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Comment by Florin_Andrei | Hacker News Reader

That's a much better title, though less catchy.

One could retort to the original title saying all matter is, in fact, "quantum".

> One could retort to the original title saying all matter is, in fact, "quantum".

Quantum matter has a specific meaning in condensed matter physics. It's anything where you can't approximate the system's behavior with classical physics at a macroscopic level. IE, the optical properties of metals are classical, but the electrical properties of topological insulators are not.

It is a bit like saying that all ecologists are chemists. Animals are, in fact, big sacks of chemicals, but that's not really the point.

So is a permanent magnet also quantum matter? Classical physics says the net magnetization of a solid is zero.

That is a good point, because the way I was taught it is that ferromagnetism is one of the few purely quantum mechanical phenomena we see in everyday life. However, people don't really refer to it as "quantum matter". I think you could argue that people have had some sort of heuristic description since long before quantum was known about.

"Quantum" matter you say? Do tell ···

I mean, atoms would not exist without quantum mechanics. The system is not stable - it's stabilized by quantum effects. Without QM, electrons would radiate electromagnetic radiation and would fall into the nucleus. The result would be lots of protons and not much else.

The properties of solids, all chemistry - these are basically chapters in QM.

To be fair, atoms had existed long before quantum mechanics was invented. It’s a theory, and not a perfect one. Potentially even “wrong,” as it is not consistent with one of the most important classical theories, theory of gravity (somehow gravitational waves resist quantization, and the graviton still remains a fantasy).

Everything existed before all theories were created, duh.

And conversely there are things that currently exist for which theories are yet to be made.

And the there are things that we thought they existed because we had theories for them which we later found incomplete or utterly wrong.

All theories are wrong.

Quantum Field Theory (QM+SR) is as good as it gets at the moment and we haven't been able to find fault yet.

Part of the issue with gravity is that we can get to high energy interactions on earth for the other 3 forces but we cannot get anywhere near for gravity. There's very little data to guide the process forward as opposed to the revolutions of the 20th century where it was the other way around.

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