Sunday, November 12, 2006

The LISA Project

The Theory of Relativity has some rather fantastic claims to make about the nature of the universe. We still find it hard to believe, for example, that time slows down relative to the rest of the universe when you travel at speeds comparable to the speed of light. Imagine then, how the scientific community at the beginning of the 20th century felt.

In 1919, British astrophysicist Arthur Eddington conducted an experiment that confirmed one of the fundamental premises of Relativity. During a solar eclipse, they measured the angle of stars behind the sun... and found that the gravitational field of the Sun did in fact bend light passing near it. From then till now, scientists have been laying out the multifarious consequences of Einstein's theory and finding ways of physically confirming them. One of these consequences is the presence of "Gravitational Waves". To the layman, one would explain it as a "wobble" in the position and shape of all matter in the universe, arising from propagating distortions caused by massive gravitational interactions like the merging of supermassive black holes or a star spiralling into a black hole.

Figure 1: The effect of gravitational waves of the two different polarizations they can exhibit: "Plus" and "Cross" (Source: Chakrabarthy, 1999)

While there do exist projects to measure the effect of gravitational waves from Earth, the quality of the data is poor. Instead of taking measurements from celestial objects, scientists want to make more direct measurements. Enter the Laser Interferometer Space Antenna, or LISA project, scheduled to be launched in the year 2015. LISA consists of three spacecraft positioned at the vertices of an equilateral triangle. Using interferometry, they can measure minute variations in their relative positions, in the range of picometers!

Figure 2: Artist's rendering of LISA (Source: NASA)

Unfortunately, such variations can be caused by a variety of factors such as solar wind, gravitational field of nearby bodies, accumulation of electrostatic charges, etc. It is an engineering challenge to develop active and passive techniques to minimize these variations in order to get an accurate measurement relating only to gravitational waves. Until the spacecraft are actually operational, it is difficult to predict how successful we will be at this.

The presence of gravitational waves is more or less accepted scientific fact, and if the LISA project is successful, it will only be the final confirmation in this regard. The purpose of LISA is much more than just confirming the nature of gravitational waves. Since gravitational waves pass through all matter whereas light and other electromagnetic variation can be blocked by various "opaque" objects, accurate measurement of gravitational waves can yield information about parts of the universe currently inaccessible to us. We would be able to settle the issue of "dark matter". We would be able to get information on the nature of the universe much closer to the time of the Big Bang than we can now. Astrophysicists are lining up issues that the measurement of gravitational waves can settle.

Since the launch of LISA is nearly a decade away, for now we can just sit back and contemplate our wobbly natures.


Indrajit Chakrabarthy, "Gravitational Waves: An Introduction," arXiv:physics/9908041 v1, Aug 21, 1999

LISA Project Home Page

Wikipedia on Gravitational Waves


Raindrop said...

I believe the issue of dark matter has already been settled through weak gravitational lensing studies done by a team led by Douglas Clowe.

Prashanth said...

Yikes... you're right. I missed that piece of news, living in a closeted grad world...

Raindrop said...

That's understandable. I didn't know how big hurricane Katrina was because I was busy working in my basement grad office and didn't come out for a few months. Besides, this made news as late as August.