Could black holes be making the Universe expand faster?

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Speaker 1: Hey, Daniel, have you been keeping up with the science news headlines? Oh? What does that mean? What do you mean? Oh, I'm guessing there was some new clickbait article about how scientists mate bananas go faster than light or something crazy. They have you eat them faster than light. But that's not news. Well they are kind of slippery. But are you saying that we shouldn't trust science headlines? You think it's fake news? Well, you know, sometimes the headlines don't reflect within the article, and sometimes the news article doesn't reflect the actual research that's been done, and sometimes the research itself it's questionable. We Oh, you're saying even peer reviewed papers can be wrong. What can we trust? Then you can trust podcasters, I guess I hope all podcasters, even the ones that make tales of sasquatch. All right, you can trust us, Just trust us, well you us, I mean, I'm a cartoonist. Padn't trust me with physics verification? Then you got to listen to the podcast Learn Physics so you can figure it out for yourself. Trust yourself. Oh, I see this is now a self improvement podcast. Hi. Am Jorheme, a cartoonists and the creator of PhD comics. Hi, I'm Daniel. I'm a particle physicist and a professor you see Irvine, and I do believe that learning physics is a form of self improvement. Well, it depends on what kind of physics, doesn't it. How about the physics of eating fatty foods? And Yeah, the more you understand it, the better you are informed, and the more educated choices you can make. Yeah, but educated choices in this stally meaning it's the right. I know potato chips aren't good for you, but I still eat him. And you'd rather eat them and not know that they're not good for you? Huh? Yeah, maybe maybe that might help my self improvement. It might help yourself enlargement. Yeah, my happiness. Oh wait, did you mean something else to each of their own chip? But anyways, Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio in which we try to help you on your journey of self improvement by teaching you everything we do and do not know about the universe. We also help you on your journey of mental self enlargement as we try to grow your brain in your mind and fit more understanding of the universe into it. Because the universe is big and filled with mysteries and all sorts of things that we have and have not figured out, things that future physicists, maybe one of you out there will figure out one day. Yeah, because it is an amazing universe, one that is always expanding, it seems, with all kinds of interesting knowledge and interesting phenomena to study, to wonder about, to ask questions about, and also to crime into your brain. And it seems like every single day we're learning something that science has figured out. They've done a new study on banana slugs, or they've done a new study on bananas. There's a huge population and scientists out there doing studies, learning things about the universe and putting them out there in papers. Well, that's kind of what you would expect, right, I mean, scientists aren't working all the time and they should becoming up Whitney results, right, Otherwise what are they doing exactly? And it's a wonderful, delicious fountain of knowledge that science is creating. And that knowledge is not just for other scientists, it's for everybody. We all want to know. What are the answers to the deep mysteries of the universe? How fast is it expanding? What's inside black holes? How did our solar system get to be the way that it is. So it's not just other physics professors who read the writings of physics professors. It's everybody out there who wants to know the answers to these big questions. Yeah, sometimes what scientists discover gets into the news media and out there into the general population. But I feel like it's it's kind of a filter though, Like only the juicy headlines make it out there into the big newspapers. It is a bit of a mystery to me what gets covered. I mean, I read a lot of physics papers, and then sometimes I'll read a popular article about one, and I'll think, like, why did this one get chosen to make a big deal about It's not really that big a deal, but you know, you can take some little aspect of it and make it sound like it's a really big deal, because most people out there don't understand a bigger picture of the field. Is this really a big step forward or is it a tiny little increment? And we're just hearing about the overall motivation for this entire line of research. So it's hard when you're not an expert to really understand what was a breakthrough and what wasn't. Well, I don't think it's a big mystery. There's probably a science reporter out there that needs to also work to write something on a deadline. Probably, Yeah, I guess you got to pick something to trumpet about. That's the job. The really good articles, though, do put things in context. They talk to experts, or they are written by experts, so the reader can really get a sense of is this a huge, huge leap forward or is this just promising potential breakthroughs or what's really going on? Well, it seems like there's a interesting science headlines every other week, But I guess sometimes people need a little bit of help figuring out which ones are a big deal and which ones are maybe a little bit, you know, over enthusiastically reported on by the reporter. If you just believe all the headlines that you read, you would think that every couple of weeks there's a result that's going to change fundamentally the way science works. That like, science is going to pivot on this result that that we'll look back on history and say, wow, there was a time before and after we knew this one fact in reality, though, a lot of times you'll read about something which sounds like a big deal, and then you'll never hear about it again, which tells you like, maybe it wasn't really that big a deal. So it's hard to sift through and figure out like which ones historically are actually going to seem like pivot moments in history and which ones are just going to have sort of filled the news cycle for that week. But I feel like that's kind of maybe one of the exciting things about science. You know, this idea that establish ideas can be overturned at any moment, and you know, everyone's working on a big idea of their own, you know, because we haven't figured things out, and so everyone has a different angle on it, and any focus that anyone makes could potentially, in reality, overturn what we know. Right, You're absolutely right, And it's tempting to look back on history and say, oh, there was an obvious line, a step from A to B to C to D, and that's how we got to where we are. But when you're in the moment, you don't know which direction is going to bear fruit and which one isn't. The true history of science is sort of like a big branching tree where lots of those branches were later abandoned or died off, and when you're at the tip of the latest branch, you don't necessarily know which direction to go. So that's why people are exploring in lots of different directions and exclaiming excitedly when they figure out something cool. That might mean that this is the future path of all of science. But maybe it's not. Maybe it just dies off after the next branch. You're right, we never do know in the moment. Yeah, you don't want to be that reporter who finds out about something amazing Indensis man, this was an okay result. Yeah, that's true. But it also means that you do need to read all these articles with a grain of salt, and sometimes a spoonful of salt. It seems like, for example, a recent headline that's made the rounds that everyone seems to be very excited about, you've got a lot of questions about it. Yes, there was an article last week that lots of people read and thought, oh my gosh, this seems like a really big deal. I wonder if it's true, And they sent it to me, so I got dozens of emails from listeners and tweets from people asking me, is this for real? What do you think? It seems like it would be more efficient if all reporters just ask you every time they write a science article, and then you could just, you know, impart your judgment. Well you know that happened. Sometimes they do reach out to me to ask me for comment, and reporters out there email me. I actually write back. I'd be happy to comment on research articles. I don't know do they want, Maybe they don't want. Maybe they don't if you're trying to get readers to read their headlines and click through. And now for a splash of cold water. Daniel Whites, Well, the article that came out, it does sound pretty interesting. That has to do with black holes and the expansion of the universe. So today on the podcast, we'll be asking the question, good black holes be making the universe expand faster? Black holes and dark energy too great taste? That tastes great together? Do they? Man? I feel like it's like black holes versus dark energy. It's like Emperor Popatine fighting Darth the It sounds to me like the last round of the Battle of the Bands. Yeah, there you go. We can just sit back with some popcorn and watch what happens. I think black holes and dark energy they've gotta be like metal bands or sort of like goth rock or something. Yeah, I'm sure there are grows up there with those names. But this is an interesting question because at first hearing it kind of sounds kind of intuitive, right, like black holes suck stuff in, they make things more compact, and ye, how can they be making the universe expand faster? Exactly? So it's got all the elements of a huge scientific revolution and big splash in the news. Right, it's counterintuitive, and it solves more than one mystery, like what's going on with black holes and what's going on with dark energy? Oh my gosh, maybe one explains the other. So it's very tantalizing. Yeah, it's always exciting when there's like a crossover event, right, like Marvel and DC, like Superman and Spiderman working together or against each other making the universe faster. It's like combining two tasty sandwiches. You know, peanut butter sandwich is good, a ruben is good. Would a Ruben with peanut butter be even better? Well, until you do the experiment, you can't know for sure, right, Daniel, you're going to do that experiment? You know, if I was a lunch eating kind of person, I might, but I'll have to leave it to you. I'll pass. I don't. I don't think I need to know that the result listeners let us know. But it's interesting. So this paper came out last week right as of this recording. It did, and it's set the physics world of buzz all sorts of cosmologists and experts in black holes and in dark energy. We're arguing about whether this paper made any sense and what it meant and whether we could believe it. Oh right, because there are experts in both areas and this one try to put them together. Did they ask for a permission or you don't need to ask for permission to write a paper. You can just write it and send it out there and see if people will read it. Why can it They need permission to publish a paper, thoughn't you? It requires the whole committee to approve your paper. To be approved, you definitely need reviewers and all that kind of stuff. But you can just write a paper and put it on the archive and you know people will read it. These days, journal review is sort of a secondary process. People read papers well before they're ever reviewed by journals. Wait wait, wait, wait what you can just post things on the internet without permission. Yeah, this is a site called archive dot org where all physicists post their papers before they go to the journals, because the journals take forever to review stuff, and you want people to read your results basically as soon as they're ready. So these days most of the actual science happens on what we call preprints, where people post their papers before they go to the journals. Wow, that sounds like having a policy debate over Twitter comments. You wait until you checked it out first, or maybe that is sort of a now part of the process of experts checking it out, you put it out to the whole community. Yeah, there's actually a vigorous debate about whether we even need journals anymore now that we have the Internet. Journals aren't necessary for actually publishing and distributing papers. You just have them online, so they're really just there to provide peer review. But you know, there's a lot of question about whether peer review actually adds anything to papers, or if it just delays them and burdens a bunch of people with extra work. I guess that feels a little risky. I mean that's sort of like calling Twitter comments peer review or like the like bunds, like, oh, this paper got two thousand likes, it must be true. Well, I never read and believe a paper just as it's been peer reviewed. I'm going to read it myself and see if it makes sense anyway. All right, Well, fortunately people out there have us, or at least they have you, to go through papers like this one to see if it makes sense, and they, I guess they have me to ask you about it. That's my role exactly. And so this paper was a lot of fun to read and to talk to my colleagues about. And I also went out there to gather opinions from random people I ran into on the UC Irvine campus. Yeah, because as usual, we're wondering how many people out there I had heard about this paper or had an opinion about whether black holes can make the universe grow faster. Usually people had to say that's not my area of expertise. My understanding was like they're an energy sync though, like the energy goes like it's like the one place where matter could possibly no one like actually be destroyed. So I'm not sure how to answer that question, but my guests would be the negative or it would do the opposite. But again I'm not I guess that would be an astrophysicist would be their expertise. I don't know. I don't really know much about black holes, and so I'm assuming maybe I wouldn't think so, because like black holes are meant to like go inwards right like almost like a funnel, and it's they seem to be pulling things in, So I would almost expect the opposite, where it would like help fast forward the I don't know when everything condenses. That's my opinion, at least. I'm not a physics I don't know. So I was actually just reading this paper last week. I think it's a really interesting result, you know. I think the media has maybe blown it a little bit out of proportion and portrayed it in a way that I don't think it's one hundred percent accurate. However, I do think there is always interesting. I think what they're doing in the paper, looking at sort of black holes as a different type of energy source to drive the expansion, is a really cool idea. So yes, I think it's possible, but maybe not in the way that's been portrayed by the media. Wow. Okay, I don't know, but since the universe is expanding and black holes are part of it, I'm gonna go with yes. No, I don't think black holes is gonna mat of his expand because they sucked things towards them with some gravity, so they wouldn't be pushing things away and expand. They would if anything decreases as the universe. I didn't read science or would probably referred to, so I'm not really sure. In my black hole compressed as a matter, So I I'm not sure how it would expand any universe. Oh. I don't really know much about black holes, so I don't really know it sounds plausible to you at all? Yeah, I mean, I guess all right. Most people had not heard of the article, although I was surprised that one person had just read that paper. Were you like what or did you ask your office mate or one of your grad students. I didn't have a whole lot of time, so I was wandering around the physics portion of the campus, and I'm pretty sure I did hit an astrophysics grad student who had actually read the paper. Oh, I see this is a little bit loaded of a sample. My favorite response was a person who suggests that I go and ask a physicist for an answer. That sounds like a very sensible thing to do. Why didn't you just ask a physicist, Daniel, Yeah, good question exactly. Maybe I should. I should go get a PhD in physics and I should go figure this out myself. You should be like a professor or something, and then you can answerr questions for a living. Yeah. I think that person misunderstood what I was trying to do with my question. I think she thought I was wandering around campus looking for somebody to explain this paper to me. Oh, I see, I see. Well, I guess there aren't that many people walking around asking physics questions. Did you think maybe you were like somebody lost on campus. Yeah, you know, it's famously hard to tell physicists apart from homeless people, and so I think maybe she would just being polite and patronizing me. Well, it's an interesting paper, and so let's dig into it. What does the paper say? So, in a nutshell, the paper says that black holes out there in the universe are the source of dark energy, that they are the reason that the universe's expansion is accelerating. That the expansion of the universe is getting faster and faster every year. That's the basic idea of the paper. That sounds pretty cool. All Right, we're done. I'm off to have a peanut butter ribbon sandwich. Yeah, I'm kind of hungry. I prefer almond butter. All right, good to know. We might have to do a side experiment on that. But let's maybe break it down for people, and let's start with just the idea that the universe is expanding. Some people might not know that the universe is getting bigger and bigger, and it's getting bigger at a faster and faster rate. Yeah. This phenomenon goes by the name of dark energy, which is a very mysterious sounding name for something we don't really understand very well. But we do know some things, Like we look out there into the universe and we watch galaxies. We measure their velocity relative to us by looking at how the light from them is red shifted, because things that are moving away from us faster will have the wavelengths of their light stretched out longer and longer. We call that red shifting. And we look out into the universe, and as we look out further and further, we're looking further back in time because it takes time to get here. So we can see how fast things are moving away from us now the close up stuff, and how fast things were moving away from us earlier. So we can see sort of how much this is changing our things moving away from us faster and faster every year, or is it slowing down? And about twenty years ago we went out and did this measurement using very precise techniques involving supernovas and exactly how they blow up and all that stuff, and we found something very surprising. We discovered that the universe is expanding, and that expansion is speeding up, meaning that every year galaxies out there are moving away from us faster and faster. And so that's what we call dark energy. We don't know what's doing it, we don't understand the mechanism for it, but we see that this is happening, and we want to understand it. Yeah, and you call it dark energy because it's kind of like an energy, right, Like it requires work and energy to make the universe bigger, because you're sort of creating more and more space. That's right, and we are making more space between galaxies actually everywhere in the universe. We think that space itself is expanding. So if you have your picture in your mind of the universe's expansion is sort of like a bomb with a tiny little dot at the center that blows up and everything flies through space, you should try instead to think about it as like a universe already filled with stuff, which then expands, creating new space between everything in the universe all over the place. So it's sort of like this stretching of space or this expansion of space itself. And you're right, that makes more energy because we think that every chunk of space comes with energy, and that energy then drives the expansion, which makes more space, which drives the expansion even more. And so that's why it's accelerating, sort of like taken off. And then it's called dark because there's no visible evidence of it in a way, right like this, like everything's glowing or something, or there's some kind of explosion that you can see. It's like an invisible force that's growing the universe. It is invisible. But I think probably it's called dark because it's mysterious, because we don't understand it. It's like unexplained. It's an area we have yet to illuminate. So I think it's sort of like mentally dark more than physically dark, though also invisible. You know. We call it dark energy, which suggests that it's like a thing we understand is something in physics. It's happening, but really we don't understand where this comes from. It's something we see happening in the universe and we can describe in some ways using our theories, but we don't know really where it comes from at all. Yeah, it's a big mystery, maybe even the biggest mystery in the universe, right is it's a mystery that kind of permeates the entire universe, and the universe is pretty big. It definitely dominates the universe. Like, if you add up how much energy it takes to make this happen, it's like seventy percent of the energy in the universe. So you take a cubic light year of space, for example, and you say how much energy is stored in like all the gas and the stars and the planets. That's like five percent of the energy in that cube. Another twenty five ish percent is dark batter that also has energy in it and the rest of its seventy percent of the energy budget of the universe. Is this weird stuff, dark energy that's causing the universe to expand faster and faster every year. But again we don't really know why it's happening or where it comes from. We can describe it in our theories, like we have general relativity that tells us how the universe works and how space works and how it can expand, and there is an option in general relativity to make this kind of thing happen. Yeah, you have some theories that it maybe is like a property of space itself, like space itself is potential energy and it can't help itself but to get bigger. That's right. And remember that while general relativity is a theory of gravity, and we tend to usually think of gravity is like something that attracts stuff. Are you're attracted to the Earth, the Earth is attracted to the Sun, And we think of general relativities like explaining that kind of stuff, that gravity is purely attractive. General relativity is more complex than that. It's not just like how much mass and energy is there in a certain place. It also depends on the distribution of that mass and energy, and also on the kind of energy. So example, if you have a lot of potential energy in a part of space, it can generate a negative pressure, it can cause the expansion of that space. So Einstein's equations of all these different kind of knobs that can make space do different kinds of things. So if you say, well, space might have a lot of potential energy into it, you add this thing we call the cosmological constant, where all of space just has this potential energy in it that can actually cause this kind of expansion. Then of course you can ask like, well, why would it have this cosmological constant? Where is this potential energy coming from? And that's sort of where we are. That would be sort of a very deep question about the very nature of space, right. That's right, as you say space we think has energy in it, Like we know that space has quantum fields inside of it. Right, There's a field for the electron on, a field for the Higgs boson, and a field for the photon. It has all these fields in it, and those fields have some potential energy. We know that because they're quantum fields can't relax all the way down to zero energy, and so for a while, people thought, oh, maybe that's it. Maybe all the fields that are out there in space they have this potential energy, and that potential energy was causing the expansion of the universe. So people sat down to try to calculate it and say, well, how much potential energy is there in all of those fields, and how much potential energy would you need to explain this expansion of the universe to provide the potential energy that will allow general relativity to drive the universe expanding this way. So you sit down and calculate those two numbers, and you hope they agree, because that would mean that it's an explanation. But instead they disagree, and they disagree not by a little bit, but by a number like ten to the hundred and twenty. So like, we really just don't understand this at all. Yeah, it's a big mystery. And so the universe is expanding faster and faster and we don't know why. And then now this paper is kind of saying that maybe black holes are the source of that expansion, and so let's get into what exactly black holes are and how they might be fueling dark energy. But first let's take a quick break, all right, we are playing MythBusters today kind of news headlines with papers that have been published. There's been a paper recently that has a pretty juicy headline that says that or that asks the question whether black holes can be making the universe expand faster? Now, Daniel, is this a paper that just dropped on the internet or is this a paper that has already been peer reviewed. This is a paper that has been peer reviewed. These guys did not drop it on the Internet before they sent it to reviewers, so they kept a little bit tight to their chest. I think also they linked it with a bunch of publicity and stuff. So sometimes people don't put their papers up in the Internet before they get peer reviewed. And I think that's actually more common in astronomy than it is, like in particle physics. Interesting, why do you think that is? Astronomers know how to play the press game a little better than particle physicists, or particle physicists just like to post them to the Internet. Well, particle physicists are the ones who invented this whole idea of putting things on the Internet. I mean, we invented the Worldwide Web. We have these big international collaborations and Also, I think for particle physics, by the time you have a paper ready, usually it's been reviewed by like five thousand of your other colleagues whose names are also on the paper, and so the peer review process feels a little bit more like a rubber stamp in particle physics than in other fields. All right, Well, this paper that came out recently says that black holes could be what's making the universe expand faster and faster. And so we talked about what dark energy is, what the expansion of the universe is. Now let's talk a little bit about black holes, Like how do you explain what a black hole is? And what don't we know about them? Right? And so the takeaway from dark energy is the universe is expanding, it's expanding faster and faster. We don't know why that's happening because we can't explain where this potential energy is coming from, this sort of vacuum energy of the universe. All right, So that's a huge mystery, as you said, right, big not understood thing in the universe. Now, one of the other really fascinatings, big misunderstood things in the universe r of course black holes that we've talked about on the podcast lots of times, because they're so fascinating and amazing and might contain within them like secrets of the nature of space and time and all sorts of crazy stuff because they are very extreme situations. They are a spot in space that is so dense with energy and matter that space is curved so intensely that nothing can escape past this event horizon. That even photons which travel at the speed of light are trapped inside because space is curved essentially so that it's one dimensional. Every direction forward once you're inside a black hole leads towards the center of the black hole, and in general relativity, it says that this force is so powerful that everything inside the black hole eventually collapses to the very very center, forming a singularity, a dot of infinite density because there's a lot of mass with zero volume. Yeah, chatted about this a lot. It's interesting that for black holes it's all about the density of mass, right of matter, because gravity gets stronger the closer you get to it, and so if you put a lot of mass in a small spot, that means you can get really close to it, and so at some point that gravity gets so crazy, so big that it actually creates a hole in space. You're exactly right. It's all about the density. Like the same mass that could create a black hole if you squeezed it down, could also not create a black hole. If it was more spread out, like the mass of our sun could create a black hole, if something squeezed it down, or if the Sun stopped exploding, which is what's preventing it from collapsing into something more dense. So it's not just about the amount of mass, it's about the density. And that means that you can have black holes of all sorts of masses. You can have black holes like the mass of our sun. You can have black holes like ten times the mass of the sun, a billion times the mass of the sun. Black holes coming in a huge variety of sizes and masses. And that's one of the big puzzles about black holes. Yeah, well, it's maybe even stepping back a little bit. We don't actually know if black holes are real, real, like we talked about them like they are, but actually they are Kenneth theoretical, and we have pictures of them, but we're not quite sure what's in the picture. Right, that's exactly right. We have a model from general relativity that predicts that this would happen, and it says, if you get matter dense enough, then you should create this event horizon and have a singularity on the inside. And for a long time that was just theoretical, and people thought, that's weird. I bet something prevents that from happening. That seems too strange. But then we saw these things out in the universe, and specifically, what we saw were very dark portions of space that had a lot of curvature to them, very strong gravity. For example, we saw stars whizzing by very close and getting turned around by strong gravity, but we didn't see anything at that location. So we crossed off a bunch of candidates. Oh maybe it's a neutron star. Nope, Oh maybe it's this, maybe it's that, maybe it's the other thing, And eventually the only thing left was a general relativity black hole. That's the only sort of explanation we had for this kind of phenomena. But it's not a direct observation, right, it's not like we've seen the event horizon literally or we verify that it really is a black hole. We just sort of like observe things closer and closer and closer to the black hole that haven't yet fallen in that tell us it must be something very dense and very dark, right, something super dense, super dark that doesn't shine. But it could be just a dark hole, not just a black hole, for example, could just be a lot of mass compacted really tightly, but not necessarily a singularity, which is what the name originally was given in General relativity exactly. Early on, it was sort of the only candidate to explain these kind of things, and that's one reason why people started believing they exist. But recently there's been sort of a flourishing of other ideas, other possibilities that might explain the same observations, Other things that would look just like these black holes but would not be black holes. We talked about a few of them on the podcast, things like dark stars. These are stars that are collapsing due to gravity, but they're collapsing super duper slowly because the gravity slows down time, so it's not actually a singularity. It's just sort of like a collapsing star frozen in time, which eventually will bounce back and maybe turn into like a white hole. Or we've talked about fuzzballs which are these weird phenomena from string theory and all sorts of other various ideas, And the thing that all these ideas have in common is that they are quantum mechanical. One of the big problems with the idea of a black hole from general relativity is the singularity is the idea of having all this mass in a tiny little dot that breaks quantum mechanics. Quantum mechanics says you can't do that. It violates the uncertainty principle and all sorts of basic principles of quantum mechanics. And general relativity is not compatible with quantum mechanics, which is one reason why See inside a black hole would be so awesome, because because they see finally a battle between general relativity and quantum mechanics and see who won. So we think almost certainly general relativity is wrong and needs to be modified by some theory of quantum gravity that tells us what else is going on inside a black hole. Maybe it's basically like a general relativity black hole, but with a quantum blob of a singularity instead of an actual dot. Maybe it's something totally different, like a fuzzball or a dark star or something even weirder. Yeah, it could be some kind of strange crossover event in their like Captain America versus Batman exactly. And it's also important to understand that the black holes that we've sort of figured out how to calculate, these predictions we've made for like you should see a black hole under these conditions, those only really describe very simplified situations. Nobody actually has been able to calculate a black hole like the ones that we see out there, that the ones we suspect exist in our universe. The kind of black holes we can calculate are the ones where you have like a dot of mass and otherwise empty universe. We know how to do that calculation in Einstein's theory. The Einstein's theory is very very messy, it's very complicated. It's almost impossible to do anything realistic like in Einstein's theory. You can't even do two dots of mass. We can't even of the Earth going around the Sun. In Einstein's theory, even basic stuff like that is too hard. And so, for example, what we haven't done in Einstein's theory is figure out how a black hole can survive in an expanding universe like we always do our calculations in a flat universe where space isn't expanding, so nobody even really knows, like what happens to a black hole when the universe is expanding, especially if that black hole is spinning. So it's not like we, even in general relativity, have a great description of what we've seen out there in the universe. You mean at least the general relativity version of them, right, But there could be other versions of a black hole, or like a dark hole or a black divid maybe that do I explain what's out there. We're not quite sure what that is right exactly, And we also don't know how they get so big sometimes exactly. That's one of the other really deep mysteries about black holes, especially the kind of black holes talked about in this paper. These are the black holes at the centers of galaxies. You can have a black hole just from a star at the end of its life, it goes to Brenova and collapses and you get a black hole. It's like five or ten times the mass of our sun. That's cool we see in those when we think we understand them. But also there tend to be black holes at the hearts of galaxies, Like at the center of our galaxy there's a very big black hole with lots and lots of mass, And at the center of many galaxies there are black holes with millions or billions of times the mass of our Sun. And we see these even very far back in the early universe. If you look at light that's been traveling for a very very long time from very distant galaxies, you can see galaxies in the first billion years of the universe that already have black holes at their centers that are like a billion times the mass of the Sun. And this is a big mystery. Nobody understands how those black holes got so big so fast. Well, it's kind of an amazing thing that we can tell that there are black holes in these galaxies so far away. Yeah, that's exactly right. It's fascinating, and we can tell them often because they are quasars. Quasars are black holes that have very strong magnetic fields that are spinning really really fast, and so they emit these jets of light that are super duper bright, so we can see them from very very far away, so they're not always like super direct observations of the black holes it's not like we've imaged them the way we've imaged a couple of black holes using the event horizon telescope. Again, black holes are almost always indirect, but we're pretty confident that there's something very dark and very massive and very dense at the hearts of these galaxies. And we don't understand how you make a gravitational object whatever it is, that massive, Like there just isn't enough time for it to eat enough gas and dust and stars to get that big that fast. So there's all sorts of theories about how those black holes might have gotten so big so fast it was super mass. Now we have two big mysteries, two big things out there in space. One is the expansion of the universe. It's getting bigger and bigger, faster and faster. We don't know that that's dark energy. And then there's black holes, which we know some about but we're not quite sure on the details or what's actually going on inside of them. And now this new paper says and maybe these two things are related, like maybe black holes are the reason the universe is expanding. So what does this paper actually say. Yeah, it's super fun and fascinating. Actually, the couple of papers. The first paper makes a really interesting just sort of observation about the masses of black holes. Wait, it's several papers. Yeah, they wrote a couple of papers. The first paper is like details of about the black hole masses, and the second paper is this crazy theoretical interpretation about it. Like they dropped the movie and the sequel of the exactly. Yeah, two seasons of your favorite show all the same time. The Netflix model of physics or the event I guess, the Avengers endgame model. There you go, film both movies at the same time. We often do this. We work on several papers all at once and then publish them all at the same time because they're all sort of connected to each other. Or you want to be the first person to write an interpretation of your crazy new observation, so you write your interpretation paper at the same time as you write your observation paper, and you publish them separately. All right, So this paper is talking about the masses of these black holes. They went out and they measured the masses of a bunch of black holes. Over time, they looked at closer by galaxies that are newer, and they look deep into the ancient past at very old galaxies, and they were interested in how fast black holes are getting bigger. Like, you have a galaxy and it's spinning, it's got a black hole at its center. Black hole is going to be eating gas and dust and stars, and the galaxies also grow. Galaxies grow by gobling up gas from the intergalactic medium and also by merging with each other. So essentially what they did is they compared these two things. They said, well, how fast are black holes growing and how fast are galaxies growing? And what they noticed is that the galaxies are not growing as fast as the black holes are growing. So one question is like, well, how did black holes get big in the early universe. The other question is how do they keep getting bigger all the time. So this is a really interesting result because they're showing that black holes are growing unexplainedly quickly. I see. Okay, So this first paper that's sort of like a survey, right, Like they just looked at into space and they looked at the younger galaxies and older galaxies that have black holes in them, super massive black holes, and they compared the young galaxies with the older galaxies, and they said, between the two, in general, our galaxies getting bigger and at what rate? And for those black holes? Are those black holes getting bigger and at what rate? And you're saying that the first paper just says black holes seem to be getting bigger faster than galaxies are getting bigger. Yeah, black holes are getting bigger, like eat to twenty times faster than the galaxies they are in. They are growing much more quickly than the rest of their neighborhoods. But wouldn't that be explained by the idea that the black holes are basically eating the galaxies because like galaxies don't have a lot of things around them, so they can't really grow that fast. But black holes have a galaxy around them, and so maybe it could just be that the black holes are eating up their own galaxies and getting bigger. That way, we actually do expect galaxies to grow. Remember that something like forty to fifty percent of all the protons in the universe are not eating galaxies yet they're between galaxies. There are these filaments of gas between the galaxies that are still flowing into the galaxies. Right now, every galaxy sits at the bottom of a gravitational well created by its dark matter, and there are these like rivers of gas flowing into galaxies making them bigger, and then also galaxies merge, and so galaxies we do expect them to grow, and you're right, black holes we also expect them to grow. And you can do studies of these things, and you can predict how fast galaxies and black holes should grow, and it should be about the same rate. You know, there's some limit to how fast a black holes should be able to grow because as it gets more powerful, it's acretion disk gets very intense the stuff that's swirling around it, and it is very hot and agitated and hasn't yet fallen back into the black hole, and it generates a lot of radiation which actually pushes away gas. So black holes can't just grow like infinitely quickly, and galaxies should be able to grow about the same rate. But what we see is a big discrepancy that we don't understand. So black holes are growing much faster than their galaxies, which is not what our models predict. M Okay, that's a mystery. That's a weird thing. So that's the first paper and the second paper says, well, you know, black holes are growing faster than we think, but it's actually connected to something else. They notice that black holes are growing at the same rate as the universe itself. That the expansion of the universe we talked about, this unexplained accelerated expansion matches very nicely the rate at which black holes are gaining mass. So these two unexplained things seem to be happening about the same pace. Like let's say the universe is expanding how fast, like a thousand percent per year or something like that. The expansion rand of universe is a little bit more tricky to measure. It's in terms of like kilometers per parsee per second, so it's a little bit complicated. But you know, in a cartoon version, it's like if the volume of the universe doubles soared the mass of these black holes. So as the universe gets bigger, black holes get bigger at the same rate, which could just be a huge coincidence perhaps, But these maybe these authors are saying that it's not a coincidence exactly. These authors are saying it's not a coincidence, and they have a theory which predicts this, which explains the connection between the black holes mask getting bigger unexplainedly, and the universe getting bigger unexplainedly. They want to explain both of these things at the same time. All right, well, I'm hooked. I want to know what this theory is, and so let's dig into it. And also let's see what our critic Daniel has to say about this theory. But first, let's take another quick break or I we're talking about the expansion of the universe, and a new paper or a new set of papers it says that maybe black holes are the ones that are somehow connected to this expansion of the universe. So we talked about how the universe seems to be expanding at a high rate. That also seems to Madge how fast black holes out there in the middle of galaxies are expanding, which could be a coincidence. But these authors are saying that it's not, and they have a theory that links the two of them. So, Daniel, what's the theory. So the theory is pretty crazy but also a lot of fun. The idea is that black holes are not black holes as we imagined in general relativity. They're not point masses at the centers of these event horizons. Instead, there's something very very different that inside the event horizon is not a point mass, but instead it's a ball of vacuum energy. So what does vacuum energy? What does that mean? Remember, vacuum energy is the thing we thought might explain the expansion of the universe. We know in general relativity, if the universe if empty space, what we call the vacuum space, particles in it that has some kind of energy, and that energy can drive the expansion of the universe. In this theory, instead of having that energy everywhere in the universe, you have like localized blobs of that energy. It can form black holes that regions of very very high vacuum energy and form something that looks like a black hole. What okay, okay, let's maybe take a step back here. Are they saying that when you make a black hole, you're creating a bubble of vacuum energy, or are you saying that when you have a lot of vacuum energy that is what you call a black hole. It's the second we're saying that the things we're calling black holes are actually bubbles of vacuum energy. They're not compressed masses. Here, we're talking about the things that the centers of galaxies, stellar black holes from collapsed stars, probably black holes that's not what these guys are talking about. They're talking about the huge blobs of the centers of galaxies. They're suggesting they're not black holes like we imagined. Instead, that are these weird blobs of vacuum energy that somehow mysteriously form, or that are that started somehow, or that the universe started with. What are they saying, are these bubbles? How can they have the gravity of black holes if they have negative energy? So they don't explain what this vacuum energy is or where it comes from. That's just sort of left a big question mark. But there is a history of people developing these kinds of ideas. I mean, go back to what we were talking about earlier, people trying to understand how you could have a spinning black hole in an expanding universe. Nobody's solved those equations in Einstein's theory. Nobody really knows if it's even possible in Einstein's theory. So that leads people to explore other kind of things, like instead of having a singularity the heart of it, what if you put like a little expanding universe inside the black hole, right, it might help you match the expanding universe outside the black hole. So they put this sort of like expanding vacuum energy inside the black hole, and what they see is an incredible distortion of space. There's no singularity, there's no event horizon, but there is an intense curvature of space, which would look a lot like a black hole, in the same way that like a fuzzball doesn't actually have an event horizon, but it's still really curves space, and so it looks a lot like a black hole, or the way a dark star is not technically an event horizon because eventually everything comes out of it. These things don't have event horizons. They were invented in the sixties original by some Souviet physicists, and people have been playing around with them. They're just like another weird prediction of something that would look black hole em but you would still get sucked into it because I thought a vacuum energy, you know, had like negative gravity or something like that. That's a cosmological connection we'll get to in a minute. They think this vacuum energy might be driving the expansion of the universe globally but locally. Weirdly, it also looks like a black hole, like if you're near by it then it bends space intensely because instead of having vacuum energy everywhere, you have it localized. It's only this one spot at the heart of the galaxy, So that discrepancy having it there but not over here creates curvature in the region between it and that looks a lot like a black hole. It looks like a black hole. But wouldn't it be like reverse gravity, Like wouldn't it push things away like in the pulling ball analogy in the rubber sheet. Wouldn't something like this be like lifting up the rubber sheet, like pinching it and pulling it up? Or am I getting vacuum energy confused with negative energy? This is not negative energy, right? Vacuum energy is just potential energy, not negative energy. And Einstein's equations are not very intuitive, right, Like, it's not very intuitive to understand why in some cases potential energy causes expansion of space. Here, this vacuum energy seems to be doing two things. It creates this almost kind of like event horizon locally and also drives the expansion of the universe globally. Whether this makes any sense at all is a topic of intense debate among cosmologists. I talked to a bunch of them over this last week. Half of them were like, this is nonsense. The other half was like, well, maybe under certain conditions that might happen. But this is definitely a very, very fringe theory that a lot of cosmologists don't accept. Even just this part of it, This idea of a Gravis star something with vacuum energy inside it, which looks like a black hole from the outside. A lot of people don't believe that's even possible. Well, what's their excuse for it, Like, how do they explain it? Why is there so much vacuum energy concentrated in one spot? What keeps it together? They don't have an explanation in this paper. What they do is they say, look, there's an apparent connection between the mass of the black holes and the expansion of the universe. And if you accept this theory that there are vacuum energy interior or objects at the hearts of these galaxies that would explain it, it doesn't argue for that theory. It doesn't justify that theory, doesn't explain where this vacuum energy comes from or what it is at all. It just says that there is a theory that allows you to connect these two observations. It feels kind of like a made up theory, a little bit like it feels like the issues came up with a theory just to say that they have a theory. It's a little bit at hoc, right, It's not something that's been thoroughly worked out. Again, remember, nobody knows how to solve Einstein's equations under all these weird conditions expanding universes, spinning stuff, vacuum interiors, or singularities. Nobody knows what the solutions are like, so nobody can even really say if this is consistent or inconsistent with general relativity. Some of the cosmologists I talk to you said, there's no way this is consistent with gr Other people thought, hey, maybe it might be. There are people working on these kinds of solutions. But the really interesting part of the paper is that they argue that having this vacuum energy inside the black holes somehow contributes to the expansion of the universe as a whole. I mean, we're used to thinking black holes like acting locally, they suck stuff in nearby. This is suggesting that because they have vacuum energy in them, instead of like dense mass. They're also contributing to the cosmological equation of state, the thing that affects the entire expansion or contraction of the universe. And that's even harder for most cosmologists I talk to to swallow. Yeah, because it's not like these black holes are everywhere and spread evenly across the universe. They're just at the very center of some galaxies, and those galaxies are pretty far apart from each other. Right, If they are the source of expansion in the universe, wouldn't you then see like hot spots of exp in some places, and in places where there are in delities or black holes, you would see no expansion. Yeah, that's exactly right, and that would be very very weird and also not explained in this paper. They don't even really talk about this aspect of it, and it would be something very very strange in physics. We have in physics this sort of like hierarchy of scales, where really tiny stuff doesn't usually affect really really big stuff, like things that happen inside the Sun don't affect the galaxy as a whole, or things that you do don't usually affect the motion of the entire Earth. Where the sort of hierarchy of scales, really really high energy stuff at very very small distances doesn't usually affect low energy stuff over larger distances, and this would break that. This would say the things that are happening like inside black holes can affect the universe as a whole. That's very very weird. It's weird, not just because black holes are weird and dark energy is weird. It would require like a very different sort of paradigm of physics. It would tell something very very new is going going on, something hard to swallow. Yeah, like, yeah, these sources of vacuum energy and somehow their effect is evenly spread out to the universe somehow. That's kind of what you're saying, right, That would be weird. That would be very strange. And that doesn't mean it's not happening. We should be ready for strange stuff. History of physics is filled with times when people are like, well, the only way to explain this would be this totally crazy idea that can't possibly be true, And then it turns out it is true. It just it requires us to accept something new. This could be one of those moments, right, or maybe not. So It's not always easy to tell, but there's a lot of skepticism. One reason is that this is like an explanation for what's happening. It's not at all a conclusive explanation. It's not the unique explanation. It might be that you could explain black holes growing at the same rate of the universe in some other way. Instead of black holes driving the expansion of the universe, maybe there is something else that's driving both. Right, So it feels sort of like this describes it, but it doesn't clinch it necessarily. We're not sure that this is what's happening just because it describes it. Science has to be predictive, not just descriptive. It could just be a coincidence, is what you're saying. It could be a coincidence, or could just be that we have the causality backwards. Instead of black holes driving the expansion of the universe, something else could be driving both of them, so they could be connected. It just might not be this theory of vacuum interior black holes driving somehow magically the expansion of the universe. Well, that would be a juicy headline too. Couldn't the expansion of the universe be making black holes bigger. I mean that's the idea, right, Like, maybe the universe is expanding for some reason, for because of dark energy, and somehow that a fact causes black holes to get bigger too. Yeah, exactly, And if you understood where this vacuum energy came from, maybe that would be the source of it. And this paper, again, it doesn't address that. Either doesn't say where this vacum energy is coming from or what it's made out of. Is it made out of quantum fields like we suspect, or is it something totally different. We just don't know. But this paper got peer reviewed, and if you had been one of the peer reviewers, what would you have set If I had been one of the peer reviewers, I would have asked for a lot more details about this theory and some comments about these obvious questions, you know, like how is it possible for localized objects to contribute globally to the expansion of the universe, and also how is it possible for black holes whose mass is a tiny fraction of the mass of the universe? Right, black holes are a little fraction of the five percent of the universe that's our kind of stuff. Dark energy is seventy percent how is it possible for this tiny mass fraction to drive this huge energy in the universe. So I want to ask those questions, and I imagine that the authors of this paper are getting those questions from their colleagues, and I'm looking forward to hearing some answers and some follow up papers. Well, it sort of sounds like, you know, they discovered something that is significant and is interesting and it is noteworthy. Right, they discovered that black holes are increasing at a rate that's higher than the galaxies around them, and they're also increasing at a rate that seems to match the expansion of the universe. Like, that's an interesting result. The right that it hadn't been published before that is definitely a very interesting result. So that's probably, you know, publish worthy. It's just that the ideas are putting forth to maybe explain this are a little bit on the fringe side, and that's probably also why they put it out in two different papers. The first one, he's here the black holes we found. The second one is here's our crazy idea to explain it. And so the second one is definitely a bit more speculative. There are also questions being raised about the first paper, you know, people are looking at this paper and saying, well, you've looked at a bunch of black holes snapshots in time. You never watched an individual black hole grow at the rate of the universe. We can't possibly do that. You have to observe it for billions of years. Instead, you look at different black holes through history, and you try to tell a story about how, in general black holes are growing. There are some assumptions there that you're making, right, that black holes in different regions of the universe who are growing at the same rates, etc. And so people are also asking questions about that paper. But I think that one's probably pretty solid. It's really this connection between black holes and the dark energies theoretical interpretation that's a lot more speculative and a lot of fun also, right, And I want to be too negative about it. I love new ideas, I love breakthroughs, I love speculation. But you know, we got to put it in context and think about all the question marks that come with it. Right. But that's kind of the norm in physics, right, Like, if you have a wild idea, you're allowed to publish a paper with a wild idea, right, Like, as long it has some sort of basis in reality, or at least some indication some hints that are based in reality, which this one did. You're sort of allowed in physics, right, the polish crazy ideas. Sure, And it's also totally reasonable to start off with a half formed idea to say, look, here's something crazy and fascinating. We don't have all the details worked out, but maybe it's something in this direction. And somebody else will read the paper and be like, huh, here's an obvious hole that needs to be filled. I wonder if And then I'll have an idea and they'll explain it. And so it's totally fine to not have solved everything in one paper, right, to say, maybe this direction works, and here's some indications that it might be a fruitful path. Let's keep going this way, and then everybody jumps on it. I need to proves them wrong or supports it. We'll see. Yeah, like the Higgs boson. I mean, Peter Higgs got the Nobel Prijec because he polished the crazy idea without a lot of paces in an actual experiments. Right, He's like, hey, maybe there's a field called the Higgs field and the Higgs boson, and and that was an explanation, right, It was an explanation and not the only explanation exactly. And one nice thing about this paper is that they suggest some ways to check these results. As a bunch of details that people can do studying the causer of microwave background and how stars are whizzing around, they make a bunch of predictions if this theory is right, things we might be able to test. And so there's a lot of really fun work we can do in the next few years to see if indeed black holes aren't driving the expansion of the universe or not. Do you think I can get my theory polish through peer review about Superman and Spider Man causing the growth of black hole? I think you have to choose very carefully the journal you're going to send that to, Yeah, the Journal of or hit cham on Twitter. There you go. Or I'll put it on archive at archive dot org. There you go, Archive dot org ya, And then I can be a polished physics theorist. Join the club. All right, Well, lots to think about here, I guess again. The main lesson is stay tuned. I mean, people have crazy ideas about things, and they observe the universe and they find interesting coincidences and that may or may not be coincidences. And that's how science moves forward, is noticing these weird things and putting out their potentially crazy ideas that sometimes turn out to be true, and we can't always tell them the moment, which paper is going to be something that resonates through history and is read by generations to come, and which is just going to be another in an exciting press release that nobody ever talked about Again. 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 product shit of iHeartRadio. For more podcasts from my heart Radio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.