We May Have Seen a White Hole Exploding, and It Was Under Our Nose This Whole Time

We’ve discussed black holes a lot on this  channel, because they are FASCINATING regions of spacetime where curvature is really pushed to  the extreme. They exhibit features and phenomena far beyond any intuition we could have built  from classical physics here on Earth. But despite all the attention they’ve been getting,  black holes aren’t the only way that spacetime can show off its most beautiful curves. In  theory, there can be equally curved regions of spacetime called “white holes,” which

get  their name because they are, in many ways, the exact opposite of black holes. And in  some cases, a black hole and a white hole can be connected by a totally different type of  spacetime called a “wormhole,” which functions as a kind of limbo zone between parallel universes.  If you’ve heard of space travel through wormholes and thought it wasn’t more than just a fancy  sci-fi invention, I don’t blame you. After all, even though these regions are possible in theory,  there still isn’t any

evidence that white holes or wormholes actually exist in our universe. But a  hundred years ago, it was black holes that were purely theoretical—and now, we think there  are literally billions of them out there for our telescopes to see. So, in this video, we’re  going to try to answer three questions for you: just what are these other holes that we can  have in spacetime? Should we have our hopes up that they might be more than science fiction?  And what do they look like if they are real? I’m

Alex McColgan, and you’re watching  Astrum. Join me today as we explore the different types of spacetime that can  result from extreme curvature. I think the possibilities will bend your mind as much as  they warp the fabric of the universe around them. Before we dive into the physics of  spacetime—described by Einstein’s theory of General Relativity—I want to start off with a  simple analogy. If I ask you to imagine a cone, you’ll probably think of either something that  points up, like a traff

ic cone, or something that points down, like an ice cream cone. These are  what we think of as cones in the real world. But if you write down the most general mathematical  equation for a cone and try graphing it, you’ll get something that looks like two cones  glued together. You see, a mathematical cone has two halves, one that points up and one that points  down, connected at their tips—and what we think of as cones in the real world are actually just  chopped-up pieces of the full mathematic

al cone. Black holes are the exact same way. Let me  explain. Many of the black holes we see out in the universe are the remnants of massive stars,  whose extreme gravity caused them to collapse in on themselves. Once a black hole is created,  it becomes permanently separated from the world around it by a spherical barrier known as an event  horizon: anything can fall into the black hole, but nothing—not even light—can come out. This  structure of spacetime can be neatly summarized in what physi

cists call a Penrose Diagram,  which is a way of representing an infinite spacetime in a finite drawing. The key feature of  a Penrose Diagram is that light travels upwards at 45º angles, making it easy to distinguish  regions where light can or cannot enter. In this diagram, Region 1 is the regular universe,  containing the original star (before it turned into a black hole) and everything outside of  it, from the infinite past, to the infinite future. Region 2 is the black hole, and it is  sepa

rated from the rest of the universe by its event horizon. You can see how it’s easy for light  to enter the black hole (region II), but it’s impossible for light to exit—it will inevitably  hit the singularity instead. The same holds true for ordinary matter, which moves slower than light  and so in this diagram can only travel upwards at angles steeper than 45º. What’s so special about  this Penrose diagram is that it accounts for the formation of the black hole at some specific point  in time,

when the star collapsed in on itself. In the far past, there was no event horizon or  black hole to speak of, and light could freely travel across all of space. But while this diagram  represents the kind of black hole we’re used to seeing in the real world, it’s only one piece of  the full mathematical description of black holes in General Relativity. In other words, it is  the lone ice cream cone of black hole diagrams. So what happens if we forget the real world and  imagine an ideal black h

ole with an infinite past, leaving behind the baggage of collapsing stars and  everything else in the physical universe? What is the black-hole analogue of the full mathematical  cone? It might look like a simple extension of our original Penrose diagram, but this diagram  comes with physics that’s a little… upside down. . Region 1 is still our regular universe, and  Region 2 is still a black hole with an inevitable singularity in its future. But the maths also  describes something that looks li

ke the inverse of a black hole in region 3. Instead of a singularity  in its future, region 3 has a singularity in its past. And if you draw the motion of light rays at  45º angles, you can see that it’s straightforward for light to leave region 3, but it can never  enter it! This type of region is exactly what we would call a white hole—it’s the spacetime  analogue of a traffic cone. But that’s not all! If you look beyond the white hole, you’ll see  there is a patch of spacetime labelled region

4 with the same connections to the black and white  holes in the middle as the regular universe. This patch is a parallel universe, and it’s entirely  disconnected from the universe in region 1, since it’s impossible for even light to travel from one  region to the other. The upshot of all this is that the same mathematical equation describing the  regular universe and the black hole also describes the parallel universe and the white hole. This  doesn’t mean that every black hole comes attached

to a white hole, though. Just like with cones,  the real universe can contain chopped up pieces of the full mathematical solution. But this does  mean that even if white holes are less common than their black hole counterparts—or even if there  aren’t any white holes connected to our universe at all—it doesn’t make them any less scientific,  in the sense that they’re equally consistent with the laws of physics. In our analogy, if you  imagine that ice cream cones remain extremely popular, while

traffic cones become difficult  to produce and are phased out of existence, that doesn’t make the idea of a traffic cone any less  real. This is more or less the status of white holes today: the notion of a white hole makes  perfect sense, but it’s possible that any white holes that existed in the past were unstable and  were similarly phased out of existence. If you’re wondering whether there could be some more stable  white holes that have just escaped our sight, you’re not the only one—and y

ou should stick  around for when we talk about the tiniest possible white holes in just a few minutes. But first,  I want to make sure we’re not leaving anyone hanging. I promised you wormholes. I promised you  parallel universes that are actually connected to each other. So buckle up, because we’re about  to go to a whole new level of warped spacetime. The No Hair Theorem says that a black hole  can have up to three intrinsic properties: mass, charge, and spin. But the Penrose  diagram I just s

howed you only described the simplest kind of black hole, which was  electrically neutral and completely stationary. The diagrams for charged or spinning  black holes are much more complicated, but they’re also much more exciting, because  they completely alter our understanding of singularities, and they give rise to new  and fascinating regions of spacetime. Let’s have a look at the Penrose diagram for a  spinning black hole as an example. Instead of four distinct regions of spacetime, there a

re  now 8 types of regions that repeat themselves in an infinite pattern of universes. Regions 1  through 4 are the same ones that we saw before: these are the regular universe, the black hole,  the white hole, and the parallel universe. But now that the black hole is spinning, its geometry  no longer has an unavoidable singularity in its future—and the white hole similarly loses  the singularity that existed in its past. So, what actually happens after you cross the  event horizon of a spinning

black hole? At first, you’ll be drawn toward the centre of the black  hole, just like you’d expect. But eventually, you’ll cross a threshold known as the  inner horizon, beyond which the geometry of spacetime un-warps and lets you stop yourself from  falling even deeper. In these innermost regions, marked 5 and 7, you can float freely toward or  away from the centre of the black hole. You could even touch the singularity if you wanted to—though  I wouldn’t recommend it. Here in these innermost

regions of a curved, rotating spacetime, you  are officially in a wormhole, and if it weren’t for the fact that you are permanently separated  from everyone who stayed in Region 1, this would have been the perfect time for you to brag about  your wild spacetime adventures. At this point, you’re also faced with a bit of a fork in the  road. One option is to keep moving inward and go around the singularity, which takes the shape  of a ring, instead of a point, for spinning black holes. This path w

ould take you to region 6  or 8 in the diagram. But it’s quite possible that the existence of this path is actually a  flaw in the predictions of General Relativity, rather than a true description of reality, because  going even in a single loop around the singularity can lead to causal paradoxes where you visit your  own past. A safer bet would be to turn around and move outwards, crossing back into the inner  horizon that you just came out of. This would take you into region 3—a white hole—whi

ch would then  carry you all the way out to a brand new universe, similar in structure to the one you started out  in originally, but sadly without your friends or family waiting for you. In fact, by the time  you get here, your old universe will have already experienced an infinite amount of time. You would  be living in a whole new definition of the future. Okay, let’s step back into reality. As fun as  that journey through the wormhole was in theory, you probably couldn’t survive it in practi

ce—and  honestly, there’s a good chance that the wormhole itself would collapse once you disturbed its  spacetime. So, how much of this mathematical structure can we expect to see in the real world?  Spinning black holes with event horizons appear to be everywhere in the universe—but what goes on  inside of them is still largely unknown. There are two main reasons for why the physics inside  real black holes might be different from what the Penrose diagram would lead you to believe. First,  when

black holes form from the turbulent collapse of massive stars, some assumptions that went into  making the Penrose diagram are violated—like that the black hole existed forever, or that the  universe around it is perfectly symmetric and doesn’t contain random infalling humans. And  second, the theory of General Relativity used to construct the Penrose diagram might itself  only be approximately correct, breaking down near the singularity where the curvature gets  most extreme. So there’s a good

chance that some predictions of the diagram—especially the  most problematic ones involving singularities and time travel paradoxes—aren’t real features  of a highly curved spacetime. But the existence of white holes is more of an open possibility,  leaving plenty of room for speculation about how they might come to be and whether they might leave  any observational footprints for us to discover. One hypothesis that’s recently gained some  traction is that a white hole is born whenever a black

hole dies. And no, this isn’t some  magical story of reincarnation or voodoo—it’s a genuine attempt to understand the full life  cycle of black holes, with at least some level of mathematical backing. You see, even an  isolated black hole in an otherwise empty space will continuously emit particles known as  Hawking radiation, causing it to gradually shrink and lose mass over time. But once the black  hole reaches the super tiny Planck mass—just about 20 micrograms—we have no way of predicting 

what future awaits it; at least, not without a full theory of quantum gravity. This is where  Loop Quantum Gravity comes in—a proposed link between gravity and quantum mechanics, in which  space itself is made of discrete loops. In short, the equations of Loop Quantum Gravity predict that  instead of continuing to shrink even smaller than the Planck mass, such a tiny black hole is instead  more likely to quantum tunnel into a white hole, spewing out its contents back into the universe  over an e

xtended period of time. Incredibly, even though this white hole will be similarly  small and light, it can contain an enormous amount of entropy, because its interior geometry  will have been stretched into a thin tube with an extremely large volume. This store of  entropy could potentially open a pathway for any information that falls into a black  hole to be recovered in the distant future, solving a decades-long problem in theoretical  physics known as the information paradox. As the white ho

le releases this information,  it begins to slowly fade out of existence; the spacetime around it loses its curvature,  and its life cycle comes to a close. But before this video comes to a close, let  me leave you with one last thought. In General Relativity, our whole universe is predicted to  have had a singularity in its past, namely 14 billion years ago, at the moment of the Big Bang.  In this way, the universe is like an uncharged, stationary white hole. But if Loop Quantum  Gravity says t

hat white holes can be born when black holes collapse, could the same be  true about the creation of our universe? Could it be that our expanding universe was born from  the ashes of an older, contracting spacetime? As crazy as this seems, Loop Quantum  Gravity says that may well be the case. But there are so many different ideas for  how this transition could have happened, that we would need a whole new video  just to scratch the surface. So if you want to hear more about how the Big Bang  cou

ld have actually been a Big Bounce, let us know in the comments below—the history  of the universe may hold more surprises yet! If any of you watched my video on the Lunar  Nodal cycle, you may remember that at the end of that video I talked about my frustration  with cold callers and companies selling my data to advertisers for profit. I’d been getting  frequent cold calls on an almost daily basis, and it was a huge irritation. The sponsor of  that video – Incogni, who are also sponsoring this

video – told me they could do something about  it. And now, do you know what I hear from phone advertisers? Blissful silence. It’s only 3 months  on, and the number of cold callers has dropped right down. This likely has something to do with  the fact that Incogni reached out to [44] data brokers on my behalf, and have got [40] of them  to delete my personal data from their systems, leaving them unable to sell my data to  cold-callers. If you sign up with Incogni and give them permission, they w

ill not only force  data brokers to get rid of your data – a process that would have taken me months to do on my own –  but will regularly do repeated removal requests, to make sure your personal data never gets  re-added to those servers. It’s fantastic. Scan my QR code, or follow my link  https://incogni.com/astrum to get an exclusive 60% off your annual Incogni plan. Thanks for watching. And thanks to our crew  of astrumnauts over at Patreon who help us make science knowledge freely available

to  everyone. chasing the algorithm can be hit or miss sometimes so your contributions help  us keep making the content we love. If you want to find out how to contribute too, check  the link in the description below. Meanwhile, click the link to this playlist for more  Astrum content. I'll see you next time.