# Black hole or wormhole?

Could a black hole be a wormhole?
04 December 2018

## Question

Since we don't know what is past the event horizon of a black hole, could a black hole possibly be a wormhole? Or would it just kill you and add your mass to its center?

## Answer

Chris Smith put this to astronomer Carolin Crawford...

Carolin - The event horizon is, if you like, the horizon beyond which you can't detect any event so it is the invisible boundary around a black hole. It’s the point of no return. If you step over that. Yes the short answer is you get killed you become part of the black hole, but the trouble is that no information can cross from the inside of the event horizon to the outside, so as the questioner says: we don’t know what goes on inside the event horizon. What we suspect is there’s lots of empty space and right at the center you've got what's called the singularity, it's the black hole itself, it's infinite mass crushed down to tiny tiny volume.

There are ideas that, say your black hole is rotating and maybe the singularity gets stretched out like a ribbon, it would be possible to cross over the event horizon, perhaps fall through and avoid becoming part of the black hole and perhaps pass through something called a wormhole which is like a tunnel through to elsewhere or ‘elsewhen’ in the universe, and get spat out in the opposite of a black hole which is a white hole. So you have this idea you fall into the black hole. Go through the wormhole get spat out to the white hole. Now all of this, if you look at the maths is okay. If you look at Einstein's equations they can predict black holes. They're also produce white holes. The only snag about white holes is you have to run time backwards instead of forwards so it's a bit of a snag for them actually existing. And also we see black holes everywhere in our galaxy. Everywhere in the universe. We don’t ever see a white hole. So then you’ve got to start questioning whether wormholes exist.

Now they’re a really nice idea, you see them in science fiction books and movies - how you get around the universe or how you travel in time. In practice when you look at the equations, and I'm simplifying grossly here, they are very unstable. You put a toe in a wormhole it will just collapse around you so I dont think its a good way of getting round the universe. So the answer, we go back to the fact that yeah if you did go over the event horizon, I think you can become part of the black hole, it’s going to kill you. Yeah, in fairly dramatic ways! And just to remind everyone a black hole, despite the name, is not a hole in space it's a thing. It is you know an area of extreme mass, extreme gravity, and you would just add to that mass and gravity.