My name is Michele (pronounced mi-KAY-leh) Vallisneri, and I am a scientist at the Jet Propulsion Laboratory. I am part of a team working on a space mission called LISA, the Laser Interferometer Space Antenna. If we work really hard and we are very successful, the mission will be ready for launch ten years from now.

Why would I work on something that takes so long to bear fruit? Well, all good things take time. But I must say it is all Albert Einstein's fault. You see, in 1915 Einstein came up with a new explanation for the way gravity works--yes, that old question of why apples fall to the ground and why the planets orbit the Sun. Newton had solved this already in the seventeenth century, but there remained a few discrepancies with observations. More important, Newton's universal law of gravitation could not be squared with Einstein's special relativity, which explains how space and time are really a single entity ("spacetime"), and how different "observers" in motion with respect to each other can have different ideas of times and distances. It's fascinating stuff, but it needs more space than I have here. (Einstein Online is a web portal explaining more.)

All the Universe a Stage?

Anyway, in 1915 Einstein pointed out that spacetime is not just a big stage where "physics" happens, but it is an active player itself; it can bend and warp and undulate! Masses, especially big ones like the Sun, bend spacetime ever so slightly, and gravitational forces occur naturally because the planets and the apple try to move as straight as possible in spacetime--but have to curve, because spacetime itself is curved! (The fall of the apple can still be seen as a curve, not in space, but in spacetime.) And what about the undulations? When masses move around rapidly, like for instance two stars in a close binary system, they create outwardly propagating waves in spacetime-gravitational waves. You can imagine them as the waves created in a pond when you throw in a stone; except gravitational waves do not move out in circles, but in spheres, and they do not affect the surface of water, but the very fabric of spacetime.

Listening to the Dark

If we could listen to these waves, we would learn a lot about the Universe, especially about its dark side, which we cannot observe with telescopes. This dark side is populated by heavy objects that nevertheless do not emit much light, such as the huge black holes at the centers of galaxies, millions to billions of times heavier than our Sun.

Since the 1960s, scientists have been trying to detect gravitational waves, but it's very hard, because when they cross the Earth, the waves create only minute perturbations. The best attempt so far is with the giant interferometric detectors such as LIGO (Laser Interferometer Gravitational Wave Observatory), which have "arms" of 2.5 miles to magnify these minute signals.

With LISA, we want to bring this quest to space, and create a gravitational-wave antenna consisting of three spacecraft positioned in a triangle, with arms of 3.1 million miles (thirteen times the distance from the Earth to the Moon). We want to go to space because it is so quiet and because you could not do something so big on the ground; also, a big antenna can measure the waves with the largest wavelengths (the distance between two peaks in the oscillations). There are many systems in the Universe that can emit such waves, so once LISA is up, we're sure to hear and learn a lot.

The Nuts and Bolts

So what's it like in our day-to-day work getting LISA ready? It takes many people with different talents, from the engineers who plan the spacecraft launch and trajectories, to the experimental physicists who are testing the optics, lasers, mirrors, and all the widgets that will make the instrument work. I am a theorist, so I am happier with pen, paper (and a computer) than around a lab. I work to prepare mathematical techniques and computer programs to analyze the LISA data, so that once it's in the sky and it starts making measurements, we'll know what we see. Is it a binary of black holes or neutron stars? How heavy are the components?

One aspect of this preparation can be especially fun. Together with many other LISA physicists around the world, we just finished playing a "mock data challenge." A group of us made a set of measurements, just like what we'd get from the real mission, and "hid" some gravitational waves in it. Another group then took the data and tried to get the waves out. There were many surprises! Some of us thought they had found a (fake) binary emitting on one side of the sky, but it was really on the opposite side. It's hard to do science in space, and that's why we must start so many years in advance; but the payoff will be great, and physicists always like a challenge.

See the LISA mission website at http://lisa.jpl.nasa.gov.