What if Black Holes Ran Backwards?

Añadido: 2026-05-12

[00:00:00]Today we're going to look at one of the strangest and most mysterious objects that the universe might contain. It's something that's been mathematically predicted that the laws of physics seem to insist should exist and yet no one's ever seen one. Today we're entering the strange world of the white hole. Let's find out more. In order to understand white holes, we need to briefly revisit black holes. A black hole forms when a massive star reaches the end of its life. Stars are essentially giant nuclear fusion reactors. They fuse hydrogen into helium and helium into heavier elements. And this releases an enormous amount of energy. That energy pushes outwards and counteracts the crushing inward force of the stars own gravity. For most of a star's life, these two forces balance each other out quite nicely. But eventually, the star runs out of fuel. And when that happens, the outward pressure disappears and gravity wins. The core of the star collapses inwards. And for the most massive stars, this collapse is so extreme that nothing can stop it. The matter is squeezed into an impossibly small point and the gravitational field around it becomes so intense that not even light can escape. And that's a black hole. At the very center of the black hole sits what we call the singularity.

[00:01:27]This is a point where our normal understanding of physics breaks down completely. The density becomes infinite and our equations just give up and stop working. Around the singularity is a boundary called the event horizon. And this is the point of no return. Once something crosses it, all possible paths through spaceime lead inwards towards the singularity.

[00:01:52]Even light which normally travels at the fastest speed possible can't escape. So what does all this have to do with white holes? Well, quite a lot actually. In order to understand white holes, we need to think about the math that describes black holes. And that maths comes from Albert Einstein's general theory of relativity. It's one of the most successful theories in all of physics.

[00:02:17]And it describes how mass warps the fabric of spacetime and how that warping is what we experience as gravity. The equations of general relativity are famously difficult. They're what mathematicians call field equations and finding exact solutions to them is a really big challenge. But in 1916, just a few months after Einstein published his theory, a physicist called Carl Swartchild managed to find the first exact solution. Swatch Child's solution describes the geometry of spaceime around a perfectly spherical non-rotating uncharged mass. In other words, it gives us a mathematical description of what we now call a black hole. And this is where things start to get interesting. You see, the equations of general relativity have an interesting property, and that's that they work equally well in both directions of time. They don't have a preference for which direction times run. If you made a film of the equations and played it backwards, the physics would still be valid. So, physicists asked a natural question. If you take the smart child's solution for a black hole and you run time backwards, what you get? And the answer mathematically at least is a white hole. So what exactly is a white hole? A white hole in the most literal sense is a time reverse of a black hole. Where a black hole is a region of spaceime that nothing can escape from. A white hole is a region of spaceime that nothing can enter. It has an event horizon just like a black hole.

[00:04:00]But this one works in reverse.

[00:04:03]Instead of being a point of no return that swallows things up, the white holes event horizon is a boundary that nothing can cross inwards.

[00:04:12]But while nothing can get in, things can most certainly get out. A white hole will be spewing matter and energy outwards constantly from its singularity. In a sense, it is the exact opposite of a black hole. A black hole devours everything. A white hole ejects everything.

[00:04:32]So, I know what you might be thinking.

[00:04:35]Well, if a white hole is constantly throwing out matter into the universe, where does all that matter come from?

[00:04:41]And that's a very good question, and the honest answer is that we're not entirely sure. One idea, and it's quite a strange one, is that a white hole is connected to a black hole somewhere else, possibly even somewhere else in the universe entirely. The matter that falls into the black hole then comes out of the white hole. And this connection between a black hole and a white hole is called an Einstein rose and bridge. And you may be familiar with it because it's usually called a different name, a wormhole. The idea of an Einstein rose and bridge came from Einstein himself along with his colleague Nathan Rosen in 1935.

[00:05:22]When they looked carefully at the full mathematical solution for a black hole, they found that the equations didn't just describe a single object, they described what looked like two separate regions of spaceime connected by a tunnel. In this picture, you'd have a black hole at one end and a white hole at the other. Matter and energy fall into the black hole, travel through the bridge, and emerge from the white hole.

[00:05:50]The two objects would essentially be two mouths from the same object connected through a passage in spaceime. In fact, completely solving the spart child solution gives four regions of spaceime like cutting a square into four parts. A black hole, a white hole, our universe, and a parallel universe all connected at a single point. Now, I know I've depicted a white holes as looking remarkably different from a black hole, but that's really just for artistic purposes. In reality, a white hole would look very similar to a black hole. And before we all get too excited about the prospect of using one as a shortcut across the galaxy, I should mention that the Einstein rose and bridge, as originally described, is not traversible.

[00:06:42]The throat would collapse far too quickly for anything to pass through.

[00:06:46]And even if it didn't, you'd have to get past the singularity, which as I've already mentioned is a place where physics itself breaks down. So, for now, at least, wormhole travel remains firmly in the realm of science fiction. Before we carry on, just a quick word. If you enjoy my videos and are not yet subscribed, then don't forget to subscribe. It really helps out my channel. And also, don't forget to hit like and leave a comment. To those of you who are subscribed, a big thank you for your continued support and a special shout out to the Darlinka who sent me a lovely super thanks. That's really kind of you. Thank you so much. Right, back to the science? So, I suppose the big question is, do white holes actually exist? Well, the mathematics say they should. General relativity demands them as a logical consequence of the equations that gave us black holes.

[00:07:45]Well, maths and reality don't always agree and we've never actually observed a white hole. Also, there are some pretty serious theoretical objections to their existence as well. The biggest one comes down to something called the second law of thermodynamics.

[00:08:01]This law tells us that the entropy of a closed system. That's to say, the amount of disorder in it always increases over time or at least stays the same. It never spontaneously decreases. And white holes pose a problem here because a white hole is the time reverse of a black hole. It represents a decrease in entropy. It's running the clock backwards on a highly ordered system.

[00:08:31]And the second law of thermodynamics says nature really doesn't like doing that. In fact, as far as we can tell, nature never does it. And this is one of the key reasons many physicists are skeptical that white holes can actually exist in our universe at all, even though the maths permits them. There's also a stability problem. Even if a white hole did somehow form, theoretical work suggests it would be almost instantly unstable.

[00:09:02]Even a tiny bit of matter or energy straying too near to it would be enough to cause it to collapse into a black hole almost immediately.

[00:09:12]So even if one popped into existence, it probably wouldn't last very long. And now here's where it gets really strange.

[00:09:20]One of the biggest unsolved problems in physics right now is reconciling general relativity and quantum mechanics.

[00:09:29]General relativity is our best description of gravity and the large scale structure of the universe. Quantum mechanics is our best description of the very small, the world of particles and fields. And both theories are really successful in their own rights, but they're fundamentally incompatible with each other, even though physicists have been trying to unite them for decades.

[00:09:54]One candidate theory for doing this is called loop quantum gravity. It's one of several approaches to what physicists call quantum gravity, and it treats space itself as being made up of discrete tiny chunks rather than being smooth and continuous.

[00:10:12]It's a bit like how matter looks smooth and continuous to us, but if you look really closely, it's actually made up of individual atoms. Now, in loop quantum gravity, the singularity at the center of black hole doesn't actually exist.

[00:10:29]Instead of matter being crushed to an infinitely dense point, the quantum nature of space prevents it from being compressed beyond a certain limit. In other words, the collapse stops. And when it does, the matter begins to bounce back outwards.

[00:10:46]In this picture, a black hole doesn't last forever. It eventually transitions into a white hole, ejecting all the matter that originally fell in. And if this is correct, and I do want to be clear that it's still very much a work in progress and hasn't been confirmed experimentally, then white holes aren't just mathematical curiosities. They're the natural end point of every black hole in the universe. Every black hole would eventually become a white hole and eject its contents back into the cosmos.

[00:11:20]However, the time scales involved would be almost unimaginably long, far longer than the current age of the universe, but still interesting.

[00:11:30]And here's another intriguing possibility. In 2006, there was an unusual gammaray burst detected by NASA's Swift telescope. Gammaray bursts are among the most energetic events in the universe, and most of them have a well understood cause, but this particular one, GRB 06014, didn't fit any of the patterns.

[00:11:57]It lasted for about 102 seconds, which is unusually long. and it had no associated supernova, which is almost unheard of for a burst of that duration.

[00:12:11]Some physicists suggested tentatively that it could have been a white hole, a sudden explosive ejection of matter that had been accumulating inside a black hole for an enormous length of time.

[00:12:24]We do however need to be clear that this is a minority view and most astronomers think there's a far more conventional explanation.

[00:12:33]But it's fascinating that the idea was even taken seriously at all. So where does that leave us? Well, white holes are one of those wonderful things that physics strangely throws at you occasionally where the mathematics is absolutely clear and the reality is really uncertain. General relativity says they should exist. The second law of thermodynamics says they probably don't. And loop quantum gravity say they might be the fate of every black hole.

[00:13:06]And one very strange gammaray burst in 2006 might just have been one.

[00:13:13]But for now and until next time, thank you for watching.