Copper across an area of 1 cm ^2 does about 300A, compare with https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8047038/ for what some superconductors can do.

Gulp!

300,000X more than copper.

Typo converting from brain to screen. I should have used exponential notation and the mistake would have been more obvious.

Also note that while there is zero resistance you still have parasitic currents and general interaction with the rest of the environment. So no perpetual motion for us today!

Superconducting magnets are very nice as long as there is no quenching. The material used for conductors must be mechanically stable and perform consistently from one production batch to another. One reason why current high tc superconductors are not popular...

I was going to ask: Why don't we use the current high temperature superconductors, and start building grid interconnects? I guess part of the answer lies in the cost that would be incurred because of the mechanical properties of the existing superconductors.

If we simply decided to make this kind of thing a priority, we could probably manufacture suspension components at scale. (Or create small tunnel boring machines and bury them?) We wouldn't need to replace all of the lines. We'd just need enough interconnects to make transferring more power economical.

Probably if we had materials with a billionth of the resistance of silver they would work, but we haven't. And we have superconductors, luckly. :)

MRI scanners work just fine with regular electromagnets, or even plain old normal magnets. However, work better with stronger magnetic fields. In practice normal magnets end up being extremely large and heavy, and electromagnets end up using massive amounts of power. Both options are also limited in their field strength because getting enough stuff close together is tricky.

A superconducting magnet is an electromagnet which is way smaller and uses orders of magnitude less power. For extremely high field strength MRIs they are the only viable option, and for regular MRIs they are often the best option.

There is no work or state change, so no reason at all to conflict with the 2nd law of thermodynamics.

So how is this possible? The explanation is acutally reasonably easy, but requires the strangeness of quantum dynamics. One basic principle of quantum dynamics is, that at least most things are quantisized. Especially energy of a state comes in discrete amounts. That is the reason we have orbitals of electrons in atoms. They can only take very specific values, which creates these separate orbitals. There is no in between state, they have always to absorb or emit exactly the amount of energy which is the difference between orbitals when moving between them. Which is a very easy effect to literally see: take glowing phosphors as you find them on your watch etc. These are transitions bound to a specific photon energy. With red light, you cannot "charge" them, as red photons have to little energy, and you can only absorb single photons. Any green or blue light would work though. And whatever light you used to "charge" them, they always glow in the precise same color, coming from their destinct energy state.

The resistance an electron encounters while moving through a conductor is also quantisized. In superconductors we have a situation like trying to charge a watch dial with red light: the amounts of energy an electron could release cannot be absorbed by the material. And an interaction would require this. The consequence is: no interaction, no resistance.

The situation is like trying to buy a $1 bottle of water with a $100 bill. That could turn out to be impossible, because no one is willing to give you back $99, and you can of course not pay $100 for the bottle. So even when having the money, you can't buy the bottle.

This is, in a very naive way, the principle how superconductivity and superfluidity work. The trick now is to prepare the conditions which allow for superconductivity. One way is to make things increadibly cold. All metals become superconductive, if the temperature is close enough to 0. But that is with single digit degrees or below, even fractions of a Kelvin. Konsequently it was a huge sensation when the first complex substance was presented which showed the effect at larger temperatures. Since then the hunt is up to find better substances.

Let me get this straight: If you have a piece of phosphor, you can't heat it up with red light, regardless of the amount of red light you shine at it? If so, does the red light bounce off? Go straight through?

At micro levels, like molecules bouncing around in a gas, collisions are lossless. What makes electrons moving through materials different?