Airbus Defence and Space

GAIA : A question of relativity

In a few days, the Airbus Defence and Space-built astrometry satellite Gaia will be launched from Kourou. As well as drawing up a 3D map of our galaxy, it will also put Einstein’s theory of relativity to the test with greater precision than ever before.

The Gaia mission was proposed in 1993 by Swedish astronomer Lennart Lindegren of Lund University. Twenty years later, his idea will be taking to the skies. Lindegren, one of the world’s foremost astrometry experts, points out that Gaia will also test out with greater precision than ever Einstein’s theory of relativity, which states that mass causes spacetime to curve. Even light rays are bent when they pass near a massive object such as the sun.

“Gaia will measure this effect with unprecedented accuracy and will also observe the deflection of light rays caused by Jupiter, Earth and other planets,” says Lindegren. “We expect all these measurements to be in line with Einstein’s general theory of relativity and thus to confirm our current understanding of the structure of spacetime. However, it is part of scientific method to constantly test accepted theories in the most rigorous manner possible and in this sense Gaia will be a hard taskmaster.”

In the early 17th century, the Florentine astronomer Galileo Galilei tried to convince the cardinals of the Inquisition that the universe is “written in the language of mathematics, and its characters are triangles, circles, and other geometric figures, without which it is humanly impossible to understand a single word of it”. According to Galileo, without these characters “we are wandering around in a dark labyrinth”. Four centuries later, Gaia is preparing to shed light on this labyrinth, although there is still much to be done. The one billion stars to be mapped by the satellite make up barely 1% of the stars in our galaxy. The remaining 99% will have to wait for Hipparcos and Gaia’s successors.

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