## How Science Is Done?

Hawking radiation is currently a completely theoretical concept. The idea goes like this: Imagine a black hole. Quantum mechanics says that every so often, random fluctuations make conjugate pairs of particles out of – nothing. That’s okay, so long as they disappear fast enough. It’s very temporary, and therefore very difficult to observe. Now put one of these pair-creation events right near the event horizon of your black hole, that place beyond which nothing can escape from its clutches. When you do that, one of the magically-appearing-out-of-nothing particles enters the black hole before it has a chance to disappear with its twin, and its conjugate gets kicked out into space, where it’s seen as radiation. Ooops. Now you’ve created a permanent something out of nothing. Well, the black hole has, anyway. How do you prove Hawking radiation really exists? First you get a black hole…

Now Iacopo Carusotto from the Universita di Trento in Italy and his colleagues say they’ve done it, using a Bose Einstein Condensate instead of a black hole. Oh, and they used a mathematical simulation instead of a real BEC.

Here’s what they did: the team created a mathematical model of an experiment with a Bose Einstein Condensate. The condensate flows along a waveguide with a particular speed, v. This sets up a kind of sonic horizon: any sound wave with speed less than v travelling back along the condensate can never cross this horizon. Seems simple enough. But because BECs are no ordinary objects, it turns out that the physics of this situation is exactly analagous to what goes on at the event horizon of a black hole. So Hawking radiation could form at the horizon.

And sure enough, in their simulation, Carusotto and co observed the emission of a particular kind of sound wave called Bogoliubov phonons from the horizon, just as Hawking predicted.

Uh, they started out with a mathematical simulation. It’s not real. Is the result real? Is this science? They think so. “*[O]ur observations can be considered as a first independent proof of the existence of Hawking radiation*” is what they say.

I’m not quite so sure.

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