Current = 25.4 ± 1.5 nA, Voltage = 17.3 ± 1.5 µV.

Making total power for the 30cm shell = 0.44 picowatts.

Well, a few microvolts is what you get from radio transmission on an antenna, although they mention "controlling for RF background", but I wonder how they managed to do that (Faraday cage)?

I checked out Quora at https://www.quora.com/How-many-mV-should-I-expect-from-an-AM...

And the first answer is obligatory an LLM, typically completely missing the mark, proving once again that Sabine Hossenfelder is right and AI bullshit should die in a fire: https://news.ycombinator.com/item?id=43498338

Lemme quote the ridiculous LLM hallucination: "A typical strong signal might produce around 100 mV. FM Radio Antenna: For FM radio, the output is generally higher due to the frequency modulation and the design of FM receivers. The voltage can range from 10 mV to 1 V or more, with stronger signals producing higher voltages."

You have to read the human answers or just know some engineering to figure out that the correct answer is "about 100uV (not mV)".

LOL. 1 volt in the antenna, ridiculous. These things have no fucking clue.

The part about FM sounds like BS, but much more than 1V at the antenna is definitely possible if you're close to an AM station, enough to cause unintentional receivers to emit sounds.

Well, I'm expecting an average case, not "playing AM radio with grass", because in the vast majority of the cases, antennas won't be situated within a few meters of the radio tower:

https://www.youtube.com/watch?v=b9UO9tn4MpI

I don't see a problem with the LLM answer. The field near an FM station can reach 100mV or more. The maximum safe exposure levels for general public at 100MHz is 30V/m according to standards.

It's easy to lose a sense of scale in a field which usually works in logarithmic scales. Signals can easily vary by more than 40dB, and it's easy to forget that's a factor of 100 already, and another 40-60dB is not crazy in edge cases. (OTOH ~100uV is a much better estimate of what you'll be seeing from a 'good' FM radio signal)

Still more net energy than fusion reactors have ever produced.

That's untrue

No, it took far more electricity to make than it produces over any conceivable lifetime.

My Stupid Question, please don't laugh:

If you did this on a massive enough scale, to generate serious amounts of power, would that accidentally slow the Earth's rotation down over time?

It isn't a stupid question, it is a good one. The answer would depend on how the field is generated in the first place.

Given a field generated by asymmetric rotation of the molten core at the center of the Earth, 'shorting it' (apply a load) would presumably affect the core's rotation. In terms of relative energy however, the poor coupling at the surface would suggest that this would be a very challenging way to divert any meaningful amount of power from the core itself. It would however have to deal with points in time where the core reverses its magnetic field. The papers on core reversals are fun to read.

I think more usefully, the presence of the voltage, might be an interesting way to localize one's location and orientation.

I remember brainstorming "off the wall" power generation ideas and one that has yet to be realized would be to inject dust ahead of a wind turbine with a collector in the back. Then using the Van DeGraf effect to generate power instead of lightning as it currently does.

If one needs location, then the magnetic field can be measured directly. It is already considered as a potential alternative for GPS, https://www.electronicdesign.com/markets/automation/article/...

The main problem is that locally measured Earth magnetic field varies on a daily basis and is strongly influenced by solar storms.

A better alternative is to use variations in Earth gravity to improve inertial navigation. That vastly more stable.

I've often wondered about a similar issue with wind power. Would enough wind turbines dampen the force of wind?

If a politician talks in front of a wind turbine, does it make a sound?

On a local level they absolutely do, in a wind farm one turbine can shadow another and reduce its output significantly. It makes wind farm layout a tricky optimisation problem. On larger scales the impact is pretty minimal though, there’s so much energy spread over such a large area that significantly reducing it a global scale is not a concern.

Fundamentally, yes, right? For some definition of “enough.”

Actually, after some quick googling (so, maybe someone actually knows better) it seems like this is an issue where there’s an active discussion? Maybe somebody actually involved in the field knows more.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2004JD00...

https://esd.copernicus.org/articles/3/79/2012/esd-3-79-2012....

But that came out in 2012. I bet you could find some other article citing it, as rebuttals.

It seems a bit implausible to think we could somehow pull enough energy from the wind to really matter, but then again carbon based climate change also seemed a bit implausible so, I guess, who knows?

fast forward a hundert years and there is a massive culture war between the "rotation slowdown deniers" and people religiously buying "rotation friendly" products.

They are one step ahead of you. :-)

"We previously showed that even in an extreme scenario where our civilization somehow would obtain all its electrical energy from the effect described here, Earth’s rotation would slow by <1 ms per decade [2]."

The term "generate power from Earth's rotation" is basically saying "convert kinetic energy from Earth's angular momentum". If you extract energy, by conservation of energy that energy has to come from somewhere. So yes, we would normally expect Earth's rotation to slow.

But I think if you do the math, it would be absolutely miniscule.

Alternatively, we could speed up the Earth! Let's get rid of those pesky leap seconds!

I'm not saying that is why we left Mars.

Yeah, after making an oopsie with a runaway greenhouse effect in Venus. All this has happened before and it will happen again.

Ah yes, the Battlestar Galactica theory of life's origins on earth

It's definitely not why we left Mars because Mars still rotates every 24:30. We left Mars because of the hostile Martians, of course.

No because of conservation of angular momentum. Maybe it would cool the Earth's interior faster than otherwise though. It's heat flow from the inside to the outside that drives the fluid flows in the mantle and generates the magnetic field.

Earth's rotation has been slowing down despite principle of conservation of angular momentum, at about 2 mille-sec/century. Dinos had an hour shorter days than we do now.

I'm not an EE, but isn't this related to Tesla's last invention which bankrupted him - I believe he was working on electricity generation from thin air.

It's slowing down mostly because of drag induced by tides, which involve the sun and the moon. The total system including the earth, moon, sun and everything else does conserve angular momentum.

But this paper seems to imply that Earth, isolated from evening else in the solar system, could be made to slow down. This does seem like a violation of conservation of angular momentum...

This is poorly discussed in the article and AFAICS it reaches wrong conclusion.

I think the energy comes from weakening of the magnetic field and the energy stored within it, not from slowing down earth rotation. Earth as the result may rotate faster as the moment stored in the field will be transferred back to Earth as in the example with a sphere from the article.

That would make so much more sense. So then the comments about only slowing down Earth's rotation by a few ms/century. It would deplete Earth's magnetic field, and likely on a much faster timescale.

This would not be good...

I once read a book (Signalz, by F. Paul Wilson), where someone got transmitted power working, and it was part of ushering in eldritch dimension-dwellers. In that book, Tesla was part of some kind of dark wizard cabal.

Don’t remember, exactly. It was a while ago.

Not stupid at all, especially if only one part of physics exists and not quantum physics.

> would that accidentally slow the Earth's rotation

No. Incidentally :)

What's with the "this http URL" in the summary?

Paper said "earth.however". Because it's missing a space after the period, it appears as an invalid link.

I had an idea somewhat related to this where we use the solar winds as a sort of road and the earth's magnetic field as a sort of rotor to convert kinetic energy from the sun into electricity.

Sounds like solar power with extra steps

This kinda sorta how auroras/northern lights work.

Nature magazine had a good article on this, which is a quicker read https://www.nature.com/articles/d41586-025-00847-0

This is behind paywall

Try https://archive.is/5GHWF

Thanks! I made a copy of your comment in the other thread (https://news.ycombinator.com/item?id=43526470) so your account gets the karma for it. I hope that's ok!

Thanks! I've re-upped a submission of that article (https://news.ycombinator.com/item?id=43526443) and will merge the comments thither.

This is really cool. Question for EEs / Material Scientists reading the paper - they mention you could shrink the cylinders and get the same voltage provided a "suitable material" could be found. Any back of the envelope or explanation of materials needed to make these cylinders say 1/1000th their current size? That'd be an extremely useful amount of energy when put into say a 1000x parallel array.

It seems hard to imagine that this kind of shrink-down could go on forever, but on the other hand, the earth is just sort of hurtling us around with great energy while it rotates.

Wouldn't this slowly slow the earths rotation down? Let's say everyone tried to build power plants using this.

Ah didn't see this comment and I asked the same. Yes, right? The energy has to come from somewhere...

Wouldn't this eventually slow down Earth's rotation? The rotational kinetic energy of our planet is 1/5 M * R^2 * w^2 with (approximately) M = 6e34 kg, R = 6.3e6m, w = 7.4e-5 rad/s, which gives approximately 5e36 joules. Yearly we need roughly 3e16 Wh. Yeah ok there's plenty. Woah! (also, I may be off by some orders of magnitude)

0.44 picowatts = 4.4e-13 watts so not in a detectable fashion before the sun consumes the earth billions of years from now.

Well, the watts that come out of the rotational energy must match the ones we need, for energy conservation.

Sure, but there’s no “eventually” it happens instantly.

The only way you’ll care about what happens eventually is if you’re concerned about some detectable result. Meanwhile individual rocket launches to Mars extract like 10^18+ times as much energy as this will over it’s lifespan and those still aren’t detectable.

Doesn’t driving west to east on a highway slow down the Earth’s rotation, via the power transferred into the ground?

Yes, but that energy is returned when you break

Things get interesting when you reverse.

Reminds me of a glorious question from undergraduate physics:

Calculate the change in the length of the Earth's day if the UK were to switch to vehicles driving on the right-hand side of the road rather than the left..

Is that due to all the roundabouts switching direction relative to the Coriolis effect? Hence the relevance of the UK?

Presumably without roundabouts it's all random directions and balanced?

Or am I barking up the wrong tree?

It was indeed all about the roundabouts. I forget the details but I do know it took us quite a while to get there(!)

Those tutorials filled me with dread at the time, but with hindsight they were - how can I put this - a fairly formative experience.

Watching your tutor use paper and pencil - and estimation - to calculate something like that was actually quite inspiring. That was, once it stopped being terrifying.

Only while you're driving.

It's actually driving north south that changes the rotation speed. Because your 'real' speed gets higher as you get closer to the equator, you 'steal' momentum from the earth as you get closer to the equator.

Its effectively the same principle as a figure skater pulling in their arms when spinning, to spin faster.

Then when you stop the angular momentum of your car is transferred back to the earth.

This is addressed in the last paragraph of the article:

> Even if it works, the method will not generate energy from thin air. It would tap Earth’s kinetic energy and, in doing so, cause the planet’s spinning to slow over time — although only slightly. If the technique provided all of Earth’s electricity needs, which was around 11 trillion watts in 2022, this would slow the planet’s spin by 7 milliseconds over the next century, the authors calculate. This is similar to the change in speed caused by natural phenomena such as the Moon’s pull and changing dynamics inside the planet’s core.

Isn't friction from the atmosphere already slowing the planet's spin? Many weather effects like hurricanes ultimately derive their energy from a combination of the earth's rotation and thermal/uneven heating effects so I don't see why this is contentions.

Like most things, nature is already doing it and has been for millions of years.

No, that's not possible due to conservation of angular momentum. Only tidal effects can transfer some of it to the sun.

Tidal effects mostly transfers it to the moon, the sun has almost no tidal effects.

Tidal effects from the sun are about 46% as strong as those from the moon.

<https://oceanservice.noaa.gov/education/tutorial_tides/tides...>

Why would angular momentum be conserved? Rotation within an atmosphere should cause friction would should convert angular momentum into thermal loss.

Interestingly, it looks like the upper atmosphere generally rotates faster than the planet, so it could be that the opposite effect actually dominates. IE the uneven heating causes a atmospheric bulge that actually pushes the atmosphere around slightly faster than the planet rotates, thereby slightly contributing to planetary angular momentum.

Energy conservation and momentum conservation are different

Because the system exhibits rotational symmetry. It follows from Noether's theorem that angular momentum is conserved. Only when you include the interactions with other stellar bodies you lose the symmetry and you have an opportunity to shed angular momentum.

There is interaction with other stellar bodies. Massive and uneven amounts of thermal radiation from the sun. Black body radiation out.

Sure. I'm not going to perform the computation, but my physical intuition tells me that it's completely negligible. The amount of thermal energy the earth absorbs or emits per year must be dwarfed by several orders of magnitudes compared to the rotational energy or the energy lost via tidal friction.

> which was around 11 trillion watts in 2022, this would slow the planet’s spin by 7 milliseconds over the next century, the authors calculate.

Really puts how small we are on a cosmic scale into perspective.

If we did it for a million years at current energy use scale it would shorten our day by about 1.1 seconds.

Wouldn't it extend our day?

Yes. Had it backwards.

How much velocity loss would be needed for an impact on the environment, or on some humans someplace?

It's kind of insane how much energy is involved in big masses of rock flying around in space.

Where does the angular momentum go?

The IERS will never stand for this!

Can we put energy in to speed it up?

That way a day can be 24 hours exactly instead of 23 hours, 56 minutes, 4 seconds, etc...

I mean, solar day is 24h, it's the sidereal day that's 23.9344696h

Don’t follow your logic: if the day is currently shorter than 24 hours we need to slow the Earth rotation down, not speed it up.

You’re right, I had that backwards

Where does the angular momentum go?

it's the angular momentum that gets transferred to the earth's spin, and all the other numbers, energy, power, are simply how the books are balanced. GP should have asked the question in terms of momentum in the first place.

with energy, you need to consider friction, losses, thermodynamics 3rd law, but with momentum it's pure.

Torque is applied, the paper mentions a magnetic braking effect.

Would this reduce the magnetic field stength allowing more cosmic rays to reach the surface.

I, for one, look forward to ground-level auroras.