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LW1.0 username Manfred. PhD in condensed matter physics. I am independently thinking and writing about value learning.
If you want to chat, message me!
LW1.0 username Manfred. PhD in condensed matter physics. I am independently thinking and writing about value learning.
This is outstanding. I’ll have other comments later, but first I wanted to praise how this is acting as a synthesis of lots of previous ideas that weren’t ever at the front of my mind.
I think for the last month for some reason, people are going around overstating how aligned humans are with past humans.
If you put people from 500 years ago in charge of the galaxy, they’d have screwed it up according to my standards. Bigotry, war, cruelty to animals, religious nonsense, lack of imagination and so on. And conversely, I’d screw up the galaxy according to their standards. And this isn’t just some quirky fact about 500 years ago, all of history and pre-history is like this, we haven’t magically circled back around to wanting to arrange the galaxy the same way humans from a million years ago would.
I think when people talk about how we are aligned with past humans, they are not thinking about how humans from 500 years ago used to burn cats alive for entertainment. They are thinking about how humans feel love, and laugh at jokes, and like the look of healthy trees and symmetrical faces.
But the thing is, those things seems like human values, not “what they would do if put in charge of the galaxy,” precisely because they’re the things that generalize well even to humans of other eras. Defining alignment as those things being preserved is painting on the target after the bullet has been fired.
Now, these past humans would probably drift towards modern human norms if put in a modern environment, especially if they start out young. (They might identify this as value drift and put in safeguards against it—the Amish come to mind—but they might not. I would certainly like to put in safeguards against value drift that might be induced by putting humans in weird future environments.) But if the original “humans are aligned with the past” point was supposed to be that humans’ genetic code unfolds into optimizers that want the same things even across changes of environment, this is not a reassurance.
Me: PhD in condensed matter experiment, brief read-through of the 3-person paper a few days ago, went and checked out the 6-person paper just now, read some other links as needed.
EDIT: If I’m reading their figure 4 correctly, I missed how impossible their magnetic susceptibility data was if not superconducting. My bad—I’ve sprinkled in some more edits as necessary for questions 1, 2, and 4.
Q1
Electrical leads can explain almost arbitrary phenomena. They measured resistivity with a four point probe, where you flow a current between two outer wires and then check the voltage between two inner wires. If the inner wires for some reason don’t allow current to pass at small voltage (e.g. you accidentally made a schottky diode, a real thing that sometimes happens), that can cause a spurious dip in resistivity.
The data isn’t particularly clean, and there are several ways it differs from what you’d expect. Here’s what a nice clean I-V curve looks like—symmetrical, continuous, flat almost to the limit of measurement below Tc, all that good stuff. Their I-V data is messier in every way. It’s not completely implausible, but if it’s real, why didn’t they take some better-looking data?
Yes, critical current changing with temperature is normal. In fact, if this is a superconductor, we can learn interesting things about it from the slope of critical current as a function of temperature, near the critical temperature (does it look like √Tc−T?).
The resistivity and levitation might be possible if only a tiny fraction of the material is superconducting, so long as there are 2D superconducting planes (a pattern that seems likely in a high-temperature superconductor) that can percolate through the polycrystalline material. However, I don’t see how this would work with the apatite structure (also the Griffin DFT paper says the band structure is 3D, and the Cu-Pb chains of claimed importance are 1D), so I think it’s more likely you would indeed have to have a high fraction of superconductor.
EDIT: I think their magnetic susceptibility data for sample 2, if correct, implies that the sample is at least 20% superconductor.
Q2
The video shows a surprising amount of diamagnetism, but it doesn’t really look like the Meissner effect, and isn’t so strong that it’s impossible to explain without it (especially since most of the weight of the sample is resting on the magnet). Locking in place isn’t strictly necessary, but especially in an impure material we should see a lot of pinning that prevents it from easily rotating. Russian catgirls are often untrustworthy.
EDIT: Actually, if I’m reading this right, figure 4a actually is pretty impossible without superconductivity. Score one for YES-Y. Although the data looks very ugly (where’s the above-Tc region with no diamagnetism?)
The diamagentism is still evidence that it’s a superconductor! It’s just even better evidence that it’s a non-superconducting strong diamagnet. The moderate difference they show between field cooled and zero-field cooled magnetization curves is likewise evidence either that it’s a superconductor, or evidence that it’s an ordered diamagnetic material.
Q3
Somewhere between YES-X and NO-C. First, DFT calculations are a good starting point but always require a grain of salt. Second, I think calling this a “flat band” is overhyping it—the density of states enhancement that makes flat bands so hype-worthy isn’t there as far as I can tell. Third, the hints of charge and spin waves in the material bear further study (if this is a superconductor they almost certainly are doing something interesting) but aren’t all that surprising given that you’ve jammed a bunch of heavy atoms together in a nontrivial crystal structure.
Q4
If getting it to conduct current at 0 resistance is as easy as they make it sound, they’ve probably replicated it a hundred times in three different ways. However, what if it’s tricky to get it hooked up to show superconductivity—you have to put the leads on just right, in some hard-to-understand way, and usually it doesn’t look superconducting… then wishful thinking has a lot more room to operate.
EDIT: The extreme diamagnetism measurement for sample 2 could just be a calibration error on a sensitive measurement, requiring neither fraud nor superconductivity.
Q5
No idea. They clearly know physics. They’re not maximally clear about everything, and I think they sweep data issues under the rug, but not in a way that makes me more suspicious conditional on the data.