Magnets - We thought we knew how they worked.
Magnets - We thought we knew how they worked.
The article's title is misleading: they actually mean a new kind of permanent magnet (that was theoretically predicted but hadn't been observed until now), not a new kind of magnetism (as in, something not predicted or accounted for by our existing theory of electromagnetism).
Yeah, for a minute there I thought they had found the monopole
Monopoles are already accounted for though, because they’re explicitly ruled out by the character and form of the laws of electromagnetism. ∇⋅B = 0, or “the divergence of the magnetic field is zero”.
I mean I we found a magnetic monopole then we'd just change that one of Maxwell's equations so it looks like the corresponding electrical equation Div(E) = ρ/ε. It essentially just happens that the thing which correspond to ρ for the B field is 0.
Except that if the divergence of the magnetic field were anything other than zero, the laws as presently written wouldn’t successfully predict electromagnetic effects. Because the laws as currently written _do_ make predictions, and exquisitely precise predictions at that, the divergence must be zero with no monopoles at all or so close to zero that monopoles would be extraordinarily weak if they did exist. Their effects would be so slight that they would be useless for any practical purpose except possibly impressing the Nobel committee.
I don't really understand your point here. If we do discover magnetic monopoles (which would not necessarily be very weak but instead very rare) then we would take the equation
Div(B) = 0
And update it to say
Div(B) = sigma
Where sigma is a field describing the monopole density. Theres a ready "gap" in Gauss' law for magnetism where you can easily stick monopoles. Of course the divergence would be zero in the absence of monopoles, just as the divergence of the electric field is zero in the absence of electric monopoles, but decidedly non-zero when there's an electron around.
It looks like this is already a polarizing topic
+1 ;)
Not too many got the joke it seems :D
Well I wasn't sure if it would be downvoted due to low effort, but it got 17 points, so thanks :p
I think your point is the current Maxwell equations explain physics so well that if we change them to accommodate magnetic monopoles they would have to be worse. If I understand you right, it overlooks that we can add terms[0] to Maxwell's equations that don't affect predictions in a world free of magnetic monopoles:
∇⋅E = ρ(electric) / ϵ0
∇⋅B = μ0 * ρ(magnetic)
∇⨯E = -μ0 * J(magnetic) - ∂B/∂t
∇⨯B = μ0 * J(electric) + (μ0)(ϵ0)(∂E/∂t)
We could switch every physics textbook to using the above today, and the only difference would be setting ρ(magnetic) and J(magnetic) to zero when there are no monopoles in the problem.
[0] Griffiths Introduction to Electrodynamics 3E, Section 7.3.4
If anything it's frustrating that there aren't monopoles, because if there were, we could make the E and B equations symmetrical under interchange of the fields. It would be a lot prettier, and I think it would be easier to teach to undergrads.
I mean you could just do that and tell the students that the magnetic charge and current densities are always zero unless we eventually discover monopoles.
The fact that standard EM theory with zero magnetic charge works well only proves that normally there aren't lots of magnetic monopoles floating around: they could be very short-lived particles or strange phase of the matter, but still real and Maxwell's equations don't say anything about this.
As far as I know there's no mathematical or physical reason to outright forbid magnetic monopoles. On the contrary, there is a well-known argument by Dirac that says that if they would exist then charge is quantised, which we know it is. This is one of the reasons people are still looking for magnetic monopoles.
This is incorrect, you can put non-zero divergence of magnetic field and all the equations and predictions stays the same. Better it would make Maxwell's equations symmetric under exchange of fields and sources. \
so close to zero that monopoles would be extraordinarily weak if they did exist
Why? I can't think of a reason why would this be the case? You are not solving Maxwell's equation for the universe. You can have divergence of electric field closed to zero because you have very low density (the field source) in the region you are studying.
When Maxwell first published his work with the equations, it contained non-zero B divergence. We say that density of magnetic monopole (which should be there instead of zero) is zero because we did not find any monopoles yet (maybe ever!). If we discover a monopole, and we remove this zero, there will no problems with EM theory, and actually we can explain some other things like quantization of electric charge (why all charge are integer multiple of electron charge).
So no, it was not explicitly ruled out by Maxwell's equations. It is not even ruled out because we did not explore the full phase space. And it depends on which monopole you are talking about (Dirac monopole, GUT monopole or EW monopole).
As a condensed matter physicist (working in the same field but not on altermagnetism specifically), I would say this is being much more picky about the language than most people in the field tend to be. Moreover, I'm not sure you're even right about the language.
You are correct that this doesn't involve any changes to our understanding of electromagnetism in general; whether or not that means that altermagnetism is not a new type of magnetism is a matter of semantics. If I read in a paper or heard in a seminar that "altermagnetism is a new type of magnetism", I would not quibble with the language, though that phrase by itsself is almost tautologically pointless.
If you want a more technically meaningful phrase, I would propose that altermagnetism is a newly-discoved "magnetically ordered phase". Of course that doesn't fit so well in a headline.
altermagnetism is a newly-discoved "magnetically ordered phase"
I would prefer this headline.
> I would say this is being much more picky about the language than most people in the field tend to be.
Perhaps, but I think that when communicating with the public (as opposed to communicating with other physicists), "a new kind of magnetism" suggests something that isn't explained by our current theories, not just something that our existing theories predict but hadn't been observed before.
Sounds like shorthand terminology in your subfield is okay with the usage of "magnetism." But that's local slang, as a (former) high energy theorist I interpret the phrase "a new form of magnetism" as a new gauge theory or something equally spectacular. So I just rolled my eyes at the headline.
As someone who isn't a physicist, headlines like this make me think they discovered magnets that work with some non-ferrous material, which would be amazing. But then I was like "wouldn't that be crazy" and then came to the comments specifically to see what the actual explanation would be.
Ok, we've downgraded magnetism to just a magnet in the title above. Thanks!
If I am reading correctly it is a new kind of magnetism:
https://en.m.wikipedia.org/wiki/Magnetism#Types
And I am not sure it can be called a magnet. It's definitely a new kind of magnetic state
> it is a new kind of magnetism
It's a new kind of magnetic medium that had not been previously observed. It is not something that can't be explained by our existing theory of electromagnetism.
> I am not sure it can be called a magnet.
It's an object that has magnetic properties. That's a magnet. It's a different kind of magnet from those we had previously observed.
Each magnetic medium exhibits its own kind of magnetism.
Sometimes words are slightly ambiguous. This is not a hill to die on.
> Each magnetic medium exhibits its own kind of magnetism.
I agree that it is sometimes described this way, although as one commenter upthread said, such use of language is more common when physicists are talking among themselves, not when they are talking to the public.
The comments in this discussion indicate that I am by no means the only one who was confused by the original wording. So I think the change was helpful.
I'd say that, for example, paramagnetism is kind of magnetism, not kind of magnet.
I agree that one could say that, but it still only makes sense in a context where you have an object that has this kind of magnetism, i.e., a magnet. And the same is true of the "magnetism" whose discovery this article is describing: it's a kind of magnetic state of an object.
Paramagnetism/diamagnetism doesn't apply to "magnets", which I assume you use to refer to materials that have external magnetic field without applying external excitation.
> Paramagnetism/diamagnetism doesn't apply to "magnets"
I also said "objects" in the GP to this post. There is no paramagnetism or diamagnetism in vacuum. You need an object made of an appropriate material. I would not insist on calling such an object a "magnet" if there is an objection to that.
However, what is described in the article is a kind of permanent magnetism; the term "magnet" applies to that in any case.
I was looking for the same and hot the paywall.
Whatever happened to "bubble memory"?
Your own link tells you!
The introduction of dramatically faster semiconductor memory chips pushed
bubble into the slow end of the scale, and equally dramatic improvements in
hard-drive capacity made it uncompetitive in price terms.[1] Bubble memory was
used for some time in the 1970s and 1980s in applications where its non-moving
nature was desirable for maintenance or shock-proofing reasons. The
introduction of flash storage and similar technologies rendered even this niche
uncompetitive, and bubble disappeared entirely by the late 1980s.There was a Konami arcade cabinet that (tried to) use bubble memory! It was considered a failure. Also from Wikipedia[0]:
It was considerably more expensive than ROM chip-based boards and extremely sensitive to electromagnetic fields that could render the game unplayable.
You can find the start-up sequence of these on YouTube. It’s pretty…idiosyncratic. It took forever because it had to physically warm the memory up. Though I guess taking forever is irrelevant if you are turning on a machine only once in the morning. In fact, the music in the ROM it plays while starting up was named “Morning Music”.
Amazing. I never realised it got to commercial production, just that about 1985 it was heralded as the next amazing thing - with however many libraries of congress per fingernail etc.
with however many libraries of congress per fingernail etc.
That's a bold claim!
I found a NASA document from 1976 that expected bubble memory to reach about a terabit per cubic meter by the year 2000. And then you need over a hundred terabits for a library of congress. https://core.ac.uk/download/pdf/42884743.pdf
Also, MRAM, PRAM and FeRAM
MRAM is available as a niche product, it just hasn't achieved the promise of being cheap and dense as dram, fast as sram, nonvolatile and higher write endurance than flash at the same time. It ticks maybe two or three of those boxes, which is still something.
Likely ruined by the reputation of bubble sort.
went the way of the stringy floppy
I thought we had long since established that magnetism is illusory, an artifact of special relativity.
But it seems like a thin film of this stuff would be a good thing to skim an electron beam over, if you wanted some extremely short-waved photons.
The electromagnetic force is one of the four fundamental forces.
It cannot be reduced.
I think GP alluded to
https://en.m.wikipedia.org/wiki/Duality_(electricity_and_mag...
It's not illusory or an "artifact", since you can have electromagnetic field configurations that cannot be reduced to simple electrostatics (i.e., electric field but zero magnetic field) by picking an appropriate frame.
Special relativity helps to explain why, even if you have a configuration that is purely electrostatic in one frame, it won't be purely electrostatic in other frames. But that's not the same as saying that all electromagnetic field configurations are that way. They aren't.
Why isn't electricity an illusory artifact of relativistic magnetism?
The magnetic field may be an artifact of special relativity. Magnetic materials are not relativistic artifacts.
Spintronic effects is how Saturn is a natural, planet-sized computer.
OK Saturn, play Thick As A Brick on Earth at 100% volume
Is that from a book? I’d like to read it if so.
It's from Jethro Tull.
I know that album inside and out. What is the Saturn reference and how does it relate?
Go on…
article limit paywall: any workaround?
This works for me: https://web.archive.org/web/20240215162623/https://www.newsc...
Does this enable hover-boot, hover-tech capabilities yet?
Here's a nice non-paywalled article on this:
https://phys.org/news/2024-02-altermagnetism-experimentally....
Spintronics, which these magnets might be useful for, have several potential advantages for low power, speed and quantum coherence for quantum computing.
So a very nice discovery. Love how we keep finding strange new useful modes of matter at “the bottom”.
Computing substrates are far from reaching any kind of final form or limit.
So in the future Arm vs x86 flame wars will be replaced by spintronic vs quantum vs carbon vs optical computers flame wars.
Anyone who claims they know how magnets work, are a liar
James Clerk Maxwell is a liar?
Are you telling me that this is not true?
∆ • B = 0
EDIT: See? Right there on the tin.
https://en.m.wikipedia.org/wiki/Maxwell's_equations
EDIT2: The meaning of this statement is that the sum of magnetic lines of force entering a frame is equal to those exiting; there are no magnetic monopoles.
Why tho?
There are four fundamental forces that are observed: the strong nuclear force, the weak nuclear force, the electromagnetic force, and the gravitational force.
Why these forces exist, we cannot know.
How these forces act is a question of physics and mathematics.
https://en.m.wikipedia.org/wiki/Fundamental_interaction
Physics and math are things people invented to build models of what we see. They don't govern reality.
If you like electricity, and everything that it does for you, then you must understand that it is absolutely described by Maxwell's laws.
No exceptions.
Strong words. Why do you believe no one knows how magnets work? What would be a satisfactory answer?
we don't know why or how there is electric charge (and their related fields), we just know that there is electric charge; it's one of the properties of the universe; same with gravity. We have uncovered mathematical laws of charge and and their relationship (via div, grad, curl and all that) to magnetic fields, but we don't know how or why, just what is.
My source is Feynman.
Feynman was awhile ago.
But which Fenyman?
"A map is not the territory it represents, but, if correct, it has a similar structure to the territory, which accounts for its usefulness." — Alfred Korzybski, Science and Sanity
You are confusing conceptual models of reality with reality itself.
The Scientific Method is used to construct an accurate, reliable, self-consistent, non-arbitrary representation of the world, which are models.
QED is one of the most stringently tested theories in physics. But it is a model and will never be proven as 'True', we just get more confident in he model after it passes test after test, after test, after test.
But it is still just the map and not the territory itself.
Feynman knew this well:
https://www.youtube.com/watch?v=EYPapE-3FRw
I believe GP is a riff on the common joke among physicists: "Anyone who claims to understand quantum mechanics is either lying or crazy."
To be more specific in the case of magenetism, you can say that, for example, ferromagnetism arises from the alignment of magnetic moments into cohesive domains, where the individual magenetic moments arise on the atomic level from unpaired electrons in the d or f orbitals.
But if you poke at that (incomplete) answer a little bit, things start to get complicated. How exactly do magnetic domains align? What if there's a disruption in crystal structure? Are there other sources of magnetic moments? Where does the magnetic moment on an elementary particle come from? The answers to these questions get pretty complicated and questions like these motivate a lot of active scientific research.
Magnets are part of the Elves technology. That's why there's a magnetic North Pole. So, we do know how they work...magic of Christmas
It’s why magnets only work for people who truly believe.
Yes, and electricity uses magic smoke technology.
Physics answers what and how. Why is for philosophers and theologians.
The why is not required. It works whether we want it to or not.
I think you misunderstand the sentiment. You can know how they work; you cannot know why they work.
For a better tomorrow?
I have upvoted you, and I don't think that you should be punished for what you have said.
There are ways that it is wrong, and ways that it is right.
...if you had said "why?" and not "how?" then you would be absolutely right.
Somebody get ICP on the phone this instant.
What is ICP?
Insane Clown Posse. They have a song called Miracles https://en.wikipedia.org/wiki/Miracles_(Insane_Clown_Posse_s... which has the line: "Fucking magnets, how do they work?" which became a meme for a while.
I highly recommend watching its video if anyone hasn't. It's got a nice groove, the lyrics are actually quite appreciative of nature... but the magnet line is a real weird inclusion.
Link - https://www.youtube.com/watch?v=_-agl0pOQfs
I was a high school science teacher when that song was popular. That was a fun time!
Older school hiphop gritty downshift order when The Beastie Boys or Biggie just won't work:
1. Dr. Octagon (Kool Keith)
2. Insane Clown Posse
3. Bubb Rubb (also memetic) https://youtu.be/DYRDuOCKr2A
Insane Clown Posse. The source of the “magnets, how do they work” meme since it’s a lyric from their song.
Inductively Coupled Plasma A method to energize samples for photometric analysis.
The Orange Man was right!
Yes, I thought it was the Covid vaccine that made people magnetic
We do. This is just a different way to build one. It's a configuration of atoms that we didn't realize could be made stable, and their atom-level magnets line up in a novel way. We understand atomic magnetism pretty well.