Perpetual motion doesn't exist... or does it? In space planets continuously spin around stars for trillions of years due to inertia and gravity balancing each other out. What if a race of brilliant beings found a way to produce energy from that process and store it locally on a moon?

How then could they theoretically transfer that energy remotely through space to the home planet without incinerating the atmosphere, causing wide-spread cancer, or other ill affects?

Is there a way to harmlessly (everything being relative) transfer stored energy from a moon to the planet, without cables, and then have that planet reliably receive that energy for distribution?

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    $\begingroup$ perpetual motion yes endless energy no. $\endgroup$ – sdrawkcabdear Feb 1 '17 at 17:50
  • $\begingroup$ @sdrawkcabdear Technically even planets and stars wear out eventually, so no perpetual motion that way either. Endless energy no. Super cheap to the point of almost being free? That's possible. $\endgroup$ – AndyD273 Feb 1 '17 at 18:09
  • $\begingroup$ Thank you for the great feedback! I never thought about where the energy was actually coming from, but yeah I guess over time I'd be potentially causing far worse damage than intended unless there was a system where the satellite was slowly moving away from the planet and the energy draw was a means of keeping it in proper orbit.. $\endgroup$ – mkinson Feb 1 '17 at 18:10
  • $\begingroup$ @mkinson Glad you could get what you needed! Stick around and see what all the site has to offer. $\endgroup$ – AndyD273 Feb 1 '17 at 18:13
  • $\begingroup$ It's traditional to leave a question for a bit longer (a day, perhaps) before choosing an answer. Gives more people time to supply potential answers. $\endgroup$ – Joe Bloggs Feb 1 '17 at 18:14

So ... endless energy does not exist. If you draw energy from a planet's spin then you will slow it down. If a object spins in vacuum and nothing touches it yes it could spin forever but no energy can be extracted from that.

Moving on lets hand wave how this energy is generated. Its on a moon now how do we get it onto a planet?

The answer is lasers. You pick a spectrum of light that passes through air well and you build a laser in that spectrum and a receiving station on planet, that converts the light into what ever energy type you prefer. The simple version would be a large visible light laser and a receiving station that is a large set of solar cells. It has to be a laser (photons all moving in the same direction) to make sure that the light stays focused and hits the receiving station rather than spreading out and being lost to space. Visual light passes through earths atmosphere with little effect, and a well focused laser will keep the high energy confined to the receiving station.


  • security and aiming there is a huge laser beaming huge amounts of energy onto earth if it is accidentally or deliberately pointed at anything other than the receiving station you could cook people, so make sure it is well aimed and well guarded.
  • $\begingroup$ Huh, we came up with basically the same answer. $\endgroup$ – J. Doe Feb 1 '17 at 17:52
  • $\begingroup$ Fun fact: Spinning objects may have their angular momentum 'stolen' by the quantum foam. But it would take so long to remove any meaningful amount of energy that the heat death of the universe would probably happen first for pretty much anything. $\endgroup$ – Joe Bloggs Feb 1 '17 at 17:52
  • $\begingroup$ @JoeBloggs interesting though planets lose spin faster to tidal effects from their moons or friction against their atmospheres. I guess great minds think alike $\endgroup$ – sdrawkcabdear Feb 1 '17 at 17:59
  • $\begingroup$ @sdrawkcabdear: I was thinking more objects on the size of microscopic dust particles. :-D Wish I could find the paper on it. It's a really cool theoretical effect. $\endgroup$ – Joe Bloggs Feb 1 '17 at 18:13

Perpetual? No. You're just stealing angular momentum from the system. Eventually the planets will deorbit.

Long lasting? Yes. There is an awful lot of angular momentum in any solar system.

Remotely? Believe it or not: we already do this. Tidal energy is us stealing angular momentum from the Earth-Moon (and also some from the Earth-Sun) system. If you want a more controllable system then a series of circumglobal canals with strategically placed hydroelectric dams should do the trick.


  • $\begingroup$ I like the dams/canal idea $\endgroup$ – James Feb 1 '17 at 18:03

Why Don't WE do that?

Hmm... I think you're looking more for a plausible sounding approximation for an answer, rather than anything solid. Since, if we knew the answer to this, we could talk about DOING IT, and having near limitless energy.

Limitless Energy?

First thought: Any energy you take out of the planets rotating around the star, means slowing them down. It may take a hundred years or a million years before this become a problem, but it does risk the planet spiraling into the star. The source of energy isn't actually perpetual, so eventually you will, "run out". And of course, the more/faster you take out the energy, the faster this will happen.


As for how you would transfer it? Well, it depends on what form it is in in the first place. At this level of tech, it might be sub-atomic-extra-spacial-gravity-photons, or such jazz, in which case: "however you want it." If it is electricity, either you have an impossibly strong materials to make cables that go from the moon to the planet (perfect for space elevators), or you'll use something akin to batteries you transfer/drop on the planet, or you use lasers.

You can't laser TOO MUCH at once, or you might (assuming an oxygen planet) ignite the atmosphere or cause nuclear explosions or have such a high energy density nothing can effectively catch the laser. I don't think laser transfers are very efficient, but they might be when dealing with presumably massive levels of energy.


There is one way that we know of that can make this happen, which is tidal energy.

Jupiter's moons Ganymede and Europa both have a lot of water, as does Saturn's moon Enceladus. As they orbit their planets and spin on their axis they have tides that slosh around, break up the surface ice, and erupt in geysers.

On Earth we are starting to use tidal generator to make energy from the moons rotation around the Earth, so it wouldn't be hard for an advanced alien race to set up something that works on the same principal to get all kinds of energy.

For transmission microwave and laser beams to send it to orbiting satellites which would then transmit it elsewhere. There would be a lot of loss with this method, but with enough energy to start with it might not make a difference.

Alternately the power could be stored in other mediums like batteries, which could be much more efficient than what we use on earth, and shipped to places where beamed power would be impractical.

The real problem with "perpetual motion" is the "perpetual" part. Everything runs down eventually, including the universe itself. The best we can hope for is really really cheap, almost to the point of being free, energy.


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