What about the tractor beam?

[ThankQ]

A fun game Trek guys like to play is the "look what Trek tech predicted" game. You know, cell phones that a similar to communicators, supermarket and airport doors that woosh open and the like.

There are also theories on warp drive and transporters and whatnot.

But I've never heard anything about the tractor beam.

The idea of the tractor beam, as I understand is: A controlled-emission particle stream that can manipulate an object in all three spacial deminsions. That is, a stream of particles that can hold an object in place, move it up down, left right, to fro.

Does anyone know if there's any theory that allows or prevents this? I've never seen any discussion on that before.

 

[Christopher]

I've never seen a tractor beam described as a "stream of particles." It's usually assumed to be a gravity beam. But there's no way a gravity or other force beam would function like a tractor beam is supposed to work in fiction, which is basically as an invisible tether. A force is a push or pull, not something that holds an object in place.

Although there are certain exceptions. I don't remember the details, but there's a kind of magnetohydrodynamic field effect that, if applied in a weightless vacuum, could allow physically distinct objects to be held in place at a fixed distance from one another. Though it's more a kind of maglev effect than a tractor beam per se, and it certainly couldn't be used to capture or hold anything that was actively exerting thrust to get away.

On a microscopic scale, it's possible to use lasers to manipulate small particles or transparent beads in a "tractor beam"-like fashion. Obviously not useful for holding starships in place, though.

Now, if you want to push an object instead of pulling or holding it, then you get into the whole field of beam propulsion. Lasers can be used to propel solar sails, or to evaporate reaction mass or trigger fusion to drive a craft forward. In atmosphere, a laser could theoretically be used to launch a craft into orbit by intense heating of the air inside its concave base, essentially using the air itself as rocket fuel. So a laser could be considered a "pressor beam" of sorts, the opposite of a tractor beam.

If you want to pull something or hold it in place, though, the best way is always going to be through a physical connection like a tether. You're still using "forces" to pull it, namely the EM forces binding the particles of the tether. And it's more concentrated and directional than a simple energy field or beam would be. Generally, tractor beams are the kind of sci-fi conceit that makes something more complicated and inefficient than it needs to be for the sake of seeming futuristic. (Like forcefield prisons. What's wrong with a good solid door? One that won't disappear when the power goes off?)

 

[JustAFriend]

Less syllables:

The only thing we've found that 'pulls' is magnets, everything else only pushes.

 

[Samurai8472]

Sorry sir, won't be installed till Tuesday

 

[Christopher]

Less syllables:

The only thing we've found that 'pulls' is magnets, everything else only pushes.

Uhh, gravity pulls and doesn't push. Same with the strong nuclear force that binds atomic nuclei together. And the weak nuclear interaction is neither attractive or repulsive. So you've got it backward -- the electromagnetic interaction is the only one of the four fundamental forces that does push as well as pulling.

 

[Asbo Zaprudder]

Less syllables:

The only thing we've found that 'pulls' is magnets, everything else only pushes.

Similar magnet poles repel (push) each other. Positive and negative electric charges attract each other. As Christopher says, there are other forces, such as Gravity, that attract (measured in the direction of time increasing).

 

[ThankQ]

Wouldn't a "gravity beam" be a "gravtion stream"? In otherwords, a stream of particles.

 

[Dingle Fritz]

Less syllables:

The only thing we've found that 'pulls' is magnets, everything else only pushes.

Gee I've played around with magnets and I can make them push...