You can amplify light by bouncing it between the horizons of a black hole and a white hole. Now physicists have worked out how to build such a device in the lab.
One of the more fascinating discoveries in theoretical physics in recent years is the formal mathematical analogy between the way spacetime and certain materials effect light.
Physicists have used this idea to show how to build black holes using so-called metamaterials that steer light in exotic ways. Indeed, Chinese physicists built just such an artificial black hole back in 2009.
The analogy can be taken even further. Not only is it possible to make black holes in this way but also their time-reversed equivalents--white holes. What's more, both these white and black holes should produce Hawking radiation. This is the spontaneous emission of radiation at a hole's point of no return, called its event horizon.
This spontaneous emission of radiation is a curious and complex phenomenon. Nobody has observed Hawking radiation either from astrophysical black holes or laboratory-based ones (although there are one or two claims currently under debate). But few physicists doubt its existence.
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