# Not Quite a Black Hole

I posted some in-game footage of black holes in Elite.[stderr] Imagine my surprise when I had a similar effect in my own kitchen. Sort of.

The water bead in the water is just me farting around with random stuff in my kitchen. More on that later.

I’m guessing that the diffraction effect is probably going the opposite way that a black hole would, since the distance light would travel through the gel/water is shorter if it’s a chord, whereas with a black hole it would bend toward the singularity. I’ve got a 50/50 chance of being right!

Here’s another screenshot from Elite, because, I have a lot of screenshots.

M/V Longshot looking right into the great drain

That’s Sagittarius A*, the supermassive black hole at the center of the milky way. The stellar background is very bright there because the core is pretty crowded (in terms of stellar distances)

### Comments

1. Rob Grigjanis says

I think you mean refraction rather than diffraction. Also, in both cases light is bending towards the centre; see here for an overhead view of light going through a cylinder (of glass/water or anything with a higher refractive index than air). Your video is done at a distance past which the light rays have crossed, so what you see is inverted.

One difference is that further from the centre, the light through the cylinder is bent more, while the light passing further from a black hole is bent less.

2. says

Rob Grigjanis@#1:
Yes, I meant refraction. That was a brain-o.

I also was not clear: there is a lens-like water-bead in the flask; it’s not just the glass and water. I don’t think the light would bend differently, though. But that’s why it has that aberration at the bottom.

I need to work on being clearer (and more correct in my wording!) when I catch myself thinking “I’ll just dash off a post…”

3. Hj Hornbeck says

Ah, ninja’d by Rob Grigjanis. I can add more details, though.

When light moves into a medium with a higher index of refraction, it bends towards the negation of the surface normal; in the case of a sphere, that’s towards the centre. When it exits, the reverse happens. This behaves a lot like light in a gravity well, which for a spherical object also bends towards the centre as gravity increases, but there’s a crucial difference. A plastic or glass bead is usually made of a homogeneous material with a constant index of refraction, and light only bends when it transitions from one index to another; this means it only bends twice, on entrance and exit. With a black hole, though, the constantly shifting magnitude of gravity causes light to continuously curve, rather than bend. So you can never perfectly match the lensing of a black hole with a homogenous glass/plastic bead.

What about non-homogenous materials with a varying index of refraction? If done right, they’re a perfect mimic. The same trick can be used in computer graphics: just make a series of concentric spheres of varying indicies of refraction, and if you get the math right you’ll perfectly model a black hole. In practice, it’s better to skip the fakery and directly use GR’s equations.

4. @Marcus
Neat. Kitchen science is fun. Why the wait on the identity of the material defracting the light?

How about ethics in game economy? I have one I’m pondering. I was mining away in my type-7 in the ring of a blue and purple Jupiter, thinking about future plans and I wondered, how hard would it be for a larger number (dozens?) of Elite players to prevent trading in slaves, or at least make it a more serious social negative as players? I’m thinking about how problematic the slave trading is in the game and was thinking about petitioning the developers to create factions that try to actively end slavery in the galaxy. There has to be something better than scanning for ships carrying them and, blowing them up? I could steal them and then what? The fact that grinding slave trading is among the most profitable of repeatable routes (if not the most profitable) is disturbing.

I can think about interacting with the problem on the inside or outside and each will have different complications.