Astrophysicist Explains Black Holes in 5 Levels of Difficulty | WIRED

hi i'm jana levin i'm a professor of physics and astronomy at barnard college of columbia university and today i've been asked to explain black holes in five levels of increasing complexity a black hole might be different than you imagine to some extent it's a place and not a thing black holes play an important role in the history of the universe in sculpting galaxies that we live in and possibly in the ultimate fate of the universe hi hi welcome tell me your name jude i wanted to ask you if you have ever heard of a black hole yeah i think that they're scary and cool because you can get sucked and get lost forever and get plopped out in a random place it's like a big giant black thingy so black holes you describe them as huge the interesting thing about black holes is they're hugely heavy but they're actually physically really small what really matters is the density do you know what density is it's not weight but it's how much of it is in it here let me show you something i can ask how heavy it is i can also ask how big it is which is a question about its volume if i make it smaller then what's happening is it's becoming more dense so imagine i crushed this really really small it would weigh the same it would have the same mass but it would be much more dense how does it go that small if a star is heavy enough to explode into supernova what's left begins to collapse under its own weight and if that's heavy enough the core will not be able to stop collapsing because it no longer has the thermonuclear fuel it's run out of fuel and if it's run out of fuel it's no longer shining and pushing outward and without that it itself begins to go dark and there's nothing fighting the collapse anymore and that's when you form a black hole so if like the sun all collapsed on itself it would form a black hole well that's a really good question so interestingly the sun itself isn't heavy enough so it has to be heavy enough that when it begins to collapse it just overcomes all attempts to fight it if you made something really dense you would have to travel faster than the speed of light to actually escape that's 300 000 kilometers per second well it goes so fast that there's it's all dark so it goes so fast that it goes completely dark any light that veers too close will fall in will not be able to make it back out again if a light is shining from the sun near a black hole buckle's not touching it why does the light get pulled in why does that happen because the black hole is taking other stuff it is taking other stuff but the funny question was like if i wanted to move your chair you'd think it was really strange if i didn't have to come near you and actually grab the chair and move it one of the things einstein thought about is he imagined that what the black hole is doing is it's changing the shape of space around it what do you think of that idea that's crazy isn't it crazy and then einstein goes a step further and thinks well what black holes must be doing is curving the space so strongly that even light gets caught sometimes you can get light caught into a whole orbit literally the light going round and round in an orbit so black hole it doesn't attract light it moves the space so that the curve is pointed towards it that's right we've been talking for a little while about black holes what are you going to walk away with in your impression of what a black hole is it's kind of curved in space that are all coming to one point everything that goes on those curves changes directions to come in and even light can't escape it nothing can you said that very beautifully does that feel like a different idea of a black hole than the one you had before we spoke yeah a lot [Music] have you heard about black holes yes i know it has a lot of mass but it's very small i know that there are several theories about the universe due to black holes like around the universe and how it's made so a lot of times stars are born together in two star systems and when they die if they're heavy enough they will collapse under their own weight and form a black hole so here you have a black hole and a big fluffy star and what will happen is it'll start to tear apart its neighboring star literally parts of the star will begin to spill onto the black hole and splatter on the black hole but let's say both those stars formed black holes and what these black holes do is they are like mallets on a drum they create literally waves in the shape of space-time as they're moving so imagine now it's on a drum how the drum ripples depending on how the mallets are moving you hear different sounds so effectively these black holes as they get very close together in the final stages of their life together they're orbiting each other at hundreds of times a second it's just really crazy event but it's happening in complete darkness eventually they bobble together and they merge and then they ring out the space times going crazy around them it's the storm in space-time and they settle down to a quiet black hole then those waves that they created travel through the universe basically undisturbed for a long time people thought well even if black holes are out there they're impossible to observe and then they got very clever you might wonder how we could possibly hear black holes that sounds crazy so i'm going to show you but i'm going to need your help this demo involves an electric guitar do you play at all a little bit you want to do the demo for me so the ligo instrument electronically records the ringing of the shape of space with this very complicated instrument it stands for laser interferometric gravitational wave observatory and the design was incredibly difficult and they didn't know if they would succeed i think of the instrument as like the body of the electric guitar and then they take the readout of the motions of the waves that they're recording just like that guitar is recording the motions of the waves on the string i just play it like a little bit and you can't hear anything right you're not meant to hear an electric guitar when it's not plugged in what's happening is the guitar strings are ringing but so quietly that we can't actually hear the sound and this is like the gravitational waves which are ringing the drum of space-time but so quietly that they're not moving the air and we're not hearing them so now play and i'm going to turn the volume up a little bit [Music] while i can't actually hear the ringing of the strings themselves i can hear the data of the shape of the string recorded and played through this amplifier and that's kind of the idea behind the ligo instrument how do you know that it's like the black hole that's making that sound and nothing else it's a great question if i didn't see you playing the guitar i would recognize the sound of a guitar and even if i'd never heard of a guitar before i could figure out the frequencies that the string was playing i could tell how strongly it had been plucked and i could tell the length of it and where it was pinned down from the harmonics of the string and i can tell the different lengths of the strings from the notes that they play so i can actually reconstruct the instrument that's playing it and it's very similar to lego we can listen to the notes the amplitude the harmonics and we can deduce the size and shape of the objects doing that and they're very massive and they're very small and they have all the markings of a black hole is there anything that like gets affected on earth because of those waves it's a really good question only this instrument and that's why it was so hard to build and by the time it gets here it's so weak that it's only squeezing and stretching space at like the fraction of a nucleus over very large distances has your understanding of black holes changed over the course of our conversation i knew there were waves for like everything but i never thought specifically oh yeah black holes have like waves i know more and less i know what you mean i'm jada it's nice to meet you nice to meet you and where are you studying i'm a senior at nyu i'm studying physics and environmental studies what is your impression of what a black hole is so it's a star that has collapsed it has so much concentrated mass and gravity that there's a point outside of the black hole called the event horizon so once you get past the event horizon nothing not even light can escape from that so that's a great definition and i want to pick that apart a little bit so what you described is just right stars when they run out of thermonuclear fuel are going to collapse under their own weight it'll explode in a supernova it'll leave a core and if the core itself is heavy enough it will keep collapsing it does as you say reach this point where not even light can escape but the amazing thing is it leaves that point you called it rightly the event horizon it leaves it behind kind of like an archaeological record because the star itself can no more sit at the event horizon then it can race outward at the speed of light so this core of the star keeps collapsing and where it goes nobody knows so in a weird way the black hole isn't any more a crush of matter it left it behind in its wake but the stuff of the star is gone i've heard of short shield black holes which is a black hole that is static a curved black hole or a ker newman black hole which is a black hole that rotates but what makes a black hole static versus rotating and what's more common it turns out that there are only three quantities that define a black hole its electric charge its mass and its spin so the most general black hole can also spin and it can also be electrically charged whether or not they are has to do with how they formed if a star collapses it will likely be spinning when it collapses and the remnant black hole that forms will likely be spinning a black hole of a certain mass charge and spin is indistinguishable from any other black hole with those same properties so in some sense they're like fundamental particles which makes them absolutely exceptional for any other astrophysical object have you heard the stories about what happens inside a black hole i remember that once you pass the event horizon space becomes time and time becomes space in like a coordinate sense so from the outside if you're an astronaut you're watching your friend another astronaut who going into the black hole it's as though your times become rotated relative to each other so the profound thing is as an astronaut on the outside looking at this round event horizon you think of the center of black hole as a point in space but to the person who's fallen in it's not a point in space at all it's a point in time the singularity or the the end of it all the crush in the center of a black hole is in their future so they can no more avoid the singularity then you can avoid the next instant of time coming so the death and the singularity is inevitable although we don't really think the singularity necessarily exists i sort of know what a singularity is i think of it as something where everything is compacted into one single point it's a place where the laws of physics don't exactly work out what did you mean when you said that you don't think the singularity really exists so the singularity is definitely predicted in einstein's general theory of relativity and that's purely a theory of space-time and in the theory of space-time there is no question that a singularity would form when the star collapses catastrophically inside the black hole now even when people talked about singularities back in the 60s they thought you know quantum mechanics is part of the story of the whole of physics it's not just gravity because if we understand quantum gravity we'll realize that singularity probably doesn't ever actually form so since we obviously have never been to a black hole um how do we know for sure like what happens after you cross the event horizon or what happens inside a black hole is it just like inferred from the math i would say to some extent we don't know for sure what we have found is that the mathematics is so unbelievably powerful that we're able to disprove wrong ideas just in pen and paper just very recently within the past couple of years the first ever human procured image of a black hole showed us what we expected to see of the event horizon so jada after our conversation today what would you say a black hole is something that i had never thought of before is a black hole as kind of a type of quantum fundamental particle i've also learned how the event horizon of a black hole kind of hides a singularity the beauty of being a student of something like black holes is you never stop having new impressions of what this enigmatic phenomena is so in a year i'll tell you what i learned that's new awesome [Music] i'm claire and you're in graduate school and you're getting your phd what what year are you i'm a second year so i'm measuring star formation histories in the small and large magellanic clouds does the large magellanic cloud have a big black hole so i think the prevailing wisdom for a while was no but my answer honestly is i'm not sure yeah and probably nobody is have you heard a lot in your studies about these supermassive black holes that we think lurk in the centers of very nearly every galaxy so i don't study agn a lot but i do have a long term interest in black holes it's one of the reasons i entered the field i always was curious about how a black hole of that size was able to form was it the result of mergers between smaller black holes ultimately creating a gravitational well deep enough to contract a proteogenic disk for a whole galaxy or man man what happened yeah i think it's a really good question the only mechanism that we know for sure can form black holes as a collapse of very massive stars so it's sensible to think well maybe some very massive stars in a young universe collapsed under their own weight and then they merged and after some time they got big enough but the black holes from stars can be tens of times the mass of the sun maybe hundreds of times in the mass of the sun if they merge to get to millions and billions and if you just do the simple arithmetic of how many years that would take there aren't enough years in the 14 billion years of the universe's lifetime so they must have come from somewhere else i am at a loss to think of what could have possibly happened in between the start of the universe and the formation of our galaxy that could create such a massive object yeah i think that's right i think people are really perplexed about how you make something so big in such a short period of time it's kind of funny the bigger you make a black hole it seems maybe counter-intuitive but the less dense the material has to be out of which you make it so you can out of something the density almost of air you can make a supermassive black hole you can't make a star out of that but weirdly if you skip the star phase altogether it's conceivable that they directly collapse and so there's a suddenly a new way to make black holes that nature is figured out we spend all of our time when we learn about black holes in school predominantly through star collapse yeah i didn't even realize that there was an alternate route to creating a black hole there might be many alternate routes it might be in the very early universe that bubbles in unusual phase transitions from very high energy universe to a low energy universe can make black holes like we haven't really thought of the range of possibilities and so there could also be primordial black holes that are still around that that also skipped the star stage altogether that were formed really in the very earliest phases and i think the interesting thing is with you're looking at like the large magellanic cloud is to wonder if we're going to merge absolutely we thought the canonical picture of the clouds was essentially that they had formed with the milky way maybe in its halo and had been in a stable orbit for about a hubble time or about 14 billion years young guns in the field have thrown a wrench in that theory that they've always been orbiting and that perhaps they're on their first orbit they're on an unstable orbit will they join us can you tell us about andromeda andromeda is part of the big three in the local group the local group being a group of galaxies that are not expanding with the expansion of the universe away from each other they're trapped gravitationally by all friends yes they're all friends and andromeda is one of the few galaxies that is traveling towards us and we are due for a merger event at some point so given a sufficiently low velocity we would just have two big galaxies that for the most part pass through each other pass by each other but given a sufficiently high velocity we will have some crazy black hole interactions and some crazy star interactions but when we do merge with andromeda presumably our black holes will emerge and andromeda indeed has a very big black hole as well at its center and then we'll have this just gigantic super massive yeah and it's very possible that as you said the collision won't be so severe that it'll be very disruptive so our entire solar system could stay intact and here we would go with the sun and all the other planets in orbit around a new black hole they're kind of misunderstood giants in a way so i was curious have you heard anything new or interesting in the field of black holes that will shape future discussions we work a lot right now on thinking of black holes as batteries so a black hole that can take like a giant magnet astronomical magnet in the form of another collapsed star like a neutron star and flip it around so fast near the speed of light that it actually creates an electronic circuit out of this moving magnet and so that the power that can come out of these electronic circuits created by these batteries can be tremendous you know i know that at a certain point for our civilization to become sufficiently advanced to travel the cosmos beyond you know the moon or mars we may have to be able to harness the power of our sun would it be similarly possible to harness the power of a black hole like you were mentioning to travel it's a great question i once did a calculation of using a black hole made out of the moon and the strongest magnet we could find on earth to see if i could make an electronic battery and honestly you only get about enough energy to power new york city but we have to find one in our neighborhood first yeah wouldn't it be my favorite thing so claire we've had this pretty fascinating conversation about supermassive black holes in particular and after our discussion what is it that has changed for you in your perspective and what is it that excites you so i think our discussion kind of exposed a piece of black holes that i don't think of often which is that they're not just life takers they're life-givers and they inform a lot about not just how a galaxy is destroyed or made but how it's shaped and how it eventually you know builds life like ours so maybe i have to give black holes a little bit more props [Music] hi dan i'm so glad you could make it what have you been working on with black holes in the time since i've last seen you there are a lot of aspects to black holes the one that's kind of interested me most lately is trying to understand them from the point of view of information how information is stored and processed and recovered from black holes which turns out to be a really interesting perspective talk us through hawking's initial revolution that led to a lot of these conversations about the information around black holes hawking's big insight was that he had to apply both the rules of quantum mechanics and the rules of gravity to really understand how black holes behaved but hawking took a point of view where he brought quantum mechanics into the game he realized that if you took that into account that it's actually not quite true that black holes are black that actually things can escape from black holes so what you're describing is the famous hawking radiation where a black hole cleverly kind of steals energy from the quantum vacuum and radiates and then the process evaporates and of course it's caused a big kerfuffle because when the black hole evaporates eventually that event horizon is yanked up and the question is is where did everything go that had once fallen in a way to think about hawking radiation is to imagine that pairs of particles and antiparticles are appear out of the quantum vacuum and the particle can escape the black hole but the antiparticle falls in but the particle and antiparticle are repaired and if the antiparticle really falls into the black hole and is destroyed at the singularity that poor particle outside the black hole has lost his partner it also violates the rules of quantum mechanics if you have two particles that are entangled that has to be preserved now to be clear nobody disputes that black holes will quantum radiate that hawking radiation is a solid prediction the black holes should in fact evaporate that's not disputed right that's right it would be wonderful if we could have some experimental evidence for this if we could really build a black hole in the lab and and test to see whether it behaves this way but i think there is hope that we'll be able to detect some of these effects either indirectly by looking at black holes out in the universe or also maybe indirectly in the laboratory by looking at systems which aren't black holes but which radiate in kind of similar ways there's this domain of black holes in astrophysics where we see stars collapse and we know that they exist and there's whole observational astronomy around them and then there's this domain that we're talking about where as you said black holes are so special because they're kind of guiding us in the right direction to understand the very nature of reality and that makes them really unusually special one of the things i wanted to draw out is that we talk about the fundamental forces of nature so there's the matter forces and then the outlier is gravity we've quantized all the matter forces in a way that we're rather comfortable with gravity keeps resisting quantization of gravity itself and now we're thinking in a way that you're describing that well maybe it's only the quantum forces altogether the pursuit of quantum gravity has taken us to places we never expected to be i think what's exciting about physics about theoretical physics that you start following a thread you start developing a chain of logic and you never know where it's going to end up do you think there's ever a hope that the kind of information that you think about the quantum gravity aspects of the universe that you think about whether it will pan out or not will ever be viably observed in these astronomical pursuits of the event horizon it's a real challenge but astronomical observations have gotten so fantastically precise and there is some hope that if you looked at things like two black holes merging each black hole comes in with its own event horizon but then when the black holes merge there's a very complicated process where these two event horizons merge and oscillate and vibrate and then settle down into a single event horizon for the final black hole there is some hope that if we can make sufficiently detailed observations of this process if we could really see the way the event horizon is behaving as it settles down to this final state that maybe that could reveal some of these quantum effects that we've been talking about it is amazing in the numerical simulations of two black holes merging you really see the event horizons bubble around and we were talking earlier about how really black holes are flawless they don't tolerate those kinds of imperfections and so you can so quickly watch the system ring away that misshapen merger and it comes out in the gravitational waves which is literally the ripples in the shape of space-time until it settles down and then it's utterly flawless again it's really happens fast it's quite amazing yeah it's a spectacular process in some sense black holes aren't anything anymore they're just empty curved space times and nothing is there how would you possibly make one and then it becomes why are there so many and where are they all being a black hole scientist means each question leads to more questions we know more and more but we also see how much more there is to understand i hope you've learned something about black holes thank you so much for watching [Music] you

Channel: WIRED

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Keywords: 5 levels, astrophysicist, astrophysicist black holes, astrophysicist explains black holes, astrophysics, astrophysics wired, black hole wired, black holes, black holes explained, eli5 black holes, elif, elif black holes, explaining black holes to a child, gravity explained, how gravity functions, how to explain black holes, janna levin, science, science explained, science explained to kids, wired, wired 5 levels, wired black hole explained, wired gravity

Id: gsMIT25iPXk

Length: 26min 55sec (1615 seconds)

Published: Thu Mar 24 2022