I'm gathering from the article and comments here and there that "room temperature superconductivity" would be an awesome breakthrough that would lead to lots of awesome things, but I'm not familiar with this sort of thing. Can you guys give some examples of why this would be so awesome?
One simple answer: lossless power transmission over long distance. A measurable percentage of our electrical generation is lost in powerlines or transformers without doing any useful work.
Zero loss is only true for DC transmission. It's true, loss is lower than copper at 50-60Hz AC but radiative losses don't magically disappear. You're also limited in how much current you can carry since superconductivity breaks down in sufficiently high magnetic fields. For all that room temperature superconductors are revolutionary because of the jump in power density in things like motors and yes power lines.
But didn't we only use AC because it was more efficient? So we switch back, and turn it back into AC for our houses, until we can switch over completely.
AC becomes less efficient (financially and electrically) at more than 1 Megavolt. The big big transmission lines in the United States actually use DC because the AC transformers would have to be so large, and the losses at that high of a voltage are huge (and that 1 MV generators get to be fairly expensive).
Adding to that high voltage more than anything is the benefit of AC.
The weight of the conductor is a big problem for long runs of power lines so if you double the AC voltage the weight of the conductor can decrease by 25%. DC over 1500 V isn't really possible/efficient (some limit of generators) but AC can be many hundreds of thousands of volts.
It appears some of my electronics training is sinking in, I put it to good use!
What do you mean by doubling the AC voltage to decrease the weight by 25%? If I continue doubling, will I eventually not need a conductor?
The true power of AC is the fact that the energy is transmitted through the electric and magnetic fields (Poynting vector). DC needs to push everything down a little copper tube. When you start oscillating things though, the effective area of your conductor increases greatly (you start using the air as a transmission medium). This is why you can do things like this (http://hacknmod.com/hack/field-of-fluorescent-tubes-powered-...).
I'm just going by my textbook, I'm still new to this.
I understand what you're saying about AC creating an emf and pushing itself through a conductor via magnetism and frequency. The skin effect would play a big role in this too. As I say I'm still new to this, I know enough to be dangerous.
Here's the exact quote in case you are interested:
"The weight of a conductor required to transmit a given amount of power a given distance with a fixed loss varies inversely as the square of the transmission voltage."
Power's given as: P = V^2 * R
R is given as: R = rhoL/(pir^2)
Substituting: and clumping constants: P = (V^2 / r^2) * (rho*L/pi)
Weight is proportional to r^2, we can see that voltage and weight are inverses of one another, and increasing the voltage for a fixed amount of power decreases the radius necessary to transmit it, decreasing the weight.
I really wish I still had my lecture notes about the energy flow through free space, this is the best I could find online - http://amasci.com/elect/poynt/poynt.html.
High-voltage DC uses voltages in the hundreds of kV. It is also the most efficient way of sending serious amounts of power over long distances (even before superconductors). Just as required cable thickness decreases with AC voltage, it has to increase with current. HVDC gives allows for smaller cabling.
No. We are using AC because it is much easier to convert voltages with AC (by using a transformer) than with DC. Generator can't give very high voltage, it is in the range of a few kilovolts, but that voltage can't be efficiently transported over long distances due to heat losses (yes avoidable with superconductivity), and super high (100s of kilovolts) voltage can't be used by consumers, so when delivered, it has to be driven down to 100s of volts (in a few stages).
Superconductivity will change all of that (maybe in a 100 years or so since existing power infrastructure is worth hundreds of billions if not trillions and is a pain to replace).
Also, tying back into what you said about efficiency: AC power can be much more efficient due to this easy transformation. The power dissipated across a resistor (which is a reasonably good model for power lines) is directly proportional to the square of the current passing through it. Thus, by stepping power up to high voltages, you can drastically cut the current and hence resistive losses in the line.
...but this whole thread was prefaced on room temperature superconductors. Hypothetically at least, this high voltage advantage wouldn't matter if you could have 0 transmission losses with DC at low voltages.
The point anovikov was making is that AC is not intrinsically more efficient. In fact, it is less efficient over very long distances dues to radiative losses. We don't use AC because it lets us use more efficient voltages today. We use AC because 100 years ago we didn't have the technology to boost direct current to high voltages.
Exactly, one of the big barriers to renewable energy now is that the sources of it, like areas with more wind or sunshine, are very far from the main consumers, like large east coast cities in the US.
On a global scale, with no transmission loss, Egypt could use the Sahara to export solar energy to Japan.
For example, super conductors can 'freeze in' magnetic fields. This means, that the super conductor can essentially only move along the field lines. ( Found this video [1], which shows the effect.)
With the same effect you can 'levitate' objects, for example a bookshelf. So there would be endless possibilities for novelty toys.
Earnshaw's theorem only applies to static electromagnetic fields. An electromagnet coupled with some sensors and a computer can give feedback to make stable levitation. But, as you said, it would constantly use energy.
I don't know how much heat in CPUs is based on transmission resistance vs something inherent in the operations done (something analogous to how a Carnot heat engine with 100% theoretical efficiency is impractical) but if you have a circuit with no or significantly less power loss you could blow up Moore's law since if I recall correctly the limiting factor is heat.
As the wires get smaller and smaller and smaller, resistance becomes a huge problem, and you wind up needing a crapload of repeaters and wasting a ton of power.
Consider that r= (rho * L / A), and that you need a ~4nm tantalum sheath around copper wire to keep it from poisoning silicon. What happens to r when the width starts getting really small? 40nm - (4 + 4) = 32nm, 10nm - (4+4) = 2nm, so for a 4x process shrink we've seen a 16x reduction in area assuming height remains constant and that the cross section of the wire is roughly rectangular (neither of those assumptions is perfect).
The trend I've seen in Intel processors is that every time they jump down a manufacturing size (eg: 32 vs. 22nm), the power usage (per flop, at least) has gone down. Why's that?
Smaller transistors take less energy to switch. The problem with heat dissipation is not that the amount of energy wasted goes up, it is that the [i]ratio[/i] of energy wasted goes up. There is a point where the increase in resistance will nullify the decrease in switching costs, it is at this point where we would need superconductors.
Smaller gates mean lower capacitance, so you need to drive less current into them to switch.
The nice thing about CMOS is that you only need to flow current when switching them (at other times current is blocked by an "OFF" transistor somewhere in the logic), so resistance doesn't matter as much as it would for a motor or a light.
This is not entirely true, in an ideal world a CMOS device just sitting there not switching would use basically no power, but in actual application there is some leakage (both form not being fully off and some current jumping from the gate). This leakage gets worse as the transistors get smaller and when you have billions of transistors even the tiniest amount of leakage adds up, the result is leakage current can be a significant amount of the power used by a modern processor.
The killer applications would probably be power transmissions (as saulrh mentions) and magnets. It would definitely help make MRI's cheaper and probably smaller, and I think it would probably help a lot with electric motors.
Easy long distance power transmission might also help with renewables (think large solar plants in the Sahara or New Mexico with superconducting lines to bring the power without loss to where we want it)
I believe you can also store energy in a super conducting loop (the current just keeps going around forever.)
So maybe we'd get a new type of battery if we have room temp superconductors. I haven't been able to find any power density figures on such a device though, so I'm not sure if it would be an improvement over Lion batteries. Anyone know?
They're currently used to regulate power grids from unexpected load changes. Superconductors are good at absorbing and releasing large amounts of power very quickly (since there's no resistance), so they are ideal for situations like this.
There is a still a big energy cost in cooling these things though.
CPU's and GPU's that don't get hot. No more need for cooling systems, no limits on hardware design due to need for temp control, smaller computers and laptops and more powerful mobile devices, and longer battery life.
A search for "superconductor heat pipe" says Niven is right and superconductors can be used for super-fast cooling.
A superconducting wine glass that fits onto a superconducting cold spot on the table. Or a superconducting sleeping bag for those hot mosquito nights. (The sleeping bag also levitates on magnetic lines so you can sleep on air.)
Unfortunately, electrical superconductors are terrible conductors of heat. Metals conduct heat well because the conduction electrons occassionally scatter off of a thermal vibration, are accelerated, and the travel a good long distance before scattering again.
But in a superconductor, the conduction electrons are bonded to each other by quantum mechanics magic. It takes a lot of energy to break one loose, more than you can get from heat. In fact, if the material was hot enough to scatter many of the electrons (the critical temperature), it would stop superconducting. Basically, superconding electrons are a perfect mirror for heat.
I have some hope for composite materials made with superconductors. Long nanowhiskers might be able to serve as antennas that carry infrared signals from point A to point B.
Doug Natelson at Nanoscale Views is a physicist who works with nano stuff, and I expected him to comment[1] on this. Basically he said it looks interesting but isn't really proof. Which fits with my viewpoint, where I discount anything reported in Technology Review or that starts with "MIT/Harvard Scientists". When it's real, it'll be in Nature.
Thanks for the article link; but in the future please consider linking to the main arxiv page[1], not a specific PDF.
The direct link will become outdated if a new version of the paper is uploaded; also, the main page will contain a lot of useful data about the publication (citations/etc), will include the abstract in the page, and give a choice of what format you read it in.
Hacker News is "peer reviewed", but that doesn't mean every top voted story is correct.
I worked in a major lab in this exact area (high temperature superconductivity) and had papers published in much more prestigious journals, and getting published was often a question of politics more than science- if your results undermine a theory that one of your "peers" built his career on, you may not be getting published in that journal, no matter how scientifically correct.
And back in those days things were a lot less political than they are now.
Don't presume that "peer review" means anything. It really doesn't. It doesn't mean the peers have reproduced the results, and it doesn't mean the peers are even up to speed specifically enough to be able to authoritatively say the results are correct.
It is about as equivalent as the fact-checkers at the New York Times, and you know how often they print retractions. At the time, quality was slipping too and it was getting more political.
I'm skeptical about this claim, but it has been awhile since I worked in that area, so I won't say either way.
But don't take "peer review" as meaning anything significant.
It's like saying Obama is telling the truth because democratic "truth squads" blessed his opinion.
Don't presume that "peer review" means anything. It really doesn't. It doesn't mean the peers have reproduced the results, and it doesn't mean the peers are even up to speed specifically enough to be able to authoritatively say the results are correct.
I know what peer review means, and I know that it's none of those things. But getting a paper published in a peer-reviewed journal means you passed a sniff test, which is better than being written up in your Alma Mater's pop-news magazine.
If this becomes verified then it is very exciting - give me my hover board.
Even if it is entirely impractical in use, the thought that a room temperature superconductor may exist in one form or other is just more evidence that little stops the march of science :)
Absolutely! I really liked that this article didn't over-hype it and made the limitations and caveats very clear. While it's extremely far from usable, if we know of even one instance where this phenomenon occurs, we can try to figure out why, and then replicate on a wider scale.
Obviously it's not going to be in our living rooms anytime soon, but when we do crack this it's going to have a rather radical impact.
The first issue you'll run into is that the graphite grains they are using "several tens of micrometers grain size graphite powder" [1]. It might not be straightforward to make that from a pencil, but you could buy the powder online.
I've not read the full paper so there might be more significant barriers to trying this at home, but it looks plausible. Good luck!
This is an attention-grabbing headline, at best. As described in the article, the scientists found highly transient evidence of superconductive behavior in a tiny subset of graphite grains. While that is incredible, it's not the same as "room temperature superconductivity found!!!".
> This is an attention-grabbing headline, at best.
Absolutely incorrect.
Superconductivity occurs because two electrons pair off. This transforms fermion behavior into boson behavior: Fermions obey the exclusion principle; bosons do not. As bosons, they fall into approximately the same low energy state, which allows them to flow without resistance.
The question is how on earth the electron coupling is occuring: At room temp, normally vibrations would overwhelm all of the known mechanisms of superconductivity.
I'm aware of the definition of superconductivity. My point is that these researchers have no definitely found superconductivity, they have found evidence that under controlled conditions they can possibly achieve short-term high-temp superconductivity. This is a huge accomplishment, to be sure, but it's not as simple as "room-temperature superconductivity."
I disagree. They did find superconductivity in graphite grains at room temperature, and it is freakin' amazing. Next, someone will figure out why it happens, and figure out a way to make it happen more, happen in different stuff, or whatever. There's obviously a big leap between "we found superconductivity at room-temperature" and "we found a practical room-temperature superconductor", but it's also obviously a good step along the path.
Of course it is, but the paper doesn't over state the claim. Basically they have detected magnetic effects which are consistent with superconductivity. It is a tantalizing hint, no more, that there may be a carbon structure which is superconductive at room temperature.
This isn't a particularly surprising find as the folks who are working with graphene have been documenting its conductive properties for a while. It was that work which has inspired people to look further to find out more.
So this might be better titled 'the investigation of conductivity in carbon structures continues, with hints of room temperature superconductivity' but it wouldn't get nearly the attention :-).
I remember how mind numbingly boring materials science was to me in school and now all this cool stuff is going on, so the whole carbon revolution thing is pretty amazing.
I think it is the same, if (and correct me if I'm wrong here) this is the first time we've observed room temperature superconductivity of any kind?
It would mean that a hypothesized phenomenon has been confirmed as possible, and more importantly would mean we could start to understand the conditions under which it occurs and see if we can apply that to anything on a slightly larger scale.
The overall results indicate that room temperature superconductivity appears to be reachable
The paper goes into more detail:
The
observed magnetic characteristics as a function of temperature, magnetic field and time,
provide evidence for weakly coupled grains through Josephson interaction, revealing the
existence of superconducting vortices. [0]
My layman interpretation is that they've observed a property of superconduction, however their graphite flakes didn't demonstrate any actual superconductivity.
1. Thanks for the arxiv link, (OP: it belongs at the top)
2. Magnetic characteristics of perfect diamagnetism are indeed "actual superconductivity." If there were some residual resistance, the magnetic field would not be completely expelled from that part of the material.
