As is often the case, I’ve had a lot of things on my mind recently, mainly work stuff as there’s been a lot of uncertainty around mine, and my mate Chris who I work with, roles. All sorted now, well, sort of, I’ll tell you about it another time, if you’re lucky.

Anyway, when things start to overwhelm me, I tend to start ruminating on random stuff I know, or have learnt, that has stuck with me. Today, for no particular reason, other than I’ve been getting quite sciency recently, it has been black holes, and as I seem to have my writing mojo back, I thought to myself, why not put these thoughts to paper and bang out an article for my blog. I know I only have a handful of readers (friends and family who humour me by showing an interest), but I find it quite therapeutic. 

So, Black Holes, what the hell are they really? They’re one of those things that you hear about your whole life, mostly in passing, science programmes, random articles, the odd bit on the news, songs by Muse etc., and you sort of think you know what they are as in they’re a big gravity thing and nothing escapes from them, right?

That’s all very true, but the more I started properly looking into them, the more I realised that I didn’t really understand them at all. Or maybe a better way of putting it is, I understood the idea of them, but not what they actually are. And that’s where things start to get a bit weird.

So, what actually is a black hole?

At the most basic level, a black hole is just a place in space where gravity has become so strong that nothing can escape it. Not even light, just as I said above, but that alone is already slightly weird, because light, as we all know, is the fastest thing there is. If light can’t escape, then whatever’s going on there must be pretty extreme.

The reason this happens is actually quite simple in principle. If you take a massive object, like a star, and compress all that mass into a ridiculously small space that it fits within a critical radius, the gravitational pull increases. Keep compressing it, and eventually you reach a point where the escape velocity (the speed you’d need to get away from it) is higher than the speed of light, and at that point, you’ve got yourself a black hole.

Simple enough, in theory.

But it’s not really gravity in the way we think, and this is where it starts to shift a bit as black holes aren’t just strong gravity in the usual sense, they’re more like a distortion in spacetime itself. And although that sounds like one of those throwaway science phrases, it’s actually the key to everything.

As Einstein pointed out in his theory of relativity, space and time aren’t actually separate things, they’re part of the same fabric. Spacetime. And massive objects bend that fabric. That is they bend spacetime. The Earth bends it a bit, the Sun bends it a lot more, and a black hole basically folds it in on itself like someone’s tried to fold up a fitted sheet and given up halfway through (to this day, and despite my wife showing me numerous times, I still can’t fold a fitted sheet).

So, what is the event horizon, this so called point of no return? I hear you say

Well, the event horizon isn’t a physical surface. You won’t bump into it like a wall. It’s just a boundary in space, once you cross it, there is literally no path back out. Not because something is blocking you, but because all possible directions you could move through spacetime point further inward, cones of light tilt inward so that all future paths lead deeper in. It quite literally is the point of no return.

And what’s really strange is what it looks like from the outside. If you were watching someone fall into a black hole, they’d appear to slow down as they got closer to the event horizon, they would become slower and slower, until to the eyes of the observer, they appear to freeze there before slowly fading away, so you never actually see them going all the way in, but from their point of view, they just fall straight through.

That disconnect between what’s actually happening and what you see is where things start to feel a bit off and one of those questions that always seems to come up is, what happens if I were to fall in to one? and the honest answer is:

It depends.

I know that answer is a bit of a cop out, but if it’s a smaller black hole, you’re in a lot of trouble very quickly. The difference in gravitational pull between your feet and your head becomes so extreme that you get stretched out into a thin strand. This is what people in physics circles call spaghettification, which sounds almost funny until you think about it.

For a really massive black hole though, like the one at the centre of our galaxy (and the one in the song by Muse), it’s a bit less dramatic at first. You could actually cross the event horizon without noticing anything particularly unusual in that moment. It’s only later, the deeper in you go, that it becomes unavoidable and you’re on a one way trip.

Either way, you’re not coming back.

At the centre of a black hole is something called the singularity. In theory, this is a point where all the mass is crushed down into an infinitely small space, with infinite density, but here’s the thing, infinite in physics usually means we don’t actually know what’s going on. Physics dudes don’t like anything to be infinite as it mucks up all the other stuff we know about the universe. It’s basically our equations throwing their hands up and saying, this doesn’t make sense anymore.

So, the singularity might not actually exist in that exact form. It’s more likely that something else is happening there, something we just don’t yet have the tools or the physics to describe properly, and that’s where black holes start to become really cool.

For one thing, they’re not actually completely black, which surprised me the most when I first came across it, and black holes can actually lose energy.

There’s this process called Hawking radiation (yes, that cool dude who wrote that brilliant book, if you haven’t read it, you should), where tiny quantum effects near the edge of a black hole allow particles to escape. It’s often explained in terms of virtual particle pairs forming near the event horizon, with one falling in and the other escaping. It’s incredibly weak, but over very, very long periods of time, it means the black hole slowly shrinks and would eventually disappear entirely. Which is a strange idea in itself, something that swallows everything, but can also slowly evaporate.

Still with me? Good, as now we get to the bit we really don’t understand and where it all ties together.

Black holes are basically where two major parts of physics collide:

General relativity (which describes gravity and large-scale things) and Quantum mechanics (which describes teeny tiny things).

Both of these work extremely well on their own, but inside a black hole they don’t agree, which leads to some big problems, one of the biggest being, what happens to information?

If something falls into a black hole, all the information about it should still exist in some form as physics says information can’t just be destroyed, but black holes seem to do exactly that, either the information isn’t actually lost (and we don’t understand how it’s preserved), or our understanding of physics is incomplete. And if we’re being honest, it’s probably the latter, there’s something missing from our understanding of physics.

The part I keep coming back to is, as all this stuffs wanders through my noggin, is why does any of this matter? And it matters because black holes aren’t just weird objects sitting out there doing their own thing. They actually seem to play a huge role in how the universe works.

Most galaxies have a supermassive black hole at their centre which influences how stars form, how galaxies evolve, and possibly even how structure forms on a cosmic scale, but more than that, they’re one of the few places where we can really test the limits of our theories. They’re not just interesting in their own right, they actually do something, we just haven’t figured out exactly what that is yet.

In the end, I don’t think black holes are really about “things that suck stuff in,” even though that’s how they’re often described. They’re more like boundaries. Points where our current understanding of reality runs out and something deeper takes over. And the more you look into them, the more you start to feel like we’re still only scratching the surface.

Which, if nothing else, makes them worth thinking about properly.