>>"I learned General Relativity in 1997 by lecturing a course, not by taking a course," Ulf Leonhardt, one of the researchers who carried out the recent study, told Phys.org. "This was a rather stressful experience where I was just a few weeks ahead of the students, but I really got to
Your comment made me read the whole article. And it is truly amazing!
They've been able to replicate Hawking radiation in the laboratory!
From the article -
>> "Our most important finding, perhaps, is that black holes are not something out of the ordinary, but that they closely resemble what light pulses do to ordinary light in fibers,"
> In their study, Leonhardt and his colleagues made light out of positive and negative frequencies. Their positive-frequency light was infrared, while the negative-frequency one was ultraviolet
What do they mean by negative frequency? That they're out of phase...?
Long answer: Take a light detector (such as a CCD camera) and place it in front of a light source. The light source emits a "pulse" of light. What you detect on the detector is that initially there is no light falling on it, then some light, then maybe a bit more, a bit less, then eventually no light anymore once you switch off the source. A pulse of light in the time-domain is just some varying level of light that can be measured by a detector. the pulse is of finite temporal length in the real world i.e. it has a definite start and a definite end.
You don't have to do the math in the time-domain. You can take the function that describes the pulse in the time domain and take the Fourier transform of it to take it to the frequency domain. In the frequency domain, the pulse is described by a function that can extend from negative to positive infinity. Each point on this function can be interpreted to be a sinusoidal wave of that frequency, which when take to the time-domain extends from negative to positive infinity time. Obviously, its not possible for light from a source to start from negative infinity time, so this is just an nonphysical interpretation of the math. For positive frequencies, the corresponding time-domain sinusoidal wave is moving forward in time, and for negative frequencies, the sinusoidal wave is moving backwards in time.
In the real world, you can't create light pulses that are exclusively negative frequencies, but you can create pulses that have both positive and negative frequency components and then exploit those separately in clever ways.
Synchrotron radiation is electromagnetic radiation emitted by radially accelerating charged particles. In this experiment, there are no such particles. In a blackhole, there might be, but we are very far away from doing such precise measurements on blackholes.
Must have been such an adventure :)