radiation hasn’t actually been observed
yet, it’s only been predicted by the late
great Stephen Hawking.
And even if it is proven true, technically,
those particles are never inside the black
hole just the edge of the event horizon, so
even Hawking radiation doesn’t break the
rule that nothing can escape from a black
hole.
However, it does change one thing about how
we perceive black holes – they’re probably
not totally black, since they emit radiation.
Then again the name ‘almost black holes’
doesn’t have the same ring to it.
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