
The Superfluid Universe - bootload
https://aeon.co/essays/is-dark-matter-subatomic-particles-a-superfluid-or-both
======
effie
> _" It is impossible to be interested in cosmology today without being
> interested in dark matter", says Stefano Liberati_

Mr. Liberati seems to think dark matter is as real and proven as the air we
breathe, but forgot that so far it is only one of ideas proposed to explain
the speeds of visible bodies. I am sure one can study other ideas that do not
depend on the concept of electromagnetically passive matter at all, like
different gravity formula or EM mechanisms. Perhaps he meant to say it is
impossible to get a grant or get attention without being interested in dark
matter, or something like that...

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donlzx
How's it compared to superfluid vacuum theory?

[https://en.wikipedia.org/wiki/Superfluid_vacuum_theory](https://en.wikipedia.org/wiki/Superfluid_vacuum_theory)

~~~
raattgift
They're pretty much entirely unrelated.

In [http://arxiv.org/abs/1507.01019](http://arxiv.org/abs/1507.01019) the
authors lean on research into axions as extensions to the Standard Model and
on Bose Einstein Condensate research in ordinary matter, and proposes a
temperature (~ 1 mK) below which the light axion-like gas condenses into a
superfluid.

It's firmly rooted in General Relativity and is proposed as an ordinary matter
field in the GR sense. The field content feels and generates curvature just
like all the fields in the Standard Model. Its non-removable vacuum background
is the standard four-dimensional smooth connected Lorentzian manifold.

Superfluid vacuum theory (SVT) is a family of emergent gravity theories that
aims to replace General Relativity by proposing that a superfluid with lattice
spacing at Planck scale is part of the non-removable background and the
dynamics of gravitation take place in the superfluid. At low temperatures, and
at low particle energies, the superfluid reproduces GR.

This approach to emergent gravity was tried with non-superfluid fluids
historically, and those attempts failed in the face of detailed study of
objects in our sky that are bright in extreme UV and higher frequencies.

Emergent gravity theories tend to get more complicated (e.g., SVT theories
have variously introduced mechanisms to suppress dissipation effects, and
introduced rotation and/or phase transitions in the background superfluid)
when they have to match recent successes of General Relativity. When you have
to keep making substantial changes to your theory to match observables
predicted using GR a century ago, it's a bad sign.

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tfgg
This is a pretty amazing and compelling idea, it feels odd that no one has
thought of it before - the article mentions some previous models, what were
they?

~~~
selimthegrim
How this article failed to mention Grisha Volovik at all is beyond me. He is
be far the most prominent proponent of this school of thought who isn't a
cosmologist. The obvious problem with all these models is that the condensed
matter theories don't obviously require Lorentz invariance.

[http://www.amazon.com/Universe-Droplet-International-
Monogra...](http://www.amazon.com/Universe-Droplet-International-Monographs-
Physics/dp/0199564841)

~~~
selimthegrim
raattgift's comments earlier are almost certainly more correct than mine. I
didn't read Khoury's paper throughly. My apologies.

------
effie
> _First predicted in 1924 by Einstein and the Indian physicist Satyendra
> Bose, this whole class of ultra-cold superfluids is now known as Bose-
> Einstein condensates._

No, this whole class of ultra-cold superfluids (referring to fluids similar to
superfluid helium) were not "first predicted in 1924", as Mrs. Hosenfelder
erroneously writes.

It is the Bose-Einstein condensate (BEC) that was predicted in 1924, not
superfluids. A Bose–Einstein condensate is a state of matter where dilute gas
of weakly interacting bosons of cold enough temperature turns into condensate,
a different phase of matter.

A superfluid was first discovered in liquid helium in 1937-1938 experimentally
by Kapitza and independently by Allen and Misener. Liquid helium is no weakly
interacting gas, but nevertheless the explanation of its superfluidity in
terms of Bose-Einstein condensate was proposed soon after the discovery. Later
on it turned out that superfluid helium is no ordinary BEC, but needs quite a
different description (interacting particles in liquid). As Balibar writes,

 _" 65 years later, the connection between superfluidity and BEC is still a
matter of debate and study"_

[https://www.researchgate.net/publication/1935151_Looking_bac...](https://www.researchgate.net/publication/1935151_Looking_back_at_superfluid_helium)

See also
[https://www.eng.fsu.edu/~dommelen/quantum/style_a/nt_sfnebec...](https://www.eng.fsu.edu/~dommelen/quantum/style_a/nt_sfnebec.html)

[https://www.physicsforums.com/threads/superfluidity-
helium-3...](https://www.physicsforums.com/threads/superfluidity-helium-3-and-
helium-4.640281/#post-4097603)

There are also other superfluids that are not BEC, like superfluid helium 3.
It is fermionic condensate, not BEC.

I remember from my studies of physics that all this was quite a common
knowledge in the circles of cold temp physics.

I wonder why Mrs. Hossenfelder, a physicist herself, neglects to reflect this
basic knowledge in her article. Perhaps she is now more of a pop-sci blogger
than a scientist?

