# How to convert a traversable wormhole into a black hole?

So the premise goes: A previously-traversable wormhole evolves into a black hole because (x) happens.

What's (x)? What would it take for this to occur? Either naturally (a cosmic occurrence), by intent (using a powerful technology), or by accident (using a powerful technology stupidly)?

EDIT: I'm interested in the theory that wormholes = quantum entangled black holes, in which case I'm wondering how that quantum entanglement might be severed... and what the repercussions of that severance might be (beyond ending up with two black holes in different regions of spacetime, no longer connected).

Thanks!

• Pretty sure that it can't happen. A wormhole is just the connecting of two points, it doesn't really have it's own gravity. – Nonafel Oct 1 '15 at 20:45
• @Nonafel Thanks. I guess that begs the question: If I work with the theory that wormholes = quantum entangled black holes, what would it take to sever that entanglement? (i.e. No more wormhole connecting them, just two black holes at different points in space?) – equustel Oct 1 '15 at 20:50
• A worm hole is a funnel that tapers down to a “throat” which connects to another funnel that opens up somewhere else. A black hole is a funnel that pinches off at a singularity. A traversable worm hole needs to be large enough that it doesn’t have an event horizon. However both would be created by different means. We also don't fully understand black holes yet. If a wormhole was in fact two black holes that were connected... they wouldn't be actual black holes nor act like them. You can fly by a wormhole safely, black hole? Close is too close. – Nonafel Oct 1 '15 at 20:59
• Let me clarify: Calling them black holes is my issue. You need another name. – Nonafel Oct 1 '15 at 21:01
• Just because both black hole and wormhole are mathematical solutions to Einstein's field equation for gravity doesn't mean they are the same thing or they can be converted into one another, okay wormhole is mathematically derived from black hole but still not all roads lead to Rome or anywhere. – user6760 Oct 2 '15 at 4:24

Many theories of wormholes require the throat to be held open by "negative matter", which is one of those ideas which is mathematically plausible, but seems to defy "real world" observations (negative matter would push against you with the same force you are exerting on it, so if you were in a hallway with a large ball of negative matter, "pushing it out of the way" would result in it crushing you against the wall with the same amount of force you exerted, for example). So if you applied enough handwavium or super science, you could create a plausible scenario where wormholes were created and held open by negative matter.

This is actually important since in their "natural" state (once again assuming wormholes are more than mathematical artifacts) are extremely unstable. The gravitational forces created by an object moving into the throat of the wormhole are supposedly enough to cause the throat to collapse and create two separate black holes at either "end" of where the wormhole was. Needless to say, the hapless traveller or stray photon caught in the collapsing wormhole has been destroyed by the massive gravitational forces unleashed, although what actually happens to them is somewhat unclear.

So (inverting the actual state of things in the theoretical wormhole), you could imagine a very powerful elastic being held open by a napkin ring to represent the wormhole throat. The elastic is so powerful that it could snap shut in a millisecond and crush most things trapped within the contracting band, but the napkin ring keeps it from doing so. If the napkin ring has any flaws from manufacture or degrades over time due to the constant compressive force, it will eventually break and the elastic will snap shut. Since negative matter has most of the attributes of normal matter, outside of its strange reversal of forces, it is fair to assume that entropy could eventually wear down the ring, much like metal fatigue can end the life of a highly stressed machine part or structural member in a building.

In story setting terms, this could be interesting if the wormholes were not created by humans but were ancient artifacts. Eons of photons and normal interstellar radiation has passed through the throat of the wormhole, and caused fluctuations in the throat and stress on the ring or rings of negative matter holding it open. Now you have a crap shoot: will the ring have enough structural integrity to support the wormhole throat as your ship approaches....?

• Ah, very helpful––thank you! That "natural" instability will work in this story's favor for more than one reason. Appreciate your input, and the helpful analogy. – equustel Oct 2 '15 at 20:32

It depends.

How are you establishing and stabilising the wormhole? What theory of gravitation do you subscribe to? How much do you object to spaghetti?

In all seriousness: The maths that deals with this kind of thing lends itself well to people making statements such as 'a wormhole is like two black holes joined together', which may be true if you use one formalism, but not if you use another. As an example: Straight relativity says that a black hole formed from a dead star is a black hole. No argument, just a singularity. However there's another theory (which I can't remember the name of right now, bonus points to anyone who can get it) which argues that a naturally occurring black hole must cause two deformities in space-time, leading to a Schwartzchild wormhole with an infinitely narrow throat.

If the second is true, and we artificially widen that throat with a ring of exotic matter, or bombardment with the right exotic particles to simulate a negative pressure, then the easiest way for a wormhole to form a blackhole is if the stabilisation method is destroyed or disrupted.

An interesting corollary to the above leads to the spaghetti question: If the wormhole is theoretically traversable, but actually small, then you're going to have a bad day travelling through it no matter what you do.

Assuming you're happy with handwaving and shallow science (and if you're working with wormholes, I think you are), you could simply shove a ton of matter into it. If you think of wormholes as paired spheres, then adding a bunch of matter to one of them could convert it from "wormhole entrance" to "black hole".

My intuitive thinking on this is that wormholes have a tiny entrance through which they stream matter to the other side. Let's further assume that when an object passes through the wormhole, it passes through the threshold at the speed of light - like a sound signal being converted to electrical signal through telephone lines. This is an arbitrary rule, but making everything pass at the same speed avoids weird states in the following calculations.

If the tiny wormhole entrance is, say, 1mm in diameter, then you can use the Schwartzchild radius formula to calculate how much mass the wormhole can contain before light can no longer escape it (6.8E23 kg, or about 1/10 the mass of Earth). If objects moving at the speed of light can't escape the entrance, then it's effectively a black hole.

What happens on the other side is up to you. If gravitational forces don't pass through wormholes, then the other side is simply a wormhole to the center of a black hole. If gravitational forces do pass through wormholes, then the other side becomes a black hole too. You might want to increase the mass required in that case, since you're no longer forcing mass into a 1mm sphere - you're forcing it into a 1mm sphere + transit tube + 1mm sphere on the other end.

So how could this come to be? You somehow need to get that amount of mass into the wormhole. That could be a problem with a visible-scale entrance like the 1mm mentioned above - how could someone shove 10% of the Earth through it? You can fix this partly by adding transit time. Maybe it takes a day for matter to transit through the wormhole. In that case you've got a full day to shove your planet-scale object into it. The other option is to make the wormhole entrance smaller, so it doesn't take that much matter. If you have a "funnel" style wormhole, maybe it has a large mouth but a tiny bottleneck, so fitting a large amount of matter in a small amount of time isn't too hard.

Finally, if you want to "unlock" the wormhole at any point, remember Hawking radiation, which means black holes "boil off" over time. If a black hole is right at the edge of the mass required to be a black hole, then it can be un-blackholed over time via Hawking radiation. You could always introduce a bit of tech-magic that stimulates Hawking radiation to speed up the process. Or even add another (large?) wormhole entrance to the network, increasing the volume of the system, which could also unblackhole the system.