Electromagnetic black hole | Hacker News Reader

Electromagnetic black hole

newscientist.com

24 pointskirubakaran14 comments

Interesting technology but it this is not a black hole -- electromagnetic or not. When i saw the title I thought it would be something much cooler such as concentrating an incredibly strong electrical field at one point so that it sweeps electrically charged particles in that point and creates a singularity. That would have been cool and is the logical thing one thinks of when one mentions an "electromagnetic black hole."

This is just a cylinder that traps microwave radiation by progressively refracting light to its core. It is cool but badly misnamed.

The name makes perfect sense. A gravitational black hole traps geodesics in the Einstein equation. This black hole traps geodesics in the Schrodinger/paraxial wave equation.

(A geodesic is the line that would be followed by a wave if it were a particle. So for example, geodesics of the wave equation obey geometric optics, and geodesics of the Schrodinger equation give Newtonian mechanics. Geodesics of the Einstein equation are weird.)

Agreed, I was thinking exactly as you were when I read the title. It's a little overblown from what it is, but I suppose it is a working allegory, however it is nothing more than a trick to reproduce the effect. It's akin to calling one of those coin collectors (where you put the coin in the slot and it circles a few dozen times, getting faster as it's pulled down the funnel shape, never learnt the name for them) charities use a black hole (I've actually heard it done).

It reproduces the effect, but in no way does it reproduce the cause. An ideal electromagnetic black hole would likely be an extremely strong halbech sphere, either concentrated to the interior or exterior.

I envision a future where fields are filled with these black holes and an area of a couple of square kilometers is completely and utterly blacked out.

Really adds drama to the post-apocalyptic scene.

I'm trying to imagine the optical effect of looking at such a device. Maybe I'm misunderstanding the physics, but if it's anything like that picture it must be quite a fascinating distortion of the visual scene. Not only completely black at the center but also a very strange surrounding.

I'm not sure. Wouldn't the angle of refraction (into the core) depend on the angle of incidence of the light hitting the device?

Two notes:

1) it will be 'visible' in other spectra than the one absorbed

2) it would have to be, otherwise even the smallest inbound radiation would melt the thing eventually.

One goal will be to produce electricity instead of heat.

Yes, but even that is going to have to be either moved 'off site' generating an electromagnetic signature somehow, at a minimum some infrared because of line losses, or consumed on the spot, in which case it all comes back out as IR.

It is really terribly difficult to 'get rid' of anything without a trace.

The device will look like a slab with a distinguished direction (say the Z direction). Suppose the black hole is at (x, y) = (0,0), z=anything.

If you shine a laser/microwaves/whatever the relevant frequency in at one side, it will always come out of the slab near (0,0). Basically, laser beams shined into the slab will be attracted to the line x=0,y=0, z = anything.

[edit: really curious why I'm getting downmodded. Did I wildly misunderstand the device?]

sounds right on to me

If anyone is interested someone also recently demonstrated an "acoustic" black hole

http://news.ycombinator.com/item?id=883537

Very cool. Imagine wrapping a jet with the black hole stuff -- great for stealth technology.

http://news.ycombinator.com/item?id=881113

and

http://news.ycombinator.com/item?id=882430

Reply on news.ycombinator.com