Using fluids to model inaccessible realms of the cosmos | Hacker News Reader

Using fluids to model inaccessible realms of the cosmos

quantamagazine.org

97 points_aleph2c_78 comments

Tangentially related:

When I was in uni, I did a brief informal undergrad-level paper on modelling cosmological inflation using superfluid He-4. What I hadn't realised, and perhaps was supposed to discover, was that one of the unis [past] professors, Prof JF Allen, had worked in that field. As I read now I find that he actually was a co-discoverer of superfluid He-4.

The journal Nature describes him as "the last of a generation of independent-minded classical physicists". We knew him as "god" for his mystical presence on campus and his cartoon-God appearance, whispers followed him around the physics lounge. He also taught me QFT, or tried. It wasn't until after I graduated that I learnt the building really was named after him. I do wish that I had known to interview him about this field of modelling [cosmology] using superfluids.

Liquid helium 3 and 4 have been a fertile substrate for this kind of exploration. I often think that the lab scale experiments will figure it out before the ultracolliders.

This 1998 article summarizes the state of the field up to that time. The rotating cryostat they used in the experiments is a masterpiece of instrument design.

https://www.pnas.org/doi/pdf/10.1073/pnas.96.14.7760

"Vortices in rotating superfluid 3 He" by Lounasmaa and Thuneberg

Scroll to the end for

"Superfluid 3 He in Cosmology

The topological objects in the order parameter field of super- fluid 3 He, such as textural point defects, quantized vortex lines, and solitons, are in many respects similar to monopoles, strings, and domain walls in relativistic quantum field theories (3, 4, 23, 24). In high-energy physics these objects are still hypothetical, whereas in the case of superfluid 3 He they can be observed experimentally. Here we discuss just one example: an experiment modeling developments in the early universe. The study (67, 68) involves creation of vortices by absorption of neutrons in rotating superfluid 3 He-B."

Addendum after the edit deadline: G.E. Volovik has an article on the theory behind this at

https://www.pnas.org/doi/epdf/10.1073/pnas.96.11.6042

"Field theory in superfluid 3He: What are the lessons for particle physics, gravity, and high-temperature superconductivity?"

I don't pretend to understand even a fraction of this but Figure 3 is a very nice Dictionary mapping the helium phenomena to the cosmological questions.

Ah, I had the guy who was the master of Helium-3. He had something like seven patents on different applications.

I watched and posted a video about He-4, amazing example of what educational videos should look like. Thank you!

For a highly in-depth look at the theory behind this, I can recommend “The Universe in a Helium Droplet” by Volovik [1].

1. https://academic.oup.com/book/11557

Bit of an aside, but:

> But physicists seek the more fundamental, quantum theory of gravity that underlies Einstein’s picture; it’s this quantum gravity theory that governs extremes like the Big Bang and black holes. And one way to inch toward this complete theory is to study quantum fluctuations in the space-time fabric.

I'm uncomfortable with the implicit framing that quantum gravity is The One True Theory and we just need to figure out how to formalize it. I'm sure this comes from the author and not the researcher, maybe something was lost in translation from the technical to the colloquial, but nonetheless it is still inaccurate to say that there is any kind of certainty that this is the right path forward. (Ditto for dark matter and dark energy, though those could more accurately be described as lacks of models than models per se.)

My understanding is that quantum gravity is a gaping hole in our theoretical understanding of the universe, and until that hole is plugged, we have no hopes of finding a One True Theory. That's quite different from quantum gravity being The theory.

What I was trying to get at is that gravity may not even be quantized. The insistence that it act like the other three fundamental forces is a holdover from earlier interpretations of physics but in retrospect there's still no solid reason to assume it has to be quantum at all.

What other approaches are there that wouldn't lead to a quantum theory of gravity?

There is more focus of late on theories of "emergent gravity", i.e., that gravity is not a fundamental force. The most interesting one to me is so-called "entropic gravity", which also resolves the issues plaguing the theory of dark matter and gives credence to MOND. Such theories have been long derided by old-school physicists raised in the golden era of quantum mechanics (and their acolytes), but have surprisingly powerful explanatory power that other theories cannot achieve without tacking on seemingly arbitrary or else otherwise unmotivated factors. Dark matter especially has always been suspect to me, since even after all this time, it is defined as little more than "the gap between our models and observations" with no strong underpinnings that would explain its existence in satisfying ways.

I am not affiliated with this blog in any way but find the arguments compelling: https://tritonstation.com/

Here's an interview with a researcher who is also trying to move beyond quantum formalisms for spacetime vis a vis gravity: https://www.quantamagazine.org/the-physicist-who-bets-that-g...

I like this idea. You need bets like this to discover things, not everyone working on the same thing.

Certainly it's a lot easier than trying to cultivate a real black hole in your lab.

Well I was thinking looking through telescopes and developing theories as the alternatives!

>"...she has detected sound waves in fluids that resemble Hawking radiation..."

[...]

"If the wave isn’t too tall, then this wave doesn’t interact with other waves of different frequencies — you can try this in the bathtub.

But if the amplitude gets high, then the different frequencies interact."

Fascinating!

Sixty Symbols did a video with Dr.Weinfurtner. Surprised it wasn't posted already!

https://www.youtube.com/watch?v=kOnoYQchHFw

"The Black Hole Machine"

Imagine a material capable to reflect gravity waves, amplifying it, creating a standing wave. A blackhole without mass, regarding the effects..

Couldn't these experiments be done using computer simulations?

Sure, you can also say we start with the ZFC axioms. QED.

Calculations provide predictions, experiments provide verification.

I mean, computational fluid dynamics is pretty mature now.

And if for some reason it doesn't work here, then that would be nice to know.

Besides, the experiments themselves are simulations.

I just spoke with an YC company. The CFD needed for their applications doesn't scale. There are plenty of reasons for experiments.

CFD is actually really hard to get right.

F1 teams for example constantly struggle getting their simulations to line up with their measurements.

I took a bunch of mushrooms and had the same idea, but when I pitched it to my freshman Physics professor, he told me I should "take more physics."

I thought he was insulting me, but apparently I would have made a decent physicist.

This is like saying everyone who tripped on acid and ranted about mind body connection and oneness to the universe is now competition to Peter Singer. Coming up with the idea is only a small part of the problem. Actually pursuing it with rigor is another.

Your professor also told you to take more physics, so he did in fact suggest you could be a decent physicist?

in my experience, the rigorous pursuit feels like a hamster wheel

the real problem is that it moves very fast, so when I've tried jumping into this "wheel", I find it impossible to hold on on to it. I always fly out due to centrifugal forces

That only suggests you were reaching further than your grasp. To stretch the metaphore, knowledge is the strength of one's grasp and the edge of the wheel is the hardest to hold on to. Most start further in, where things are known and easier to grasp - gradually making their way to the edge over a decade(s) long journey. This goes for nearly all research fields.

Ideas are cheap and typically wrong. Proof is the only thing that matters. I am certain some human has already stated the right idea to unify QM and GR, but so what?

One of my favourite things about SerenityOS is that the community all but bans "idea guys" for this very reason

I was going to mention centripetal force here but decided to do some research first: https://physics.stackexchange.com/questions/109500/does-cent...

Turns out that centrifugal force "does exist" in side the rotating reference frame. As if, your looking down on the object rotating around a center, the only force there is centripetal pointing in and Inertia pointing tangent to the circle. However if you enter the reference frame of the object being flung around you lose the inertia term since your already the center of the system and then need a centrifugal term to make up for that.

So in reference to _being_ on a hamster wheel, the outward sensation could be attributed to a centrifugal apparent force.

There is a chasm of difference between taking some shrooms and testing a black hole analogue.

Even if this is supposed to be a joke, I don't get the connection between physics and drugs that the joke implies

There's a few instances in science where ideas were borne after the researcher took drugs. A good example is PCR assay.

> Mullis has credited his use of LSD as integral to his development of PCR: "Would I have invented PCR if I hadn't taken LSD? I seriously doubt it. I could sit on a DNA molecule and watch the polymers go by. I learnt that partly on psychedelic drugs."[86]

https://en.m.wikipedia.org/wiki/Polymerase_chain_reaction#Hi...

While I'm open to the idea that breakthroughs can come from unorthodox places, I don't think that Mullis is the best example. My highschool biology teacher had some negative opinions about the guy and claimed that it was an open secret that you do not invite him to speak at events, noble price not withstanding.

So, I looked him up. If anything my biology teacher was being polite.

https://en.wikipedia.org/wiki/Kary_Mullis#Views_on_HIV/AIDS_...

https://alumni.berkeley.edu/california-magazine/winter-2019/...

EDIT: My opinion is that this is a case of a broken clock being right twice a day. The second article talks about his PCR breakthrough. It sounds like he was clever and lucky. But based on what else he seemed to have believed, I really don't think we should take his word on the LSD being the key.

I agree he's a terrible person but it is a good example of where drugs helped in discovery. The key point IMO is that he may not have discovered or invented PCR without drugs. But PCR would have been invented one way or another.

On a separate note, I find your main argument not at all helpful to the current thread. Terrible people can create and do amazing things. But it's still an a good example.

Many more ideas in science have been discovered sober than on drugs. In fact I would probably say it's one of the disciplines with the least drug use in my own experience. That's why I'm confused about what the connection is. I'm a physicist and I know very few colleagues who take drugs.

EDIT: honestly, looking at the user's other comment doesn't fill me with confidence https://news.ycombinator.com/item?id=36756514

I don't know, man. The last time they tested my IQ, they wanted me to come back and take the test again, because I was "out of bounds" for the test they gave me. My parents refused, because none of us cared enough to spend another $800.

And I took a _lot_ of shrooms.

Unfortunately, I majored in Philosophy. So, I'll never find the right answer to life's great mysteries. I did get fairly good at pointing out the wrong ones, though.

IQ is totally irrelevant to this discussion

The point is that some ideas may never be discovered without the use of mind expanding drugs, and some notable discoveries in physics have come from the use of mind expanding drugs, and possibly more than in other disciplines, so there is a notable link, if even in jest, between physicists and mind expanding drug use.

Yes but you can say this about literally any idea in any field ever. Surely arts and music have a much stronger connection with drugs than physics? In fact, we are on Hacker News, so surely software development has a far stronger connection. I'm just failing to see how physics is in any way especially connected to drugs compared to pretty much any other human activity. In fact, it seems almost the bottom of the list to me

> Yes but you can say this about literally any idea in any field ever.

Great! That's why it's fun to say.

I do find the prospect of scientists using a bit more amusing than the average employee, however, as the public expects them to be holy.

In mathematics, there is a certain prestige in having a low Erdős number. Paul Erdős was famous for his (ab)use of amphetamines. The role which stimulants played in the sheer volume of papers he published over his life is up for debate.

"You shouldn't have mentioned the stuff about Benzedrine. It's not that you got it wrong. It's just that I don't want kids who are thinking about going into mathematics to think that they have to take drugs to succeed."

-Paul Erdős responding to the author of a 1987 Atlantic Monthly article profiling his work (as well as his use of benzedrine).

I agree 100%. I should have mentioned this in. My first post.

black holes - I've seen a few

cosmic wonders that leave me askew

they gobble up matter with voracious delight

sucking everything in, day or night

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