I don't know if there is any real use for this, I just like the idea.
John Walker built a device that could show the gravitational attraction between two small objects in about half an hour. Basically a balance arm with weights on the end, hanging from a nylon line. Put the other weights nearby (he uses 2 more, on opposite sides, but one should do). The device rotates the hanging masses to line up with the other masses.
My idea is to use this as a communication or control signalling device, capable of transmitting around 50 bits per day. Unfortunately, the signal quickly gets weaker as the range increases, but you might get a range of roughly the length of the arm (30cm) without reducing the bit rate by much.
With all these limitations, what are the features? The gravity signals can go through anything. Suppose someone wants to live in an impenetrable stone or steel fortress, shielded somehow from all electromagnetic and sonic radiation, and has worked out how to do everything but the doorbell. Put the detector on the inside, and the button on the outside can be attached to a device that moves a weight, and in under half an hour, the doorbell rings.
Maybe you can think of another use.-- caspian, Dec 26 2004 Gravity Demonstrator http://fourmilab.ch/gravitation/foobar/ [caspian, Dec 26 2004] Gravity Waves Gravity_20Waves[Vernon] has done something similar. [Detly, Dec 28 2004] Communicating via gravity is theoretically possible, but in practice will almost certainly not be workable. Gravity has two major problems, being both (1) very weak, and (2) absolutely ubiquitous.
It may not seem at first like gravity is all that much weaker than forces such as electrostatic or magnetic attraction or repulsion, but there's a major practical difference: if you rub a heavier-than-air balloon to impart a static charge and stick it to the ceiling, not the static charge stronger than gravity, but that comparison is between the static charge between a small area of the ceiling and the balloon, as compared with gravitational attraction between THE ENTIRE PLANET at the balloon.
Generally, unbalanced electrostatic charges only exist in fairly small areas; over larger areas, they tend to cancel out. By contrast, gravity doesn't (so far as scientists know) ever cancel, so the gravity we perceive is the sum of the attractions from everything on or near the planet (actually everything in the universe though objects outside the solar system are for all practical purposes a non-factor). Compared to that, the effect of swinging even a 1-ton weight would be trivial.-- supercat, Dec 28 2004 In [Vernon]'s idea, there has been some discussion on the practicability of using gravity waves for communication. This idea is not identical, as it uses the strength of the field as the signal. That's if I've read it correctly.
But as [supercat] points out, noise is a huge issue, and at large distances a static field is far too weak to be detectable.-- Detly, Dec 28 2004 This idea would be a very slick ending to a high SF tale. The explorer team would be stuck in an ancient alien fortress as described above. They cannot get out without help from the team on the outside. They try various means to break through as does the outside team. The difficulty would be not only to communitcate using gravity, but to let folks on the outside know you were trying to communicate with gravity.-- bungston, Dec 28 2004 The movies on that first link are mind blowing.-- JesusHChrist, May 02 2005 //The difficulty would be not only to communitcate using gravity, but to let folks on the outside know you were trying to communicate with gravity.// Once we figure out how to make phase shifted quadrature waves with a mass driven quadrupole antenna, everyone will communicate with gravity.-- Space Machine, Apr 24 2010 random, halfbakery