Are black holes really black holes?

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Speaker 1: Hey, it Jorhan Daniel here, and we want to tell you about our new book. It's called Frequently Asked Questions about the Universe because you have questions about the universe, and so we decided to write a book all about them. We talk about your questions, we give some answers, we make a bunch of silly jokes as usual, and we tackle all kinds of questions, including what happens if I fall into a black hole? Or is there another version of you out there that's right? Like usual, we tackle the deepest, darkest, biggest, craziest questions about this incredible cosmos. If you want to support the podcast, please get the book and get a copy not just for yourself, but you know, for your nieces and nephews, cousins, friends, parents, dogs, hamsters, and for the aliens. So get your copy of Frequently Asked Questions about the Universe is available for pre order now, coming out November two. You can find more details at the book's website, Universe f a Q dot com. Thanks for your support, and if you have a hamster that can read, please let us know. We'd love to have them on the podcast. Hey Daniel, how do you know that an electron is actually an electron? What do you mean? I mean, what else could it be? Well, what do you really know about an electron? Well, that's a good question. I mean, you can measure things about it, like it's mass, and it's charge and it's spin. So even if you can, you know, look at it directly, that's enough to tell you that it's an electron. I guess. So, I mean if it quacks like an electron and it walks like an electron, then you call an electron a doctron. But I guess you know, how do you know there isn't another particle with like the same charge and mass and spin, but is not an electron like another particle hiding and electron clothing. Yeah, like the incocniton or the full electron, or the non electron or the electron. Not. Well, I'm glad we have a name for it, even if we haven't discovered it yet. I am or Hammer cartoonists and the creator of PhD comics. Hi, I'm Daniel. I'm a part of Gold physicist or at least I walk like one and I quack like one. Oh really, physicists quack that a thing you do when you discover something amazing about the universe. Oh yeah, we quack about corks all the time and quasars. Yeah, I guess regular nerds a snort and when they laugh and we're get excited. Physicists are hardcore and you quack, yeah exactly, don't quibble about the way we quack. And that's why you fly south every winter, right, that's why I live in south southern California. Sabbaticals in the South Pacific. No, i' made a mistake. I took my sabbatical by going north. I went to Copenhagen briefly, but you went in the summer though, right, days were long, Right exactly, it's the right place to go in the summer. This is one smart duck. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of I Art Radio, in which we fly north and we fly south, we go on sabbatical, and we engage our brains in the big questions of the universe. We try to ask the biggest, deepest, darkest, craziest questions about the nature of the universe, what's in it, what's out there, and what it really means? Is the reality we see around us, the reality that's actually out there independent of human thought, or is it vastly different than our crazy, tiny human brains can't imagine? Is the worldlined us and hiding and pretending to be something that it isn't or is it just the way it looks? Yeah, because it is a pretty tricky universe. You know, it's not only big and almost a hidden from us because it's so large, but there's also, you know, kind of strange things about it, because you know, the only things that we know about the universe are the things we can see or at least measure with our instruments, and sometimes, you know, the universe places tricks on us. Yeah, and you can ask really fun, interesting philosophical questions, like how do you know what some thing is? Like you eat an ice cream cone? You know, it feels like an ice cream cone in your hand, it tastes like an ice cream cone. How do you know it's not actually something else and you're being fooled and it tastes like an ice cream cone, but it's actually something crazy and weird, like an assembly of nanobots that's been collected to like invade your body and taste like ice cream. Oh, my gosh, you just give me nightmares about eating ice cream. I hope I didn't just ruin ice cream for everybody you might have. Yeah, No, I'm gonna worry eating nanobots or something evil nanobots fooling my tongue. There is a deep question there because we are limited in the ways that we interact with the universe, right, We can't see the absolute, ultimate, complete truth of the universe. Ever. We have these narrow little ways. We can see, we can taste, we can touch, we can smell, and that paints a picture in our minds of what we think the universe is like. But it's a very narrow way to interact with the universe, and it is possible that we are confused about what's actually out there. Yeah, because I guess the universe is tricky like that, And I mean it's so complex. That's something that it seem like, you know, ice cream could be something else. You know, it could have fake sugar or nana bots or artificial flavors, you know, or artificial nana bouts, Like, hey, I ordered nano bots of my ice cream. These aren't real nano bots. Now, I can't even trust the nana bouts They could be you know, the cheap kind or something. That's right, they kind of give you indigestion later, you don't want to eat those. It could be po bots or fempty bots. Well, I paid for Nana bots and I just got these Milli bots. Man, I can even see these with my eyeballs. What's going on? They're too crunchy. Yeah, they ruined the texture of your fake ice cream. But mostly we're not that worried about ice cream. As long as it tastes good, it's fine. Mostly we're worried about the nature of the universe and what's in it, what's out there in the universe. Yeah, and one of the most interesting things out there for people to study are black holes. It seems like we get a question about black holes almost every week on the podcast, right, Yeah, this should basically become a black hole podcast. We're basically just falling into the gravitational attraction of the mysteries of black holes. Yeah. I guess the r very attractive and deep. Yeah, and once you start talking about them, you basically can't escape. There's like a question horizon or something. Yeah, it's a massive topic. But even black holes, as you know, as much as we know about them, Like, we know they're there. You can see them gravitationally. And now recently, in the last year or two, we've actually gotten pictures of black holes. Right, Yeah, we have a lot of information about black holes, and you just said we know that they are there, And that's a really interesting question. Like, we know a lot of things about black holes. We've measured a lot of things about black holes. A lot of things that we see makes sense a black holes were there. But you know, how do we really know it's not just a bunch of nanobots out there fooling us in deep space? Oh? Man, I imagine we're not going to be licking the black holes or eating them, hopefully not. I don't think anybody ever said licking the black hole until you just said it. Then it's the first time in human history anybody ever said that. We'll trade that and put it on our T shirts. Daniel and Horror explain the universe liking the black holes. That's like a pitch for the science fiction version of a Christmas story. Yeah, you're going to shoot your eye out and or well into a singularity forever. Alright, we're talking about black holes today and this sort of philosophical question almost about the true nature of black holes and whether or not we are actually looking at or feeling black holes. Yeah, what's actually out there that's giving us the impression that black holes exist? And could it be something else masquerading as a black hole? Oh man, sneaky. So today on the program, we'll be tackling the question what if black holes are not actually black holes? And Daniel, are we questioning you know that they're not actually black the color black, or that they're not actually holes or both both and everything? We're questioning everything today, we're blowing it all up. No, we are wondering what we actually know about the nature of black holes. What evidence do we have that they are this we your conceptual object that really just exists in our minds and existed only in the minds of physicists for fifty years before we discovered them. Well, actually, I guess maybe they existed in the universe before that, but the idea is only fifty or so years old, and so we're asking the question, is what's actually out there consistent with what's in our mind? Yeah, Because I think black holes have had sort of an interesting journey, right, Like first week thought up of them as an imaginary thing, like we saw the theory and we imagine that they could exist, and then we sort of confirmed that they're there but not actually seeing them. They sort of looked like they were there gravitationally, and then more recently we've actually seen them. We have pictures of them. But now we're asking the question here today, are they really actually black holes? The things that we're seeing in feeling? Yeah, because can you really see something that's just black? You know, it's like sort of not seeing it is seeing it. You know, we didn't see light from the black hole, which would have told us it's not a black hole. What we saw is not light, which is not the same thing is seeing the black hole. We didn't see the not black hole, or we saw the not black hole we didn't. I don't know. I'm confusing myself. Did it not see a not black hole that is not actually there? Let's just keep going in exactly consistent with the black hole prediction. We didn't see photons from it. What does that actually proved? Right? Right? If it looks like a triple negative and it walks like a triple negative, it's actually true. Maybe I don't know these philosophical jokes are too much for me. But I guess if a black hole is not actually a black hole, what else could it be? Yeah, and so there are a bunch of other ideas for what could maybe be masquerading as a black hole. What out there in the universe, other theoretical concepts for what could give us the same sort of set of observed data that could give us the same experience without actually being a black hole. Interesting? Do we have a name for these mysterious fake full black holes or black holes? We do? And this is this call these things dark stars, which is how sort of cool in science fiction? E. It does sound like another Marvel superhero or villain. I think, actually that is maybe a d C hero, thinking we'll have to google it. It sounds to me like the jet black version of the Death Star. Interesting, that's for the next Star Wars equal when there's another death Star like the fourth one, but actually bigger and darker. Is that what you're saying? Yeah, well, you know in Star Wars they're always saying that's not a moon, that's a space station, and this one they'll say, that's not a black hole, that's a dark star space station. Oh my, gosh called j J Abams. I'm sure he's a listener, So j J you call us, that's right, you have Daniel's email for waiting. So a dark star. So that's kind of what we'll be talking about today, is that, you know, maybe black holes are not black holes. Maybe there's something called a dark stars. Yeah, exactly. These are fun, crazy concepts that might be real out there in the universe. So as usual, we were wondering how many people out there had thought about the trueness of black holes and had heard of these things called dark stars. So Daniel went out there and ask people on the internet what is a dark star? And if you are out there in the Internet and still don't feel safe venturing outside and talking to humans in person, I get it. And so if you'd like to participate in these questions online please they'll be shy and right to us two questions at Daniel and Jorge dot com. We'd love to hear your voice on the podcast. So think about it for a second. If I say the words dark star, what comes to your mind? It was what people had to say. I think a dark star is a white dwarf that has sufficiently cooled to become a black dwarf and doesn't emit any radiation. Sounds like it's one that would not emit any light, but maybe it's still emits radiation. Why that would be, I have no idea, but that's my guess. So I think I've heard of this where like say a brown dwarf, a brown dwarf is niclear a star, but it's a lot gammer and a lot cooler, and typically a lot smaller. So that would be what I would think a dark star is. White dwarfs are going to burn out and become dark. It could also be you guys thinking about dark matter somehow forming a star, but the dark matter cannot interact with itself, so does that work. At the beginning, I thought this dark star was black hole, but lately I read that dark star might be a type of star from the beginning of the universe, really really big star, much bigger than battle Juice or any other type of star that we've seen until now. So this is from the really beginning of the universe. If I say to you, what is the dark star, what would you think? Well? Probably it could also me and not very bright stars, and mostly there are rampwarfs like Barnold Star are proxima centauri. All those dark not very dark, does not be bright. A dark star also awesome name for a band or opening cover of a band. Dark star definitely, I'm going to go with the dark matter star, even though dude, I have no idea how such a thing could exists, because what even is dark matter? No one knows. But if it could clump and immage energy in the form of dark radiation, well, even better band name. Then you will get a dark star. I think a dark star is probably maybe a theoretical object in dark matter, So maybe it's a star made entirely of dark matter, but I'm not arrely sure. I guess a dark star would be the star that's not emitting light, so maybe a star that has already undergone a supernova or that has collapsed into a black hole or something otherwise. Um, I guess a rock star that trash is hotel rooms would also be a dark star. Right. Interesting answers here. I feel like all of these answers could be a theory of physics in itself. There are some great answers, and you hear some real knowledge in there. There are people talking about dark matter stars or black dwarves. Black dwarves are a real thing, are they? They absolutely are. There are when a white dwarf, which is just a huge hunk of hot metal no longer actually fusing and giving off light, just sort of like glowing in the universe, when they cool down eventually and stop glowing and become dark, and so that's a black dwarf. I like this suggestion that maybe it's like a dark matter star, which we actually talked about on the podcast, right, Yeah, we did talk about whether you can make dark matter stars and maybe whether they would make dark photons using dark fusion or something crazy like that. So if you're interested in dark matter stars, go check out that whole episode. I see, but that's its separate rock band, right, There's a Dark Star and there's Dark Matter Star. Yeah. I think they toured together once in the eighties, but it didn't go very well. The Extra Dark Tour is epic and the story well, they never turned on the lights and so nobody could tell if they were there. Yeah, they all right, And then someone at the end said that maybe it's a black hole. So they were sort of close to the truth here, maybe yeah, yeah, maybe there are masquerining as black holes. All right, let's jump into this subject of whether or not a black hole is actually a black hole and what else it could be. So let's start from the basics. Daniel, why do we think we've seen black holes? It's a really fun story. Actually, we did a podcast episode about the discovery of black holes, and it's really cool to trace the history of the idea and then the history of the observation, like, this is not something I think we could have ever discovered if we didn't know to look for it, because in the end, the evidence is not a smoking gun. It's like the kind of thing you can hunt for subtle signals of if you know to see it. So it's sort of like, you know, a story. The moral of the story is you should really think carefully about what's out there in the universe, because it might give you crazy ideas for what to look for. And this crazy idea came from Albert Einstein himself in nineteen fifteen when he came up with general relativity, which is the way to describe how space bends in response to mass, and then how mass moves through that bend space. So that's the theory of general relativity, and just a year later somebody solved his equations and discovered they predicted something really, really weird. And that's when the idea of a black hole was born. Now more than a hundred years ago, right, maybe you can step us through this a little bit. So what was Einstein looking at? Like, he was looking at the equations of gravity, and like, what happens if you get enough gravity into into or mass into one tiny spot? How does that affect the equations that he was coming up with? What exactly was he looking at? He was looking for a general equation, one that described, you know how space bends when you have mass in it. So if you put a son here and you put a planet there, then how does space curve? And then how do things move through that curved space? But his equations are famously hard to solve, Like, we can't solve them for even very basic simple scenarios like a son and a planet. We've only been able to solve them for very simple situations like an empty universe with nothing in it, or a universe like filled smoothly with matter with no lumps or bumps at all. These kinds of very simple situations lead to solutions where we say, if you have a certain mass distribution, then I can tell you how space bends. It's not easy for a given arbitrary mass distribution to solve Einstein's equations and know how space bends. It's like, it's very difficult. Einstein's equations just tell you, like the rules that it has to follow. But as we talked about once in the podcast, knowing the equations doesn't necessarily mean you know how to find a solution. And so even though we had these equations, nobody had ever solved his equations, including Einstein. When he put them out there, he was like, here are the equations. But just a year later, a soldier on the front lines of World War one, kurse short child, solve them for this easy scenario where you have a really immense amount of mass all in one place. And so that was the first ever solution to the Einstein equations. This one really weird, extreme scenario. And sometimes in math, like the really extreme weird scenarios are easier to solve than the more complicated general ones. I see. So Einstein didn't even think about black holes. He just put out, you know, general equations for like everyday life and somebody looked at that and say, well, what if I crank up the mass and put it onto one spot that leads to like a special solution, which is a black hole. Precisely in Einstein was like, wow, nice work and never thought of that. That's very cool. He was like man penning himself on the back, kind of like, wow, that's a pretty awesome thing that came from something I did. Yeah, I think it's always cool in science to see somebody follow up on your work. You know, you don't want to write a paper and then have nobody read it and nobody respond to it. You want people to read it and build on it. And of course lots of people have done that for now, but this was like the first step. This is the first time somebody took his equations and said, all right, you know what kind of universe is him this describe So Einstein hadn't really thought about this idea of like a volume in space that if you go into it you can never escape. No, he had not thought about that at all. And in fact, even though this solution existed in general relativity since the nineteen sixteen, people didn't really understand the impact of the concept. What it meant, you know, what it would actually look like in space until decades later. It was like in the fifties that this concept of an event horizon was even invented. You know, before that people were like, well, what would that mean? Would it just looks like sort of a frozen star because there's so much gravity to be crazy time dilation. So it wasn't until the fifties of people realized that no information could leak out of this, that there was like a barrier beyond which all information was hidden. So it takes decades sometimes to understand the consequences even of theoretical ideas interesting. So I guess the black hole wasn't really a black hole for for forty years until somebody figured out that, you know, if you actually were in the presence of one, it would look like a giant black ball. Yeah, but even then it was like a crazy idea. And you have to understand, physics is filled with crazy hypothetical ideas that nobody believes are real, that nobody thinks actually exist in our universe. Like if you read papers, there are papers describing all sorts of crazy, bonkers things, and these are just theorists exploring, like what could happen. What about this, could this work? What would it mean? And this was in that category for a long long time, not something anybody ever expected to see in the universe or actually observe. And that changed in the sixties when there was the discovery of neutron stars. I made a podcast recently about the discovery of pulsars, which was very cool. That shocked people because these are closely related to black holes. They're very dense, very compact objects with incredible gravity. So people start to think, hold on a second, if neutron stars are real, could black holes be real? Also, so neutron stars are totally different because you can still escape a neutron star, right, Yeah, they don't have an event horizon, but they are crazy dense gravitational objects. Okay, so we found it, and that made people think, Hey, maybe this other crazy idea called the black all exists out there. Let's go look for it. Yeah. And then around the same time, we started seeing unexplained radiation from the sky, like people were sending rockets up into the upper atmosphere to measure the radiation from space, and they found an incredibly bright X ray source that nobody could explain, like something out there was generating very very high energy photons. To have high energy photons, you need like really really hot gas, and you know, you look in the sky and you don't see anything there, so you're like, what's out there? It's dark and it's generating this crazy X ray source. So that was weird and interesting. Well, I mean it's dark and like the visible light spectrum, is that what you mean? Right, Like you can't see with the naked eye, but if you have an X ray telescope you can see the light in that frequency. Yeah, And so that tells you there's something out there which is glowing only in this very very high energy photons. That's weird, you know, And so we knew it was something and it had to be kind of small because it was like not a whole lot of room around there. You could like pinpoint where this was coming from, and it couldn't be some like huge, massive extended object because there was like other stuff nearby. And that was the sort of the second clue, like we saw that there was something out there that was dark because we couldn't see it in a visible light, but it was generating these X rays and it was pretty small. We found another example of one that was orbiting a super giant blue star and it was emitting this crazy radiation, but there was nothing visible there and there wasn't a lot of room for anything, So that suggested it had to be something which was like very small but very high energy. Did you call them like X stars or x essence? There were so small, extra small, all right, So then people went out to look for black holes. But I guess the question is was what they found actually black holes? So let's get into that question and what this dark star is and what it means. But first let's take a quick break, all right. I know we are questioning black holes. Are black holes actually black holes, like in the sense of the concept of a black hole that Einstein helped figure out, or maybe there could be something else that acts like something that could be a black hole. Yeah. I feel like we're in you know, act two of some murder mystery where we have a bunch of clues and we have a suspect, and we're like, all these clues pointed that suspect, and then we're wondering, hole on a second, is it possible that it was actually the ex husband or the sun or whatever, were that one character that you didn't pay attention to, and you have to reassess your evidence. You're like, what do we actually know about who killed this person? So this is the part where you like twiddle your mustache and like what if, Yeah, you know, maybe that was just a paste on mustache or maybe there's shaved their mustache off or something. You know, the whole thing was just a deep fick. And so I think it's useful to like catalog exactly what we do know about these objects that we've been calling black holes. But maybe it's really just the ex husband or an ex black hole husband. Anyways, So you're telling me that we sort of figured out theoretically that there could be black holes out there, and then we saw some clues and then we actually went and found what we think are black holes. Yeah, we have identified these objects out there in space, and essentially we know that they are small, that they are dark, and that they are heavy. Right. We know they're small because sometimes we see other stars orbiting nearby them and coming very very close, so they can't be that big. We know that they are dark because they don't give off a lot of visible radiation or almost none or exactly none, and We know that they are heavy because we can measure their gravitational impact on other stars nearby. We see stars like whizzing around them really fast, which only happens you have like a lot of gravity. So we have something that's small and dark and heavy. And for a long time we had, you know, only one candidate that could fit the bill, one candidate that could satisfy all of those requirements, and that was black holes. So I guess, yeah, I guess from a far enough distance, that's how you would define it, right, if you're far away enough, it's just something that is not visible in the in the light invisible light spectrum. But it's also very heavy, yeah, because we've never like actually seen an event horizon in the sense that we haven't like dropped something in it and see it disappear, you know, or measure the gravitational impact on it. Even the direct photograph we have of a black hole, right, the one that was a big hullabaloo in the news and etcetera, Like, what is it? Really what you're looking at is an accretion disc is the gas around the black hole, and in the center you see something black. So again you know that it's small, that it's dark and it's heavy, you don't actually know it's nature. And the argument that it's a black hole is basically like nothing else can do that. So if you can think of something else that can do that, then you know, maybe it's that other thing instead. But we've also seen gravitational waves right from black holes or what we think are black holes crashing into each other. We have exactly we've seen gravitational waves from black holes merging from neutron stars merging from neutron stars, and black holes merging. What does that tell us? It tells us again that there's something very massive with a lot of gravity and that general relativity mostly works, So that could be explained by something else, you know, just as massive and small and dark in that same location that would also emit gravitational waves, like anything that dense and small would emit gravitational waves also, So that's also not a unique signature of black holes. Like let's not jump to conclusions. And so maybe a possible thing this could be instead of a black hole is something called a dark star, So like what is the dark star? Then? Yeah, So the idea is, you know, exercise your brain, think about other ways to arrange matter that gives the same sort of outwards appearance but looks different fundamentally. And so a dark star is like again very very dense matter. You know, you take star and it's done burning, and so it no longer can provide like ready Asian pressure to push outwards, and gravity takes over and it pulls the star in and it collapses into something very very dense. And there's lots of different scenarios. One scenarios it becomes a neutron star, right, and that's a scenario where to avoids total gravitational collapse because of the neutrons putting pressure on each other. But there's this other idea that it could collapse to something even more dense than a neutron star, but not a black hole. And so that's what a dark star is. It's got something called a plank core where the core is collapsed and gravitationally, but it doesn't go all the way to a black hole because something prevents that, something does actually push back. Interesting, Yeah, I remember a neutron star. It's like the stuff is squeezed together so much that it like dissolves into almost pure corks. Right, And so you have this giant wall of corks kind of holding together because there's enough energy there to pushing the quarts pushing each other away, but it's still super super dense. Yeah, and we do not understand the internal physics of the neutron star very well at all. It's like a really active area of research, and it's really difficult to study because corks are complicated. You know, they used the strong force, which is a big mess to do calculations in. Every time you emit a gluon, it emits more gluons. You have infinite numbers of gluons every time you want to do a calculation. So we don't really understand what's going on inside a neutron star. But roughly, yes, it's like a huge particle because all the corks are bound together into this incredible you know, like ten fifteen kilometer objects that's the mass of the Sun. So you're saying that there's another step that you can take between that and a black hole, which is maybe a dark star. And so what's happening, Like are the corks somehow running out of juice and so they squeeze in a little further, Like what's going on? How would this dark star come to be yes. So the reason neutron star is stable is because the corks are pushing back against each other. And so to go deeper and darker and go beyond a neutron star, you need more gravity. So if you have more mass than a neutron star can be, like neutron stars can be at most, you know, mass, maybe twice the mass of the Sun or so, we're not exactly sure. If you have more mass than that, then you can have enough gravity to overcome whether corks are doing to resist the collapse, just the same way like our son currently is resisting gravitational collapse. It's doing so by burning and his fusion and photons pushing out. The neutron stars pushing out because of the cork forces. If you have more gravity, you can overcome that, and then you can go deeper. And there's another layer. People think this is all hypothetical. People think that there's another layer where quantum mechanics itself prevents you from getting to a black hole. So the particles get so close that the quantum mechanics uncertainty principle prevents you from collapsing even further. Interesting, so I would have like a neutron star super dance, and I add more neutrons to it, more mass to it, and before it actually collapses into a black hole, maybe there's something about quantum mechanics that keeps it not collapsing, because quantum mechanics doesn't like having particles localized in a very specific region. Right, The whole idea of a singularity inside a black whole huge amount of mass and basically zero volume, is nonsensical when it comes to quantum mechanics. Quantum mechanics says, if that happens, then the uncertainty and the momentum of all those particles would basically be infinite, so they would basically have infinite energy, and then they would escape. The whole thing of a singularity doesn't make sense from the point of view of quantum mechanics. So the idea is maybe quantum mechanics prevents you from getting there, that as the particles are collapsing, that the uncertainty principle prevents them from getting so close as to actually form a singularity. I guess the key thing here is that it's small, it's dark, it's super dense, but it's not technically a black hole because it doesn't get dense enough to form an event horizon, which is like the actual like point where nothing can escape. Yeah, this dark star would not have an event horizon exactly. And also it wouldn't have a singularity at its core. You know, the really defining characteristics of a black hole are the singularity at its core and the event horizon. And so this would be a very very dense object, even denser than neutron stars, but not actually a black hole, and quantum mechanics would be preventing that. And something else that's super fascinating about these objects is that they're not stable like a neutron star is stable. It's a balance between these two foss squeezing down gravity and pushing out because of the corks, this plank core is not actually stable. People think that quantum mechanics is more like a rubber sheet, you know that You're like it collapses and then it bounces back, so it provides like a maximum density or like a minimum size to this object, and then it pushes back and then the star expands again. But wouldn't that be evidence or an argument against these dark stars, Like if they don't last very long, why do we think they could exist, right, Well, they might not last that long in their own time, right, but the gravity is really really intense and so time is slowed down. So what these dark stars might be is like this object that's collapsing, that's going to bounce back from this plank core. But from our point of view, it might take billions or trillions of years for that bounds to happen because it's super slowed down by the gravity aational time dilation. So it looks stable to us on our time scale, but you know, if you're inside of it, the whole thing would be over in a blip. It's like a loophole. Like it's unstable and it won't last for long. But it depends on what you mean by long, all right, So so from our point of view it would look like a stable thing, but it's actually not. Yeah, and it doesn't have an event horizon, and so unlike a black hole, it could actually emit information. It could like actually leak photons. But I guess why is it dark and why is it emitting X rays but not visible light? Yeah? Great question, right, Because we have to match all the observations for these things to explain what we see. They have to actually predict what we see. So how could these things be dark? Again, it's gravity and the relativistic effects. If these things really do have this much gravity, because they're very, very dense objects, so much so that they have this crazy time dilation. They have another effect on things, which is that they read shift. So they might be emitting photons, but those photons would be shifted towards the red, so far towards the red that they're essentially invisible. Like, take a visible light photon that has a wavelength of you know, a few d nimes and stretch that thing out past infrared, out past radio, so it has like a wavelength you know, like the size of the galaxy, or maybe a little smaller. That would be a photon that's so big it would be almost invisible. And so this would look like a black hole. Wow, photon the size of a galaxy. That's wild. Well, let's get into why we think these dark stars might be real and whether or not they actually maybe supplanted black holes and make them not real. But first let's take another quick break. All right, we're talking about dark stars and whether the things that we call black holes are actually maybe not black holes, and maybe there are these dark stars, and so we talked about what those are. Now, Daniel, why do we think that maybe black holes are not black holes, but they're actually these so far theoretical dark stars. Yeah. Well, one reason is that black holes are a headache. You know, they don't really make sense. There's lots of puzzles, like they're fascinating, they're amazing, and they're sort of a fun headache. But you know, there's lots of things about black holes that we don't understand, like can a singularity be real? Is that something which actually exists in our universe? You know, as we said, general relativity predicts that singularities are real, but quantum mechanics says they can't exist. And so we've long struggled to understand that contradiction. And so this is sort of like a way around this to say, like, oh, well, maybe they just never happened and so we don't have to explain them. So would this supplant even like the black holes we think are at the center of galaxies, Like could those supermassive black holes in the center of galaxies that we know are humongous, could at those actually be dark stars? Or are we only talking about the smaller black holes. Now we're talking about all of them, so we could supplant all of them, and that You asked a question before the break about the X rays, like how do we ling the X rays and the other radiation because the supermassive black holes at the center of our galaxy. You know, from the actual black hole, there's no light right there black but around them are these crazy accretion disks of hot gas that are emitting X rays and other very high energy radiation. But that's just from the gravity of the object. And so a dark star with the same gravity as a black hole, but without the actual singularity in the event horizon would have the same gravitational impact on nearby stuff, heating it up and swirling it around and generating that same radiation. So yeah, you could have a huge dark star at the center of our galaxy that's like in the middle of a billion or trillion year collapse and rebounds out, but it looks to us like a black hole. I feel like you're kind of saying that maybe black holes in themselves are impossible, Like maybe it's impossible to have a black hole, and actually, like when you try to get a black hole, the most you get is one of these like super compressed dark stars which are being kind of prevented from collapse by quantum mechanics. Yeah, exactly. And so maybe the reason that black holes make no sense theoretically and inconsistent with quantum mechanics is because quantum mechanics prevents them from happening. Right, If the universe really does follow these rules of the uncertainty principle, then that's inconsistent with singularities, and so maybe the uncertainty principle prevents the singularity from ever forming. Oh man, I feel like you just blew my mind if you had how many podcasts about black holes and now you tell me like, maybe they're not actually real, Like maybe they're impossible. Yeah, and in some sense, like coming up with this other explanation for them solves all these other problems that black holes bring with them. Right, we've had multiple episodes about like the black hole information paradox. We know the quantum information is not destroyed, So what happens when things fall into a black hole? What happens to their information when the black hole eventually evaporates, We don't know. It's not something that makes any sense to us, and we can't explain because we have no good theory of quantum gravity that tells us what happens when there is gravity between part of goals. And so maybe the solution of that is just scratch black holes from the list of things we want to explain, right, we don't need to get about it, you know, like never mind, you know these things we've been talking about forever. Uh, whoops, never mind, it's actually not possible. Yeah, it's really fun idea, you know, like take something off your to do list by erasing it instead of doing it. I gotta clean the toilet. No, toilets don't exist. Done with that, Yeah, you're gonna have other problems if you think toilets don't exists. But the cool thing about dark stars is not only do they get rid of this thorny problem of black holes, but they could explain other mysteries of the universe that are out there. Yeah, other dark and mysterious stuff. Right. Yeah. For example, we've long wondered, you know, what is the stuff out there in the universe that's creating all this gravity that seems to be holding the galaxy together, some weird new kind of matter that we don't know what it is and we can't see it, but it has gravity, and it's affected the structure of the universe, and it affects how galaxies spin, and it seems to be everywhere and really important, and it's more of it. And then there is a normal matter, but we don't really know what it is and we haven't been able to see it or interact with it or detected. So this stuff dark matter. We have a long list of candidates for what it might be, but now because of dark stars, we have sort of a new candidate that appears on that list, and that's these crazy long wavelength photons. So you're saying that the light from these the dark stars is what could be dark k matter or are you saying that maybe the universe is like riddled and filled with tiny dark stars everywhere. You know, it's the light and the radiation from these dark stars. So these dark stars look a lot like black holes, but they do give off some light, but that light is invisible to us because it's so low frequency, and that light itself might be the dark matter. It could be that there's so much of it out there that the light itself is helping curve space. Because remember photons have no mass, but in general relativity, space bends in the presence of energy, not just mass, so photons can contribute to that. And so these things can contribute photons or even gravitons that are hard to detect, but overall, having lots and lots and lots of them around, they can bend the shape of space and exactly the way dark matter does. I feel like now you're saying that maybe dark matter doesn't exist, and really it's just dark light. Dark stars emitting dark photons could explain everything. But wouldn't black holes also emit you know, these dark photons, if black holes existed. But black holes don't emit anything, right, I mean, black holes don't emit light. The stuff around them emits light. But this is the one thing that would be different between black holes and dark stars. That these dark stars, because they don't have event horizons, they do emit light, and that light is crazy stretch to low frequencies by the gravitational strength of the dark star. Can we measure these long wavelength light? Can we have a detector to see if they're there? It's very difficult to interact with something that's such a long wavelength. They're basically just ignores you. That's why, for example, we do radio astronomy because radio waves can go through like clouds of gas and dust and tell us what's going on in the center of the galaxy. Because to them, the clouds of gas and dust are like nothing, and so it's very, very difficult to interact with those photons. You need a detector like the size of the galaxy almost in order to interact with them. I feel like you're telling me, like, maybe you know that dark matter halo that we know is or a cloud that is sort of covering our galaxy. Maybe it's just it's not dark matter. May it's just like one giant photon, like one one ginormous photon, you know, confusing us. That'd be hilarious if it's like, Hi, I'm Bob, I'm a photon and I've been the dark matter of the whole time. Yeah, there you go. We found our culprit. Why didn't you introduce yourself in Act one? Man? Why did you wait on to Act three? That's just bad mystery writing. Well, that's really interesting to think about. But you know, photons are quantized and really really low frequency photon would not have that much energy right, because the energy the photon depends on its wavelength. So in order to explain the dark no matter, you need a lot of these photons. They have to be Bob and like ten to the twenty seven of his friends. I think, kind of like the nuta book, they're fooling ice cream flavor of the galaxy. Yeah, and you know, this is a fun theory for people to think about, like could this be becauld it really exists out there in the universe. What are ways we could separate them from black holes that we could actually detect. But it's a new area. People are playing with it, you know. Carlo Rovelli wrote a fun paper about them. I read a few papers on this topic. It's still something that's in people's minds. I see, like we don't know if it's even possible to have these dark stars or whether they would just collapse into the black hole. Yeah, the signs of them is still very new and tentative, and people are doing calculations and making all sort of assumptions and disagreeing with each other about what these things might look like. It's really at the forefront of knowledge. But you know, black holes were at the forefront of knowledge. For decades before we understood really what they would mean and what they would look like in the universe, and so it might just take a little while for sort of like people to digest this stuff intellectually and figure out how to look for them correctly. Well, it's at that picture that we took up the black hole last year or two years ago. It was pretty convincing. But now when I look at it, and maybe I'll imagine a little tiny bob in the middle there laughing at us and twitterling. It's a mustache, yeh, exactly. Maybe it has a totally jet black mustache and you can't see it, and it's laughing at you and admitting dark matter. That's crazy. All right, Well, I guess once more the universe is full of potential surprises. And I guess the main lesson here is don't trust physicists. You know, maybe we're talking about this whole podcast. No, the lesson is fund physicists to think of crazy ideas, because they might find stuff that's actually out there, and then they might come up with even better explanations to describe what you see. We definitely need creative brain story about how the universe works. That's a good positive spin. All right, well, we hope you enjoyed that. Thanks for joining us, see you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. Or more podcast from my heart Radio. Visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.