Gravitational Waves

3843 Words 16 Pages
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 LISA. From our research of these groups
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It was discovered in 1916 that the general theory of relativity predicts the existence of gravitational waves. “Gravitational waves are perturbations in the curvature of spacetime propagating with the velocity of light. They are caused by accelerating masses.”2 In order to understand the concept of a gravitational wave it is helpful to understand gravity as explained by the general theory of relativity. Relativity does not analyze gravity in terms of forces and acceleration as in Newtonian physics. 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.

3

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
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However, this same percentage in the 2-meter stick will be twice as much as the stretch of the meter stick. Thus for the detection of gravitational waves, longer arms allow for more sensitive interferometers.
There are other factors that could cause the arm lengths to fluctuate or appear to fluctuate, such as, thermal expansion, a non-stable laser source, or a poor vacuum. Anything that interferes with the detection of a gravitational waves signal is referred to as noise. If the laser source does not emit a constant, or stable, frequency of light the photodetector will detect a change in the intensity. Thermal expansion will change the arm lengths of the interferometer, thus changing the detected interference of the recombined beams. If the vacuum environment in the system is not low enough the particles in the air can interact with the laser beam, changing the interference of the recombined beams. These are just some of the factors that could hinder the ability of the interferometer to detect gravitational waves. For this reason the interferometer must be isolated from these and other noise sources.
LIGO
Laser Interferometer Gravitational-Wave
Observatory, LIGO, is a collaboration of

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