Gravitational Waves: LISA Project
Jessica Gifford, Stephan Schlamminger · 2010
The detection of gravitational waves within our universe has been a topic of interest since its prediction by Einstein’s theory of General Relativity. General Relativity addresses the concern that there is no difference between a homogeneous gravitational field and an accelerated reference frame. One of the best analogies for this is Einstein’s elevator in which a man on earth in a non accelerating elevator drops a ball and sees no difference in the ball’s motion to that of his friend. His friend is in an elevator in space, with no gravitational field, that is accelerating upward such that he also sees the ball appear to drop. This is known as the equivalence theory where in one case gravity is causing the ball to drop to the ground, but in the other case of space, an accelerating reference frame causes this same motion. By introducing the notion of space time curvature, which in fluencies the motion of objects by a homogeneous gravitational field, Einstein is able to account for this equivalence problem. The more massive an object is the more the curvature of space time distorts. As objects accelerate in space gravitational waves are created. The metric of our universe is mostly Minkowskian, which in simple terms means that the influences of space time curvature are very small, and in particular for gravitational waves are 1 part in 10. LISA which stands for Laser Interferometer Space Antenna is a constellation of three spacecrafts which will orbit the sun. A schematic of LISA can be seen in figure 1. LISA will follow earth’s orbit 50 million km away. Each of the three arms of LISA will be 5 million km apart and will have masses on the ends. Each mass will compose of a mass in an enclosure where the gap between the two may vary. To measure the effects of gravitational waves LISA will use a system of lasers at each arm to measure the time it takes for light to travel between masses. The light travel time is influenced by the presence of gravitational waves. When the gravitational waves are present then space time is distorted and the time for light to travel between each arm will change. Figure 1: LISA Schematic which shows the layout of LISA relative to the earth and sun. Lasers are reflected off of test masses that are housed in three different spacecrafts.