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SUB BY : DENI AUROR@
https://aurorarental.blogspot.com/
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Cosmologists are battling over the universe's greatest enigma.
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Black holes.
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We've never seen them.
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It's near impossible to study them.
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And their existence challenges everything
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we think we know about space.
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The black hole represents the absolute limits
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of what we understand about nature.
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The truth is, we have almost no idea what these things are
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and how they work.
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Black holes are at the very heart of cosmology.
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Yet, some scientists question if they're even real.
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Black holes present lots of paradoxes,
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and the simplest way to resolve the paradoxes would be
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if black holes didn't exist at all.
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Solving the mysteries of black holes
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pushes our understanding of physics
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to the edge of reason.
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But it's the only way to discover
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if black holes really exist.
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captions paid for by discovery communications
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Black holes are the monsters of the universe...
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Terrifying cosmic beasts that devour all they encounter.
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But black holes scare scientists for very different reasons.
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They challenge our theories to the breaking point.
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This is at the forefront of theoretical physics.
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When it comes to the detailed nature of black holes,
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it would not surprise me if we got it all wrong.
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The science of black holes is so challenging
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that some scientists question whether they exist at all.
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Despite their fearsome reputation,
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we've never actually seen one.
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Black holes are everywhere. They're all over the universe.
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They're all throughout our galaxy.
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But that doesn't mean that they're easy to find.
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They're black, and space is black,
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and black-on-black is kind of hard
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to see in a picture of space.
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This is paradoxical
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because scientists believe black holes are born
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in some of the brightest explosions in the universe...
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rising from the corpses of detonated stars
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many times larger than our sun.
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A star that burns for 10 million years
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collapses to form a black hole in a period of seconds.
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As it collapses,
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the outer region of the star hits the core,
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triggering a huge explosion... A supernova.
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We see the bang, but not what's left behind...
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a dead core with the enormous mass of the star
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crushed down into an infinitesimal, tiny area.
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From this minuscule high-mass core,
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a black hole is born.
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The flow of gravity is so strong that nothing can escape...
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Not even light.
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But how can scientists claim that black holes exist
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if we can't even see them?
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You could say that about the existence of the atom.
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We knew they had existed for decades, centuries
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before we had actually seen one in some sort of imaging device.
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And so it's the same sort of thing with black holes.
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Just because you can't see it doesn't mean it's not there.
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Not seeing black holes but knowing they're there
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is a possibility,
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just like we know that wind is there,
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even though we can't see air.
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Air is invisible, but when the wind blows,
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its effects can be measured.
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It's the same with black holes.
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You just need to know what to look for.
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While they emit no light themselves,
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black holes are tremendous sources of x-rays,
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and that's because as things get close to a black hole,
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they're accelerated by the gravity,
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and they can heat up to millions of degrees.
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Million-degree gas gives you lots of x-rays.
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To find and measure these telltale x-rays,
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scientists turn to the NuSTAR space telescope.
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In 2017, it spots a burst of x-rays
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in a cluster called 47 Tucanae,
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at the edge of the milky way.
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When scientists analyze the data,
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they realize they're looking at two objects
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orbiting each other very closely.
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All we see is that there's a star being ripped apart,
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and gas is spiraling down to a very dense, very dark object,
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so something weird is going on.
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As one of the objects accretes matter off the other,
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it causes it to emit x-rays,
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and those x-rays can be used, then, to trace out the orbits
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and, therefore, extract the mass.
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When scientists work out
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the size and mass of the two objects,
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they find the first is the fading corpse
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of a sunlike star.
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And while the second object is tiny,
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it has the mass of a giant.
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Is this an elusive black hole?
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What we're talking about here is an object
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that is very massive, very small, very dense,
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with intense gravity.
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But it turns out there are lots of different ways
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to create an object like that.
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There is another type of ultra-dense object out there
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in the universe, called a neutron star.
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Neutron stars form in the same way we think black holes form...
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When stars die, explode,
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but then collapse down into a tiny ball of matter.
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The gravitational attraction of a neutron star is enormous,
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pulling in gas, dust, and asteroids.
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But light can still escape.
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Black holes and neutron stars are kind of cousins,
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but in the case of a neutron star,
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it didn't have quite enough mass to collapse out of control.
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So you can sort of think of it as just barely hanging back
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from collapsing into a black hole.
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The tiny object discovered by NuSTAR
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does have enormous mass.
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But size and mass alone
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are not enough to prove it's a black hole.
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Cosmologists need more evidence.
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They can't see black holes, but is there another way?
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What if they could hear them?
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Think of two massive cars colliding... boom!
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When they do, they radiate sound,
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and then we can tell whether or not that collision occurred
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and maybe even how far away it was.
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It's like that when black holes collide.
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So, by listening for a black hole crash...
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could scientists conclusively prove they exist?
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Black holes are gravitational giants of the universe.
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But we've found only circumstantial evidence
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that they exist.
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To make it a slam dunk,
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cosmologists are listening for proof
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in the hidden world of gravitational waves.
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There are gravitational waves going through this room
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all the time.
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Every time I move my hands like I just did,
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I create gravitational waves.
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The problem is, gravity is so weak
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that you don't detect those gravitational waves.
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In order to detect those disturbances of space and time,
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you have to have cataclysmic events
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involving massive objects.
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Black holes are some of the densest objects in the universe.
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So we should be able to hear and measure the waves
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created when they collide.
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LIGO, the laser interferometer gravitational-wave observatory,
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listens for waves that can come
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from over a billion light-years away.
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In 2017, LIGO heard an enormous crash.
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Two very massive objects
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collided at near the speed of light
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in one of the most energetic events
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that we've ever witnessed in the history of humankind.
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Two ultra-heavy, ultra-dense objects whirl around each other,
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hurling powerful gravitational waves through space.
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The closer they fall toward each other,
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the more gravitational energy they throw out.
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Finally, they collide,
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in one of the most violent events in the universe.
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The smash sends out immense gravitational waves
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that ripple across intergalactic space,
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until, eventually, LIGO detects them.
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Listening to a gravitational wave
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is like listening to a musical instrument.
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If it's making certain tones or certain vibrations,
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you can figure out the size of the musical instrument,
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the type of the musical instrument,
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who's playing the musical instrument.
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The thing that's really amazing about the LIGO detection
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is it allowed us to measure the mass of these objects
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and how quickly they coalesce together.
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So we actually have an idea how dense they must have been,
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and with modern physics, we say,
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"well, it has to be a black hole."
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But the question is, "have we missed something?"
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the information gathered by LIGO is groundbreaking.
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But some scientists think that the gravitational waves
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could have come not from black holes,
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but from something even more mysterious.
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It's possible that what we identify as black holes
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in our universe are really another object like gravastar.
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Possible... there's a capital "P" on that "possible."
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A gravastar is what scientists call an exotic compact object.
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This bizarre theoretical body has exactly the same mass
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and gravitational pull as a black hole,
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but it's made of exotic matter.
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A gravastar would be impossible to see with the naked eye,
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but because it forms differently than a black hole,
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it has a strange, incredibly dense surface.
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In the formation of what we think of as a black hole,
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the catastrophic gravitational collapse of a dense object,
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maybe it doesn't go all the way down
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to become an infinitely dense point.
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Instead, maybe there's some interaction
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that prevents the formation of the black hole,
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and instead, you have a tight, little, dense ball,
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which is what we call a gravastar.
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So the LIGO data could be the signature
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of two black holes colliding, but it also could be
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the signature of two gravastars colliding.
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Right now, we can't tell them apart.
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So, for now, gravitational waves have led to a dead end
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in the hunt for black holes.
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We can't be completely sure that we're hearing them,
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and we already know we can't see them.
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But what about the mayhem they leave behind?
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Even though you can't see the black hole itself,
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it's going to leave behind a trail of destruction,
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and that is something you can see.
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By picking apart a cosmic crime scene,
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can scientists finally solve the mystery of black holes?
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This is the hydra "a" galaxy cluster.
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840 million light-years from Earth,
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it's a region of space filled with galaxies
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and dense intergalactic gas.
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But a dark and massively destructive force
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is at work here.
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And it's blasting holes in the gas
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that are bigger than the milky way.
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Could a black hole be responsible?
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It's almost as if an intergalactic bomb has exploded
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to blow these cavities out.
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Some of these cavities are tens
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or even hundreds of thousands of light-years across,
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and to create a cavity that large
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requires an immense source of energy,
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a powerful engine that's driving it.
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To discover what's creating the cavities,
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scientists combine images taken at different wavelengths.
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They reveal something remarkable.
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The cavities are being carved out by enormous jets
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emanating from a galaxy in the center of the cluster.
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As the jets are ejected from the galaxy,
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they can actually slam into the surrounding material
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and form a shock wave, which we can see.
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And eventually, that jet inflates a bubble, a cavity,
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and the cavity grows as it's inflated
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with hot, dense plasma ejected from this jet.
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These jets are incredibly large and incredibly powerful.
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This is like a death star, but for real.
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It's much, much more energy
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than it would take to blow up a planet.
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Carnage like this could have been created
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by the energetics of a supermassive black hole
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in the form of a quasar.
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Supermassive black holes
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are millions or even billions of times the mass of the sun.
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They can be voracious overeaters,
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cramming in huge amounts of matter.
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As gas and dust swirl toward the supermassive black hole,
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it rubs together, causing friction
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that heats the material up to millions of degrees Fahrenheit.
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The magnetic field around the black hole
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forms the material into twin jets
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that spin out at enormous speeds
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for hundreds of millions of light-years.
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A quasar is born.
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The jets emitted by black holes are not only
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incredibly high-energy, but incredibly intense.
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More energy than is emitted in almost any other object
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is observed from quasars.
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Those quasars are intense enough
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to vaporize objects that they hit.
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They're deadly rays from space.
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They almost sound like science-fiction objects.
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In order to generate that much energy,
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what kind of physical process do you need?
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And pretty much the only answer we have is a giant black hole.
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Jets are absolutely
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really, really convincing smoking-gun evidence
274
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for the existence of black holes.
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The awesome power of a black hole
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can explain the vast mysterious cavities
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in the galaxy cluster hydra "a."
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So, is the case closed?
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Can we say conclusively that black holes are real?
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Although there's great evidence for black holes,
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we have to keep questioning whether they are real.
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As a scientist, I'd much rather have questions I can't answer
283
00:19:16,610 --> 00:19:18,410
than answers I can't question.
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One question scientists are struggling to answer
285
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is how black holes work.
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Are cosmology's greatest minds in danger of flunking out?
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00:19:45,300 --> 00:19:46,630
There's always going to be details
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00:19:46,640 --> 00:19:48,440
that we still have yet to figure out.
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That's true for black holes right now
290
00:19:49,910 --> 00:19:51,570
and a lot of the problems are big ones,
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00:19:51,570 --> 00:19:54,270
like how do they even exist, how do they behave?
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I mean, we're seeing that the math doesn't seem to work out,
293
00:19:59,450 --> 00:20:02,650
so there is an issue here.
294
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To show that black holes exist,
295
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scientists need to solve the math.
296
00:20:08,390 --> 00:20:09,660
If they can't,
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they might fail to prove that black holes exist at all.
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00:20:33,820 --> 00:20:38,220
Cosmologists say the universe is filled with black holes...
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Big and small.
300
00:20:41,760 --> 00:20:44,990
But the evidence for them is not conclusive.
301
00:20:48,560 --> 00:20:51,160
Even if there's 9 out of 10 pieces of evidence
302
00:20:51,170 --> 00:20:54,970
for black holes, there's still one piece of evidence left.
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00:20:54,970 --> 00:20:56,970
That can open it up to the possibility
304
00:20:56,970 --> 00:20:59,370
that maybe black holes don't exist.
305
00:21:03,650 --> 00:21:07,050
Experts instead look to the theoretical science
306
00:21:07,050 --> 00:21:08,880
of how black holes work.
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00:21:11,650 --> 00:21:14,790
They're thought to have the superdense collapsed core
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00:21:14,790 --> 00:21:16,760
of a star at their center.
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Around this is a sphere known as the event horizon,
310
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a place where the rules of physics go out the window.
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00:21:30,000 --> 00:21:31,870
The event horizon, in many ways,
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00:21:31,870 --> 00:21:34,670
cuts a black hole off from the rest of the universe.
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00:21:34,680 --> 00:21:38,410
Whatever comes in can never come back out.
314
00:21:38,410 --> 00:21:42,420
It's almost like an invisible line in space.
315
00:21:42,420 --> 00:21:45,420
It's not until you try to turn around and leave
316
00:21:45,420 --> 00:21:48,320
that you realize you're never going to escape.
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00:21:52,890 --> 00:21:55,360
It's Einstein's theory of general relativity
318
00:21:55,360 --> 00:21:58,800
that tells us nothing can leave a black hole.
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00:22:01,370 --> 00:22:02,640
This set of rules
320
00:22:02,640 --> 00:22:05,370
governs the giant structures of the universe...
321
00:22:05,370 --> 00:22:08,880
Galaxies, star systems, and planets.
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00:22:12,050 --> 00:22:14,580
General relativity is Einstein's theory of gravity.
323
00:22:14,580 --> 00:22:16,450
It is the all-encompassing theory
324
00:22:16,450 --> 00:22:19,390
that describes everything we know about gravity
325
00:22:19,390 --> 00:22:22,120
and how the universe on large scales functions.
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00:22:24,990 --> 00:22:28,500
But the universe functions on small scales, too.
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00:22:30,930 --> 00:22:34,000
Everything in the universe... Including us...
328
00:22:34,000 --> 00:22:37,870
Is made up of tiny bits of matter.
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These are governed by another set of rules,
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00:22:41,280 --> 00:22:43,610
known as quantum mechanics.
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00:22:46,480 --> 00:22:49,220
Quantum mechanics allows you to understand
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00:22:49,220 --> 00:22:50,750
at the smallest levels
333
00:22:50,750 --> 00:22:54,620
the smallest scales of what builds our universe.
334
00:22:54,620 --> 00:22:57,020
Weird stuff happens in the quantum world.
335
00:22:57,030 --> 00:22:58,830
It defies all intuition,
336
00:22:58,830 --> 00:23:01,500
and one of the weird things that can happen is you can have
337
00:23:01,500 --> 00:23:05,200
the empty space of a vacuum creating particles.
338
00:23:08,040 --> 00:23:09,500
In the quantum world,
339
00:23:09,500 --> 00:23:15,310
tiny particles can pop spontaneously into existence.
340
00:23:15,310 --> 00:23:19,980
They're drawn to each other like magnets.
341
00:23:19,980 --> 00:23:23,350
But when they collide, they annihilate each other.
342
00:23:26,260 --> 00:23:28,920
So, you've got two particles... They can pop out of the vacuum,
343
00:23:28,920 --> 00:23:30,460
and they annihilate very quickly.
344
00:23:30,460 --> 00:23:32,590
That doesn't break any laws.
345
00:23:32,590 --> 00:23:34,590
Now in the vicinity of a black hole, though,
346
00:23:34,600 --> 00:23:36,430
things get kind of complicated.
347
00:23:39,870 --> 00:23:41,800
Gravity is usually too weak
348
00:23:41,800 --> 00:23:44,600
to affect the particles in the quantum world.
349
00:23:48,540 --> 00:23:52,810
But British physicist Stephen Hawking theorized
350
00:23:52,820 --> 00:23:55,480
that at the event horizon of a black hole,
351
00:23:55,480 --> 00:23:59,690
the normal rules don't apply.
352
00:23:59,690 --> 00:24:01,620
What Stephen Hawking realized is that
353
00:24:01,620 --> 00:24:03,690
if you have a pair of particles
354
00:24:03,690 --> 00:24:05,890
that pop up at the edge of a black hole
355
00:24:05,890 --> 00:24:08,290
and one gets sucked into the black hole,
356
00:24:08,300 --> 00:24:09,760
then the other is forced to become
357
00:24:09,760 --> 00:24:11,630
a real particle in our universe.
358
00:24:11,630 --> 00:24:14,830
In order to do so, it takes energy from the black hole,
359
00:24:14,840 --> 00:24:16,370
and in that mechanism,
360
00:24:16,370 --> 00:24:21,440
black holes very slowly over time lose mass.
361
00:24:21,440 --> 00:24:22,840
With Hawking's work, we see
362
00:24:22,850 --> 00:24:25,580
that the black hole will eventually evaporate,
363
00:24:25,580 --> 00:24:28,950
and that was a complete shift in how to think about black holes.
364
00:24:32,190 --> 00:24:33,850
According to Hawking,
365
00:24:33,860 --> 00:24:36,720
when black holes aren't eating material,
366
00:24:36,720 --> 00:24:42,800
they actually shrink by emitting thermal radiation or heat.
367
00:24:42,800 --> 00:24:44,130
In this process,
368
00:24:44,130 --> 00:24:48,600
a black hole will eventually evaporate completely,
369
00:24:48,600 --> 00:24:52,340
and this creates a problem for scientists.
370
00:24:52,340 --> 00:24:53,870
Everything in the universe,
371
00:24:53,880 --> 00:24:56,810
from atoms to planets to spacecrafts,
372
00:24:56,810 --> 00:25:00,080
carry information about what they're made of,
373
00:25:00,080 --> 00:25:04,880
how fast they're going, and where they've been.
374
00:25:04,890 --> 00:25:06,420
The laws of physics state
375
00:25:06,420 --> 00:25:10,290
that this information can't be lost from the universe,
376
00:25:10,290 --> 00:25:12,890
and that should apply to black holes.
377
00:25:15,230 --> 00:25:17,160
So if an object passes through
378
00:25:17,170 --> 00:25:19,900
the event horizon of a black hole,
379
00:25:19,900 --> 00:25:22,500
all the information about that object
380
00:25:22,500 --> 00:25:25,540
becomes part of the black hole itself.
381
00:25:28,510 --> 00:25:32,450
Once they've fallen in, all you can see is a heavier black hole,
382
00:25:32,450 --> 00:25:35,380
and you don't know what fell in if you weren't watching it.
383
00:25:35,380 --> 00:25:37,920
Well, that doesn't violate the laws of physics,
384
00:25:37,920 --> 00:25:39,990
but if the black hole continues to evaporate,
385
00:25:39,990 --> 00:25:42,320
evaporate, evaporate with thermal radiation
386
00:25:42,320 --> 00:25:43,720
and then disappear,
387
00:25:43,730 --> 00:25:46,130
then all you have afterwards is thermal radiation.
388
00:25:46,130 --> 00:25:48,900
You have no information, even in principle,
389
00:25:48,900 --> 00:25:50,800
about what fell in.
390
00:25:50,800 --> 00:25:53,270
And that information is precisely
391
00:25:53,270 --> 00:25:57,200
what quantum mechanics says can't be lost.
392
00:25:57,210 --> 00:26:00,210
The thermal radiation coming out of the black hole
393
00:26:00,210 --> 00:26:02,280
contains no information.
394
00:26:02,280 --> 00:26:04,410
It's a blank slate.
395
00:26:04,410 --> 00:26:08,010
If this continues until the black hole evaporates,
396
00:26:08,020 --> 00:26:11,480
then all the information is completely lost
397
00:26:11,490 --> 00:26:14,290
when the black hole disappears.
398
00:26:14,290 --> 00:26:17,560
If that information disappears,
399
00:26:17,560 --> 00:26:21,490
then the laws of quantum mechanics are violated.
400
00:26:21,500 --> 00:26:25,470
And we don't know how to solve that paradox yet.
401
00:26:27,100 --> 00:26:30,440
We're trying to combine quantum mechanics and relativity,
402
00:26:30,440 --> 00:26:33,510
and the first time we're able to do it
403
00:26:33,510 --> 00:26:36,640
leads to this giant mess that calls into question
404
00:26:36,650 --> 00:26:39,780
fundamental assumptions about the way the universe works,
405
00:26:39,780 --> 00:26:42,950
so... that's kind of a problem.
406
00:26:44,450 --> 00:26:48,120
The problem is known as the information paradox,
407
00:26:48,120 --> 00:26:52,190
and if scientists are going to find an answer to it,
408
00:26:52,190 --> 00:26:55,130
they'll have to unify their two theories...
409
00:26:55,130 --> 00:26:58,330
General relativity, the rules of the large,
410
00:26:58,330 --> 00:27:03,270
and quantum mechanics, the rules of the tiny.
411
00:27:03,270 --> 00:27:08,210
And so far, that's proved impossible.
412
00:27:08,210 --> 00:27:12,010
I think the single biggest embarrassment in physics
413
00:27:12,010 --> 00:27:14,410
is that we have these two theories...
414
00:27:14,420 --> 00:27:16,820
General relativity describing the big
415
00:27:16,820 --> 00:27:19,690
and quantum mechanics describing the small...
416
00:27:19,690 --> 00:27:22,090
That simply don't get along.
417
00:27:22,090 --> 00:27:24,690
Nature obviously knows what it's doing,
418
00:27:24,690 --> 00:27:29,760
but we just don't have a single, unified explanation.
419
00:27:29,770 --> 00:27:31,230
The past few decades,
420
00:27:31,230 --> 00:27:35,840
as we've tried to describe black holes fully,
421
00:27:35,840 --> 00:27:38,240
the more work we've done,
422
00:27:38,240 --> 00:27:41,440
the more of a tangled mess we get.
423
00:27:41,440 --> 00:27:44,040
It will take at least one brilliant mind
424
00:27:44,050 --> 00:27:45,510
to figure this out.
425
00:27:48,050 --> 00:27:50,580
Maybe someone already has.
426
00:27:50,590 --> 00:27:54,850
The classical black hole has a shell-like event horizon
427
00:27:54,860 --> 00:27:57,520
beyond which nothing can escape.
428
00:27:57,530 --> 00:28:00,130
And according to the information paradox,
429
00:28:00,130 --> 00:28:06,070
information is lost when a black hole evaporates.
430
00:28:06,070 --> 00:28:09,800
But here's a radical, mind-bending idea...
431
00:28:09,810 --> 00:28:14,540
What if black holes have hair?
432
00:28:14,540 --> 00:28:17,740
What Hawking and his collaborators pointed out
433
00:28:17,750 --> 00:28:21,010
is that black holes can have soft hair,
434
00:28:21,020 --> 00:28:22,880
and if that's true, that would be a way
435
00:28:22,880 --> 00:28:24,950
of encapsulating all the information
436
00:28:24,950 --> 00:28:27,950
that went into the black hole.
437
00:28:27,960 --> 00:28:31,960
Scientists propose that these so-called hairs
438
00:28:31,960 --> 00:28:34,030
somehow store the information
439
00:28:34,030 --> 00:28:38,300
of whatever has fallen into the black hole.
440
00:28:38,300 --> 00:28:40,430
The information is then imprinted
441
00:28:40,440 --> 00:28:45,410
on the thermal radiation emitted as the black hole evaporates.
442
00:28:47,640 --> 00:28:53,050
These hairy black holes could solve the information paradox,
443
00:28:53,050 --> 00:28:57,780
but they're entirely theoretical.
444
00:28:57,790 --> 00:28:59,190
These are really new ideas,
445
00:28:59,190 --> 00:29:01,720
and people are still trying to figure them out.
446
00:29:01,720 --> 00:29:03,920
So it's hard to give a really good explanation
447
00:29:03,930 --> 00:29:05,520
of something that is...
448
00:29:05,530 --> 00:29:07,390
This is theory in the making.
449
00:29:07,400 --> 00:29:09,430
People are working this out now.
450
00:29:13,270 --> 00:29:15,540
Solving the information paradox
451
00:29:15,540 --> 00:29:19,140
is pushing science to its limits.
452
00:29:19,140 --> 00:29:21,010
But an even bigger problem
453
00:29:21,010 --> 00:29:24,280
is sitting at the heart of a black hole.
454
00:29:26,350 --> 00:29:29,080
The big problem about the idea of black holes
455
00:29:29,080 --> 00:29:32,420
is that at its center, there's what we call a singularity.
456
00:29:32,420 --> 00:29:36,090
At this singularity, matter has infinite density
457
00:29:36,090 --> 00:29:37,920
and space is infinitely curved.
458
00:29:39,760 --> 00:29:44,300
That's not something that really sounds like physics.
459
00:29:46,370 --> 00:29:49,370
Singularities do not exist in nature,
460
00:29:49,370 --> 00:29:52,910
and when they appear in the mathematics,
461
00:29:52,910 --> 00:29:55,310
that's a signal that you're doing something wrong,
462
00:29:55,310 --> 00:29:57,180
that you're incomplete.
463
00:29:57,180 --> 00:29:59,710
It's like the ultimate curse word,
464
00:29:59,710 --> 00:30:03,720
and mother nature doesn't like it when we curse.
465
00:30:03,720 --> 00:30:08,790
To complete the math and understand black holes,
466
00:30:08,790 --> 00:30:10,120
cosmologists grapple
467
00:30:10,130 --> 00:30:14,190
with one of science's most mind-bending concepts...
468
00:30:14,200 --> 00:30:15,830
Infinity.
469
00:30:38,950 --> 00:30:41,690
Black holes... They're thought to be
470
00:30:41,690 --> 00:30:45,230
a fundamental part of the universe.
471
00:30:45,230 --> 00:30:47,360
But scientists are not only struggling
472
00:30:47,360 --> 00:30:49,500
to explain how they work,
473
00:30:49,500 --> 00:30:53,070
they're struggling to prove they even exist.
474
00:30:55,300 --> 00:30:58,300
So, black holes have some problems.
475
00:30:58,310 --> 00:31:00,970
Every time we try to think of something,
476
00:31:00,980 --> 00:31:03,840
some creative mathematical solution
477
00:31:03,850 --> 00:31:05,910
to describe black holes fully,
478
00:31:05,910 --> 00:31:09,320
it breaks down, and we just can't make any progress.
479
00:31:11,390 --> 00:31:13,190
We can't make reliable predictions,
480
00:31:13,190 --> 00:31:15,260
we can't compare to observations.
481
00:31:15,260 --> 00:31:17,790
What is the solution?
482
00:31:17,790 --> 00:31:19,990
We honestly don't know.
483
00:31:23,400 --> 00:31:24,930
Scientists are finding
484
00:31:24,930 --> 00:31:28,470
that general relativity and quantum mechanics
485
00:31:28,470 --> 00:31:31,200
go haywire at the edge of a black hole.
486
00:31:33,470 --> 00:31:37,680
But inside a black hole, things could be even weirder.
487
00:31:46,750 --> 00:31:49,490
When a giant dying star collapses,
488
00:31:49,490 --> 00:31:53,690
the mass of the star falls in and keeps falling in,
489
00:31:53,690 --> 00:31:56,900
crunching down into an infinitely small point.
490
00:32:02,100 --> 00:32:06,240
This is called the singularity.
491
00:32:06,240 --> 00:32:07,840
A singularity is troubling
492
00:32:07,840 --> 00:32:11,110
because although it sounds cool and scientific,
493
00:32:11,110 --> 00:32:13,050
it's really just a fancy word of saying,
494
00:32:13,050 --> 00:32:16,380
"oh, we have no clue what happens here."
495
00:32:16,380 --> 00:32:19,790
the way our physics describes black holes when they form,
496
00:32:19,790 --> 00:32:22,190
you're taking a finite amount of mass
497
00:32:22,190 --> 00:32:24,460
and you're collapsing it down.
498
00:32:24,460 --> 00:32:27,990
And its volume should shrink all the way to zero,
499
00:32:28,000 --> 00:32:31,660
but that means it has infinite density and infinite gravity,
500
00:32:31,670 --> 00:32:33,330
and that doesn't make sense.
501
00:32:38,270 --> 00:32:41,070
If you make a prediction and the answer is infinite,
502
00:32:41,080 --> 00:32:44,540
it tells you there's something wrong with your prediction,
503
00:32:44,550 --> 00:32:47,780
'cause we've never seen an infinity in the universe today.
504
00:32:51,090 --> 00:32:55,360
Once again, quantum mechanics is at the heart of the problem.
505
00:32:58,760 --> 00:33:00,830
Have you ever thought about the term "quantum mechanics"
506
00:33:00,830 --> 00:33:02,900
and thought about what those words mean?
507
00:33:02,900 --> 00:33:04,300
Well, everything in the universe
508
00:33:04,300 --> 00:33:06,830
is broken up into tiny, little units.
509
00:33:06,830 --> 00:33:11,170
There really is a basic unit of energy, a unit of time,
510
00:33:11,170 --> 00:33:14,640
even a unit of space that cannot be divided any further.
511
00:33:14,640 --> 00:33:17,440
There's a limit to how small things can be.
512
00:33:20,250 --> 00:33:22,850
The smallest unit of space in the universe
513
00:33:22,850 --> 00:33:26,850
is what's known as a Planck length.
514
00:33:26,850 --> 00:33:28,520
If you took a human hair
515
00:33:28,520 --> 00:33:32,060
and blew it up to the width of the observable universe,
516
00:33:32,060 --> 00:33:38,130
one Planck length would be about 1/4000th of an inch.
517
00:33:38,130 --> 00:33:42,470
If there is a universal limit on the smallest size,
518
00:33:42,470 --> 00:33:47,740
then something infinitely small can't exist.
519
00:33:47,740 --> 00:33:50,480
Well, if infinity doesn't exist, then singularities don't exist,
520
00:33:50,480 --> 00:33:52,010
and if singularities don't exist,
521
00:33:52,010 --> 00:33:54,010
then Einstein's theory of general relativity
522
00:33:54,020 --> 00:33:56,280
is not correct.
523
00:33:56,280 --> 00:33:58,080
The simplest thing to do is to say,
524
00:33:58,090 --> 00:34:00,020
"well, let's choose some new equations.
525
00:34:00,020 --> 00:34:02,960
Let's change Einstein's theory of gravity somehow.
526
00:34:02,960 --> 00:34:06,030
Let's invent what we would call exotic speculative physics."
527
00:34:11,630 --> 00:34:15,440
This speculative physics has led scientists to invent
528
00:34:15,440 --> 00:34:18,240
the idea of the Planck star.
529
00:34:23,910 --> 00:34:25,910
If you passed one in space,
530
00:34:25,910 --> 00:34:28,180
it would look just like a black hole.
531
00:34:31,590 --> 00:34:35,720
But a Planck star doesn't have a singularity at its core.
532
00:34:37,730 --> 00:34:39,730
Maybe things can't collapse down
533
00:34:39,730 --> 00:34:42,660
to less than the Planck's length,
534
00:34:42,660 --> 00:34:47,130
that maybe you get stuck with this little Planck-size nugget
535
00:34:47,140 --> 00:34:50,100
that stabilizes things, keeps everything finite.
536
00:34:52,070 --> 00:34:56,280
So, where a singularity is at the center of a black hole,
537
00:34:56,280 --> 00:35:01,150
a Planck-sized nugget is at the center of a Planck star.
538
00:35:03,820 --> 00:35:06,950
A Planck star is just like a black hole,
539
00:35:06,960 --> 00:35:11,690
except it plays by the rules of quantum mechanics.
540
00:35:11,690 --> 00:35:16,700
The problem is, Planck stars are just another exotic theory.
541
00:35:18,970 --> 00:35:22,370
The reason there are so many exotic alternatives
542
00:35:22,370 --> 00:35:25,970
to black holes is because you can write down a gazillion
543
00:35:25,970 --> 00:35:29,370
different postulated, mysterious new kinds of matter
544
00:35:29,380 --> 00:35:32,440
and say, "suppose this kind of weird stuff exists.
545
00:35:32,450 --> 00:35:34,380
Then maybe that could explain the data."
546
00:35:34,380 --> 00:35:35,650
Problem is, there's no evidence
547
00:35:35,650 --> 00:35:37,520
that any of that kind of stuff exists.
548
00:35:44,190 --> 00:35:45,930
Scientists are getting creative
549
00:35:45,930 --> 00:35:50,460
as they try to prove that black holes exist.
550
00:35:50,460 --> 00:35:55,740
They've imagined strange objects and used exotic workarounds.
551
00:35:55,740 --> 00:36:00,010
But one black hole idea is the strangest of all.
552
00:36:00,010 --> 00:36:04,480
What if we are living inside of one?
553
00:36:04,480 --> 00:36:06,350
It would be the most mind-blowing thing ever
554
00:36:06,350 --> 00:36:08,480
if we were actually living inside a black hole.
555
00:36:08,480 --> 00:36:10,480
And the crazy thing is, it could happen.
556
00:36:10,490 --> 00:36:12,290
It could be true.
557
00:36:42,020 --> 00:36:46,650
Black holes are full of theoretical holes.
558
00:36:46,650 --> 00:36:50,660
Scientists say they're out there, but we can't see them.
559
00:36:50,660 --> 00:36:54,990
Math says there's a singularity at a black hole's core,
560
00:36:55,000 --> 00:36:57,900
but in nature, these don't exist.
561
00:36:57,900 --> 00:37:00,930
The rules we use to understand the universe
562
00:37:00,940 --> 00:37:04,400
simply don't seem to apply to black holes.
563
00:37:04,410 --> 00:37:06,810
So where does that leave us?
564
00:37:08,480 --> 00:37:10,810
Maybe a classical black hole
565
00:37:10,810 --> 00:37:13,880
with an event horizon described by general relativity
566
00:37:13,880 --> 00:37:17,280
just isn't the proper description of the physics.
567
00:37:22,490 --> 00:37:24,760
This lack of understanding
568
00:37:24,760 --> 00:37:28,690
opens the door to some outlandish theories
569
00:37:28,700 --> 00:37:31,800
that aim to show black holes can exist.
570
00:37:35,840 --> 00:37:40,240
But one idea stands out as the strangest of them all.
571
00:37:42,710 --> 00:37:44,710
In our understanding of the universe,
572
00:37:44,710 --> 00:37:47,980
there are two places where everything seems to break down.
573
00:37:47,980 --> 00:37:50,380
One is inside the heart of a black hole.
574
00:37:50,390 --> 00:37:53,120
The other is what happened right before the big bang.
575
00:37:53,120 --> 00:37:54,520
And some people have wondered
576
00:37:54,520 --> 00:37:56,460
if these two things could be linked.
577
00:37:59,130 --> 00:38:01,860
It sounds crazy, but there's actually a model
578
00:38:01,860 --> 00:38:03,330
that you could put together
579
00:38:03,330 --> 00:38:06,270
in which all of our observations of the universe
580
00:38:06,270 --> 00:38:08,400
are entirely consistent
581
00:38:08,400 --> 00:38:12,000
with us actually being inside of a black hole.
582
00:38:12,010 --> 00:38:13,810
How would that work?
583
00:38:13,810 --> 00:38:16,340
Well, a black hole is supposed to have
584
00:38:16,340 --> 00:38:19,480
a tiny, dense region at its core
585
00:38:19,480 --> 00:38:23,180
containing trillions and trillions of tons of matter.
586
00:38:25,150 --> 00:38:27,820
There is a theory that as matter is crushed
587
00:38:27,820 --> 00:38:30,360
into the center of a black hole, it actually reaches a point
588
00:38:30,360 --> 00:38:32,960
where it can be crushed no further.
589
00:38:32,960 --> 00:38:36,360
An event like this could, in fact, lead to a big bang.
590
00:38:39,500 --> 00:38:41,970
When the collapsing matter in the black hole
591
00:38:41,970 --> 00:38:44,400
reaches a maximum density...
592
00:38:46,510 --> 00:38:48,240
it bounces back,
593
00:38:48,240 --> 00:38:54,050
expanding outwards in a cataclysmic explosion.
594
00:38:54,050 --> 00:38:58,650
The matter gradually cools over time to form atoms,
595
00:38:58,650 --> 00:39:02,090
building galaxies, stars, and planets.
596
00:39:04,790 --> 00:39:06,990
If that sounds familiar,
597
00:39:06,990 --> 00:39:10,700
it's because it's just like the universe we see today.
598
00:39:13,070 --> 00:39:16,200
This is one idea for how a universe like ours is formed...
599
00:39:16,200 --> 00:39:18,940
That, in fact, we all live inside of a black hole
600
00:39:18,940 --> 00:39:20,940
that was created this way.
601
00:39:20,940 --> 00:39:22,340
Within our galaxy alone,
602
00:39:22,340 --> 00:39:25,210
there are tens of millions of black holes.
603
00:39:25,210 --> 00:39:27,010
And just think... Inside each one of them
604
00:39:27,010 --> 00:39:29,610
could be a baby universe waiting to be born.
605
00:39:29,620 --> 00:39:30,650
That's incredible.
606
00:39:32,490 --> 00:39:35,290
Are we inside of a black hole that exists in a universe
607
00:39:35,290 --> 00:39:38,490
that has other black holes that has other universes
608
00:39:38,490 --> 00:39:40,230
which exists inside of a black hole?
609
00:39:40,230 --> 00:39:43,700
It goes on and on and on ad infinitum.
610
00:39:43,700 --> 00:39:46,900
Once again, this is all theoretical,
611
00:39:46,900 --> 00:39:50,240
but it's a compelling idea.
612
00:39:50,240 --> 00:39:53,840
I mean, are we actually existing inside of a black hole?
613
00:39:53,840 --> 00:39:55,310
I don't know, but, you know,
614
00:39:55,310 --> 00:39:57,510
sometimes when I'm sitting in traffic waiting to get home,
615
00:39:57,510 --> 00:40:00,510
it feels like time is stretched out infinitely.
616
00:40:02,050 --> 00:40:04,050
I don't think that you should lose sleep at night
617
00:40:04,050 --> 00:40:06,720
wondering if we're actually inside of a black hole.
618
00:40:06,720 --> 00:40:08,720
The answer is "probably not."
619
00:40:08,720 --> 00:40:12,260
But because black holes are just pushing at the edge
620
00:40:12,260 --> 00:40:14,730
of what we understand about nature,
621
00:40:14,730 --> 00:40:16,400
they are the perfect illustration
622
00:40:16,400 --> 00:40:18,600
of everything that we don't know about the universe,
623
00:40:18,600 --> 00:40:19,930
and that is a lot.
624
00:40:28,540 --> 00:40:31,140
So, what do we know?
625
00:40:31,140 --> 00:40:32,950
We can't see black holes.
626
00:40:32,950 --> 00:40:37,480
We can only find circumstantial evidence of them.
627
00:40:37,490 --> 00:40:42,420
They violate the laws of physics that predict them.
628
00:40:42,420 --> 00:40:45,760
They may even be hairy.
629
00:40:45,760 --> 00:40:49,430
So, do they actually exist?
630
00:40:54,300 --> 00:40:56,500
So, I will tell you that right now in modern physics,
631
00:40:56,500 --> 00:40:58,570
we have no idea what is going on
632
00:40:58,570 --> 00:41:00,770
inside the heart of a black hole,
633
00:41:00,770 --> 00:41:03,380
whether black holes in the true sense really exist at all,
634
00:41:03,380 --> 00:41:05,910
but the wonderful thing is that physics is now taking us
635
00:41:05,910 --> 00:41:10,720
down paths that we would never have imagined before.
636
00:41:10,720 --> 00:41:14,920
Lack of evidence of how black holes work
637
00:41:14,920 --> 00:41:18,320
is not evidence against the existence of black holes.
638
00:41:18,330 --> 00:41:20,830
It's just evidence of lack of understanding.
639
00:41:23,000 --> 00:41:25,060
If you ask me what I believe,
640
00:41:25,070 --> 00:41:27,070
I'd have to tell you that I don't believe in black holes.
641
00:41:27,070 --> 00:41:29,470
I believe in something which behaves like black holes.
642
00:41:32,940 --> 00:41:36,010
It could be that all the objects in our universe
643
00:41:36,010 --> 00:41:38,680
that we currently identify as black holes
644
00:41:38,680 --> 00:41:40,680
aren't really black holes,
645
00:41:40,680 --> 00:41:43,320
but if I were to bet, I would bet on black holes.
646
00:41:46,150 --> 00:41:48,420
I think they're the simplest explanation.
647
00:41:48,420 --> 00:41:51,560
Yep, they have a lot of problems that we have to resolve,
648
00:41:51,560 --> 00:41:54,030
but I do... I believe in black holes.
649
00:41:56,630 --> 00:41:58,700
Whatever it is that we're seeing,
650
00:41:58,700 --> 00:41:59,970
it smells like a black hole,
651
00:41:59,970 --> 00:42:02,230
walks like a black hole, it quacks like a black hole.
652
00:42:02,240 --> 00:42:03,770
It's a black hole.
653
00:42:06,310 --> 00:42:10,040
Right now, black holes are the best explanation
654
00:42:10,040 --> 00:42:12,380
for what we see out there.
655
00:42:12,380 --> 00:42:15,910
But if we can find a way to unify our theories,
656
00:42:15,920 --> 00:42:18,780
we might finally prove they exist
657
00:42:18,790 --> 00:42:24,490
and discover a whole lot more about how our universe works.
53119
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