GRAVITATIONAL WAVES, HOW CLOSE ARE WE?
PHSCS 222 Collective Paper November 23, 1999 #123 #272 #666 #895
The Detection of Gravitational Waves, How Close Are We?
Since the realization that the general theory of relativity predicts gravitational waves, there have been attempts to actually detect these waves. Indirect observations have been made that support their existence but no direct measurement. This paper gives a brief explanation of gravitational waves and discusses the current condition of the experimental search for gravitational waves. It deals with the newest techniques that will enable their detection. The focus of the paper is on three experimental groups: LIGO, VIRGO, and ...view middle of the document...
Instead it explains gravity in terms of the geometry of spacetime. Space time is a very difficult concept to visualize. It is made up of the three positionaxes, x, y and z, but also includes the dimension of time. It is the fourth axis of time that makes spacetime difficult to conceptualize. Spacetime is all around us. It maybe helpful to think of it as a medium that encompasses everything: earth, our galaxy, the universe, etc. All planets, suns, moons and celestial bodies are “submersed” in this medium called spacetime.
According to the general theory of relativity mass bends spacetime. Larger masses bend space-time more than smaller masses, just as a more massive object would bend a trampoline more than a less massive object. If the gridlines in Figure 1 represent spacetime it can be seen how the Earth bends it. Objects that approach the Earth will be affected by this curvature around it. Specifically, an object will be moved towards the Earth. This is how general relativity pictures gravity. As mentioned gravitational waves are perturbations in the curvature of spacetime, and are created by accelerated masses. A similar occurrence can be observed with water. As a fish in a bowl moves around underwater it produces movements, or waves, in the water that spread throughout the bowl. In this same way accelerated masses produce waves in spacetime. These waves travel throughout the universe affecting spacetime and other masses within it. The magnitude, or strength, of the gravitational waves is directly proportional to both the mass and the acceleration of that mass. The magnitude of the wave also depends on the distance it travels before it reaches us. The further it travels the smaller its magnitude will be. It is this fact that has made detection of the gravitational waves unsuccessful in the past. It is difficult to understand how a gravitational wave affects matter. It is best to consider the wave's effect on the spacetime around the matter. As the wave passes through spacetime it bends it, and any material in the spacetime must also bend accordingly to move with the spacetime. Gravitational waves tell spacetime how to curve, and spacetime in turn tells matter how to move. The theoretical analysis of gravitational waves is quite difficult compared to that of a wave on a string because they are not one-dimensional. Gravitational waves have characteristics similar to both longitudinal and transverse waves. These types of waves are easily understood in
one dimension but become extremely complicated in more dimensions. Gravitational waves are actually classified as both quadrupolar transverse and quadrupolar longitudinal waves. Properties of these kinds of waves are difficult to conceptualize. Figure 2 explains how gravitational waves have transverse and longitudinal components. Theoretically gravitational waves, like light waves, can be polarized, components with certain orientations could be absorbed as the wave passes through a...