
Testing Hawking radiation in laboratory black hole analogues - dnetesn
https://phys.org/news/2019-01-hawking-laboratory-black-hole-analogues.html
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godelmachine
>> _" 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 _

Must have been such an adventure :)

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thunderbong
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,"

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roywiggins
> 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...?

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abdullahkhalids
Short answer: light moving backwards in time.

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.

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chadmeister
What an excellent explanation! Thank you!

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platz
I'm curious how they distinguish it from synchrotron radiation

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abdullahkhalids
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.

