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Radio Waves Employed in Space Construction
CDeity writes "Researchers at the Georgia Institute of Technology claim that radio waves could be used to shape and fuse debris in space to form massive structures according to this article. Scientists have in the past employed sound and light waves to position small particles, and every expectation indicates these techniques could work on a large scale. One engineer estimates " it would take approximately one hour to form a rubble cloud into a 50-meter long enclosed structure.""
All electromagnetic waves, including light, are made up of photons and they do excert a force. The momentum of light can be calcuated via its frequency. The smaller the wavelength the more momentum and energy it has. According to Einstein: E^2=p^2c^2 +(mc^2)^2 Since the mass of a photon is negligable, if it even has one, E=pc where the energy is dependant on the momentum. C is a constant, ~ 3.0e8 m/s P is the momentum of the photon. Light is both a particle and a wave. P = h/(wavelength) where h is plancks constant. In fact P = h/wavelenght is true for all matter as well. If you want to learn more do some reading on quantum physics.
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As several people have mentioned, photons have momentum and do exert pressure (called radiation pressure).
Looking at it classically, though, electromagnetic waves are made up of electric fields and magnetic fields. Electric fields exert a force on charged particles. So if you point a radio wave at an object that reflects waves, then the wave's electric field will push the electrons in the object back and forth. The moving charged particles then interact with the wave's magnetic field, pushing them in the direction the wave was traveling.. Which is the same thing we could have predicted from conservation of momentum. (Warning: IANAP.)
What is your point? Of course you can send sound through space encoded in some form of radio transmission. But radio is not sound. There is no sound in space. Saying that there is sound in space is like saying there is sound inside the telephone wire. Sure there is information about sound waves traveling through the wire, but there is no sound. Sound is a vibration of matter. There is no matter in space to vibrate. Hence, no sound. (if you want to be pedantic about it, there is matter in space but the amount is so incredibly tiny, on the order of a few atoms per square meter, that it is not worth talking about. Certainly not enough matter there to carry sound).
main(c,r){for(r=32;r;) printf(++c>31?c=!r--,"\n":c<r?" ":~c&r?" `":" #");}
I _do_ know about the physical processes involved, and while I'm a physicist rather than an engineer (and hence less quick at estimating these things), this idea sounds completetly loony. You'd need to transmit an enormous amount of power to move a big chunk of rock even a small distance, because the power radiated by your transmitter will fall off rapidly with distance, and the rock will only absorb a small part of the radio wave anyway (for the same reason the walls of your house don't block radio reception).
And don't forget - NASA is funding research into an anti-gravity machine too, so the fact that they may be taking this seriously is no sign that it makes any sense....