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JohnnyCanuck t1_j9nak5p wrote

An accelerating magnet does, just not at a wavelength that you can see. Keep in mind that the electromagnetic spectrum (light) includes radio waves, microwaves, infrared, visible light, UV, X-rays, and gamma rays. If you wave a magnet around, the emissions are going to be at the sub-radio end of the spectrum.

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Ethan-Wakefield OP t1_j9nb940 wrote

Okay but fundamentally speaking, if I say rotate a magnet continually, it actually emits radio waves? That is… weird. I am tempted to ask why, but I know the answer is, because the math says it has to. But this makes no intuitive sense. At all.

So if I take a magnet, and I flip it into a charged black hole, it’s going to emit radio waves all the way until it gets to the event horizon? I don’t understand this at all.

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gsohyeah t1_j9nid0g wrote

If your wave your hand around and water does it not make waves in the water?

That's just an analogy, but why is the same concept so hard to believe when it's magnets in the EM field?

(It's just an analogy. Don't try to think of the EM field as little "molecules" of light that you are making waves in. It's a field and the photon is the discrete unit ("quantum") of energy in that field.)

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very-based-redditor t1_j9ob5vz wrote

I have a very basic question. What is a field? I mean I know what the definition is, but what is it really? What makes a field, a field? Do they even exist? How does light, which is an excitation in a field, interact with physical things?

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Not_Pictured t1_j9oktkf wrote

All of our understanding of physics comes from making up models of reality and seeing how close to reality they match. The model of reality that treats all particles as excitation in fields is part of the single most accurate model humanity has ever come up with.

Is this model a true analogy of reality? Yes? Maybe?. At some level our 'real' understanding of realty turns into a version of "shut up and calculate" or "we don't know". It 'seems' reality is a bunch of rubber sheets stacked on top of each-other. Waves and ripples move through them and the energy from one sheet can transfer into other sheets like as if they touched eachother. Waves in one can 'bump' and create waves in other fields. "Physical things" are again just excitations in one or more of these rubber sheets.

The best answer to "what is a field?" is the definition of a field because that's what the model of reality assumes it is. True or not.

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Implausibilibuddy t1_j9ou88q wrote

> The model of reality that treats all particles as excitation in fields is part of the single most accurate model humanity has ever come up with.

Isn't that just "ether theory" with extra steps?

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agate_ t1_j9pgp8i wrote

It’s “ether theory” that works. We adopt or discard models of the universe based on whether they make accurate predictions, and the ether theory of light didn’t.

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sticklebat t1_j9y2cji wrote

Superficially, kind of? There are many differences though. One is that the ether was proposed in order to provide a rest frame for light, whereas the fields upon which modern physics is based are fully relativistic. Another is that the ether was thought of as a physical thing thing with density, velocity, etc., and whereas fields can’t really be described in those terms, at least not as directly. It’s more that fields can give rise to them.

TL;DR an ether theory is similar to fields in that they permeate all of space, but they’re fundamentally different from each other in properties and mechanics.

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Skarr87 t1_j9p6zqh wrote

A field in quantum field theory (QFT), which is what this is about, is something that has a value at each point at space time. This value can be 0 but not null. More specifically every point in space is a quantum object that is a harmonic oscillator and according to QFT this is actually what everything is. Everything is emergent from these values, for example a particular wavelength of light is a particular value of these oscillators in the electromagnetic field of oscillators and its movement through space is just this value propagating through these oscillators like a wave. Objects can have values from multiple fields. For example a neutrino interacts with the Higgs field and the weak field but not the electromagnetic field so it is famously hard to detect. It also means that light literally does not exist to it.

In my head they are kind of loosely analogous to splines where one dimensional values can control the motion or path of an object through space.

What are these oscillators and do they actually exist? We don’t know. Maybe? Probably? I believe the current consensus is they may be fundamental as in they aren’t made of anything and are irreducible but in physics every time we have thought this we were shown to be wrong. The thing is it seems to be correct, very correct. This model has made predictions that turned out to be experimental verified later.

The problem is it’s essentially a purely mathematical construct and we’re getting into the realm of philosophy asking if it’s real or not. It depends on what math actually is/describes. It might be that at the very basic level of everything all there really is is math. All we can say for sure is QFT works very well.

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TinyTarget t1_j9ohdyh wrote

Phisical things consist of atoms, which consist of subatomic particles, which are disturbances in their coresponding fields, so fields interact with other fields.

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Holgrin t1_j9pjilg wrote

It is irresponsible how incorrect this explanation of physics is. Rotating a magnet does not simply create EM waves. The changing magnetic field from the rotating magnet is not the same oscillating magnetic field induced by a photon.

Photons are not simply ripples that propagate outwards from some disturbance of a field.

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sticklebat t1_j9y8krp wrote

Rotating a magnetic does quite simply create EM waves, alongside other electromagnetic field changes. It just doesn’t only create EM waves. There is certainly nothing irresponsible or even really incorrect about their explanation. It’s a bit of a simplification, sure, but that’s appropriate in this context.

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luckyluke193 t1_j9npldb wrote

A changing magnetic field induces an electric field. This is why moving a magnet through a coil of wire induces causes an electric current to flow in e.g. a bicycle dynamo.

Similarly, a changing electric field induces a magnetic field.

An electromagnetic wave propagates because a change in electric field causes the magnetic field to change, which causes the electric field to change, etc. in a self-sustaining wave travelling at the speed of light.

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JohnnyCanuck t1_j9nem4p wrote

Yeah it’s difficult or impossible to have an intuitive sense of this. This might help though:

Electricity and magnetism are fundamentally linked to each other. They are not exactly the same but they work in similar ways.

A radio antenna works by accelerating the electrons in the metal back and forth. You could theoretically make a radio signal by doing the same with a magnet, but it would be much, much harder since you would have to move the whole mass of the magnet back and forth, not just some of the electrons.

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agate_ t1_j9pg9v1 wrote

> Okay but fundamentally speaking, if I say rotate a magnet continually, it actually emits radio waves?

Yup! The connection between magnets and light is one of the most surprising parts of physics. If it were intuitive, it wouldn’t have taken us centuries to figure out!

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Hapankaali t1_j9o739p wrote

A radio broadcast is made by waving around electric charges in a broadcast antenna. It is received by those radio waves themselves waving around electric charges in the receiver antenna.

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Ethan-Wakefield OP t1_j9ohoh5 wrote

So is the magnet here an antenna?

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NeverPlayF6 t1_j9omsx6 wrote

It isn't a permanent magnet... you can't use it to hang a picture on your fridge. But the antenna is the medium in which the moving electric field/moving magnetic field is created.

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Ethan-Wakefield OP t1_j9oo7s2 wrote

No I mean if I throw a permanent magnet into a black hole, is it an antenna? Because it’s radiating radio waves. Does that make it an antenna?

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mfukar t1_j9or9az wrote

An antenna is one or more conductive elements electrically connected to a receiver or transmitter. What does a black hole have to do with anything?

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Ethan-Wakefield OP t1_j9oz4l5 wrote

Suppose the following:

I throw a permanent magnet (a chunk of iron or something) into a rotating black hole. The black hole has enormous mass, and it has to conserve angular momentum. So, as the chunk of iron falls into it, it should rotate. And if the magnet is very small, it should rotate very quickly (again, to conserve angular momentum).

My questions are:

  1. As the magnet rotates, does it emits EM radiation?

  2. If the magnet is emitting EM radiation, is it an antenna? Is it more-or-less a broadcast antenna that's powered by the black hole?

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numatter t1_j9q6jl3 wrote

A stationary magnet has a static (fixed) "field" around it. In a perfect vaccuum, it doesnt emit any photons, because theres nothing interacting with it that would cause it to become "excited" and emit EM radiation.

A rotating magnet, regardless of being near a black hole, produces a dynamic (changing) magnetic field, and since those interactions contain information (quanta), we're all familiar with something heating up - which are photons in a spectrum we can't see with the human eye. Given enough time, in theory, the entire mass of the magnet would eventually be irradiated outward as light energy.

Lenz's law provides details on extracting energy from this very thing. You can spin the magnet around an electrically conductive material, like an iron nail. The nail becomes excited by the photons, and electrons start moving around (electricity). Alternatively, you can shake or spin the iron nail around a permanent magnet and produce the same thing via induction.

Your question in regards to a black hole is quite intriguing. Yes, a rotating magnet can act as a broadcast antenna, but its not very efficient to do so because magnets and all ferromagnetic materials have the uncanny ability of picking up and amplifying extra signal "noise" (ingress). What's fascinating to think about, is that a magnet in orbital motion around a black hole would indeed act as a "pickup" in exactly the same way a guitar pickup works. All these frequencies being thrown around together would be picked up and turned into the electrical signal version of the EMFs, then be induced back into the magnet in a Jimi Hendrix-esque feedback loop.

So when you're saying a "magnet" is spinning around a black hole, don't imagine a handheld rectangle magnet. Imagine instead that it's a magnetar... I mean... I can't even fathom the magnetic power of one of these alone, much less being involved in a stellar dance off with the energy source of a black hole. If something like a pulsar/magnetar were to be energetically involved with each other, theoretically you could place the magnetar in an energy jet stream of the black hole, and it would emit a "fucking huge" broadcast signal of their blended frequencies... may I say, "spacetime modulation?" Hmm...

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sticklebat t1_j9y9092 wrote

> Given enough time, in theory, the entire mass of the magnet would eventually be irradiated outward as light energy.

I don’t think this would happen. I think the spinning magnet would preferentially emit light with polarizations that would slow down the magnet’s rotation over time, until it’s no longer spinning. I think hardly any of the magnet’s mass would be converted into light in this process.

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numatter t1_j9z1zz3 wrote

Thank you for that. I was thinking in terms of Newtons 1st law of motion in a perfect vacuum (and over eons of time) and didn't consider that light itself has inertia and would affect its angular momentum as its being radiated. But, isn't it still conceivable that even down to the last atom of the magnet, there's a mathematical improbability that the spin would be zero, considering entropy? Or maybe the opposite is true, that entropy was working toward bringing the very last atom down to the lowest energy state possible, essentially converting any remaining angular momentum into light so that it can achieve the lowest energy state possible. I could see it going both ways, maybe even being in an entangled state of both outcomes until an observation is made.

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sticklebat t1_j9z3v8i wrote

Wait long enough and every system will tend toward its highest entropy and typically lowest energy state. But then we’re not really talking about the effect of the magnet’s magnetic field anymore so that’s a whole different conversation that depends on things like the stability of atoms and protons.

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fuerdiesache t1_j9sewfy wrote

it emits not just radio (electromagnetic) waves, but also sound waves and gravitational waves.

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