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Comment by mmastrac | Hacker News Reader

This is an extremely useful summarization of the original paper.

> The authors believe that the modified/strained structure of their material creates a large number of “quantum wells” between particular lead atoms and the adjacent oxygens of the phosphate groups bound to them, in effect making a two-dimensional “electron gas”. They propose that electron tunneling between these quantum wells, which are between 3.7 and 6.5 Ångstroms apart, is the superconducting mechanism. I am not enough of a solid-state physicist to judge this proposal, but the authors are making a detailed mechanistic claim that is subject to experimental proof, which is very good to see, and and they adduce a good deal of data to back it up (x-ray diffraction, EPR, and more). And they demonstrate the behaviors that a superconductor should have, such as the Meissner effect (expulsion of a magnetic field), sudden resistivity changes at a critical temperature (bizarrely high though that is in this case), current-voltage (I-V) plots at different temperatures and under different magnetic field strengths, etc. If these data reproduce, the superconductivity of this material seems beyond doubt.

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I don't think the actual proposed superconductivity mechanism is the relevant part of this paper. It is much easier to prove that this is superconducting than to prove why. And in a sense it is a bit less relevant. Although developing a working theory for room temperature is also probably worth a Nobel prize, so I am willing to bet some theorists are also running to their blackboards as we speak.

Yeah. BCS was proposed a half century after the first conventional superconductor was discovered, and even today we don't have a convincing mechanism for "regular" high-Tc superconductors. But if it superconducts, it superconducts, and research into the how is useful but not a blocker to using it.

That depends. If it super conducts, but it isn't useful in the real world, then we will be waiting for theory to - hopefully - give us some insight into how to improve things to useful.

This only can carry a small amount of current. I'm not sure how to figure out what small means (numbers are given in the article if you know how to use them!), but if the losses using regular wire are less than the energy needed to make this stuff then it isn't useful.

This is made out of lead. Even if it is useful for transmission, the difficulty of working safely with lead in a factory may mean it is impractical. Or it make leach lead into the real world making it not safe to deploy.

There are probably other ways this can turn into a "it works but isn't practical" thing that would force us to wait for theory (or luck!) to point to something better. What I wrote above is what I can think of in a couple minutes. Only time will tell though, I hope it works out.

> If it super conducts, but it isn't useful in the real world, then we will be waiting for theory to - hopefully - give us some insight into how to improve things to useful. This only can carry a small amount of current.

Thank you for this.

> This is made out of lead. Even if it is useful for transmission, the difficulty of working safely with lead in a factory may mean it is impractical.

Have you been to a hardware store lately? A huge amount of pipe fittings for gas and non-potable water are made from lead. Factories don’t find it hard to work with lead. It might be inadvisable but it’s not hard.

We can argue about the "working safely" part, but in terms of "does this make it impractical?" the answer seems to be no under the current global regulatory environment.

> This is made out of lead. Even if it is useful for transmission, the difficulty of working safely with lead in a factory may mean it is impractical. Or it make leach lead into the real world making it not safe to deploy.

Lead is still routinely used in many applications today, either in metallic form, from ICE car batteries, to fishing or hunting gear, or as chemical compound in different kinds of glass. And the same can be said about other heavy metals like Cadmium or Mercury. Industries also routinely work with much more nasty things than lead, so it really doesn't sound like a show-stopper.

In particular, lead is still extremely common in radiation shielding, possibly because the drop in demand for other applications made it so cheap. Lead-lined drywall is the default approach for setting up a radiography, fluoroscopy or CT suite.

> possibly because the drop in demand for other applications made it so cheap

Maybe a little bit. But I think it is more that it is a material with heavy atomic nuclei and high density, and thus effective at blocking radiation. And it is also relatively cheap.

Lead is absurdly cheap. One dollar a pound! Cheaper than much more common metals like aluminum or magnesium. So I diagnose a low demand.

They used to talk about using barium cement but it just can't compete, price-wise.

I believe that most of the lead used today is a by-product or co-product of mining other more valuable metals like Zinc and silver. Lead is quite abundant in the Earth's crust and found in easy to access deposits.

I think >80% of the current industrial use of lead is for batteries. It's probably still in the top ten most mined metals by dollar value and definitely by mass.

The mineral containing Zinc is called Sphalerite, which is based on a greek etymology for "deciever" because it commonly occurs with Galena (which has Lead and Silver) and looks similar.

It may not come as a complete surprise that the economics of metals are more complex.

Aluminium, was so expensive until the Hall/(that other guy) process was developed, that it was used for jewellery [1].

Even today it's expensive and difficult to reduce Al ore to metal, which is a supply side problem.

[1]https://www.bellandbird.com/products/aluminum-bangle

75% of aluminium supply is from recycling aluminium products.

The economy sort of has a "working capital" quantum of aluminium which also grows steadily from aluminium mining.

Lots of metals have very different and complex supply structures and thus completely different $$$ / volume curves for their supply.

Understanding the $$$ / volume curve of commodities is not something that is commonly considered when people try and predict the future. Mining a billion tonnes of Aluminium from an asteroid for example and safely landing it on Earth can never be profitable because the $$$ / volume curve for Aluminium is $0.00 at billion tonne volume.

Now I'm curious where that recycled aluminium is coming from? My guess would be mostly from airplanes and beverage cans...

Engine blocks too. If you go to a scrap yard though you’ll be pretty amazed at all of the stuff they’ve got collected and sorted. Metal recycling (compared to, say, electronics recycling or plastic recycling) has a very clear economic model and financial incentives. If you’re demolishing a building or scrapping old machinery it will cost significantly less to recycle the metal (because you get paid decently by the pound) than to take it to a landfill (where you pay by the pound instead).

Cars too

TIL! Aluminium is an extremely useful metal, but I would never have thought it would be used for jewelry - I mean, it's not enough for the metal to be expensive, it also has to look and feel desirable, which soft and dull Aluminium definitely doesn't. If you have ever held Aluminium cutlery in your hand, it just feels cheap compared to stainless steel (not to mention silver).

Today it isn't used for jewelry. 200 years ago it was - not so much to wear, but to show off that you were rich enough to afford it. Only royalty could afford things made out of aluminum.

As a young fella, I carried a lot of that lead-lined drywall, it's (obviously) really heavy, and expensive so you got yelled at a lot if you damaged the edges, couldn't just trim it off like normal drywall.

Unfortunately, most companies seem to have little compunction about exposing workers, consumers, or the environment to toxic materials. The use of lead is not in any way a blocker, for better or worse.

It seems a 50/50 situation so long as the lead is able to get the products most companies don't seem to bother a lot about the risks of this exposure

250 milliamps still sounds great for use in antennas.

Ding ding ding! We still don't know how bikes work, we have a pretty good but incomplete model for lift on airplanes, and no one has the faintest why Tylenol works.

We should figure that out! But we can definitely keep using all the applications until then. (Except for Tylenol, we keep learning how bad that stuff is)

EDIT: It won't let me post more, so here's the answers to responses.

For sure!

https://www.cbc.ca/news/science/science-of-cycling-still-mys...

http://www3.eng.cam.ac.uk/~hemh1/gyrobike.htm

https://www.newscientist.com/article/mg22730370-400-how-does...

It's a fun little fact. We know a ton about BUILDING bikes, which is a more useful tool anyway

Do you have a link handy for "we don't know how bikes work" ?

I'm assuming they mean the balance mechanism, and specifically what allows us to balance. How much is it the rider shifting their weight, how much is micro steering adjusts as we move forward, how much is the gyroscopic forces of the wheels, how much of it has to do with the angle of the handle bars to the wheel verse the center of weight.

That said, I'm guessing this one is well understood by experts, but more complex than someone would assume at first glance, and many who have some understanding likely have an incorrect or at least incomplete understanding of how balancing works.

I wonder what learning the specific system by which bikes are balanced would teach us about the world or human beings?

It's such a banal thing to be so fascinating.

We don't know until we know.

The smart phone is the culmination of understanding a million facts about materials sciences (applied and theoretical), some of which were obvious, some of which were non-obvious. Starting from a transistor you could see from across the room down to ones you can't even see with a magnifying glass.

It's the reason I got a degree in physics, if you have good professors - discussions like this cause you to break down the problem quite quickly in your head in a working model. Think force diagrams, but with a ton more math backing it up.

I actually find the ice skate a better example than a bike. We have all the physics solved for bikes, it's a complicated system but so is everything in motion. Hence we assume a spherical cow for the sake of the problem.

But ice skates... Now that's a funky one. Why do ice skates works? Ice skates aren't sharp bladed, they actually have flats. Ice is not slippery, it's when something is on ice in between our shoes and the ice that cause it to be slippery. Some people think it's the localized pressure of the blade that causes ice to locally melt. Hard to really wrap your head around. But it works :)

Ice skates aren't sharp bladed

Not sure how you meant that, but ice skates are sharp. Each edge of the blade is sharpened by grinding a hollow out of the center.

https://weekendwarriorshockey.com/how-sharp-should-my-skates...

I thought it was not just about ice skating but the question of why is ice very slippery is the hard part to explain.

>We have all the physics solved for bikes, it's a complicated system but so is everything in motion. Hence we assume a spherical cow for the sake of the problem.

This depends upon the question one is trying to answer. If one is trying to create a bicycle that can self balance, that involves considering different factors compared to trying to determine why certain injuries result in a person losing the ability to balance on a bicycle while others do not. Is the focus the bicycle or the human?

We have self-balancing bicycles. We clearly know it well enough to replace the human with a computerized machine.

Maybe we don’t know how humans use the bicycle but we know how bicycles balance, we can write programs to balance them physically.

0: https://youtu.be/Ya7iacmVjUM

1: https://youtu.be/2Z67NkvXIF4

You are correct, a lot of forces are canceling out on the long term(instead of instantaneously) it can easily be manipulated into increasing periods of unbalance in one direction until a point is reached then a separate mechanism is used to force it to a balanced state. Conservation of energy is always in effect. Gyroscope effects that bike wheels can be added with other separate gyroscopes. Thus, a self righting bike. The effect called precession is understood well enough.

How a human is able to manipulate it is simply by using the force of gravity from shifting their weight(moving the center of gravity). However, the movement of the center of gravity has to be perpendicular to the wheels axle. The steeper the angle of attack the wheel has to the ground, there will need to be an exponential increase in distance to move the center of gravity. Once the wheel is parallel to the ground, there will be an undefined distance needed to move the center of gravity.

e.g. What keeps bicycles balanced with or without a rider is still an active area of research, and even the seemingly basic idea that, for a bicycle to be self-stable, it needs to turn the handlebars into the fall, has not yet been proven.

[*]https://ciechanow.ski/bicycle/

"Active area of research" is quite different to "we don't know how they work".

We know how they work. We might not have fully characterised the stability conditions, but that's not the same thing.

Cmon, man

You can write out the equations of motion for a bicycle that will very accurately predict the dynamics. You can put these equations into a numerical simulation and predict motion very accurately. You can change the parameters of the model and do simulations with high confidence. Just because there isn't some neat little equation that says exactly what each parameter change is going to do (without doing the simulation) doesn't mean that we don't understand bicycle physics. It's a silly line of reasoning. Those articles are hyperbolic.

You are contradicting yourself:

> You can write out the equations of motion for a bicycle

> there isn't some neat little equation that says exactly what each parameter change is going to do

I mean, if you have the equations you can see what each parameter is doing !

Algebraic versus differential if that wasn't clear

Something smaller than may help you grasp this idea: https://www.youtube.com/watch?v=5nW3nJhBHL0

There are things we can characterize to any desired degree of accuracy but that e don't get cute little equations out of... and some of those things are so simple they've been staring you in the face since middle school and you just didn't ever notice their absence from your formula sheets.

This is not the exact same situation being described but it's a similar thing. Being able to put a complex system into a computer and arbitrarily manipulate it still doesn't mean we can extract some simple explanation.

On the other end of the scale, see all the AIs coming out. They're 100% computer artifacts with theoretically no mystery in them whatsoever... but they're just tables of billions of opaque numbers and doing anything with the numbers beyond just running them is amazingly difficult.

I think their point still stands, even if "we don't know how bikes work" is a flowery exaggeration.

But then we don't know how anything works...

Yet we still have Insane Clown Posse refrigerator magnets.

https://www.insaneclownpossemerch.com/collections/insane-clo...

Scientists Try To Teach ICP Fans How Fucking Magnets Work

https://metalinjection.net/av/scientists-teach-icp-fans-fuck...

But their point is we don't need a 100% complete scientific understanding of something in order to engineer it into something cool or useful.

That is true, but it's still incorrect to say we don't understand how bicycles work.

As a bit of an aside, most people don't know how bicycle wheels work. There's a whole section in https://en.wikipedia.org/wiki/The_Bicycle_Wheel that talks about how they actually work. It's not tension at the top, it's compression on the bottom.

what do you mean it's not tension at the top? did you misspeak? bicycle spokes are solely under tensile forces. they can't support compressive forces at all. i'm a hobbyist wheel builder and a once upon a time professional bicycle mechanic during hs & college.

if you want to test this take nearly all the pretension out of your spokes and sit on your bike. feel which ones are taught and which ones are completely loose. or just go to walmart. those bikes hardly have any pretension in their wheels.

They even make spokes that are rope

https://berdspokes.com/pages/technology

I wonder if those have less or more breakin issues compared to spokes. With a spoke you have to reset the angle of the bend to the shortest distance between the hub and the rim. But with cables they have to settle in along their entire length.

Doesn’t change the answer. They’re still compressing. They’re just pretensioned.

you sound highly confused, what is compressing? the rim? the spoke?

You need to reread Brandt.

There are two situations when you can push on a string. One is when it’s frozen, and the other when it’s tensioned. How do you unload a bow string? You push it off the notches.

bro. you're wrong. just build a bicycle wheel some time. it becomes very obvious how they work as you take it through the various stages of tensioning.

Why do you think someone would talk about Brandt’s work if they hadn’t used it?

I’ve built more than half a dozen bicycle wheels. My set, my spare that my brother road (into the ground - my first set and practically the only problematic ones, but he road over bumps without getting out of the saddle), a set my dad commissioned from me, and a pair that he had me build for a friend. All by age 17.

I then worked as a mechanic for two summers of college. I was never the fastest, but if we had a customer we could not afford to disappoint, I or the senior mechanic got the job because my repairs did not come back.

I saved three or four wheels that would have been scrap by unwinding the spokes halfway and building it back up again like a wheel build. Only added an extra ten or fifteen minutes but it works a charm. When a good customer comes in on Wednesday before an out of town bike ride you can’t afford to fuck it up. I think I only built a couple professionally, and usually singles. That’s a lot of labor and few will pay.

There's a lot more creep early on, which is compensated for by a staged tensioning over the course of a few days. They may require the spoke holes in the hub to be radiused, which can be a warranty issue between you and the hub manufacturer. Windup is controlled by a flat on the small bit of spoke used for threads.

They're ok (i.e., made it through Tour Divide with no issues), done well they're certainly better than badly done steel spokes, but it's not clear if the best builds are better than the best steel builds.

That book I linked has another name, “the wheel building bible”. Jobst Brandt earned an obituary in Bicycling magazine including quotes from his friend Tom Ritchey (one of the original mountain bike makers). Jobst was a bike fanatic and a mechanical engineer.

Bike spokes are not loose, they’re under substantial tension. Bolts, I just learned a couple weeks ago, work in the opposite way. A tightened bolt compresses the two pieces of metal together, and when you tug on them, the bolt doesn’t stretch more. The tension instead first cancels out some of the compressive force on the two pieces of metal, before the bolt ever feels more load.

Conversely, all the spokes on the wheel are under tension. When you put the wheel on a surface and push down, the compression cancels out some of the tension on the bottom of the wheel. Cancel out all of the tension, and the wheel turns into a potato chip if you don’t reload it exactly, perfectly on axis. IIRC, none of the prior models or theories for how a spoked wheel works could adequately explain how potato chipping happens. His does.

I used his book to build half a dozen wheels or so and the information it contained to fix many more.

i own the book.. and also The Art of Wheelbuilding - Gerd Schraner

of course in a properly built wheel usually all the spoke are under tension...

i was just demonstrating the fact that the spokes on the upper half of the wheel are supporting the hub and are under greater tension than the bottom ones, the spokes on the bottom half of the wheel should remain in tension, but only through the fact that they are already under tension applied during the building of the wheel.

the fact that the wheel works by tension of the spokes becomes obviously apparent when you start to remove the pretension and then the spokes will feel loose on the bottom half. of course you'd never want to ride a wheel like that because it will quickly become out of true.. just like a walmart wheel.

I think one of us needs to reread that book, because he emphatically denies that tension at the top of the wheel increases. It’s tension at the bottom that decreases.

> of course in a properly built wheel usually all the spoke are under tension...

No, a properly built wheel all of the spokes are always under enough tension you can bounce a penny off them. Always.

no. you're assuming the rim has no deflection which is untrue. if you build a rim out of schedule 80 steel pipe then yea. but 300-400-500g rims on high performance bikes do not act like that. the spokes are constantly loading and unloading tension as they bash through rocks and over jumps. the point is that the pretension on the wheel needs to be high enough the spokes do not loosen too much under these forces. if they do in fact loosen too much the nipples will begin to loosen and unwind and the wheel will become out of balance.

I’m not assuming the rim has no deflection. What makes you think that.

Anyway, this sums it up pretty well. Someone has a longer memory than I:

https://news.ycombinator.com/item?id=36891231

If you’re talking about twisted spokes unwinding, you don’t have to reach zero load for that to happen. You just need to reduce the load enough so the rotational force overcomes friction. Tension will also try to unwind a screw as well. But the thread pitch on spokes is very fine, which lessens that force. If you build spokes like wood screws we would have problems and that has nothing to do with reaching 0 newtons.

You can release a lot of those tensions by squeezing the spokes mid build. Just don’t wait until they’re too tight to do it. I had a pulse in my rear wheel that probably came from doing that wrong the first time. Unless it was a factory defect, I must have overtensioned and warped a brand new Mavic aero rim ever so slightly. Expensive lesson, but it could have been worse.

This dialogue is reminiscent of rec.bycycles.tech arguments with Jobst, ca 1993.

A bike wheel is a linear elastic system, that can be thought of as a superposition of a uniformly set of tensioned spokes as one state, and a set of spokes in compression in the loaded zone (bottom of the wheel) as the other state. So long as the superposition of the two states obeys the limiting conditions (i.e. spokes in tension) they can be analysed separately.

The size of the loaded zone is related to the relative stiffness of the spokes (axial) and the rim (bending), and can be calculated using beam on elastic foundation methods. For typical rim/spoke combinations, this is approximately 4 spokes.

Outside of the loaded zone, spoke tensions essentially don’t change.

And thread. Thereby proving my point: Almost nobody knows how bicycle wheels actually work.

Well. I wish we could sit in front of a bicycle wheel and discuss it. Because I have a feeling we are shooting arrows at different targets. As a mountain biker I'm more interested in what happens when an extreme amount of load is applied to the wheel, not the model with assumptions applied. Definitely a difficult concept to discuss with only text. Anyways.. glad to have a good discussion with you about bicycle wheels. Don't find many people like you. :)

I think I would have been a mechanical engineer if I were born 20 years earlier or 20 years later. Software was just new and shiny enough and it let me build things with my mind, at a time when I believed I was clumsy (I actually have always had excellent fine motor skills, it's macro motor control I lagged behind in). One of my better friends in college was an ME. Learned all sorts of things about metal fatigue and oddly enough picosecond lasers from him.

I don't know if I found Lego or Lego found me, but I definitely think in terms of shapes. I was past my midlife crisis before I realized that I don't have a large working memory (smaller than average in fact) it's just that I've been doing mind palaces without pictures since I was very small. When I'm thinking of large computer systems I'm essentially thinking of them as physics problems.

I really should figure out space to have a bike again. I never rode when I lived in Seattle (Seattle drivers are nuts) but I don't live there anymore and I need to catch up on 20 years of tech.

I think you're both in violent agreement using different terms.

You're looking at the macro "It's all in tension" (superposition of two states) and hinkley is looking at the "bottom is a compressive change" (dynamic portion of the load).

What I'm not clear of is if you think that the upper spokes change tension between the unloaded case and the plain gravity load case (force on hub down, ground on rim up at the bottom), or if you expect the top half spokes to increase and the bottom half to decrease in tension. I think this is what hinkley thinks you think.

That was indeed my interpretation of that half of the conversation. That they were claiming that the axle is suspended (tension increases with downforce) by the spokes above the midline of the circle, which is what Brandt vehemently contended was false.

Nah they both understand it. One of them is just arguing to show off.

The real winner will be who comes up with application for LK-99 to improve bicycles

Electric bicycles baby.

Hey do you happen to recall, did Brandt prove this theory with a tensiometer or did I just hallucinate that?

Pretty sure he did, but I don't have r.b.t. archives. He was definitely a proponent of them, preferred a specific brand/style, and would have easily been able to do the experiment.

Not to appeal to authority, but I wrote my thesis on bicycle wheels. You got it the wrong way around.

And have you read Brandt’s work?

https://news.ycombinator.com/item?id=36891231

The world is full of papers that are wrong. Including maybe the one this whole thread is about. It’s okay, it happens. Science doesn’t find right or wrong, though a lot of people think so. It finds more wrong and less wrong.

Yeah, that's complete crap. Bike dynamics is well researched and the instability and stability mechanisms are numerous but well understood.

Nonsense. There's nothing incomplete about our model for lift on airplanes.

Oh really, so why do the Navier-Stokes equations work?

Conservation of momentum?

There's no a priori reason conservation of momentum would apply; for that matter in 0-angle-of-attack aviation it doesn't.

Maybe to put it differently, the "Newtonian" model of flight comes out of assuming CoM applies, which we know isn't universally true.

EDITING: of course it always "applies" in the sense that there is a definable system in which total momentum will be unchanged, the point being that there is no guarantee that's a system in which the plane gets lift greater than its weight

A symmetrical airfoil at zero angle of attack doesn't generate lift because it doesn't turn the fluid. A non symmetrical airfoil will generate lift even at zero AOA because air has viscosity and the lack of symmetry causes it to turn around the shape. When you bend fluid flow, COM comes into play.

If you're asking how to apply the Navier-Stokes equations: apply boundary conditions

If you're asking how to derive the Navier-Stokes equations, use continuum / conservation principles.

We don't know how photosynthesis works but we know a ton about GROWING things. And life as we know it depends on photosynthesis.

I thought we had a pretty good understanding of this up until the molecular and electron level.

Am I missing something?

My daughter did her research in this field while an undergrad, and explained to me that photosynthesis is not yet well understood. Some of the theories of the mechanism are discussed here: https://physicsworld.com/a/is-photosynthesis-quantum-ish/

How photosynthesis works at a cell machinery level is high school level biology.

That's not an understanding of how it works

I disagree. It very much is an understanding of how photosynthesis works, it isn't a complete understanding sure, but an understanding nonetheless.

Unless you're going to argue that we don't know how an MRI works because we don't fully understand the physics behind superconductivity.

Do we know whether the mechanism was proposed before or after observing the results? If they found the material because of the theory, then I think it's very relevant.

Someone who speaks Korean may have to go through the original paper. It is LK-99 though; I wonder if they tried 99 other combinations first!

No,

Lee and Kim first discovered the material in 1999 and have spent 20 years doing other things in between getting help to figure out how to isolate LK-99 and reproduce the correct grain structure.

They eventually got a world class physical chemist, Kwon.

There is now a huge bust up within the team, hence the muddled race to publish and claim credit.

Ahh that makes sense. I was wondering what was going on with the two papers and thought it might be something like that too. Thanks for the extra details.

Somewhat similar compounds are superconductors, so it's possible that a wrong theory gave them a lucky hint to modify an old superconductor into the new superconductor.

They made a synthetic a priori prediction proven by experiment. In science, that's the strongest type of claim.

You might also say it's the only type of claim science recognizes. Though, whatever or how strong a claim is, the question is how important is what is proven and will it lead to real superconductive materials.

The strongest type of claim is when an a priori claim is called absurd, someone goes to make observations to disprove it and comes back convinced of your theory.

> I don't think the actual proposed superconductivity mechanism is the relevant part of this paper.

Plus even if the proposed-mechanism is incorrect and even if the effect is not strong enough for practical engineering... There's value in a "real" (if weak) superconductor which is both easy to fabricate and easy to run tests on.

It could become a starting-point for dozens of other tweaked formulations, enabling all sorts of not-so-expensive experiments and fresh data about how different parameters lead to different electromagnetic outcomes.

I’m not entirely sure that’s true. A posit in the paper is this is a novel super conducting mechanism and as such if the mechanism is true it’s totally unexplored. That leaves open a huge field of new research. That’s certainly a relevant part of the paper. Super conductivity at room temperature is an amazing breakthrough alone, but if it was with a clever tweak with an existing well established technique that would be the end of the story. The fact it’s an entirely new technique opens a world unexplored and indicates a pathway to even more amazing discoveries to be had (and funding for entire generations of physicists).

Right. The mechanism itself seems extraordinary. And it seems like that mechanism is exactly the "why", the commenter is claiming is more important.

Moreover, you can have more than one thing about a paper be the "relevant" thing.

>I don't think the actual proposed superconductivity mechanism is the relevant part of this paper. It is much easier to prove that this is superconducting than to prove why.

As another commenter has pointed out, the proposal of a new mechanism seems to be extraordinary and novel, and could lead to an explosion of new research, so it does indeed seem to be "relevant" on its merits.

I also don't see this as a case of the "why" being left unexplained. In the history of superconducting it has indeed been the case that new cocktails have led to superconductivity without the underlying why being understood. But the commenter that you're responding to quotes part of the paper that shows an awfully specific mechanism.

I understand the sense in which there can be a "why" that remains to be explained in certain circumstances, even when you have a mechanism. Who do monarch butterflies have the black and orange pattern on their wings? There's a cause and effect answer but there's also a "why" answer. But with superconductivity, the mechanism is the why, unless I'm misunderstanding here. If other forms of superconductivity rely on other mechanisms, there isn't going to be a general why connecting this case to the other cases, but nor is there anything left unexplained just by explaining the "why" of this case by explaining it's extraordinary mechanism.

> They propose that electron tunneling between these quantum wells, which are between 3.7 and 6.5 Ångstroms apart, is the superconducting mechanism.

That is a very strange explanation. As someone who has done a decent amount of solid-state physics work, I would expect the explanation to involve a mechanism for pairing of electrons. Mere tunneling between quantum wells has been a staple since the "metamaterials" of the 80s and 90s.

That said, the measured curves do not lie, and I haven't kept up with the field. So I'm all ears (and very much hoping the superconducting revolution is upon us!)

Are you referring to a Cooper pair?

Yeah, that’s the generally used explanation for superconductivity

Would it be accurate to describe it as "lattice peristalsis"?

That’s sort of the proposed mechanism for Cooper pairs forming, but I don’t think I’d call Cooper pairs themselves “lattice peristalsis”

Totally agree. This is science at it's best, with maximum skepticism (and a dash of hope), in front of our eyes!

Even better, it's a HUGE claim that is going to show how epistemology in science works (reproduction!!)

I want ONE breakthrough like this in my lifetime. Something completely game changing.

Live to see SPARC turn on, there are some pretty smart people with models actually showing it breaking Q>3. Turns out the hardest part about productive fusion is the sustained high compression, and HTC tape really helps increase the compression by a large amount. (See their 20 Tesla test at the start of the pandemic)

Just want to mention for others: The first result for SPARC on google is SPARC (Scalable Processor Architecture), whereas SPARC (tokamak) [1] is what relates to Q>3.

[1]: https://en.wikipedia.org/wiki/SPARC_(tokamak)

Neutron damage is the real filter for fusion.

It would be great though if they stopped sponsoring the war in Ukraine. Yes it's unfortunate that their main HTS tape supplier is Russian, but pretending that it's not and just ignoring the issue (or obscuring the supply chain through that Japanese middleman) is pretty immoral.

Meanwhile as someone who had to deal with writing code for Solaris and using Sun's compiler, I think I've achieved my goal by seeing my last SPARC turn _off_!

But yeah, nuclear fusion is cool.

> sudden resistivity changes at a critical temperature (bizarrely high though that is in this case)

How high? Just wondering if it might eventually be possible to use it in some power/clocking distribution layers of a semiconductor chip without bulky cooling.

127C!

That's a good idea. Honestly, I find it pretty amazing that modern CPUs don't just instantly turn into a puddle of molten metal as soon as you turn them on.

The critical temperature is 127 C, as the other commenter mentioned. That seems like it's high enough to be useful in a computer CPU.

I suppose there might also be applications for power distribution in a data center. You might use a few large, high-efficiency low voltage DC power supplies to supply the whole site instead of hundreds or thousands of individual power supplies if electrical resistance in cables was less of an issue. (I think this sort of thing is done now, but more at the rack level, since long cable runs cause losses.) You might even use 1V power instead of 5V or 12V.

(Granted, superconducting materials don't have unlimited current capacity, and bad things happen if you exceed the limit.)

The critical temperature is not 127 C. They did not actually measure the critical temperature. They just said it's at least 400 K (~127 C), probably because that was the maximum temperature the equipment they used could measure.

> Just wondering if it might eventually be possible to use it in some power/clocking distribution layers of a semiconductor chip

There's an additional obstacle factor here which is that the material has to (a) be "sputterable" onto the surface, which may rule out things with fancy crystal requirements, and (b) not adversely react with the rest of the chip, which is why coppper is ruled out (!) and chips use aluminium for metal layers.

Copper replaced aluminum some time ago (starting ~1997) regardless because of the resistivity, and they just had to find different barrier materials to prevent electromigration and overcome other issues.

Short answer: talk about quantum wells in this context is meaningless .

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