Tractor beams, IRL

[lilphil1989]

Tractor beams can exist theoretically!

arxiv link

The basic principle is to shine a beam at some angle to the object you want to pull, and choose a form for the beam such that it is possible to maximise scattering from the object in the forward direction.

Unfortunately, it relies on interference effects which only exist for objects that are smaller than the wavelength of the radiation used, so this along with the fact that absorption as opposed to scattering tends to become dominant for large objects, scaling this up to move macroscopic objects doesn't really seem feasible .

But the fact that this exists, even if it is just in principle and for microscopic objects, is pretty awesome!

[Anomalocaris]

Maybe it can work with macroscopic objects via exceptionally powerful source of low frequency radio waves

[lilphil1989]

Maybe it can work with macroscopic objects via exceptionally powerful source of low frequency radio waves

The power required really would be exceptional!

Take a metre cube object, weighing 1kg, and assume 1% scattering (this is quite optimistic). To give it a macroscopic acceleration, say 0.1 m/s^2, you'd need an RF generator putting out about 10^9 Watts!
For comparison, communication radio stations put out about 10^4 Watts.

And that's not even mentioning the difficulties associated with getting the necessary beam profile; getting a decent short wavelength pseudo-Bessel beam (for optical tweezers and the like) is difficult enough, I wouldn't want to think about doing it with radio waves!

But by the time we can build the Death Star, I'm sure this won't be a problem

[Anomalocaris]

Considering the power required to accelerating a 1kg mass from rest at .1 m/s^2 for 1 second averages only 0.005 watts, I might say the tractor beam is a loser.