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Dumb question: why is it hard to make something spin really fast?

Simple example: put your frictionless spherical cow on a spinny plate. Make it a very small cow; it's only there to have a point of rotation. Why frictionless? You don't want its butt to catch fire. Why spherical? It'll need to maximize volume dedicated to arm muscles; see below.

Have the cow hold two ropes, each leading to a full-sized cow 10m away. Apply force to those cows (blow on them, or magnetize them and do a solenoid thing, or just make them very gassy cows and orient their spherical butts in opposite directions). Get them spinning at 1Hz. (This is very fast; remember the diameter is 20m.) Now have the middle cow pull the ropes, shortening them to 10cm. It's now spinning at 1Khz. 10mm gives 1Mhz. Conservation of angular momentum, baby.

Do this in a vacuum in microgravity, and you don't need the center cow.

Sure, if you're doing this at a bovine scale, the tension is ridiculously large. What makes it infeasible at a small scale?

The main issue is that when objects spin really, really fast, they tend to explode due to centrifugal force.

The tensile stress on a spinning round, homogeneous object is p * r^2 * w^2, where p is density, r is radius, and w is angular velocity. Using your numbers for a steel cylinder with density 8 g/cm^3 gives a tensile stress of (8 g/cm^3) * (5 mm)^2 * (2pi*1 MHz)^2 = about 8 TPa which vastly exceeds the tensile strength of steel or any other known material. Using cows connected by ropes would be even worse because the enormous centrifugal force would be borne by only a small rope.

Consider nano-dosing instead of micro-dosing going forward.

How would a spherical cow hold onto ropes? By inference, a spherical cow would have no appendages of any kind.

Centrifugal forces on the spinning object will tear it apart once it goes “really fast”

Apparently this effect applies to sound waves as well: https://arxiv.org/pdf/2005.03760

Does this mean impossibly small subwoofers? Would the rotating part have to precisely match the audio frequency to be amplified?

The mechanical driver part of the subwoofer might be able to be made smaller, but the surface that moves the air still needs to be large - there is a relationship to the wavelength of the sound involved that I no longer remember. This is why tweeters are small.

So, if you use eddy currents to delay the phase of an exciting field long enough that the object those eddy currents are inside of can spin more than 90 degrees, the response eddy current fields now AID instead of opposing the original field?

This sounds quite a bit like what Steorm[1] was doing years ago. If ultraconductors[2] worked, you could actually build a mechanical device that had losses low enough to actually gain energy once a critical speed were obtained.

[1] https://en.wikipedia.org/wiki/Steorn

[2] https://patents.google.com/patent/US5777292A/en

(Claim 7 is for material with a conductivity of 10^11 S/cm, which is 150,000 times better than copper)

> This sounds quite a bit like what Steorm[sic] was doing years ago

Steorn was a scam, and they never actually showed anything off. The only thing they did was rob some investors.

> If ultraconductors[2] worked, you could

Not familiar with that idea, but this construction sounds a bit like: "If only you had an (infinitely) rigid rod, you could push one end to communicate faster than lightspeed."

Or in balder terms: "If only we had a subtly impossible component, we could make a blatantly impossible machine."

I am somewhat curious where the math on a perfect rigid rod breaks down (that is, where does the 0 end up under the line)

My gut instinct is you’d really need perfect incompressibility such that pushing one end of the rod would propagate the pressure wave to other end instantaneously. In other words, you have to make the speed of sound faster than the speed of light. I have no idea what the physical construction would look like. Maybe a string of singularities lined up and touching (hey, there’s your 0!) without tearing spacetime apart?

Force cannot transmit through the material faster than the speed of sound and because fundamentally at a subatomic level, mechanical force is the interaction of electromagnetic and gravitational fields between molecules, the speed of sound cannot exceed the speed of light in a material. The rod will compress or physics breaks down. Solid particles are an abstraction.

> Maybe a string of singularities lined up and touching (hey, there’s your 0!) without tearing spacetime apart?

At that point it's starting to sound less like a rigid rod and more like changing spacetime itself so that the two locations are closer together. :p

I think this is where the math breaks down:

> you’d really need perfect incompressibility such that pushing one end of the rod would propagate the pressure wave to other end instantaneously

I.e. by pushing an abstraction of "perfect incompressibility" and "instantenous propagation of pressure waves" to the point stops corresponding to reality. Those ideas are descriptive simplifications, abstracting away the underlying process of matter / fields interacting sequentially, an interaction that propagates at the speed of light.

It's the same kind of thing like assumption that array access is O(1). It is, until the array gets so large the process of finding the right place in memory becomes visibly O(n).

Or, on a more basic level, arithmetic on numbers seems to be O(1) with respect to the values of the numbers. Almost all programming practices and popular algorithms depend on that assumption, but it only holds for numbers that the hardware can process in one go. Adding 64-bit numbers is constant-time. Adding 64000-bit numbers isn't.

Right. "Let's assume force propagates instantaneously--" "Let me stop you there."

I think the math is fine, but a perfectly rigid rod cannot exist in our universe, so there's no paradox, even though it would let you send messages faster than light. It's like calculating how strong of a hydraulic press you'd need to compress matter into neutronium in your garage, or claiming that if a spaceship could travel at 2x light speed, then it could fly its way back out of a black hole.

There simply are no such things as rigid bodies in this universe. Everything is composed of particles that act on each other with forces, which take time to transmit the information that something is pushing on the other side.

So a perpetual motion device!?

(I didn't understand the math in the paper)

Would this mean that a rotating body in space would eventually slow down? In other words, amplifying EM radiation draws energy from angular momentum?

There's a similar effect https://en.wikipedia.org/wiki/Yarkovsky_effect

Cool. Also may be useful to read Zel'dovich's second paper on the phenomena. http://jetp.ras.ru/cgi-bin/dn/e_035_06_1085.pdf Interestingly, in his paragraph about previous work, he did not mention Yarkovsky:

"According to a remark by P. L. Kapitza, the effect is analogous to amplification of sound by reflection from a resting-medium boundary that moves with supersonic velocity... In the case of plasma waves, a similar effect was considered recently by Ostrovskil. Mention can also be made of earlier studies dealing with the motion of a conducting liquid in a resonator or the motion of carriers in the interior of an elastic piezoelectric or over its surface."

reminds me of:

https://en.wikipedia.org/wiki/Crookes_radiometer

On a wiki rabbit hole from that link to the Apophis asteroid, to rage and rage 2 video game plots.

all such rabbit holes lead either to SCP or tvtropes.org

Yes, it probably even works in total isolation from any radiation, because it can interact with quantum vacuum and give off energy to create photons. That's the next thing they are trying to prove.

Could this be used as an engine of some kind? The spinny thing giving off EM waves and those waves are caught by something like a solar sail?

No idea, but "amplification", "electromagnetic fields", "rotating bodies", and "published in Nature" are the keywords that get all the UAP podcasters drooling.

Get ready for an onslaught of "Physics behind flying saucers LEAKED" clickbait coming to a feed near you. Whether any of it is actually applicable doesn't matter, the clicks must flow.

I'm picking up a lot of projection in this reply;

• To know what keywords get UAP podcasters drooling, you must have watched your fair share of UAP podcasts.

• Your comment is the only one so far to make the association between the article's keywords & UAP, implying that you are yourself making the same association that someone interested in watching UAP podcasts would be making, in which case..:

• ...what is the difference between you and the would-be viewer of the next UAP podcast you are warning away?

> • To know what keywords get UAP podcasters drooling, you must have watched your fair share of UAP podcasts.

They’ve been coming up on the front page of Reddit several times this year. I’m in agreement with the OP and I’ve only casually observed those threads

Another confirmation. I see it in my /r/all list fairly frequently. I am neither subscribed, a reader of said posts, or a believer in any of that (or at least, i avoid belief until it feels there is reasonable supporting evidence).

Though i don't recognize all of the terminology of OP, so perhaps that disqualifies my observation.

Besides reddit front page, this stuff also appears in enough other pop culture podcasts and the occasional NYT expose that it's out there in the popular zeitgeist. Unfortunately, here it's just my science immune system flaring up on a random internet board.

Also, between the "could this be used for vehicles" parent comment and that downvoted interdimensional energy transfer comment below, it doesn't take a Aliens-Did-the-Pyramids Guy to see what dots were starting to be connected... I might as well be the one to flag it explicitly and earn some imaginary internet points.

But who knows, maybe I'm actually the goberment disinformation agent trying to keep all this under wraps...

I have no exposure to UAP media but the first thing that came into my head was, “like some oddball theory of how a classic ufo works from the 70’s.” That and the send $5 for paper on the secrets of antigravity ad from the back of Popular Science magazine back then.

Even if your implication is correct (GP is a would-be viewer), doesn’t mean they’re wrong..

"Flying saucers are closer than you think, and all my bitterness about academia"

Huh, so Unidentified Flying Objects have been renamed to Unidentified Anomalous Phenomena...

“The fastest rotation achievable by standard motors is of the order of 10 kHz and a record of 667 kHz is reported for a millimetre-sized magnetically levitated sphere.”

From the spinning metal cylinder you can extract EM energy. It’s like a flywheel. The trick is how do you bring up the spin in the first place. The indication here is I guess that you can amplify the spin with EM waves.

“…depending on its rotation speed Ω compared to the field oscillation frequency ω, it can either absorb or amplify.”

Definitely getting some giant magnetoresistence vibes - you know, that thing that (among other things) makes modern hard drives possible: https://en.m.wikipedia.org/wiki/Giant_magnetoresistance

Perhaps in reverse (which should be equivalent, since Maxwells laws are time reversible).. rather than having waves amplified by stealing energy from the cylinder, waves could amplify the rotation of the cylinder.

At first glance, the concept appears to serve as the basis for a 'portable' magnetic field generator, which could be installed on an interplanetary spacecraft.

ScholarlyArticle: "Amplification of electromagnetic fields by a rotating body" (2024) https://www.nature.com/articles/s41467-024-49689-w

> Could this be used as an engine of some kind?

What about helical polarization?

"Chiral Colloidal Molecules And Observation of The Propeller Effect" https://pmc.ncbi.nlm.nih.gov/articles/PMC3856768/

Sugar molecules are asymmetrical / handed, per 3blue1brown and Steve Mould. /? https://www.google.com/search?q=Sugar+molecules+are+asymmetr....

Is there a way to get to get the molecular propeller effect and thereby molecular locomotion, with molecules that contain sugar and a rotating field or a rotating molecule within a field?

The plot in figure 4 looks a lot like the torque/frequency plot of an induction motor.

That would fit:

> "Here, we show that this 60-year-old long-sought effect has been concealed for all this time in the physics of induction generators. Induction motors are constituted of two components: an external stator, composed of circuits generating a rotating magnetic field, and a rotor, also composed of several elementary circuit loops, usually in a squirrel cage configuration. By replacing the internal circuits of the rotor with a solid metal cylinder as in Zel’dovich’s original proposal, and using a gapped toroid within a LC resonator as stator, we isolate the key physical effect and unambiguously observe Zel’dovich amplification, which manifests itself as a negative dissipation induced by the rotor in the LC circuit."

Could it be true for gravitational waves?

I'm not sure if the maths are related, but there is a different (though similar) idea in gravitational slingshots. It's not the same because it simply uses "normal" linear momentum. But I also only read the abstract, lol.

As someone uneducated in the subject I'm curious what stopped this being discovered earlier? Is the setup particularly challenging?

The challenge is in making a physical object rotate fast enough to produce the effect. The article says "the fastest rotation achievable by standard motors is of the order of 10 kHz", which is apparently too slow. The frequency of visible light, for comparison, is about 400–700 terahertz (THz).

Yes; in the same way you can influence gravity by a spinning mass, albeit we do not possess (by orders of magnitude) material or energy required to spin a mass fast enough to detect an effect. Spinning supermassive blackholes show a gravitation/time frame-dragging effect dependent on speed of spin. Showing it occurs with EM is amazing.

I keep thinking about all the sci-fi I've seen where a machine with rotating parts opens up a portal or a wormhole...

Liberate tute me

Just don't travel trough warp withou a Gellar Field, unless you really know what you are doing. ;-)

Honestly it reminds me a bit of the macguffin used to amplify a signal to insterstellar distances used in The Three Body Problem book. Which given the rest of the novels makes me a little scared

Instantly thought of this as well. Loved that book.

the three body problem is one of the most terse piece of writing I have ever read if being absolutely honest

What’s wrong with tenseness? People praised Hemingway for it.

I don’t think that’s the word you meant to describe TBP though.

Reminds me of Kerr-Newman black holes.

https://en.wikipedia.org/wiki/Halo_Drive

Sounds like a crappy Alexanderson alternator.

[flagged]

The experiment provides support to the idea that the Superradiance effect (where waves are amplified when interacting with rotating black holes) may not be pulling energy from the blackhole, but from different dimensions. In theories involving extra dimensions (like those proposed in string theory or braneworld scenarios), rotational effects could alter how energy and momentum are distributed across dimensions, leading to observable phenomena similar to what was demonstrated in the experiment.

If rotation within this higher-dimensional space causes analogous effects to the rotational amplification observed in the experiment, it could imply new ways of energy transfer between dimensions. AKA -- ZPM from Stargate

What? There is no pulling energy from different dimensions here - it's pulling it from the angular rotational energy.