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!)
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.
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.
Thank you for this.
$$$
This is straight wrong. To this day scientists cant agree why commercial airplanes can stay aloft in the sky. There are two competing theories (from what my zero science brain understands), but they have failed to reproduce the mechanism enough to conclusively say it is because of "x." You can build a whole bunch of stuff around an idea that you don't fully understand.
$$$
Sometimes you get arguments between partisans for each of these two simplified explanations, but really both are bogus.
It really isn’t that mysterious, unless you insist that only a single physical law is allowed to come into play.
That's orthogonal. Planes flying upside down still have air flowing faster over the new "top" of the wing than the bottom.
Though, a common misunderstanding is that air must be taking the same "time" to go over the top and the bottom. This is not true.
You can build a pretty good mental model of flight with either simplified mechanism, but you end up underestimating performance by a fair bit.
I've never hear of a good mental model built on Bernoulli's Principle. They are either:
- Wrong
- Give no intuition
The key question is /why/ air moves faster on one side, and once you get away from the misconception of same time, I've never heard an intuitive argument.
Redirecting air down:
- makes complete sense
- can be demonstrated by sticking your hand out the window of a car
- works with flat airfoils (sails, kites, etc.), and explains those well too
And the shape of the wing comes in from wanting the leading edge parallel to incoming airflow, and the other edge parallel to outgoing airflow. On a sail, I can adjust the shape. On a steel wing, I can't much, so I make a shape which works across different angles of attack.
All of the other mechanisms, you can gradually work in from there to get accurate models. Toss in air moving to the low-pressure area, and having momentum, and you get why helicopters are less efficient than planes, as well as vortex shedding. It all builds up.
As a corollary, Bernoulli tells you where air moves faster, but that follows from lift. Not the other way around. At least in any model which fits the human brain.
I'm sure models can accurately compute how much of the wing lift comes from the suction effect on the top of the wing versus the push on the bottom of the wing.
"You can build a pretty good mental model of flight with either simplified mechanism"
For computational models, neither of these are great starting points. When I last looked, finite element methods were where the action was.
And if you don't apply the same to quantum -- looking for intuition -- you'll have a bad time. Quantum computing algorithms came from human insight.
Since the air follows a curved surface instead of straight ahead, you could perhaps apply your intuition for centrifugal force. Momentum sort of pulls the air away from the surface.
I’m not even sure this explanation is wrong.
Counterpoint: A wing with the opposite curvature would work too, just much less efficiently. Your explanation has an element of truth, but an element of untruth. It'd take more analysis to tease them apart.
>"Composites are causally redundant. Believing in chairs is like believing that, while yes, the burning gas from my stove completely describes why the water in a pot boils, there’s ALSO a magical invisible substance called boil-o that comes out of my stove that does the same thing as the flame at the same time, and if there was no boil-o, the flame would warm the water just the same, but there IS boil-o... Chairs are no more real than boil-o. Composites over-determine what happens in the world."
Like your example with lift and fluid dynamics, simple explanations like "plane pushes air downwards" or "faster flow sucks the plane upwards" might be insufficient, but they're at least useful to the layman. It also reminds me of how Richard Feynman answered the question, "What is the feeling between 2 attracted magnets?" by explaining that it would be impossible to give a complete answer. Feynman pointed out that when you ask why two magnets attract each other, there are different levels of understanding depending on your background knowledge. For someone with no knowledge of physics, the simple explanation would be the existence of a magnetic force causing the attraction. However, delving deeper into the question raises complexities that can be challenging to explain.
Feynman highlighted the difficulty of answering "why" questions in general. Explaining magnetic attraction in terms of something else that we are more familiar with, like rubber bands, would be misleading and circular, as it ultimately comes down to electrical and magnetic forces. He acknowledged that some aspects of the natural world may need to be accepted as fundamental elements without a more profound explanation.
This is echoed in the Vsauce video, where defining boundaries and attempting to explain everything can lead to paradoxes and vagueness. The concept of "boil-o" illustrates how composites, like chairs, can over-determine what happens in the world and our own perception, making their actual explanation even more elusive.
Where are you getting this terrible information that we don't know how flight works? Have you ever talked to literally anyone who has worked in aeronautical engineering, or even studied the basics of fluid dynamics?
Yeah, didn't think so. ;)
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.
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.
They used to talk about using barium cement but it just can't compete, price-wise.
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.
Aluminium, was so expensive until the Hall/(that other guy) process was developed, that it was used for jewellery [1]. It's expensive and difficult to reduce Al ore to metal, which is a supply side problem.
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.
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)
We know how they work. We might not have fully characterised the stability conditions, but that's not the same thing.
> 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 !
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.
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...
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.
It's such a banal thing to be so fascinating.
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.
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 :)
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...
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?
Maybe we don’t know how humans use the bicycle but we know how bicycles balance, we can write programs to balance them physically.
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.
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.
Doesn’t change the answer. They’re still compressing. They’re just pretensioned.
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.
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.
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.
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.
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.
> 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.
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.
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.
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.
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.
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.
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
If you're asking how to derive the Navier-Stokes equations, use continuum / conservation principles.
Am I missing something?
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.
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.
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.
Moreover, you can have more than one thing about a paper be the "relevant" thing.
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.
Even better, it's a HUGE claim that is going to show how epistemology in science works (reproduction!!)
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.
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.)
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.
But yeah, nuclear fusion is cool.
> 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.