A 'Black Hole Survival guide' and your brief life in a paradox of space and time

Black holes are puzzling entities. They're massive, but somehow they're nothing. There are billions of them in the cosmos, and they shape the galaxies we live in - and yet we can't really see them. 

While these sinister, perplexing whirlpools of destruction aren't exactly on the top of anyone's must-visit list, sometimes, it's fun to imagine. And now, thanks to a new book, we can do just that. 

In Black Hole Survival Guide, physicist Janna Levin takes us on a virtual adventure through the cosmos, to experience what it would be like to travel to - and into - a black hole. And it turns out, it's a trip that we maybe, possibly, could even survive — at least, briefly.

Bob McDonald spoke with Professor Levin about her new book Black Hole Survival Guide. Here is part of their conversation.

Why frame this as a survival guide for black holes? 

I wanted to combat the preconceived notions about black holes to kind of shuck away the veneer and expose the fascinating attributes of black holes that I think are lesser known, but yet are really more core to their definition than the ones that are floating out there.

You spent quite a bit of time making sure that people understand that black holes are actually nothing. Why is that such an important concept to grasp?

I love it because people often will say, aren't black holes a dense state of matter? And that's a confusion. What the black hole is, is the remnant left behind after a star is totally gone. And so what the star does when it collapses, is it creates a curvature in spacetime that's so strong that eventually, yes, when the star gets dense enough, you create what we call an event horizon, a region beyond which not even light can escape it. It's as though you were trying to launch a spacecraft off the surface of this collapsing star and you would have to go faster than the speed of light to escape it. It doesn't mean that the star as an object is the black hole because crucially, it continues to fall. That star can no more hover around the event horizon than it can travel faster than the speed of light. So the star continues to collapse interior to the event horizon, leaving behind nothing, empty space.

And like an archeological imprint, this event horizon is a record in the shape of spacetime. But it's really a place. It's no longer a thing. And I think that is a really intriguing concept for people to wrap their heads around, because it's a shift from the normal image of a black hole.

You talk about them as a paradox. They suck everything in, but they contain nothing.

Once you cross that event horizon, it is inevitable that you will continue to fall to what remains an unknown fate. We speculate about it, but it is just speculation because this event horizon, this imaginary region around the black hole, forbids information of any kind to be transmitted from the interior to the exterior of the black hole. So if we live safely on the outside, all we can ever know is what's encoded on the event horizon. We can never know details about the interior. 

You say in your book that black holes are bigger on the inside than they are on the other side.

So black holes, contrary to reputation, are small. The whole point of the black hole is that it has tremendous heft for its incredibly small size. So if I look at the sun, the sun is a million and a half kilometres across. If I were to imagine some evil genius converting the sun into a black hole, its event horizon is only six kilometres across. So you've taken all the heft of the sun and jammed it into the size of a city. And so black holes really are spatially small. 

As you fall in, you would see eons passing, civilizations come and go. You would see kind of paparazzi flashes of exploding stars.- Janna Levin

You might presume, well, if it's only the size of a city on the outside, it should only be the volume of a city on the inside. But that's not the case. Black holes can harbour an incredible volume on the inside due to the benefits of curving spacetime and the trickery that allows you to do that. And some people have even speculated that there's an entire universe inside the black hole, that when things fall in, they get blown out into a new big bang and a new ecosystem with new stars and new black holes all inside that six kilometre perimeter.

Take me through some of the lessons shared in your survival guide. If I were being sucked into a black hole, what would be important to know?

Well, some of my lessons would start outside. First of all, don't get in the way of the jets. So if you throw matter around a black hole, if there's a nearby star that the black hole is cannibalizing, and the tops of the atmosphere of the nearby star are splattering on the black hole, it can create these magnetic storms, which power jets, which are basically ray guns of lethal radiation. So first of all, on the outside, you want to be smart and avoid things like the ray guns, the jets, because with it will come all of the physical consequences of being irradiated. 

If you're going to fall into a black hole, I advise you to go into as big a black hole as possible. That seems surprising to people. They think the bigger the black hole, the more destructive. But it's actually kind of like the difference between standing on a basketball and standing on the Earth. On the basketball, you're more aware of the curvature and you would struggle. On the Earth, the curvature is so gradual, the bigger the planet is that it actually seems flat locally. And it's similar with the black hole. The bigger it is, the less you'd be damaged by the curvature. 

A very big black hole, you have longer to live. If you went inside [a black hole the mass of] the sun, it would be a fraction of a second, but if you went inside a black hole tens of billions of times the mass of the sun, you can be approaching a year. But it would be an anxiety provoking year.

Once you are inside the black hole, what's it like in there? 

This is another one of those beautiful, seemingly paradoxical statements. Black holes are completely dark on the outside, the darkest phenomena in the universe, but they can be bright on the inside because all the light from the galaxy can rain in behind you. And because time is sped up out in the galaxy relative to your experience of it, as you fall in, you would see eons passing, civilizations come and go. You would see kind of paparazzi flashes of exploding stars. And so it could be quite spectacular visually on the inside of a black hole.

Do you think we'll ever actually know what it's like inside a black hole?

It's not inconceivable we would make black holes in other ways than dead stars, that we would make black holes in high-energy accelerator experiments. Maybe we'll make one in an accelerator and have one in a little laboratory that we try to stabilize. There are wild things that can happen, so I don't want to say never.

Q&A has been edited for length and clarity. Produced and written by Amanda Buckiewicz.