Comment by alecst | Hacker News Reader

Comment by alecst | Hacker News Reader

Parent Full thread

A few comments on diamagnetism:

The most strongly diamagnetic materials that aren't a superconductor are bismuth and pyrolytic carbon, a graphite-like material.

Bismuth has a density of about 10g/cm^3, and a diamagnetic strength (X) of -16.6 x 10^-5. It won't levitate above a magnet because it's just too heavy.

Pyrolytic carbon has a density of 2g/cm^3, and a diamagnetic strength of -40 x 10^-5. Thin sheets of this lightweight material will levitate over strong magnets, provided the magnetic field alternates in a chessboard pattern.

LK-99 must be similar in density to bismuth, and the videos (like below) show large chunks of it levitating. If it's not a superconductor, it's the most diamagnetic room temperature material ever seen, by orders of magnitude.

And on top of that, if pure diamagnetism were at work, the samples would have to slide off the magnet. They wouldn't stay there and float. It's similarly unclear why the material seems to always float at an angle. It seems to track the field lines in some way.

https://www.nytimes.com/2023/08/03/science/lk-99-superconduc...

https://en.wikipedia.org/wiki/Diamagnetism#Materials Diamagnetic strength = susceptibility

My background: physics, but not superconductors.

Yeah, I think unless the authors are deliberatly misleading the public (which is of course a possibility, though not very likely I think) it is hard to imagine a scenario where all of this won't turn out to be highly interesting in one way or another (even if it might turn out to not be a superconductor)

I really doubt there’s intentional fraud here, but they were forced to publish (or pre-print to be pedantic) early. [0] This certainly led to less rigor.

[0]: https://twitter.com/8teAPi/status/1684385895565365248 apologies for the Twitter link, I didn’t have time to find a better source.

That Twitter user is making up details and writing a fan-fic: https://twitter.com/8teAPi/status/1686217806298423299?s=20

So you won’t find any other sources, other than other people who have also been misled by @8teAPi.

Frustrating because it’s also chaotic, trying to keep the events straight.

This is hilarious. I love that @8teAPi did this, hopefully it knocks some sense into people.

> It's similarly unclear why the material seems to always float at an angle. It seems to track the field lines in some way.

I've seen some people talking about the LK-99 samples only having these properties locally due to internal structure or something like that, could that not explain the angle if one part of the sample had more "pockets" of material with these properties than another part?

> If it's not a superconductor, it's the most diamagnetic room temperature material ever seen, by orders of magnitude.

If it’s not a superconductor, can it still be used for e.g. maglev trains?

Do highly diagmagnetic materials have any practical use?

Frogs provide a wide array of ecosystem services.

https://youtu.be/KlJsVqc0ywM

I eat frogs.

Frictionless travel

Reply on news.ycombinator.com