What are high-frequency gravitational waves? Visualize the luffing of a sail as a sailboat comes about or tacks. The waves in the sail’s fabric are similar in many ways to gravitational waves, but instead of sailcloth fabric, gravitational waves move through a “fabric ” of space. Einstein called this fabric the “space-time continuum” in his 1915 theoretical work known as General Relativity (or GR). Although his theory is very sophisticated, the concept is relatively simple. This fabric is four-dimensional: it has the three usual dimensions of space: (1) east-west, (2) north-south, (3) up-down, plus the dimension of (4) time. Here is an example: we define a location on this “fabric” as 5th Street and Third Avenue on the third floor at 9 AM. We can’t see this “fabric ” just as we can’t see the wind, sound, or gravity for that matter. Nevertheless, those elements are real, and so is this “fabric.” If we could generate ripples in this fabric, then many applications become available to us. Much like radio waves can be used to transmit information through space, we could use gravitational waves to perform analogous functions. Still the question arises … how can we generate and detect these gravitational waves in the space-time fabric?
 
One way we can generate wind waves is by the motion of fan blades. Likewise, gravitational waves (GWs) can theoretically be generated by the motion of masses. We can detect wind waves by the motion of a weather vane. Similarly, we could detect gravitational waves by a transient change in a dimension, such as the distance between two points at the ends of a ruler. Gravitational waves will make the ruler seem to behave, to an outsider observer, as if it was made of rubber, stretching and contracting. However, the change in length would be extremely small, smaller than the diameter of a proton! Ordinarily we would not be able to observe it, but scientists are now testing techniques to detect gravitational waves by very accurately measuring the distance between two points (technically it is called the Laser Interferometric Gravitational Observatory or LIGO).
 
So, Gravitational Waves are like other waves, but they exist in a rather strange fabric of space-time. Now comes the tough part: how are gravitational waves generated in nature? One possible generation mechanism is a double-star orbit, two stars that circle around or orbit each other. If these stars are very heavy, perhaps black holes, then there exists an incredibly large change in force, called centrifugal force, as they orbit one another. According to Einstein ’s publication in 1916 (a year after his GR) such a rapid change in force over a brief time generates gravitational waves.
 
However, the gravitational waves generated by these stars are of very low frequency. So if the stars rotate around each other with a period of, say, one second (for comparison, the period of our motion around the Sun is one year), then the gravitational-wave frequency is two cycles per second or two “Hertz,” (2 Hz for short) according to Einstein ’s theory. For a reference, US house current has a frequency of 60 cycles per second (60 Hz) whereas radio waves have frequencies of thousands of Hz.
 
These Low-Frequency Gravitational Waves (LFGWs) generated by rapid changes in force (for example, during the orbiting of two black holes), could be detected by LIGO if they exhibited frequencies from 40Hz to 2000 Hz, but what use are they if we can ’t harness their potential? To be useful we not only need to detect them… we need to generate them. So, could gravitational waves be generated in the laboratory? It’s obvious we cannot have two black holes orbiting in a laboratory, but it turns out we really don’t need to. The trick is that we don’t require gravitational force to generate gravitational waves! It’s really the motion of the mass that counts, not the kind of force that produces that motion. How do we obtain a large force change? To make it practical we need a force that is much larger than the force of gravitational attraction. Let’s do a thought experiment and think of two horseshoe magnets facing each other (North poles facing South poles). They will attract each other strongly. If we reverse the magnets, put them down back-to-back with their poles facing outwards, then primarily their gravitational force acts due to their masses and we sense little or no attractive pull. As a matter-of-fact, magnetic and other non-gravitational forces are about 1,000,000,000,000,000,000,000,000,000,000,000,000 times larger than the gravitational forces! So, if we have our choice, we want to use “electromagnetic force” as our force, not weak little gravity.