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 youâre in you're
not getting back out again. It's impossible for anything to escape one
of those things. Even light. Theyâre 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 weâve ever believed in and give the biggest brains on the planet something
of a headache, thereâs one thing everyone agrees on, you canât get out of one. Neil deGrasse Tyson put it pretty simply,
âLIGHT DOESNâT COME OUT, NOTHING COMES OUT. IF YOU FALL IN, YOU DONâT COME OUT.â NEIL DEGRASSE TYSON | ASTROPHYSICIST But is this really true, can nothing, absolutely
nothing, escape from a black hole? Iâm 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 âBrilliant.orgâ! 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 theyâve gobbled something up,
their gravitational pull is so strong that thereâs 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 thatâs 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, thatâs not what would happen. The black hole would exert the same gravity
as the Sun, so the planets keep orbiting as normal. Thereâs 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 holeâs
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 canât travel faster
than the speed of light, so once something is in a black hole, itâs 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 youâd 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 theyâll be dead. Sure. But their mass would now be dense enough to
produce gravity so strong that light wouldnât be able to escape â in other words youâve
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 youâd create a gravity so strong that light
canât escape. Collapse the Earth down so its got an 8.7
millimetre radius, making it roughly the size of a peanut, and youâve guessed it, youâve
created a black hole. Fortunately, black holes arenât created
by collapsing planets or people, usually theyâre 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, theyâre 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 arenât exactly sure how these
black holes form, but theyâre 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, youâre probably wondering what supermassive
even means. Okay, so if the mass of our sun is 2 nonillion
kilograms â thatâs a lot of zeros. Well, a supermassive black hole can be billions
of times more massive than that, meaning weâre talking about billions of nonillions of kilograms. Letâs take the supermassive black hole thatâs
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 doesnât 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 universeâs
top speed, the speed of light. So, if you were able to look directly at a
black hole, what would you see? Well, you wouldnât be viewing the singularity
that makes the black hole, instead youâd be looking at the black holeâs 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 itâs game over. Thereâs no getting out, because youâd
need to travel at or above the speed of light to do so, which Iâm afraid is just impossible. Even if you got close to a black holeâs
event horizon, itâs important to remember that you couldnât 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 doesnât mean there isnât
a load of other cool stuff going on outside the black hole. What youâd see here is a swirling ring of
gas and dust thatâs gathered there because of the holeâs 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 weâre on the subject of black
holes and light, because theyâre 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. Letâs 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, youâd 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, itâs still
a bright spot but the black holes gravity has distorted light so much that it looks
completely different to us. But enough of whatâs 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... youâd die, but how youâd
die is still up for debate. Letâs look at scenario 1. Youâve 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 isnât good. Youâd 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 youâre a lot closer to the singularity, so those tidal forces start
to have an effect much earlier. In fact, they could kill you before youâd
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 thatâs 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 isnât exactly popular
in the scientific community. Raphael Bousso, a physicist at the University
of California, Berkeley, said âA FIREWALL SIMPLY CANâT APPEAR IN EMPTY
SPACE, ANY MORE THAN A BRICK CAN SUDDENLY APPEAR IN AN EMPTY FIELD AND SMACK YOU IN
THE FACEâ. 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 itâs not going to be pretty. So, crossing the event horizon wasnât the
best idea. Letâs rewind and this time, maybe you trick
an enemy, letâs 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 weâve 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 heâd appear to be moving increasingly slowly and his watch would tick more slowly
than yours. Also, youâd never actually see him cross
over the event horizon, instead heâd 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 heâd 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 heâs 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 doesnât 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: âA HOLE IN SPACE WITH A DEFINITE EDGE OVER
WHICH ANYTHING CAN FALL AND NOTHING CAN ESCAPEâ 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 thatâs true when these particles spawn inside a black
hole. Theyâre 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. Iâm talking seriously slowly though, for
Sagittarius A*, our neighbouring supermassive black hole, it would take 10^87 years before
it evaporated away. Thatâs 1 octovigintillion years, and no,
thatâs not a made up number! ITâS 87 ZEROS! Although we should point out that Hawking
radiation hasnât actually been observed yet, itâs 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 doesnât break the rule that nothing can escape from a black
hole. However, it does change one thing about how
we perceive black holes â theyâre probably not totally black, since they emit radiation. Then again the name âalmost black holesâ
doesnât have the same ring to it. If you enjoyed this video then please help
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next.
Wait until you learn that a ton of lead and a ton of feathers weigh the same. Mind blown.
Same mass, sure, but the size of a black hole with the mass of the sun would be about 2 miles across. A black hole the size of the sun would destroy this solar system; it would have about 236,000 times the mass of the sun.
Is one solar mass enough to cause a black hole?
Kinda like "if everything in the universe suddenly doubled in size nobody would notice any difference because proportionally nothing changed"