How can I hit a planet with an energy beam from ten lightyears away?

Question

My interstellar empire is powered by a quasar.

Or at least it will be once I finish my scheme.

See that cloud of glowing dust? That's called the quasar's accretion disc. When stuff falls into the centre, most of it is gobbled up by the collapsing star. But due to conservation of something I can't remember, about six percent of the mass energy is converted into kinetic energy and shot back out at the speed of light (the fastest speed there is) as radiation. That's the beam.

The quasar is in the middle of the inhabited part of the galaxy. There are hundreds of loosely confederated planets and artificial habitats within dozens of lightyears of the Zar.

The Zar. That's what I call the quasar by the way. Or what I will call it, once I have finished my scheme. Once I am Emperor, or Tzar (pronounced Zar) as my subjects will call me. It's a pun. You are allowed to make puns when you are Emperor.

The plan is to turn the Zar into the best and most efficient power plant in the galaxy. Once I have driven my competitors out of business, and established a galactic monopoly on cheap clean energy, I can demand anything I want. Fail to comply and the lights in your houses go out. Fail to comply and the lights in your swimming pools and hospitals go out.

The project is already half complete. I have finished construction of the Unobtanium shell around the outside of the Zar, and I have coated the interior surface with shiny tinfoil. When I want energy I chuck more matter into the hole. The outgoing radiation gets reflected and concentrated into a beam that I can split and shoot across the galaxy to power the worlds in my empire.

I am now accepting bids from any interested parties for the following project:

What is the most reliable way to transmit a beam of energy from my stellar powerplant to the various worlds in the empire?

My original plan was to split the Main Beam and shoot one minibeam to the giant beam catcher on each world. But my team of Eggheads has informed me that many of the worlds in my empire like to move around. Some of the planets orbit their stars. This makes a fixed beam a big no-no. Some of the worlds revolve while orbiting their stars. So even if we move the minibeam to follow the orbit, the beam catcher will point the wrong way most of the time and we end up beaming the planet in half.

The Eggheads also say it is hard to predict the motion of things at this scale. You do not shoot the beam at the planet. You shoot the beam where the planet will be in six years. The planets are very small and very far away and due to a "chaotic system" as they call it, we cannot predict with enough accuracy. Again we either miss the planet entirely or chop it in half. Not good for business.

Hence I come to you, talented investor. Bids are now open for a state-of-the art beam delivery system. The ideal system will provide an effectively unlimited and supremely reliable supply of power to each world in my fledgling empire.

Interested parties are informed that money and resources are no object, as I have recently received a small loan from my father. The successful bidder will have full access to the company fleet as well as our cutting-edge Star Foundries and nano-labs. Please include in your bid an enumerated list of any starships, megacruisers, satellites, artificial habitats, repurposed planetoids, genetically-engineered beings, or works of seminal art you will require.

Other benefits include free Deliveroo breakfasts and lunches for you and your team for the duration of the contract; access to the company parking lot, gym, swimming pool and sauna; complementary haircuts; and free tea and coffee in the break room. Each applicant will receive a goody bag consisting of a company tote bag, lanyard, t-shirt, pen and journal.

Inspired by this answer

Answer 1

Everything is so much worse than you think

• Planets don't just rotate, they wobble.

• Planets don't just orbit, the orbits wobble.

• Suns don't just sit still, they move, too.

• And they wobble.

• And just to put icing on the cake, the galaxy doesn't sit still, it moves, too.

• And I wouldn't be surprised if it wobbles, too.

Which means the predictability of hitting your target is pre-tty challenging. But that's not all!

• Space has stuff in it. Gas. Dust. Plasma. You might think it's pretty empty but at the energy levels you're talking about and the distances you're talking about you might as well as be diving into a pool full of jell-o. Just punching through the heliopause might be interesting.

• Space has gravity, too... and what's the one thing that can bend light without a medium? Yup! Gravity!

• And just to add some imagination to our collection of woes... you might have come up with the one way you can actually prove there's Dark Matter. With this much energy flowing through it, it should light up like a Grateful Dead T-shirt under a black light.

It's a bit like hitting the worst moving target in human history with an unrifled bullet made of styrofoam.

But you're saved!

Because what you need is the most awesome, most amazing, most astounding set of waveguides in human history!

A waveguide is a structure that guides waves, such as electromagnetic waves or sound, with minimal loss of energy by restricting the transmission of energy to one direction. Without the physical constraint of a waveguide, wave intensities decrease according to the inverse square law as they expand into three dimensional space.

There are different types of waveguides for different types of waves. The original and most common meaning is a hollow conductive metal pipe used to carry high frequency radio waves, particularly microwaves. Dielectric waveguides are used at higher radio frequencies, and transparent dielectric waveguides and optical fibers serve as waveguides for light. In acoustics, air ducts and horns are used as waveguides for sound in musical instruments and loudspeakers, and specially-shaped metal rods conduct ultrasonic waves in ultrasonic machining.

The geometry of a waveguide reflects its function; in addition to more common types that channel the wave in one dimension, there are two-dimensional slab waveguides which confine waves to two dimensions. The frequency of the transmitted wave also dictates the size of a waveguide: each waveguide has a cutoff wavelength determined by its size and will not conduct waves of greater wavelength; an optical fiber that guides light will not transmit microwaves which have a much larger wavelength. Some naturally occurring structures can also act as waveguides. The SOFAR channel layer in the ocean can guide the sound of whale song across enormous distances. Any shape of cross section of waveguide can support EM waves. Irregular shapes are difficult to analyse. Commonly used waveguides are rectangular and circular in shape.

Now, obviously you can't drag bazillions of kilometers of tubes through the galaxy. I mean, you could... and that would also be awesome... but realistically you need something a bit more practical.

Magnetic Waveguides

Magnonics, or spin wave based spintronics, is an emerging technology where magnons—quanta for spin waves—process the information analogous to electronic charges in electronics. We introduce the fundamental components of a magnonic device and briefly discuss their electrical control. The magnetic waveguide—an integral part of a magnonic circuit—guides the spin wave signal (magnon current) of desired frequency, wave vector, phase, and amplitude, which are the key ingredients for wave based computing. Typically, a bias magnetic field aligns magnetization to satisfy anisotropic magnon dispersions for low-energy and long-wavelength magnons, and thus it hinders on-chip device integration capability. We discuss strategies to eliminate the requirements of such a bias field by utilizing self-biased waveguides, which are based on either exchange coupled magnetic multi-layer based magnetic micro-wire or dipolar coupled but physically separated chain of rhomboid nanomagnets. We emphasize that the self-biased waveguides offer additional functionalities as compared to conventional waveguides. In this regard, manipulation of spin waves or the gating operation is presented by utilizing reconfigurable remanent magnetic states of the waveguide externally controlled by field or microwave current. We discuss the prospects of these bias-free waveguide strategies in the rapidly developing field of nano-magnonics and their potential for practical realizations of a magnonic-electronic hybrid technology. (Source)

Now, if you ignore the fact that magnons are a bit small (kinda, not really a particle...) and that the frequencies are a bit high for effective energy transmission, what you have is a scientific basis for the following science fiction:¹

In your universe, scientists have discovered how to create a series of satellite space stations scattered across the galaxy The purpose of these satellites is to create magnetic waveguides. The satellites are "close enough" that they can keep themselves in reasonable (read: believable) alignment with each other, which means you're not shooting blind at the planets. They siphon off enough of the energy to not only maintain the waveguides, but to move, which they're constantly doing. Your running your energy along the intersteller equivalent of ocean buoys connected with rope.

And if you're thinking Borg Transwarp Conduits... you're not too far off the inspiration for this answer.

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_{¹ I'll be honest with you, you used the science-based tag. Humanity hasn't tried to move a thousandth of one percent of the energy you're talking about... and you used the science-based tag. I'm doing my best, but my answer will default to the science-fiction tag because, frankly, there is no science today that can move that much energy across that much distance. So... yeah.}

Answer 2

Zar frequency radiation

The problem with radiation is that is scatters. Also it hits stuff you don't want it to hit, and wastes its energy, or hurts that stuff. That is especially true of energetic short wavelength stuff like Xrays. That kind of radiation is bad for beaming power.

Longer wavelengths scatter less, and tend to go right thru things in the way. Really long wavelength radiaton like extremely low frequency radiation has a wavelength of thousands of kilometers.

Zar frequency is longer than that. Much longer. This is a really long wavelength, as shown in the picture. All subjects of the Empire will know Zar frequency is so long as to be cumbersome for any but the Zar but the Zar makes it work for the good of the people. This long Zar radiation penetrates all things in its way with impunity as it travels to the collection point, where special collectors inured to the extreme longness collect the radiation and convert it to gentle warmth for the subjects.

Answer 3

As good as it might be, the beam will diverge over cosmic distances, spreading over. I think your best option is to to use a gravitational lens to focus back the beam on your receiver.

It might be tricky to be always in the focus area, but that can be mitigated by a fleet of orbiting receivers of which one at least is the right area.

Answer 4

Bismuth synthesis

If you've got mass-to-energy conversion, you can convert energy into stable matter, transport the matter somewhere, and then convert it back to energy as needed.

• You could make uranium, establishing a galactic surplus of nuclear fuel. Spent fuel can be fed back into Zar instead of accumulating on planets.

  The big problem here is that any habitable world is going to be at minimum dozens of lightyears away from Zar, so transporting any matter there will take years unless you have FTL. Even with FTL, "vessel filled with tons of uranium" is just a euphemism for "gargantuan nuclear bomb." Maybe there is a way to arrange a buttload of uranium such that it stays sub-critical, but if contents shift during transit (as contents are wont to do) it becomes a bomb. It's just too dangerous for transport.

• Goojle says that bismuth-209 is the heaviest non-radioactive element ("its radioactivity is much slighter than that of human flesh" -- Wiki). I figure most pilots will have no problem transporting, and most planets will have no objection to receiving, regular cargoes of several tons of wholesome, non-radioactive human flesh, so that's what I would generate at the power station above Zar: huge ingots of bismuth.

  When they arrive at their destination, you can probably just drop them from orbit into the largest body of water -- no need to waste fuel or time carefully lowering them into the gravity well. Recipients planetside can tow the giant, pink Zarpto-Bismol ingots to an Einstein facility where it can be shaved down into fuel pellets and fed into Ye Olde Matter Furnace.

• Lead is also very non-radioactive (and similarly massive, as lead-208), but it is also very toxic, so you would not want to be throwing it into planetary atmospheres or slamming it into the ocean.

Answer 5

Have you considered a radically different method from beams as the primary way of getting from the Quasar to the individual solar systems: - the great and mighty Zar could catch the beam in a primary beam catcher, convert it (possibly flare off some excess energy for style), then use some form of quantum entanglement in nodes to transmit the energy to paired locations on each planet - avoiding having to track them.

The energy given to each planet possibly is greater then the needs of the planet, and those local entanglement centres would have to have a lot of technology to absorb, and again, flare off excess energy - possibly a minor beam sent harmlessly into space, (like a flare on an oil rig).

To the locals, this would probably look like the energy was coming in via this beam, rather than it leaving it. Any science sufficiently advanced will look like magic after all.

A sub-idea: The cost of making the energy receiving plants would be significant - in a solar system, depending on the reach of your magnificence, you might only be able to afford a single entanglement node, and so you might have to make space stations that are receiving the power and then beaming it down to the local planets using targeted process (e.g some form of polar-star orbiting station like Gateway, that then beams to a planets satellites that then reflect to the ground. This would then still have beams incoming to the planet, but remove the cumbersome effects of giant beams over the grand distances which are much trickier to aim.