Why Are Black Holes Astonishing? | Episode 209 | Closer To Truth

[Music] [Music] black holes are unimaginably strange they warp space and twist time squeeze matter to a vanishing point and trap light so that it cannot escape that's why they're called black black holes sit in the center of galaxies and shape the universe but if we can't see them how do we know they're real they challenge our notion of space and time they change our sense of what is real and true what mysteries they are what secrets do they hold why are black holes so astonishing i'm robert lawrence kuhn and closer to truth is my journey to find out i begin at cal tech with the feynman professor of theoretical physics kip thorne we meet in kipp's lab a prototype of a gravity wave detector kip is one of the world's leading experts on gravitation which is the essence of black holes the dark side of the universe kip describe the structure of black hole so a black hole has a horizon which is the surface of the black hole except it's not a hard surface like a surface of a billiard ball and it has a singularity at the center and it is made in the vicinity of the horizon and down to the singularity by warped space and time the horizon is a very special place it's the place that that that has the property that if you fall into a black hole you pass through the horizon you don't notice anything special until you try to get back out and you can't get back out you're pulled inexorably toward the center and we know they are there with 99.9 confidence from observations mixed with a little bit of theory we know that in our own galaxy there are roughly a hundred million of these objects that have sizes of about say 10 miles or so across thing sizes like that we know that at the center of our galaxy in all almost all other large galaxies there's a huge black hole that has a size more like the distance between the earth and the moon and the equivalent of mass of how many suns and yes and in the center of the galaxies masses of a million to a billion to 10 billion times the mass of the sun all contained in this size that is more like a small piece of our solar system the smaller black holes the ones that may be 10 miles across weighing the same as maybe ten sons so they're remarkable objects from that point of view but the thing that has gripped me about black holes in the same way as black holes grip by their gravity anything that falls in their vicinity is the fact that a black hole is an object that is made not for matter but from warped space and warped time what does that mean [Laughter] well so suppose that you were to measure the circumference around a black hole and so you go marching around and around and you see that the circumference is 30 miles and then suppose that you measure the diameter you would think that diameter ought to be 30 divided by pi or 10 miles roughly 10 but no you measure that diameter and it is enormously larger than 10 miles it may be a thousand miles it may be a million miles it's unbelievably large so space is warped and you might ask me well how is it possible that that you can have a huge diameter and a small circumference don't the laws of euclidean geometry forbid it the answer is they do so including geometry doesn't apply it's like you take a child's trampoline a large rubber sheet and you put a heavy rock heavy very dense rock in the center and it sinks way down and then you're a bl an ant but you're a blind at so you can't see what's going on and you march around and measure the circumference around the trampoline and then you go in and you measure the diameter by marching down and back up around the rock and the diameter's huge compared to the circumference wow it's the same thing and that is what the black hole is made of there is no matter in that black hole it's not a dense object made of very dense matter there's no matter at all there was matter in the star that gave birth to the black hole long ago a star like our sun but somewhat heavier will have burned its nuclear fuel can no longer keep itself puffed out by its internal heat it starts to cool off and it then implodes and all of the matter in that star much more matter than we have in our sun goes crashing into the center and is destroyed at what we call a singularity at the center where that rock was on the child's trampoline all the matters destroyed there's nothing left to accept this warped space and warped time now most people would think that if we have this 10 mile object like a big bowling ball if it was possible not to be destroyed i got there i could knock on it be solid but if if i pass through that boundary i wouldn't know the difference that's right you wouldn't know the difference however you would know the difference if you tried to come back out but there's nothing special the boundary that you can see locally in your vicinity there's no hard surface and if you look above yourself you can still see the universe above your head they just can't see you it's a one-way membrane light can come in from the universe into the interior uh bringing you an image of what's going on in the universe but you can't send any light back out to your friends outside to tell you what's going on you pay the ultimate price when you go in that you can never publish the results of your expirations of course and by the way you also die einstein taught us that mass and energy are the same thing you can convert them back and forth okay e equals mz square c squared and so the mass or energy of in this black hole is actually not concentrated in the singularity it's concentrated in the warping of space and time in the same way as if you take the child's trampoline and you put the rock on it and the rock deforms it it takes energy to deform it you have to really push on it to deform it you've got to put energy in to stretch the rubber in the same way as the star gives birth to the black hole the star does a lot of work as it creates the black hole as it implodes and all of the mass and energy of the star in the end goes into the warping of space and the warping of time [Music] black holes have no matter at all all their massive gravitation comes from converting the original matter of the exploding star into the equivalent energy e equals m c squared and that energy is expressed and trapped in the warping of space and time [Music] the secrets of black holes lie in fundamental law so that's where i must go [Music] and i go to leonard suskind professor of physics at stanford and an originator of string theory what do black holes reveal about fundamental law [Music] leonard the concept of black holes is something that common people can talk about today to a physicist and you've studied black holes why are they so important from a theoretical point of view because they lead to what i would call a conflict of principles and when principles clash that's where progress is made we have two separate theories of nature which are incompatible apparently and which need to be put together one of them is the theory of the very very small quantum mechanics the quantum mechanics of atoms molecules and so forth the uncertainty principle all these marvelous things that were discovered at the beginning of the 20th century about microscopic physics at the same time physicists einstein the same guy incidentally was also thinking about the very big and the very heavy he was thinking about gravity gravity governs the very big and the very heavy quantum mechanics governs the very small two different regimes of the world then you have black holes black holes are objects which belong to both regimes they're big and they're heavy but they have quantum properties in fact they're very quantum mechanical objects the fact that they belong to both domains tells us we have no choice we have to put these two theories together we have to make sense out of them even though they appear to conflict with each other black holes are the entry into the world that combines them both so there is a basic paradox and a conflict in our in the principles of physics that we don't understand at the moment and that conflict is the laws of quantum mechanics the laws of information the laws of physics as we've known them for 300 years says nothing must ever be lost and that must say that it cannot pass through the horizon but must be radiated back out on the other hand everything we know about black holes says that things fall into the black hole and are destroyed at the singularity that is the big conflict that physics is trying to deal with and is trying to reconcile the answer whether things fall into black holes and are destroyed or whether before they actually get to the horizon they're kicked back out and radiated back out seems to have the answer that both are true i will leave you with that that both are true but we have to reconcile them will that do black holes force us to reconcile quantum mechanics which describes the smallest features of subatomic particles with general relativity which describes the largest features of the entire universe the two theories quantum mechanics and general relativity seem to contradict each other but that's impossible so can they be combined the quest is called quantum gravity juan maldecina at the institute for advanced study in princeton has remarkable ways to describe quantum gravity and astonishing ways to explain black holes they're not easy to understand but really important i'm going to try black holes are a wonderful thing they're a wonderful prediction of the einstein theory of gravity which is a theory of space time and how space time curves and how the geometry of space-time affects the motion of particles and so on but black holes are also important for understanding quantum gravity because the whole mass of the star is concentrated in a very tiny region and when you have lots of matter concentrating on a very small region quantum effects become important in the same way that quantum effects are important for an atom which is a very small thing quantum effects are important at the singularity so these quantum effects imply some very strange things and things that naively contradict the picture of of black holes according to the classical theory so in part the most surprising thing is that they imply that the black hole will slowly evaporate so quantum mechanics says that the the black hole can evaporate whereas classical general relativity says that nothing can escape it's very compacted and it's the densest thing you can imagine yeah that's right so when you have a space stamp that is changing this this background that changes creates fluctuations creates small perturbations in the fields and in the quantum fields and so this arises quantum particles that are emitted from the black hole so these particles could be photons could be just radiation it could be gravitons also the quantum of gravity and neutrinos and so what this implies is that the black hole is losing energy it's emitting something while according to the classical theory everything should fall into the black hole so there is some tension between classical and quantum and if you calculate what this radiation is you find that this radiation is completely thermal so thermal means that this random contains no quantum information however according to the rules of quantum mechanics quantum information has to be preserved so if you knew what fell into the black hole you should know what comes out of the black hole so this cannot be completely random in a thermal way it should only have the randomness of quantum mechanics which contains some information in it otherwise the rules of quantum mechanics would be wrong and would need to be changed this is an important question so do we need to modify the rules of quantum mechanics when we include gravity or not and some people argued so hawking in particular argued that one should modify the rules of quantum mechanics in presence in the presence of black holes on the other hand people from let's say the string theory community hold this quantum principle as sacred so in the sense that we are we're not modifying quantum mechanics we might modify the natural space-time but we don't want to modify quantum mechanics and one of the main reasons is we don't know how to modify it so the simplest approach is to well let's suppose quantum mechanics is not modified and let's try to make a theory of space time and quantum gravity and so on and so the black hole is a very good laboratory for understanding this problem so basically a black hole has been utilized to show the power and the consistency and the triumph of quantum mechanics yeah and that's right and well also of string theory that the fact that string theory originally was made as a theory of small fluctuations of space-time so small ripples of space-time but even when you have big deformations like as you have in a black hole string theory can still describe these things and in a consistent quantum way so it's a powerful test also on string theory so it's a very nice achievement of the fear of quantum gravity of course in the future we'd like to apply similar ideas for describing the big bang but well that's really for the future [Music] nothing if not ambitious describing the big bang quantum gravity and string theory all with the same stroke how far can black holes take us to find out to harvard i go to meet one of the world's leading young physicists nima arkani hamad whose interests span from quantum theory to cosmology well first of all black holes were the first place where the full glory of general relativity uh in the way that it curves space and time um manifested itself in fact it was the existence of a black hole was so surprising that even einstein himself didn't really believe that they would physically exist but black holes are really the first time when when a very radical departure from a newtonian picture of the world was needed when you add quantum mechanics black holes are a great little laboratory where the ideas of quantum mechanics and general relativity really collide and while normally we think that the effects of quantum mechanics and gravity should only be important at very very tiny distances maybe near the center of the black hole near the beginning of the universe since hawking's realization that black walls actually emit radiation there has been a very big puzzle known as the black hole information puzzle regarding what happens when you form a black hole and then it evaporates away and gets smaller and smaller until it finally reaches a tiny size and it disappears altogether this process appears to be describable using only long distance physics without knowing anything about the details of quantum gravity on the other hand when you apply these rules you get an apparently crazy answer that information is gobbled up by a black hole and so if you throw an encyclopedia in by the time the black hole is gone all the information in the encyclopedia has totally disappeared so black holes have a theoretical significance because they're a place where away from regions where you would think quantum mechanics and gravity are fighting each other but where the curvatures of space and time are low everything is very macroscopic something very funny and quantum is happening in a way that we still don't understand in great detail so does that give us any possibility for using black holes as a window into other universes or any of these possibilities that's a really fascinating possibility and if we understood the inside of black holes better we might indeed be able to make such a connection what we have a good uh at least theoretical understanding of now is what happens when you throw stuff together to make a black hole and it evaporates and the stuff comes out we still don't understand how to describe what happened to someone who falls into a black hole and eventually hits the singularity of the black hole and i suspect that progress on that problem will translate to new ways of thinking about the multiverse does the singularity of the black hole have any significance for the singularity of the initial big bang well just as you approach the singularity uh energies get higher and higher curvatures get larger and larger and it's also a singularity in time because uh because falling towards the center of a black hole has the uh there's nothing you can do to avoid hitting the singularity much like in a universe that's collapsing the march of time makes it impossible to stop you from hitting the inevitable big crunch singularity that's in fact what characterizes the inside of a black hole the role of space and time gets reversed relative to what you think is going on uh outside and so there's there's analogies there's certainly analogies between the sink the black hole singularity and a cosmological singularity they're not identical in detail but they're certainly strong analogies between them [Music] black holes express the full glory of general relativity but something funny is happening with quantum mechanics can black holes give clues to the origin of the universe to multiple universes lee smolen at the perimeter institute for theoretical physics challenges current belief he thinks black holes may generate multiple universes and explain the fitness of ours you've hypothesized that black holes can somehow become the mother of future universes how is that possible first let me say that's not my idea that's an idea that i learned from my teachers from bryce dewitt from john wheeler it's one of the oldest ideas in the subject of quantum gravity that when you take quantum mechanics into effect the singularity at the end of the evolution of the star that collapses to a black hole when everything becomes infinitely dense and time stops is removed and time continues now where does time continue to and the most natural point of view is that time continues to a new region of space and time since space and time is dynamical and is created by evolution you create a new region of space and time which can't be perceived from the original region because of the horizon of the black hole quantum effects would remove the singularity so you could keep going and then you get a new baby universe what i did was i realized that if the laws changed just a little bit just like on the average generation to generation biology in a species the genes change just a little bit you don't get a radically different creature when you have a child okay then there could be natural selection then there could be accumulation of positive and negative selection by having more or less progeny if you imagine now of population of universes growing there's one each time there's a black hole in our universe so if the law has changed slightly at that event one gets a large number it's about a billion billion is what we expect in our universe black holes now let's suppose there's another universe which has a different set of laws that only makes a handful of universes then each of those is very close to that so they're likely also to only make a handful so after several generations there's a vast number of ones like ours and there's a small number of others just works just like natural selection and biology if one therefore imagines after a long time goes by almost every universe in that population has the property that its parents had a lot of children right because much more likely to be the child of a chain of descendants that had lots of children that had a few so that leads to an explanation for why are the laws of physics the way they are and the conclusion is that again just like biology that a typical universe will be very fit that is if you change the laws slightly in almost any possible way you'll get a universe which is either roughly the same or is less fit that fitness means how many children it produces why would a universe that selects for black holes be so favorable for life why would this possibly be [Music] okay so what then is the singularity where space and time are destroyed singularity is a mystery big mystery that's why i came to you to find out the mystery i'll tell you about the mystery [Music] black holes reveal the warped side of the universe within their horizons everything we think we know space and time particles and forces changes radically [Music] what emerge are clues about the deep structure of both the largest and the smallest features of our world on the largest level of galaxies black holes affect their structure [Music] on the smallest level of quantum mechanics black holes are the ultimate proving grounds [Music] can black holes go further still give insight on how the universe began generate multiple universes like natural selection in biology we can never see them but the light of black holes brings us closer to truth [Music] for complete interviews and for further information please visit closer to truth.com [Music] you

Channel: Closer To Truth

Views: 77,533

Keywords: closer to truth, robert lawrence kuhn, Why Are Black Holes Astonishing?, Black Holes, understanding black holes, what is a black hole, black holes explained, Kip Thorne, Leonard Susskind, Juan Maldacena, Nima Arkani-Hamed, Lee Smolin, black holes in space, space and time, how do black holes work, dark energy black holes, closer to truth full episode

Id: u_859TI-tgU

Length: 26min 46sec (1606 seconds)

Published: Wed Apr 14 2021