Albert Einstein first predicted gravitational waves almost a century ago, but only since September 15, 2015, have scientists been able to observe them directly.
According to Einstein, anything with mass exerts a gravitational pull on everything around it. When an object moves, this gravitational pull changes. If you could detect the gravitational tug from a bowling ball, you would know when someone threw the ball, even if you were standing outside the bowling alley. The pull would grow stronger or weaker as the ball traveled closer to or farther from you. You wouldn’t know about the ball’s motion instantaneously, though, since nothing–not even information–can travel faster than the speed of light. News of the ball’s acceleration would be carried through ripples in spacetime called gravitational waves.
However, most gravitational waves are extraordinarily weak. In order to emit strong gravitational waves, an object would need to be massive and to accelerate very quickly. You would be more likely to feel gravitational waves outside the bowling alley if the bowling ball were as dense as a black hole, and if someone bowled it at close to the speed of light.
Scientists built the Laser Interferometer Gravitational-wave Observatory, or LIGO, to directly measure gravitational waves. The collaborative research team is led by the National Science Foundation and builds on research to understand the universe done at Fermilab, one of the Department of Energy’s 17 National Labs. In early 2016, scientists twice announced that they detected waves from black holes many times more massive than our sun spiraling into one another more than a billion lightyears from Earth. The detection of these gravitational waves has opened a brand new window on our universe–a window that lets us see through bowling alleys, planets and even stars. Welcome to the era of gravitational wave astronomy!
Editor’s Note: A version of this post originally appeared in Symmetry, an online magazine about particle physics jointly published by Fermilab and SLAC, two of the Department of Energy’s 17 National Laboratories.
