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Researchers create a sonic tractor beam

By Hanae Armitage 27 October 2015 1:00 pm

Using a simple set of loudspeakers, scientists have figured out a way to levitate and rotate objects in midair. If perfected, this “sonic tractor beam” could find uses ranging from treating kidney stones to creating artificial gravity on the International Space Station.

That isn't going to work for my aliens when grabbing onto other spacecraft. There are no sound waves in space. How can they use electromagnetic or other physics to create their tractor beam?

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    $\begingroup$ Are you sure you want the hard-science tag on this question? I don't think there is anything that comes close to a "tractor beam" in terms of known physics (well, unless you are going to include a mechanical device e.g. rope + grappling hook) $\endgroup$ – Neil Slater Oct 28 '15 at 11:18
  • $\begingroup$ A quick google for laser tractor beam pulls up a few good examples of small but working tractor beam experiments. Hard science is an applicable tag for this question, but I feel that most of the answers are going to suggest that it'll be impossible unless you're A: in a lab or B: are ok with reducing the other ship into a glowing ball of slag. $\endgroup$ – Joe Bloggs Oct 28 '15 at 11:33
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    $\begingroup$ Read my first answer sentence "Forget science articles from non serious science sources. They are misleading to say the least". Those devices are pushing not pulling particles $\endgroup$ – jean Oct 28 '15 at 11:37
  • $\begingroup$ There's at least one that features fine control for pushing or pulling by inducing hotspots on the opposite sides of the object to be pulled. Also: The peer reviewed papers in various laser physics journals are pretty serious, even if the popularist reporting on them is wishy-washy. $\endgroup$ – Joe Bloggs Oct 28 '15 at 11:43
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    $\begingroup$ I think you should take off the hard-science tag since this is entirely speculative. Also, since your "sonic tractor beam" doesn't make any sense, it's kind of pointless to say that it "won't work in space" - it won't work anywhere. You might as well reword your question as "can anyone come up with any vague ideas for how a tractor beam might work?" $\endgroup$ – Max Williams Oct 28 '15 at 16:14
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Forget science articles from non serious science sources. They are misleading to say the least.

Basic Science

The two attractive forces that can work from distance are electromagnetism and gravity. So if you want any tractor beam you must use one or both.

Unfortunately neither can be directed (as far as we know) and they "spread" in all directions meaning you cannot select a specific object and pull it. You will affect anything in range in the same way.

Also gravity cannot be created (as far as we know). An electromagnetic field can be created by an electric current. So a tractor beam is most likely to be a big electromagnet.

Electromagnet attraction doesn't work on everything.

Also you will need a lot of energy to create a strong enough effect.

In space note that your ship attracting another object will make both to move as by Newton's third law.

Finally consider that if you need to grab something in space to your spaceship it can be a lot easier just to use some kind of "crane". The means to attach to the target can be by harpoon (but can damage the target), suction (very hard in space without an atmosphere and also needs a smooth target surface) or electromagnets (needs a iron-like object and can damage/impair sensible electronics)

The next cool option

Maybe a good and cool option is to use space drones. A swarm of small rocket robots can move far away from your spaceship and grab things for you. But remember it's not that easy to move a complex object like ISS without it starting to rotate and derive in funny ways.

Laser pulling particles

There are some claims in that but let's read it carefully.

Those devices work by heating one side of the particle so air in contact with that particles ascends and this movement pulls the particle (like a miniature vacuum). It don't works in space and is limited to very small targets. A bigger laser to move a big object is more likely to use enough energy to burn it.

To pull or to push from the other side?

Note: high potency lasers work by just reducing its pulse duration to a fraction of second. The shorter the pulse, the higher the potency using the same energy amount. This means to continuously fire a high potency laser needs a huge amount of energy

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    $\begingroup$ Phased arrays give EM directivity, and the interference patterns may even be useful for the tractor beam (on this side of the object, the net force is toward the aim point, one the other side, it's also toward the aim point, which means in an opposite direction). $\endgroup$ – Ben Voigt Oct 28 '15 at 12:33
  • $\begingroup$ Phased arrays are useful to strengthening a signal in one direction by causing an constructive interference between transmitters. In some sense it's some kind of beam steering. But even if you can focus it as alaser (light is a eletromagnetic wave too) it's principle ill not be much different of the laser pulling and it's limitations ill be the same $\endgroup$ – jean Oct 28 '15 at 12:47
  • $\begingroup$ @BenVoigt In fact pretty much any kind of antenna or optics can be used to direct EM waves. In fact, classical optics can direct EM waves to apply both pushing and pulling forces, as well as lateral forces, in a vacuum: see optical tweezers. $\endgroup$ – 2012rcampion Oct 28 '15 at 16:59
  • $\begingroup$ What the difference between pulling and pushing from the other side? Seems pointless to limit yourself to the perspective of "pulling". $\endgroup$ – Samuel Oct 28 '15 at 19:04
  • $\begingroup$ @Samuel How do you ill shot a beam from the other side from the spaceship? $\endgroup$ – jean Oct 28 '15 at 19:13
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Shoot sticky electrically charged goo towards the object you want, and use the opposite charge to attract it. This is somewhat doable, but for any realistic masses and charges you will have a problem making the goo not to disintegrate because of the charge it contains. So realistically this will work only on rather light objects not far away (certainly not astronomical distances).

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If the aliens have artificial gravity inside their ships, they should be able to focus fields from a gravity generator outside the ship to manipulate objects within some distance. The larger the other item and the farther away it is, the greater the energy needed to do so.

If the other ship has engines, if it turned them on, then both ships would move, the 'tractor' beam would still only work on the relative frames of the two ships.

To fulfill the 'hard science' I'll add this.

the 'tractor beam' would be a special harpoon with a head depleted uranium to penetrate the hull and carbon nano-filament cable to 'pull' the ships together...

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  • $\begingroup$ [hard-science] tag does not allow "gravity generator" $\endgroup$ – jean Oct 28 '15 at 19:11
  • $\begingroup$ @jean True, but then I might as well just say to use a harpoon, with carbon nanofilament rope. $\endgroup$ – bowlturner Oct 28 '15 at 19:20
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The goal of a tractor beam..

  • To bring distance objects to your position, without requiring you to move (or with the least effort possible)

While the article you linked is very interesting, I did notice that the one side their speakers were on is the bottom of the object. I'm curious if it could also make the object levitate if the speakers were above, because then it would be "pulling" the object, rather than just not "pushing" as much and allowing gravity to bring it back towards the speakers.

In space, you could easily create "pushing" pulses with launched explosives. Or maybe a tiny laser with enough energy to break a single bond on the other objects surface (also resulting in an explosion) Tons of "tiny" explosions could push an object and rotate it however you'd like. But, like I suspect the acoustic tractor beam works, it probably can't pull anything towards you very well. Obviously, depending on the object, most spacecraft would be annihilated with this strategy - but if you had, for instance, some kind of sci-fi futuristic shielding or armor, it might be plausible.

(More realistically, you could also achieve a similar effect by hitting them with many projectiles: but, similar to the explosions, I don't know of a way the projectiles could transfer their velocity without damaging the target. You also have to worry about pushing yourself backwards!)


That leaves other strategies, which accomplish the goal but aren't really considered "tractor beams".

In addition to other answers, (which at this point includes harpoons, drones, and goo+magnets), you may consider using a net or bola-like device which could wrap around the target.

If the weights on your net had the propulsion mechanism necessary, it could pull the target to you and work across vast distances (as long as you hit them and it has enough fuel) - otherwise you're stuck using a "rope" (it'd actually have to be something light-weight and strong) which would cause the net to have a worse maximum range, plus require your ship to "pull" them in - which is probably pulling yourself just as much.

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My honest advice would be don't explain it. In truth justifying a tractor beam existing with hard science is very hard, and further more any technology that makes it possible would likely have other uses, meaning you would then have to expand your world to include all the other technologies that would invariably come from the first.

However, one of the cool things about science fiction is you get a certain free reign to say 'scientists invented it and it works like X', and so long as you don't violate any obvious hard constants of the world, most noticably in this case conservation of energy, you get allot of leaway to say it works because of principles that we just haven't discovered and trust me on this, so long as you set clear rules and stay consistent to them.

Trying to justify the science with hard facts is something I don't suggest trying unless you have very strong physics skill, because otherwise your likely to get part of the science wrong when explaining the technology and end up with a situation where the obvious flaws with the science just make it more obvious that the technology doesn't make sense

However, that's writing advice, not world building advice so moving on...

If you want to justify this the best explination I can suggest is gravity manipulation. Some method of shaping gravity was created such that you can create a strong gravity field which projects outwards from your ship, making objects 'fall' towards you. This works much better if your tractor beam can only pull, not push, objects, though with only a bit softer science you could probably handwave by saing you can manipulate gravity enough to create limited pushing effect.

This works best because it's drawing on a basic force of nature which already does what you want, and gravitons and gravity in general still is not entirely understood on a full quantum level, making it at least mildly possible that creating of gravitons may be somehow possible. Though already my mind is throwing up questions as to how this would work that I don't think about if someone just says "we have a tractor beam" without justifying it as gravity. In short this is the best answer I can think of, but I still advice against not giving any.

If you do have the ability to manipulate gravity you know have short range weapons to crush ships, potentially shields to deflect projectiles (depending on how much control you have of gravity), anti gravity ships that can 'float' at high speeds through the air of any planet, and of course artificial gravity for your ships, to name but a few related technologies that come from this. To minimize the questions people ask I would suggest saying that gravity is created only through a process like nuclear annihilation, or that you can only shape gravity but not create it, to justify the fact that only massive ships can manipulate gravity, to avoid question as to why small scale gravity manipulation isn't used for technology X.

Also keep in mind that whatever technology you create your need to abide by conservation of energy. Moving anything large, like an astroid, in space means applying a massive force to it, which in turn means a massive energy expenditure. Your want to think about just how much energy your spending to move objects, and rather the ship engaging the tractor beam has that much energy readily available to expend (suggesting an order of magnitude more energy then the tractor beam used is available to it). It's easily possible to explain that ships do have that much energy available, but keep in mind just how massive energy that is and what someone can do with that much stored power. Any ship with that much power is capable of being quite lethal to anything around it if it transfers enough energy rapidly enough, just for starters.

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If you don't mind becoming really freaky science wise, make the tractor beam be several beams of exotic particles that generate negative mass then the streams collide. The negative mass should be able to cause space-time distortions much like a warp drive and carry the entire section of spacetime, ship included, towards any direction you wish.

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  • $\begingroup$ This is my favorite idea since the "Negative mass" thing also implies the possibility of a warp drive, arguably something thats really useful in a story with interstellar space travel. $\endgroup$ – Shayne Apr 18 '16 at 7:23
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Its probably worth noting that Star Trek Enterprise used a fairly primitive form of tractor "beam", the grappling hook. Just fire that thing at your foe and drag them around like a jerk.

If I was to imagine however what a real one would like, I'd assume that in our space future we have some sort of FTL going, and the only feasible way to do that would be something along the lines of the Alcubierre warp drive idea, where you make space in front of the ship less dense, and the space behind it more dense thus pushing a pocket of space containing the spaceship along.

I think you can see where I'm going here. If you could do that, then I see no reason you couldn't make a tractor "beam" that creates a low density of space between you and the object pulling you and the object together. The best part of this is that you get to ignore a whole bunch of messy physics like newtons second law, because your not ACTUALLY pulling things together, just reducing the space between them.

All it needs is a whole heckload of negative energy unobtanium.

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