The Stoner Episode with Janna Levin & Neil deGrasse Tyson – Cosmic Queries

[Music] this is star talk neil degrasse tyson here your personal astrophysicist we're gonna do cosmic queries today everything black holes and space-time and i got with me my guest co-host matt kirsch and matt welcome back dude thank you thank you i'm joining you from my family's spare bedroom in london right now oh you mean your parents basement where you live just say that's exactly it yeah i uh i commute to la every day from from the basement where all my toys and games are i i knew you were full geek but the full of the whole story you're still in your parents basement that's it you're on safe grounds here to admit that this is no judgment podcast no judgments at all uh good to have you back and you're the host of of sometimes science is probably science probably science damn probably science uh on which i have been a guest in the past you have indeed i have and i enjoyed my time there so matt i while i know a little bit about black holes and a little more about space time i don't count myself among the world's experts but we have a friend of star talk who is of course that's jenna levin janna welcome back to star talk thanks i'm glad to be here sort of here i'm out of here virtually yeah yeah janna you're you're like a neighbor up the street from the american museum of natural history uh you're a professor of physics and astronomy at barnard college of columbia and it's just great to have you just a friend of what we do and a supporter of all of this yeah i love being here and to lend your expertise you're not lending it because we're not giving it back you're giving us your expertise on black holes cosmology uh the space time continuum and all that goes on uh so just before we start off i just want to alert people that in your spare time you actually are one of the founders of a marvelously conceived project pioneer works over in brooklyn across the river um you you merge art and science in highly creative and imaginative ways i just want to congratulate you go in there and you've been and you've been at it for like years now right yeah i really appreciate that yeah we we have a live programming where we feature scientists in conversation you've been over we've had parties with you now yeah but you haven't put me on the stage i'm waiting for the right time oh okay i i have also been there and and not on the stage i mean they didn't want my expertise but i uh i went to uh yeah you and i don't cut it yeah we just don't know for the audience but not to actually do it i mean i think i'll get there eventually but i'm not so sure about you neil i i i've got some deep expertise to share i'm happy to put you both to work be careful what you wish for so the big the big project there has been lately broadcast pioneer works broadcast since the pandemic which is our virtual manifestation it's pioneer works beyond the walls where we cover art science music tech kind of multimedia extravaganza excellent so they can reach a far greater audience than who shows up in brooklyn so matt you collected questions from our patreon members there they have exclusive access to our cosmic queries format and everyone else gets to hear their questions and so let's what do you have lined up for us this is like a grab bag there's a grab bag of black holes and stuff right yeah there's a there's a really nice assortment of questions i'm going to start off with this one from from matthew power my kind of superhero namesake that's uh but um you're matt kirschen and this is matthew powers it's matt power this is matt from new jersey who is current also currently reading black hole blues which is one of janna's books i've read that it's an excellent book and matt is also enjoying it but and matt says uh my question is if there were two black holes orbiting one another and generating powerful gravitational waves is there a possibility that a small object says perhaps a ping-pong ball could actually be carried away by the waves thus making gravity a repulsive force in this particular case wow this is like a surfing ping-pong ball wow love it that's i i love it i love the idea so because probably he's thinking deeply because if you're surfing on a wave in the ocean um the water isn't actually moving it's just going up and down and you're somehow exploiting this fact isn't that right even with it yeah i i think it's a subtle question i i've worried about this but i haven't ever really worked it out i'm sure somebody might off the cup know the answer but definitely what you're doing in space time if you're near those two black holes is you're falling freely we literally call it free fall so you're falling freely on the natural curves in the space so if those curves are changing that's certainly going to change your fall for instance the earth is falling around the sun on a curve on a circle and if the sun were to disappear tomorrow the gravitational waves would radiate out taking the time it takes until it reaches us and then we'd go in a straight line as though the sun was gone right so in some sense we are definitely moving with those waves uh but thinking of it as like surfing it's cool i don't know right right if we're not if we're not so heavy as the earth let's say or or something as responsive as a ping-pong ball yeah wouldn't the waves wouldn't the expanding gravitational wave from the disappeared sun or from the collapsed black hole will that have any effect on us at all to push us how can a wave move out but we can't now move with it it yeah i mean the this the gravitational energy in the wave can be quite powerful right we that the collision of the two black holes was the most powerful event human beings have detected since the detection of the big bang right and all of it came out in the gravitational waves but actually um i think their effect is really quite weak in the sense you would feel the squeezing and the stretching as you kind of bobbed around on the wave but i don't think it would have enough power to actually carry you along but we also do know i think the question was also about repulsive gravitational forces and actually we do know that gravity can be repulsive so for instance the dark energy in the universe creates a repulsive effect on the expansions the universe is expanding things are getting farther apart because of the dark energy and that's happening at an accelerated rate yeah but you're calling that gravity and when are we allowed to do that yet well there's this dark energy and it's actually the opposite of gravity so are you legitimately calling it negative gravity no i'm not calling it negative gravity i'm saying that when we think about curved space-time that coming together is not the only possibility although that is with newton's laws in general relativity when i think of uh dark energy as a particular source for the way it deforms space-time we see a very clear example where its effect on space time is expansive and uh oh wait wait i gotta answer i gotta get another good answer i gotta can i can i okay can i raise my hand you pick on that janet yeah thank you thank you so just thinking about this more holistically the very expansion of the universe is carrying galaxies in the fabric of exactly expanding space time so in a in a way we are moving in a sense not through space but with space and space is carrying us and no it's not a gravitational wave but it's uh i'll take it as something it's sort of surfing even if it's not yeah that's excellent the dark energy is just a particular example of that causing the expansion in an accelerated way but lots of things cause the universe to expand like the fact that it's full of light and energy in all directions causes the universe to expand and i think you really hit it on the head neil we are moving with the expansion of the space we are not moving uh with respect to our local area right so that is like the surfer riding the wave yeah yeah cool and then we just get further and further away from each other eventually we won't even see the other galaxies for a question that is very theoretical to one that i i know you've have a good answer to because i know this is something you've both been asked before alexander new house wants wants to know what is the universe expanding into yeah jana i know you've done this a bunch of times no no i just make stuff up what i think what i read but you actually work on these problems so let's hear it out of the horse's mouth well uh if let's take it as though the universe was expanding into something just pretend then we would be saying oh there's some distance the universe has traveled into this other space but what we mean by the universe is the space so there's really no logic to thinking of it expanding into something else the universe is the whole space there are um some relational possibilities that you can think of where the expansion of the universe is like a map of the universe where we're only reading the legend between things as changing over time but the map itself doesn't move into anything else that's one kind of very strange relational way of thinking about it but um but no we do not need to nest the universe into another universe to have it expand okay i get that but but who what okay so let's let's uh let's up this game a notch what conditions would what dimensionality what location what what state of existence must one have to observe the entire expansion of our universe well you okay that's from the outside so there is there is no way to stand outside the universe no not really but so but so you're trying to disprove the existence of god with me right now what kind of trouble are you getting into i don't think i really mentioned god in that nobody can see and know the entire universe at one time there's no way who are you to say that you can't there is not some platform some vista outside of everything we know and see that can just simply observe what's going on well by observe we mean collect particles and interact and we do that through pause in space time so if you want to literally be in a position where you're gathering lights so that you can see the universe and deduce what's happening to it you're really talking about interacting with something and that requires that we be in the same universe now i mean you could fundamentally you're no fun you know we could say things that i think are actually matt she could have said god is out there and he's watching us all right or santa claus he knows when you are bad or good and then we sing some hymns and then roll credits it is interesting to push this idea and to say look these ideas about space being infinite or being finite or expanding these are just ways of talking we could also talk differently about the entire universe only as relations only as interactions and that's the only thing we understand that interactions happen over a certain span of space and time and there's no need to even think about geometry at all or to think about the universe as a space at all it's just appeals to our intuition you're looking at me like i've had this woman on the show many times okay a match she's crossed over and i don't know that they're bringing her back at this point okay i mean and we know that we're often fooled by these interactions so right now i have the illusion that you're a solid person that matt's a solid person but really you're mostly empty space these are illusions that we cling on to to ease more easily comprehend the world but we know that they're not matt is mostly empty space yeah a lot of people say that about me i'm solid here nearly solid [Laughter] there's nothing going on in here no no so you're referring to the fact that atoms are mostly completely empty yeah right and then even if you look at fundamentally what what the fundamental particles are with atoms we only understand them in terms of the way in which they interact with things that that's the meaning of an electron is the way it interacts with things so in some sense we're just these sort of lists of interactions yeah she got all philosophical on this map matter quickly go to the next question before this gets worse because you got so philosophical i'm going to jump on to scott allen's question because scott from arlington who who by the way gives the caveat that scott is stoned right now uh okay i'm putting that right in there and if scott is still stoned trying to listen to these answers i think we're gonna put him in some real trouble we should use the donor version of this show i'll host it and just get my mate i mean that's basically is my podcast that is probably like we're just winging it don't look for stoners oh my gosh we get all scott wants to know best best suited for when you're high oh my gosh you know janet we'll bring you back that's going to be a show i promise our audience that's going to be a show okay i just fall asleep it'll be a very boring show eating potato chips yeah okay okay so so scott says is everything just a form of energy is time just a human invention combining the two ideas is what we call life and everything we can observe and understand with unlimited senses and minds simply a flow energy constantly changing form there is no beginning there is no end there is no past there is no future there is just the present in whatever form of energy we can sense and understand with our mind definitely it's don't make of that what you will yeah okay professional scientist wait did you just give the answer and you said definitely and now we move on to the next question i think the answer is yes and everything's fine right now and i i just think he's definitely stoned her question is is how do how what confidence is do i want to restate the question what confidences do we have janet can you and i offer as scientists that there is a physical reality and just we're not all just perceiving ourselves in the moment and that what what yeah we have that i think you made it worse for me outside of our perceptions yeah i mean um we're all i mean which one of us is the one perceiving am i in your mind or solely or are you still in my mind which one of us is a genius started viva scott started combining his his ideas there are two questions at the beginning that i don't uh that are more grounded in i think physical of theory and that is everything just a form of energy uh and also is time just a human invention and i think i think those two are questions that are potentially yeah more answerable well to do with the first one yes i think matter and everything is a form of energy that is that's interesting know that janet be careful how you use the word think yes okay but you think it might rain tomorrow but you know matter energy okay right it's true we know that matter is definable essentially yeah and um and that is interesting i mean i think that's also related to this kind of tangent we went on which is that what does it mean to have atoms in your body what does it mean to be made up of atoms is it means that you have a certain amount of energy and that those uh particles interact in very prescribed ways that's what makes an electron different from the positron is just the prescribed interactions if not their energies so um so yeah that's really all we are it's beyond that to say what's real is is again part of this illusion we have to cope with our perceptions of the world we'll take a quick break and when we come back we'll pick up the second part of that question whether time is just some kind of a human construct with the help of jenna levin giving us her insights into the universe on star talk cosmic queries we're back start talk cosmic queries uh i got matt kirschen as my co-host matt how do we find you on social media uh i'm matt kirschen on twitter i think mac underscore cushion on the instagram i very rarely use uh twist is the main place i am okay and if you don't know the spelling just kind of get vaguely close and google will find me yeah okay and we'll find you on twitter then without the underscore because that's what you mostly post that is janna tell me about your social media footprint yeah i'm i i'm more on twitter uh at jan 11. um two ends like anna and um i'm on the insta same handle um i sort of treat them a little differently on instagram i kind of post my personal stuffs my personal business okay you want to get all up in your situation okay you know uh yeah exactly i you know not exactly what i had for lunch but yeah so but twitter i have pretty serious conversations with people if they want to ask questions i'm there i love answering questions when i'm in the mood at least you know very good all right so we left off uh what's the name of that last questioner uh matt so scott we left off his part of the question was is time just a human invention yeah there's a quote i remember from einstein or from his student uh john archibald wheeler was it a time is invented to make motion look simple have you heard that i have heard it i feel like it was wheeler because he said lots of witty things i also think it was wheeler who said time is what keeps everything from happening at once all at once yeah okay which is a good one and just just i gotta throw it throw it in here i first noticed the woman who would become my wife in a class taught by john archibald wheeler the the cosmologist oh wow yeah no way i didn't know that i was sitting in the back row she was in the front row so i i don't she probably didn't notice me but i noticed her yeah yeah that's adorable i can say i noticed her in the space-time continuum on the chalkboard okay okay so what do you have to say about his comment about about time well i think i definitely don't think it's a human construct um whether time exists in this kind of block time model of the universe where the past exists the future exists every bit as much as left and right exists but we're confined on a particular path through this four-dimensional space where time is the fourth dimension um that wouldn't be just human beings though that would be everything would be confined to that space i presume my cat's death comes before it's you know after its birth rather and you know i just presume flowers die after they bloom and that those are um things that are happening to everything in the universe there are other models that time is sort of an not an invention of uh the mind but it's like it emerges from very subtle processes and that in some sense it's not fundamental but i think that again it's a very good thing to talk about so if we want to meet we don't just specify a point in space we have to say a moment in time and it's very convenient that we all are able to find that moment in time and collect and get together at that moment in time so that suggests it's not just a figment of our imagination or a human construct so maybe i should save this for the stoner edition but if if you if you could find a region of the universe where nothing changes then time cannot possibly have meaning absolutely true absolutely and in fact there's that's kind of a you know a death of the universe model that the universe will everything that can fall into black holes will possibly if the expansion doesn't dominate and those black holes will evaporate into random particles and then the expansion will just make it so that there's only one particle in the entire observable horizon that you know and that's disconnected from all the other particles and so there will be no meaning to time passing i mean even for me to experience time passing there has to be change which is my thoughts changed my breath accumulated uh there's there's actual measurable change that i experience as the passage of time so that is true that we do have internal clocks um but they are very well aligned with our external clocks making it seem as though there is something external and universal well while we're talking about external and internal clocks jeff johnson wants to know why does gravity or high speed cause an entity to move faster through time oh uh i see the question time dilation is the question yeah why does time so um but first first he got it backwards so gravity slows down time and that speeds it up so take it up janet yeah so it doesn't actually slow my experience of time so my experience of time if i'm standing near a black hole is exactly like very ordinary my nicely made watch that i had once synced with my friend back at a safe space station is working perfectly well it's still matching the number of breaths i take time seems to be passing completely normally your heart rate everything my heart rate everything is absolutely normal i don't get any benefit out of this dilation the dilation is only relative to somebody far away and to somebody far away i look like i'm moving slowly like i'm breathing slowly like i'm aging slowly like my watch is ticking slowly so it's only uh relative to them that it looks odd but in my experience it's quite normal i think the deeper question is why does this happen and we can think of both gravity and moving quickly as creating rotations between the space times of two observers so if one observer is thinks that this is left and another observer's facing them they understand that they're going to disagree about which way is left they're not surprised but they know they can just rotate their systems and then they'll agree right so at some sense as you go closer and closer to the black hole it's as though you're rotating in space time so some of what you were calling space is folding into some of what your friend was calling time and that leads to time almost as though you're rotating left and to right almost as though you've rotated time away entirely relative to your other observer and um right so matt we have we should just re-name this show stone story i don't think it's happening they're not stoned it is there is a beautifully related question as well on this note from um from frederick johansson uh from sweden wait wait wait wait man i just gotta like i just gotta wrap something wrap my head around with what janet just said so janna so what you're saying is you use the left right as a as an interesting analog to this what you're saying is when you are in the moving faster in the vicinity of a black hole you're time coordinate is let's use the term rotates in such a way that it's giving of itself to this a space coordinate and that's right so one is losing time relative to the other exactly and uh just like you can rotate left all the way into right at the edge of a black hole in particular you've basically rotated your time away entirely and in fact when you cross the event horizon what your friend far away thought was a region in space a center of the black hole is for you a direction in time so you've rotated it completely by the time you cross event horizon to the point where you think that the dire singularity at the center isn't a point in space at all it's in your future and it is as inevitable that you will crush into that singularity as the passage of time is inevitable and that was roger penrose that was roger penrose yeah he yeah yeah actually i wrote this little article after he won the nobel prize for that beautiful work in 1965 for pioneer works broadcast actually because we do this series called picture this where you draw we scientists write about technical articles like technical drawings and roger penrose has the most wonderful drawing that he drew in this 1965 paper where he shows basically time starting to move in a spatial direction he shows that rotation and he proves that at the event horizon what's happened is basically um time is starting to point inward towards the black hole so i love that and i love the left right starter analogy there you know that reminds me so matt do you ever hear this joke it's funny it says so someone says well two two wrongs don't make a right right but then you can say but three rights make a left [Laughter] do the geometry on that it works out all right cool janet thanks for that answer we will totally i'm going to i will have to talk to my producers here but i think we should rebrand this uh for stoners aka first owners the stoner edition of cosmic queries keep them coming well so friedrich frederick johansson asks and this is related because you just talked about the difference of effects of both speed and gravity uh frederick wants to know if i stand on the equator my head would age less compared to to my feet due to the speed difference but would it wouldn't we have the opposite effect due to gravity uh would my feet or head age more in the end so i believe he's asking that if he's standing standing on the globe his head is moving faster than his feet because it's go it's further out but also his head is further away from the gravitational center of the earth than his feet so do these two things both have an effect on the time perception of your head and your feet and if so do do they cancel each other yeah who wins i would have to i would have to actually do the calculation because both are pretty tiny right but i can tell you that with this with like the gps units we see the effect of the time dilation when we send signals to satellites and back again and they have two effects um one is your deeper and the gravitational potential so so let's say let's say we take the twins like one astronaut that was in the iss and the other twin astronaut who stayed on earth the kelly twins um which one actually was younger the one who stayed on earth uh deeper in the gravitational potential well the one who was traveling and very quickly in the iss and it's actually a known answer i forget which one it was i think i think the speed of the um iss out dominates over being on the earth in that case i'm pretty sure okay however with gps satellites the the fact that it is they are much farther away from earth than the international space station that they experience much much less strength of gravity which speeds up their time relative to us and so their time that they send us is pre-corrected right to accommodate the fact that their clocks tick faster so right janet you have to do the math right because there are two competing effects and yeah to know for sure but i agree with you everything i know about the the orbiting astronauts which are in low earth orbit rather than middle earth orbit matt it's not middle earth like okay just to be clear not a basement nail i'm not in a basement it's not the middle earth it's uh mio uh uh mio leo mio and geo right low earth orbit middle earth orbit and geosynchronous orbit so they um when you do the math there the the lower gravitational field wins out over what effect their speed has on their time keeping so yeah oh interesting yeah yeah we're good interesting so thinking about the gps we could also think about how if we didn't correct for the time dilation we would never be able to catch our uber because it wouldn't it wouldn't be in the right location and i learned this from neil recently that it's actually the rotation of the earth that's the issue that uh that if the satellite in a let's suppose we lost a second if the correction was never made and the error accumulated up to let's say a second then if you consider how quickly the earth is rotating and that the grid would be changing you would find that we could be off by several blocks so um so you'd be trying to catch your uber you know in chinatown and it would be in little italy which is fine these are adjacent uh communities in lower manhattan little italy and yes they're adjacent neighborhoods yes yeah for those who are not native to the city all right let's take a quick break and when we come back more cosmic queries stoner edition with janet we're talking about black holes uh cosmology and the space time continuum we'll be right back we're back third and final segment of cosmic query's black holes and space time continuum edition which we are dubbing cosmic queries stoner edition based on the answers we've been getting and what kind of state of mind we have to be in to even follow them much less understand them so janna again it's always good to have you here your your your last two books so one of them was the black hole blues uh published by was that uh uh alfred kanoff yeah by knot yeah yeah black blues why i didn't know black holes had emotional states well the people who were searching for black holes had emotional stuff oh god okay they have the black hole blues so this is a story of black holes in our field of astrophysics and the relationship we have to them got it got it and more recently you have a book called the black hole survival guide which is like a pocketbook fits right in your coat pocket and yeah how useful did you how soon do you think such a book will be useful where everyone has to have one yeah they have to have a survival guide uh well i hope not very soon at all any second now i have it's sort of a i have a spoiler alert uh it doesn't end well there you go the survival guide doesn't go well it's pretty much many ways to die yeah so don't you have a book titled death by black hole i've always wanted to steal that title from you oh death by black hole yeah yeah i do it's one so that's that title is the title of one chapter in a book that goes a lot of different places that's right right it was this collection of essays yeah that's right that's right on all manner of things in the universe that's right yeah so that's the survival guide could also be called like death by black hole okay all right it's how to not so it's the non-survival guide if it's death by plaquemines all right matt what more do you have for us well i've got i'm gonna turn this to some black hole survival questions because we've got a few and uh and they're great so from the czech republic uh patreon patron gindrick uh procupec i hope i've got that close to correct asks you i read that black holes are almost zero kelvin inside why are they so cold and not very hot due to a high pressure caused by enormous gravity forces and lack of heat escape is there a temperature gradient between a black hole center and its event horizon and what's 0k anyway janna oh it literally it just means particles are so cold they have so little energy that they're just not moving it's as though you know what we experience temperature what we're really experiencing uh experiencing is the collection of atoms moving at a certain rate and a certain speed on average and that creates the temperature and the faster that they're moving the hotter it feels um and the slower they're moving the colder they are and it is true there's an expression pv equals nkt that you know in highly pressured situations the temperature can go up right that's the that's the thing i the the level of physics that i understand like a bicycle pump gets hotter and if you if you spray one of those compressed air canisters they get cold because you're uh yeah jenna i can't believe you wrote it on the chalkboard i i love the cans in front of her the people who are audio only are not aware that janna isn't as you look like you're posing for a professor photograph right now matt was sharing his life experience that in a bicycle pump you uh because he's living in his parents basement he doesn't own a car he's just a bicycle bicycle pump the valve gets hot all i've got is compressed air to keep me happy right and a spray can as the spread as the air releases the nozzle feels cool so so the pressure can or or cool it depending on which way it's going so so what's happening inside a black hole is is is the person right about it being zero caliber um no uh it's but they're not right for a very interesting reason so we know that as the core of a remnant star what's left after it goes through some very violent throws at the end of its life continues to collapse and is in fact extremely dense and probably absolutely uh an unusual extraordinary exceptional state of matter we know that because we see neutron stars which aren't even black holes they're a step on the way to black holes they don't quite make it there and we know that they're incredibly unusual in terms of their composition but once it makes it to be the black hole so it has created a curve in space-time that is so sharp that we know not even light can escape that's what we mean by the event horizon and you might think therefore the event horizon in the black hole is full of dense stuff but it's not actually because the star can no more sit there then it can expand outward at the speed of light you can almost think of spacetime as like a waterfall raining into the black hole and it would have to swim against the waterfall just to stay at the event horizon and it can't do this so it just continues to get dragged in with the waterfall of space-time and you know this is the great mystery what happens to the star we don't know but it's gone the star is gone so black holes are cold because they're empty so if i go up to the event horizon of a black hole nothing's there there's no dense object there's nothing solid the it's empty space so i like to say you know and i've said this i'm sure on your show before black holes are more like a place than they are a thing they're like a place in the universe but there's really not no matter left but you can measure the gravity that it has right so something's got to be there yeah that's right it has gravitational energy in the curvature of the space time there is energy in the curvature of the space time that is a gravitational energy so it you know it's often really hard to define gravitational energies but in the case of a black hole i can actually have a well-defined mathematical prescription for measuring its gravitational energy and it happens to equal not surprisingly the mass of whatever fell into it so it's as though the matter like throws its heft into the gravitational imprint but you don't but the stuff is gone now there's another question you could ask about temperature which is about the hawking radiation so at the event horizon we do think that through this very subtle quantum process black holes do have a temperature actually and they are radiating actually but the bigger the black hole the colder they are and the smaller they are the hotter they are so they have they're very cold they live their lives absorbing things not emitting but at the end you know very very far far far future of the universe those black holes will eventually evaporate away and the final stages will be explosive yeah in fact if i remember correctly the original paper that described this phenomenon by hawking uh explained these as that they would be bursts of high-energy gamma radiation because they right at that last moment it would be at its hottest and very hot things emit gamma rays and so exactly it's interesting yeah so you know if you if you are foolish enough to try to make a black hole in the laboratory it will explode on you because the smaller they are the more unstable they are and you can kind of figure out like how big would it be if it was like kind of a stick of dynamite versus what you're describing gamma rays or nuclear weapon grade and um and uh you so you're kind of ill advised to make a small black hole but if you do you should start with a bigger one just to just for safety well then you're going to fall in so you got it you know it's a so what a trade-off that is oh and and earth it could suck in the earth so yeah that would be in your day yeah that would ruin a lot of days people's days so we can so janet we can't call a black hole an area of nothing if it contains the severe curvature of the space-time continuum because that is something is that a fair statement yeah um i guess right that's fair we can say um what do we notice how she didn't say it was right she just said it's fair right okay hey man you're you're right you're absolutely right space time is something and spaceman has energy and space-time moves and it's a thing and in that sense it's a thing but it's also by definition space which is a place i'll i'll take that they very much act like things black holes move around they they orbit they can fall together they can collide you know but when we talk about the size of a black hole we're talking about a shadow that's all we're talking about we're talking about a shadow like the shadow of a tree and there's nothing there no matter there's no you know no matter there um while we're talking about mata so uh listen to gonzalo castilla uh from mexico us and uh gonzalez mentions black mata i'd imagine this is uh what we would also call dark matter yeah unless there are two different things no yeah so i i'll say dark matter for this i'd imagine that's a that's a language thing um but if dark matter can interact gravitationally with normal matter uh it is attract is it it is attracted and eaten by a black hole just like normal matter right what happens with the dark matter as the black hole evaporates could there be a black a dark matter version of hawking radiation or it only radiates normal matter and a black hole has some sort of mechanism that transforms this dark matter into normal matter absolutely the black hole will figure out how to radiate uh all of the information that went into it if this works so that includes um dark matter information so that the fact that it was dark would would come out in principle everything comes out okay so so the parking radiation that calculation does not discriminate between ordinary matter or dark matter any other kind of matter no it can be electrons and positrons it can be light coming out in the hawking radiation it can be dark matter pairs pairs of dark matter particles and that assumes so everything you said assumes that dark matter is actually comprised of matter and not some other mystical substance right right right and there are people who think that black holes themselves might be uh enough to explain the missing mass and the dark matter um so that's not a particle answer at all yeah yeah yeah okay matt keep him coming see how many we can do there's a couple of faster than light questions so dylan asks um i've heard a lot about wormholes on this show and have a question how do we open up a wormhole i know as of right now they're impossible but hypothetically speaking what steps are taken how much energy would it take and could we just use a black hole how do we cut space time uh janet we're waiting for this and why aren't you giving us the black the wormhole we're so disappointed i know i'm busy i'm i'm gonna do it in the future and then come back oh let's do it later good answer good that's it matt that reminds me during the science march which is sad that in the united states we needed a march to defend science back several years ago one of the placards said what do we want time machine when do we want it it doesn't matter that's perfect um i think mit once scheduled a a time traveler conference uh for the previous year [Laughter] they were like let's meet in 2019 and have a time traveler conference nobody showed up nope yeah time travels didn't show up yeah i can tell you this about the wormhole we absolutely on paper know how to make a wormhole so basically what you do is you you you write down the shape of the space time you want namely a wormhole shape and then you force matter and energy to create it and you ask then well what is the distribution of matter and energy have to be to create this shape so you can go backwards um and and and deduce what kind of matter and energy would be required the problem is it requires negative energies and that's not something we see in our ordinary experience everything has positive energies negative energies are super weird we some people think that they're forbidden in nature the one circumstance in which you can get negative energies is in some strange quantum situations i've actually wondered about this could we create where you have um like finite spaces made out of uh metals and the quantum oscillations or the quantum vibrations create a certain negative energy between like these strange geometric configurations so you need the energy the negative energy to pry open a hole that would otherwise on its own want to collapse and just make a black hole i guess yeah it just wants to keep pinching closed so that sounds really dangerous to enter one of these because suppose you're in one and then it collapses on you that's a bad day right there i'm just saying this yeah okay so we're nowhere near this now even though you can make it happen on paper yeah i mean you know people at kip thorum they were writing down wormhole solutions decades ago and they just looked around and said well we don't see any matter like that in the universe so we've got to go back to the drawing board and think of a new way okay so just because something is mathematically possible doesn't mean the universe is going to cooperate right that comes down to there's other time machines that we know we can make we can take two cosmic strings which are literally strings of energy tension and energy density and cross them in a very funny way that creates a kind of cut in space time that allows you to do a little time travel jig but the problem is is they have to be infinitely long and take an infinite amount of energy so there's never anything that seems compatible with the universe that we live in and even kurt godel first when who was friends with einstein used to walk to the institute for advanced study with him in the mornings to talk and he was inspired by einstein's work and he wrote down a description of a hypothetical universe that was rotating uh not our universe and he showed that you could travel in time in these this peculiar space he invented um and einstein didn't dispute it it was correct mathematically but we just don't live in those kinds of okay so just to admit it janet all we really need is 1.21 gigawatts of energy okay that's really all we need just i believe it's pronounced gigawatts oh jake's jen i think we got to call it quits there uh we ran out of time oh shame it's always so fun man okay so matt with your permission and with with i don't want to call it the stoner edition unless we have total buy-in from the three of us it's gonna can't be called i'm fine calling it the stoner edition but anybody who knows me knows if i'm stoned i'm asleep and anyone who knows me knows i have a green card and [Laughter] that's right northern europeans have green cards too i have a green card which means i can't get the other kind of green card [Laughter] so we're good here so uh janet thanks for coming back to star talk it's always good to have you good luck with the and it's not luck it's your talent that helps make uh pioneer works what it has been and what it will continue to grow to become so thank you so much and matt and i are still waiting for our invitation to be something other than in your audience now i can't wait oh are you going to get an invitation you got it all right matt always good to have you dude lovely to be here thank you for having me this has been star talk cosmic queries black hole space time continuum which we dubbed the stoner edition i'm neil degrasse tyson you're a personal astrophysicist keep looking up [Music] you

Channel: StarTalk

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Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics, time, fourth dimension, death of the universe, gravity, velocity, gravitational waves, gamma radiation, Hawking Radiation, the universe, energy, reality, expansion, atoms, electrons, positrons, perception, event horizon, wormhole, time travel, time travel conference, spacetime, 420, stoner, marijuana

Id: UwRAat-MUKc

Length: 48min 51sec (2931 seconds)

Published: Thu Mar 10 2022