The Discovery of Superconductivity (2010) (opens in new tab)

(pubs.aip.org)

59 pointssegfaultbuserr1y ago12 comments

12 comments

Superconductivity is like anti-matter in that it really does like science fiction when you first hear about it.

Knowing superconductivity makes magnets less mysterious. Once you accept that physics absolutely allows the creation of a static magnetic field from a circulating current that flows forever in a zero-resistance inductor coil, then the existence of ferromagnetism is no stranger than that - to a first approximation, it also comes from circulating currents, "just" on a subatomic scale. [1] It's kind of surprising that the Atomic Current Hypothesis of ferromagnetism was already proposed by Ampere back then. Following the same heuristics, the fact also becomes clear that the energy in an inductor coil can't really be "spent" to do useful work forever without de-energizing it, and the same is true for permanent magnets. [2]

[1] https://www.feynmanlectures.caltech.edu/II_36.html

[2] This intuition debunks many types of incorrect "infinite energy of magnets" ideas that lead to perpetual motion. Although it can't debunk the "perpetual motion solely from an uneven static (electromagnetic or gravitational) field" idea, which is even older.

tagrun1y ago

Ferromagnetism has nothing to do with currents, it is due to aligned spins of partially filled shells. Below a certain temperature (Curie temperature of the material), exchange interaction (which penalizes any misalignment, in the case of ferromagnetic exchange interaction) between electrons leads to this alignment.

Spin is a type of intrinsic angular momentum that is not associated with any spatial motion.

The Feynman lecture you linked to is an explanation why currents fail to explain ferromagnetism. You need to read the next chapter, but being a lecture for undergrads, it doesn't go deep into the subject anyway. If you're really interested, any modern book on magnetism would be much helpful.

3 more replies

eternauta3k1y ago

I wonder what discoveries are taking place now which will give people in 100 years the chills to read about.

freeqaz1y ago

Transformer models perhaps?

pie4201y ago

VR porn

dang1y ago

Could you please stop posting unsubstantive comments and flamebait? You've unfortunately been doing it repeatedly. It's not what this site is for, and destroys what it is for.

If you wouldn't mind reviewing https://news.ycombinator.com/newsguidelines.html and taking the intended spirit of the site more to heart, we'd be grateful.

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