Extraordinary claims require extraordinary evidence
Carl Sagan - Cosmos
Several people have been in contact with questions about a new physics paper on a room temperature superconductor. It’s a big thing it’s real and if it can be developed into something practical. I skimmed the paper at first and then gave a more careful read. So here are a few early comments.
First the background. Superconductors conduct electricity without resistance, but there are caveats. The most useful ones need to be cooled to liquid helium temperatures. At normal atmosphere pressures that’s about 4.2 K .. really cold! (absolute zero is 0 K). Helium is very expensive, in short supply if you want scale and expensive to liquify and keep in a liquid state. LHe temperature superconductors are used in superconducting magnets that produce very high magnetic fields - physics experiments, maglev vehicles and MRI machines are major users. For the last 25 years or so we’ve had superconductors that work at liquid nitrogen temperatures. LN2 is comparatively inexpensive and fairly easy to handle. The problem is they don’t support high electric currents or magnetic fields.. There’s been a lot of focused research working on this with the best materials known as ReBCO (rare earth barium copper oxides) - there’s a largish family. They do support relatively high current densities and magnetic fields at liquid hydrogen temperatures. LH2 is between LHe and LN2 in temperature. It’s much cheaper than liquid helium. Currently the cost of LH2 temperature superconductors is about four times that of conventional materials in high field magnets. Getting down to the same cost would be a big thing.
There has been work on much higher temperature superconductors - some work suggested it could be done at room temperature, but at very high pressures. That was a couple of years ago, but there are questions with the experimental work and the very high pressure requirement makes it impractical. But if it turns out to be real, it could provide useful insight.
So onto the current paper. It shows superconductivity at and somewhat above room temperature (up to 400 K!) and at sea level pressures.
Reading the paper I see a number of red flags. It hasn't been peer reviewed yet. None of the authors is known in the field and they’re from an institute that doesn’t have a track record. Important discoveries are sometimes made outside of the field, but it’s VERY rare. They talk about critical (magnetic) field and critical current. Both numbers are extremely low - far too low to be practical. Also critical current doesn’t mean anything .. the right metic is critical current density. It’s not a typo .. their graph shows current rather than current density. More troubling is they don’t find a Tc (critical temperature).. they only state it’s still superconducting at 400 K. The fact they can’t make it go away raises red flags.
You also need to demonstrate the Meisner effect - the exclusion of magnetic fields - it gets technical, so I won’t go into details, but just noticing a drop in resistance isn’t enough. They do claim a Meisner effect, but their graph doesn’t show it. It looks like garden variety diamagnetism.
There are a few other technical issues, but I think I've made my point.
They offer a theory of what’s going on, but it’s ad hoc-ish. That’s not really a problem - an experimental result doesn’t need a theory. But why do they try? red flag.
It should be easy to replicate. Their technique strikes me as sloppy. It’s possible they’ve discovered something. We’ll know quickly as this should be straightforward to try and replicate. If it’s real and the magnetic field is what they show, it isn’t practical. It would offer a window into a different class of materials to try.
For now, color me skeptical. Extraordinary claims require extraordinary evidence. They don’t offer much in the way of evidence. I worry we have another Pons and Fleishmann paper. A big sin was P-F publicly claimed they had made a fusion breakthrough with cold fusion and the media jumped onto it. At least these guys don’t seem to be banging the publicity drum.
LH2 class superconductors may be very practical for many commercial applications in the next five to ten years. That’s a very important area that could become commercial soon. It would be even better if it can work at LN2 temperatures, but so far it’s been disappointing.
there's no cow on the ice
A close friend and I have been exchanging emails several times a week for nearly thirty years. I hadn't heard from him in a week, so I asked if everything was alright. He replied with a single line:
Der er ingen ko på isen.
He's very Danish and, although I'm barely read-only in that tongue, I knew immediately there was nothing to worry about. The idiom means there's no cow on the ice. Danes happen to be a practical people. If your cow was on the ice, you'd have something to worry about.
Idioms mean more than the words that make them up are a wonderful window into a culture. They can come from different periods, subcultures, age groups, common experiences and so on. And they can hold on well past the time they were coined. 'Hun stikker ikke op for bollemælk' means 'she doesn't stick up for milk dumplings' and is still in use even though the farming references are lost on almost everyone.
Courtesy of a couple of Danish friends, I keep a list of Danish idioms and think I understand where they came from a bit more.1 I'm sure they don't think about where they come from, just didn't think about 'it's raining cats and dogs', until I heard the Danish equivalent which translates to 'it's raining shoemaker's apprentices'. We're like the fish who doesn't realize it's swimming in water.
A few years ago I started wondering about quantum leap/quantum jump - the idiom that is entirely different from what quantum [anything] means in physics and chemistry. Of course it's so wired in popular culture that it's completely displaced the original meaning.
Pulling out my tiny text two volume OED with its magnifying glass, I find an early use in 1649 referred to a share or allotment: “Poverty is her portion, and her quantum is but food and raiment.” In about 1870 it was first used in physics to describe the the smallest quantity of electric fluid. At the turn of the century Planck and Einstein started using it in the sense that light consists of small and measurable pieces of energy. Something very small. In the 20s as quantum mechanics developed the energy change in an atom or molecule was discrete - it was quantized. In physics and chemistry a quantum jump or leap represents a tiny amount of energy.
Quantum mechanics is the study of this tiny world that has properties that are counter to what we're used to experiencing. It includes particle/wave duality, superposition, entanglement and so on. By the 50s a deeper understanding had emerged. It was becoming clear the subatomic world could be more accurately described by fields rather than just particles and forces. That's what I think about when I hear quantum. To shift gears to culture outside of physics I must 'at sluge en kamel' - swallow the camel.
According to the OED (I had to resort to the electronic version in the library as my copy is too old) the first use of 'quantum leap' to mean 'very large' came in a 1956 document describing the US-Soviet balance of power:
“The enormous multiplication of power, the ‘quantum leap’ to a new order of magnitude of destruction.”
It had been used as its opposite and somehow it caught on. This isn't uncommon with words and phrases.. smart, nice, awful, awesome and many others have been turned around. There's probably a term for this.
I was going to write something the Schrödinger's Cat thought experiment as it has also become an idiom, but that can wait as it's fascinating for other reasons.
Så er den ged barberet
__________
1 Note that I use English idioms to explain some of them
At stå op før fanden får sko på -- "get up before the devil puts on his shoes"
Spis lige brød til -- "have some bread with that" (telling someone to calm down)
Hold da helt ferie -- "take a whole holiday" (no way!)
Lokummet brænder -- "the toilet is burning" (there are big problems)
Der er ugler i mosen -- "there are owls in the bog" (something suspicious is going on)
Man kan ikke både blæse og have mel i munden -- "you can't blow and have flour in your mouth at the same time" (you have to choose)
Skægget i postkassen "beard in the mailbox" (caught red handed)
At gå som katten om den varme grød "To walk like a cat around hot porridge" (to beat around the bush)
Så er den ged barberet "The goat is shaved" (done with a big task .. big enough for a celebration)
Posted at 01:21 PM in general comments, history of science | Permalink | Comments (0)
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