Black Holes and a Superluminal River of Glass

If I told you that scientists have been able to make black holes in their labs for years, you probably either wouldn’t believe me, or would suddenly get exceptionally paranoid. Turns out it’s true, provided you understand a little bit about black holes.

A black hole is, at its most basic, an object that light cannot escape. That’s why it’s “black”: it absorbs all colors of light. That’s really, deep down, all you need in order to have a black hole.

Black holes out in space, as you are likely aware, are the result of collapsed stars. Gather enough mass into a small enough space and, according to general relativity, space and time begin to bend. Bend space and time enough and the paths that light would follow curve in on themselves, until inside the event horizon (the “point of no return”) the only way light can go is down, into the center of the black hole.

That’s not the only way to get a “point of no return” though. Imagine flying a glider above a fast-moving river. If the plane is slower than the river, then any object placed in the river is like a “point of no return”:  once the object passes you, you can never fly back and find it again.

Of course, trying to apply this to light runs into a difficulty: you can have a river faster than a plane, but it’s pretty hard to have a river faster than light. You might even say it’s impossible: nothing can travel faster than light, after all, right?

The idea that nothing can travel faster than light is actually a common misconception, held because it makes a better buzzword than the truth: nothing can travel faster than light in a vacuum. Light in a vacuum goes straight to its target, the fastest thing in the universe. But light in a substance, moving through air or water or glass, gets deflected: it runs into atoms, gets absorbed, gets released, and overall moves slower. So in order to make a black hole, all we need is some substance moving faster than light moves in that substance: a superluminal river of glass.

(By the way, is that not an amazingly evocative phrase? Sounds like the title of a Gibson novel.)

Now it turns out that literally making glass move faster than light moves inside it is still well beyond modern science. But scientists can get around that. Instead of making the glass move, they  make the properties of the glass change, using lasers to alter the glass so that the altered area moves faster than the light around it. With this sort of setup, they can test all sorts of theoretical black hole properties up close, in the comfort of a university basement.

That’s just one example of how to create an artificial black hole. There are several others, and all of them rely on various ingenious manipulations of the properties of matter. You live in a world in which artificial black holes are routine and diverse. Inspiring, no?

5 thoughts on “Black Holes and a Superluminal River of Glass

  1. delton137

    These are really exciting times we live in. Just a few years ago it seemed like Hawking radiation may never be possible to experimentally test — the amounts predicted to be emitted from black holes in outer space being way too low for that.

    Who would have imagined, just a few years ago, that people would be making event horizons and observing Hawking radiation in the lab, using tabletop equipment?


  2. edouardwatteel

    A few years ago I wrote a rather critical piece in which I stated that it would irresponsible to study mini- black holes because although there were firm theoretical reasons to think they would just ‘dampen’, even a 0,01% probability that they wouldn’t is enough reason not to carry out the experiment (expected gains – 0.01*swallowing of earth in black hole). At that point Hawking radiation was not yet observed, at least not that I knew of. What do you think about this issue (now)?


    1. 4gravitonsandagradstudent Post author

      A couple things:

      First, a while after I posted this, some people pointed out that there were some theoretical objections to actually labeling the experiment I link to here as really producing Hawking radiation. So this might not change matters.

      Second, the percent here is important. 0.01% seems conservative, but it’s actually absurdly high. When there is an 0.01% chance of anything going wrong at the LHC, not “end of the world” wrong, but merely “break the equipment” wrong, the machine is shut down until the problem is fixed. If the chances were anything like that people wouldn’t be trying to cause mini black holes. Rather, the chance is (presumably, haven’t seen this particular calculation worked out) low enough that the equation (expected gains – chance*swallowing of earth in black hole) actually gives a positive value, as crazy as that is to believe. In the case of the LHC itself, the most common point made is that the sort of events at the LHC have the same energies as events that happen naturally in the atmosphere, so if an earth-swallowing black hole was never formed in the atmosphere in the entire history of the earth then the chance of it happening here and now is so small that the equation works out.


      1. edouardwatteel

        Thanks for the reply.

        I have indeed heard that cosmic rays with even much higher energy “crash” on the atoms in the atmosphere all the time, but I was wondering if this is truly the same thing because the density of the matter there is much lower, so that any such mini hole would have much less time to “consume” new matter and much more time to dampen. I used to think that it is better to leave risk calculations to the professionals, but that was before the financial crisis 🙂

        It is in particular “don’t spoil the party- dynamics” that I think could be dangerous. Also I think the risk a physics professional would be willing to take is much higher than that of an outsider. Solving the riddles of the cosmos for only 0.005% of risk? Hell yeah!

        That being said, I could not help but notice that according to your “Nemesis”-post (a nice and enlightening one btw) I must be a philosophical type, because I worry too much about black holes. But even philosophers can’t ignore hard science forever, that’s why I like coming to this site. It even made me start reading Leonard Susskind’s and George Hrabovsky’s “The Theoretical Minimum”, a perfect book for me because it focusses on the necessary mathematics to do physics calculations. Unfortunately, I’m still just at the (necessary) classical mechanics.

        Keep up the good stuff.


        1. 4gravitonsandagradstudent Post author

          Actually, the density is higher up in the atmosphere. The inside of a collider is a very good vacuum, any worse and the proton beams would collide with the air inside rather than eachother, which would be disastrous.

          I agree that there’s definitely potential for an element of bias in the risk assessment, though I think the error is more likely to be someone getting hung up on proving the risk is acceptable via some cute analogy rather than overestimating the benefits (intellectual vanity seems to trump overreaches of ambition around here). I think the main point in this case is that if we’re taking the same risks that nature takes already, there’s nothing to justify.

          I definitely agree that philosophers and hard scientists need to have some level of dialogue, glib Nemesis posts aside.



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