[HN Gopher] Physicists create compressible "gas of light"
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Physicists create compressible "gas of light"
Author : gmays
Score : 55 points
Date : 2022-03-25 15:39 UTC (7 hours ago)
(HTM) web link (www.uni-bonn.de)
(TXT) w3m dump (www.uni-bonn.de)
| brimble wrote:
| > To do this, we stored light particles in a tiny box made of
| mirrors," explains Dr. Julian Schmitt of the IAP, who is a
| principal investigator in the group of Prof. Dr. Martin Weitz.
| "The more photons we put in there, the denser the photon gas
| became."
|
| This seems like the kind of clever but also crazy thing a kid
| would come up with based on limited information about the world,
| but that definitely doesn't work.
|
| There's got to be more to it than this description... right? Or
| this is one of those things where a physicist said "mirror" but
| actually means something totally different that no normal person
| would call a mirror, as physicists seem to do often and which
| causes so very much misunderstanding of physics?
| im3w1l wrote:
| Can confirm, did think of this as a kid. Also wanted the box to
| have a hole that could be opened to release all those stored up
| photons in the form of a deathray.
| brundolf wrote:
| Hey me too xD
| [deleted]
| cshimmin wrote:
| Good question; had to go to the supplementary materials of the
| paper in Science [1]. It is called a Bragg Mirror [2], which
| basically seems like a special coating consisting of layers of
| alternating refractive index. I don't know the details but this
| isn't _necessarily_ more exotic than, say, the antireflection
| coatings on eyeglasses or photographic optics. The
| supplementary material states that the mirror is 99.998%
| reflective in the wavelength under study.
|
| [1] https://www.science.org/doi/10.1126/science.abm2543 [2]
| https://en.wikipedia.org/wiki/Distributed_Bragg_reflector
| Filligree wrote:
| What's the difference between photons bouncing in a box, and a
| gas? ...no, really?
|
| There's a lot of them, starting with the fact that gas
| particles have mass, and photons generally don't. However,
| confinement causes mass. The gas particles are in a sense
| confined even when floating free (by other fields), and photons
| are only confined when they bounce off the walls, however-
|
| They do that a lot. As you zoom out, the phenomena start to
| look alike.
| eurasiantiger wrote:
| > confinement causes mass
|
| So the Pythagoreans were on the right track!
| brimble wrote:
| Sure, I'm more hung up on the "just shoot some photons into a
| mirrored box and they'll bounce around forever". That...
| can't _possibly_ be very close to what they actually did,
| right? This is one of those cases in which the description
| that makes it to the public has almost nothing to do with
| what actually happened, surely? Or did they really do that,
| and if so, _how_? It seems like it 'd fail for a hundred
| different reasons. That's more interesting than the
| phenomenon, to me.
|
| I watched the video and nothing they showed looks like a
| mirrored box.
| anon_123g987 wrote:
| A mirror is an object that reflects an image / light /
| photons. There are mirrors with different reflectiveness
| and different construction. In the video the prof says they
| are using a "highly reflective nanostructured mirror", so
| it's obviously not exactly your silvered glass bathroom
| variety mirror, but in principle it's the same: a surface
| that reflects almost all photons, and absorbs or transmits
| almost none.
|
| The box is also not necessarily like your average shoe box,
| I'd guess it's much smaller (millimeters), show it's not
| shown on the video directly, up close.
| kurthr wrote:
| Well, photons are bosons (spin 1 not 1/2) as result they have
| very different statistics. You can get population inversion
| (e.g. a laser or bose condensate) where many of the bosons
| all sit in a single energy level. That's not possible for
| fermions due to the fermi exclusion principal (e.g. electron
| orbital shells).
| nextaccountic wrote:
| > However, confinement causes mass
|
| That's interesting, can you elaborate? Or point to some link
| that discuss this
| ars wrote:
| See also
| https://en.m.wikipedia.org/wiki/Kugelblitz_(astrophysics)
| steviedotboston wrote:
| no they didn't, why would you think that? you must be going crazy
| adamsmith143 wrote:
| Yes they did?
|
| Compressibility and the Equation of State of an Optical Quantum
| Gas in a Box; Science; DOI:
| https://doi.org/10.1126/science.abm2543
| awhow wrote:
| https://en.wikipedia.org/wiki/Gaslighting
| adwn wrote:
| It was a pun on the term "gaslighting". I also didn't get it
| until I read awhow's comment.
| adamsmith143 wrote:
| My face went through my palm.
| nathancahill wrote:
| User died for this joke. Commitment.
| ben_w wrote:
| By a curious coincidence, I've just been listening to _The Black
| Star Passes_ by John W. Campbell, where a gas made of light is
| used as a fuel by Venusians.
| throwawaycities wrote:
| These crazy physicists are going to create a white hole in the
| lab.
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