In my previous post I explained what gravitational waves are and how important they are (or may become) for the observational astronomy. Before we can proceed and explain what we do in practice to achieve this formidable goal, I need to tell you in short how you can detect gravitational waves.

The most important concept is the concept of “geodesic”. We all know that in Newtonian mechanics a particle not subjected to any external force remains either at rest or travels in space at a uniform velocity in a straight line. I have explained in my previous post that Einstein extended Newton’s concepts applicable to particles in motion in a “flat” space, without gravity, to those moving in a “curved space-time”, deformed by the presence of gravity. Well in General Relativity, a particle not subjected to any external force travels in a gravity curved space-time at uniform velocity in the straightest possible way: this path is called “geodesic”. I said the straightest possible way and not straight, as in a curved geometry, the straightest line between two points is not a straight line, but a curved one. Think of the straightest way to get from Amsterdam to Los Angeles. This is an arc with radius of curvature approximately 6378 km (the Earth radius) crossing Iceland, Greenland, Canada’s Labrador and the Rocky Mountains. it is approximately the route of a long haul airplane, which needs to save fuel. Similarly the geodesic is the most economical way of traveling in a curved space-time. The beauty of the geodesic is that once two particles move on two geodesic, their relative acceleration is a direct measurement of the change of the space time curvature. We have learned that a Gravitational Wave is a ripple, a change of curvature in space-time, thus we can detect the gravitational waves by carefully measuring the change of relative distance between two test masses traveling on geodesics. Isn’t that nice??

Yes, but how do you make sure that the particles, the test masses travel on geodesics? This is exactly the purpose of our project: LISA Pathfinder (see http://sci.esa.int/lisapf).

In my next post I will explain how you can achieve in practice “geodesic motion” in a spacecraft.

In the mean time, a leisurely note: last week at team from ESTEC ran the Ariane Slalom in Avioraz (F), a ski competition between teams of several European companies and organizations involved in space activities. Well, the winning team was…. ESTEC!!! and here you are a picture of the winning team

This entry was posted on Sunday, January 25th, 2009 at 10:10 pm and is filed under Astronomy, Science Communication. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.