This week's is a mash-up of two of my favorite things, black holes and sci-fi/speculative fiction!!

As an astronomer who researches black holes, I know how they work (well, what humans have learned so far). As a media consumer, I love when the science is plausible at first glance. I'm not a very interrogative fiction reader/viewer & I can suspend my disbelief pretty well, so it just needs to past the shrug test:
"Could something along these lines work?"
*shrugs* "Maybe?"

Robert (@userthree) asked about theoretical uses for a month or so back on one of my intro posts/threads, so here we go!

(Image is a screencap of unknown origin, please reply if you know!)

Black hole use 1: A garbage dump.

At a very fundamental level, black holes eat stuff. It goes in, it can never come out. Remember from last week's thread that ! They're just a hole that things fall towards and into, and if they don't have any energy to escape, then they fall past the event horizon and they're stuck.

This sounds like a convenient garbage dump! You could probably even dump radioactive material if you aimed super well so you *knew* it was *all* going in.

Black hole use 2: An energy source.

Black holes tend to be messy eaters, so not everything you throw at them will go inside (see: winds, jets; and yes this complicates the end of my last point), but the material they're accreting gets *incredibly* hot (see my thread on X-ray Binaries). If we developed a solar panel equivalent that worked for X-ray light, you could have a passive energy source. Would only work during outburst, so pick sources carefully.

Black hole use 3: Tidal energy.

If you were on a planet that orbited an X-ray binary with a black hole (big "if" IRL, but works in scifi), and if there were liquid oceans on the planet's surface, you could try to harness the tidal energy. Something something raises blocks, converts kinetic to potential energy, something something turbine something electricity. I wouldn't bet the house on this, but it passes the shrug test!

Image from the movie Interstellar.

Black hole use 4: Spaceship slingshot.

A maneuver we've done with spaceships in the solar system is to go around a planet or moon and use your momentum to slingshot off at a faster speed in your preferred direction. The technical term for this is "gravity assist (flyby)". The Mercury misson BepiColombo did it of Earth and Venus on its way to Mercury! This is handy because it means the spaceship can carry less fuel, making it less massive and easier to launch.

Image credit: ESA/BepiColombo/MTM.

Forgot to mention the black hole part of that since I got excited looking up BepiColombo pictures. The black hole's much larger mass (compared to a planet) means that you'd get QUITE the speed boost!

Sure, you wouldn't want to aim wrong and get stuck forever, but aiming wrong around a star or planet is also Bad News.

Black hole use 5: Interstellar highway on-ramp.

Hear me out! Nobody's going inside the black hole, and we aren't slingshotting via gravity assist (per se).

Instead, we would use the relativistic jets that shoot out the top and bottom of some black holes like firehoses. These jets accelerate particles near the black hole to speeds close to the speed of light. You'd need some kind of sail attached to your ship to harness the energy? Idk, but I can envision a creative writer making this happen.

I'm sure someone wants me to talk about wormholes, so let's chat! I don't mind them in fantasy-scifi, but they don't pass the shrug test. Here's why:

The definition of a black hole is that nothing can escape. Using a wormhole implies that you can enter the black hole alive & unscathed (possible for supermassive black holes, not for stellar ones), traverse where the black holes are somehow connected together? and then exit the black hole on the other side. Which is just Not Possible. Sorry 😞

You could do some really creative stuff with what's inside a black hole! For supermassive black holes, since they're SO much more massive than a spacecraft with humans would be, you'd probably plop right inside past the event horizon. Then you're inside the black hole! You'd still be falling towards the singularity at the center, but time would probably get weird.

Image from NASA/GSFC/J. Schnittman.

From what I remember from my theorist days, the math of How Stuff Works inside a black hole's event horizon gets super strange. Basically, time and space switch with each other. How would that work in practice? I've heard it described this way:

Timey-wimey sh!t 

Wherever you are right now, outside a black hole, you have no control over your body in time but control over your body in space. For example, time will progress forward one second at a time, and there's nothing you or I can do about it, but the laws of physics allow you to move side to side, back and forth, up and down.

Timey-wimey sh!t 

Inside a black hole, you would instead have absolutely no control over space -- your spaceship would progressively move forward towards the singularity and you could do nothing to change the speed or direction. However, you would be able to change or affect time?! Moving forwards or backwards in time for your body, however you see fit?!?

Still stuck in the black hole though, because you can't change space. But...time travel that passes the shrug test!?! It's mind-blowing.

Please reply with more ideas for hypothetical uses of black holes that you've come up with or encountered elsewhere! This list is just what I could think of right now, so it is by no means complete. 💫🕳

If you want personalized research/fact checking/science advising, let's chat! I have sliding scale rates that are very reasonable for indie/independent/small-press writers and creatives (and appropriately large for multimedia execs).

@alstev you would need some pretty heavy radiation shields, wouldn't you?

@alstev With very little thought: long-term storage. Want to keep some fish fresh for a Very Long Time? Park it near a black hole where time passes slowly. Pick it up a century later (for me) but minutes later for it.

@readsteven Miscalculate something or put it in the wrong orbit, and oops! You've found fish that's been sitting in a spaceship for [it's reference frame] three weeks!

@alstev This was amazing, I love everything about it! 😻

@alstev Time sharing on a scarce resource, like at a supercomputer or a telescope. Park two space stations on two orbits with different time dilation and a rendezvous in apogee/perigee of the two. Put the instrument in the outer orbit ship where a limited group of scientists has all the fun. And the other, inner, ship will be the waiting room for the rest of the crew where they can brief each other on their findings.

@alstev Did you, by any chance, read "The freeze-frame revolution" by Peter Watts? It features a spaceship with a black hole used as propulsion. The idea was apparently based on some scientific paper, but I don't remember the details.

@varelse Ooh no I haven't read this, thanks for the recommendation!

@alstev As far as I can tell, it was based on this paper: (not a peer-reviewed paper, just an arxiv one). Although I don't have the book with me, so I cannot confirm.

@alstev I've always liked the idea (not sure where I first heard it but it's been floating around for a while) of a civilization harnessing energy from a black hole to travel to other solar systems... swallow their stars to fuel their journey for <insert revenge/quest>

which I saw most recently in Charlie Jane Anders' YA lesbian princess space opera books

@alstev I've also been thinking about what happens if you send a telescope with a camera pointed out into its light-cone and a laser to transmit that video feed with into a black hole. like, information can't get out faster than the speed of light, but can compression/models/metadata be generated from some whacky nonsense like this? probably not but it's a fun scifi idea

@amsomniac I don't think so, but I love hearing ideas for how you (general "you") would try to get some kind of information out of a black hole!

@amsomniac That's so cool! We'd need to have interstellar travel already since the closest black hole to us is about 1,500 light-years/460 parsecs away, but if we could get it to fly with us in the spaceship and stop when we stop (which I don't think passes my shrug test, sadly), it would be such a cool way to generate energy!

Timey-wimey sh!t 

@alstev for us to move in space we need some sort of propulsion mechanism that somehow works with newtons law (push the floor backwards, move forwards). Would we need a similar mechanism for moving through time? What would we push?

Timey-wimey sh!t 

@categulario This is SUCH a good point it broke my brain. I don't know!! But also, we don't think about Newton's laws when we're first learning to move in this world, so maybe learning to move through time inside a black hole would be similarly intuitive?

Timey-wimey sh!t 

@alstev certainly! What muscles would we use? Or could we _just do it_.

What does the math for that look like? Can you point me to a paper to dig deeper?

Timey-wimey sh!t 

@categulario I don't know of a paper off the top of my head, but I'll reply here if I come across one!

Timey-wimey sh!t 

@alstev In our world, we can move our body because we have muscles. If we were rocks we wouldn't be able to move even when we are outside a black hole. To do temporal movement, we probably need to grow some time-limbs. Perhaps, rocks in our world do have time-limbs. That's why they seem eternal to us ephemeral organisms. They literally arrived from the past and traveled onward into the future.

Timey-wimey sh!t 

@alstev so you could move forward or backward in time? Are there limits? Could you move backward until before the black hole formed (and then exit at that time to explore the universe a long time ago)? Or after the black hole evaporates? Or has a radius reduced enough that you are now outside?

Timey-wimey sh!t 

@youen You would still physically be inside the black hole event horizon, moving towards the singularity. I don't know what limits there are, it's been ages since I looked at the math for this! I wouldn't expect the black hole to evaporate, since if that happens at all, it happens particle by particle.

Timey-wimey sh!t 

@alstev what I mean is that if you can move back in time, at some point you would arrive at the time the black hole formed. Before it formed there was no event horizon.

So maybe you can exit the black hole, using the 4 dimensions, since the radius of the event horizon gets smaller as you get back in time (you wouldn't get farther from the center, it's the black hole that would get smaller).

Timey-wimey sh!t 

@alstev Would you really be able to move in time from your perspective, or just from the perspective of an outside observer?

Timey-wimey sh!t 

@lilianalytic I think it would be from your own perspective. And anyways, you'd need to define a new "outside observer" who was still inside the black hole with you.

@alstev wow it took this picture for me to understand why a blackhole would look like this. I thought it was just some art for the interstellar movie .-.

@categulario Yeah isn't it strange looking at first? The visualizations for interstellar have everything but Doppler boosting! Doppler boosting makes the image look asymmetric, so the stuff flowing towards you is brighter and bluer, and the stuff flowing away from you is dimmer and redder. The Interstellar movie people didn't like the asymmetry so they didn't keep it, but you can see it in scientific 3D renderings like this one from my colleague at Goddard!

@categulario Also, the whole idea that the "hole" of the black hole is a 3D sphere, not a 2D circular hole in the ground. The event horizon is a surface, not a circumference. Up close, black holes don't really have "top" and "bottom", just "inside" and "outside". 🤯🤯🤯

@alstev if you turn your head to your wristwatch while inside the event horizon, do you see it? Omg I have so many questions

@categulario Some people say that you see all the stuff in a black hole, some say that you only see the things you came in with ("at rest" with you in your local reference frame), and some say you see absolutely nothing. I don't remember which is most likely to be correct 😂🙈

@alstev does the visualization change between a super massive black hole vs a stellar one?

@categulario No, many (though perhaps not all) aspects of black hole accretion and black hole physics are what we call "scale-invariant", meaning that it works the same for stellar black holes as for supermassive black holes.

@alstev I take it the “white hole” idea my late 70s junior astronomy books were so excited about died a death, then ☹️

@considermycatjohn Sadly it's not something we've ever seen any evidence for. I will say that we're limited in our observations: it needs to emit light, tiny particles like neutrinos, or gravitational waves, in the direction of Earth, and not be so far away that the signal gets totally washed out. But given how we can see energetic events like supernovae in distant galaxies, we *should* be able to see a white hole as classically defined.

@considermycatjohn There's also the more boring (though incredibly important) aspect of conservation of mass and conservation of energy. If the white hole is spewing out (or dribbling out) matter and/or energy, where is it coming from?? Where are the reserves of matter falling out of the white hole and how did they get there?

@alstev wormholes and black holes are unrelated phenomena though, right? I’ve never heard of wormhole->black hole in sci-fi (which is my way into this rabbit hole), only wormhole->wormhole. And that requires “exotic substances” that may or may not exist.

@kazarnowicz The way I've heard it defined, wormhole = black hole -> black hole


totally agree. I would regard warmholes as an exciting to understand natural phenomenon and that would be enough. No unlikely science fiction theory to travel thru. Leave that to Holywood. Any chance the sapiens sapiens will develop a system to detect one?

@sepmark They are pretty fun in Hollywood stories though.

I don't think we could detect one, unfortunately. Unless it existed and were used and we saw something come out of it.


Yep... I admit that in Interstellar the scene of the wormhole passing thru was quite emotionally engaging.

I have the same feeling humans wont detect such a cosmic tunnel (if any) for at least the next million years. Pitty! I dont have all that time, I guess.

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