Detecting Gravity (2017 Nobel Prize Winning Research)

Gravity. The stuff that keeps you grounded. And the stuff (from extremely distant stars and galaxies) that ripples all of earth's atoms a tiny, tiny amount all the time. Can we detect those ripples?

For eons, we've speculated (at best) as to what gravity is, and where its physical basis comes from. Albert Einstein, who pioneered the theory of general relativity which described gravity as a fundamental consequence of mass, and can lead to the strange distortions in space and time, thought it would be impossible to directly measure gravitational waves on earth, unless there was a nearby cataclysmic event (such as a neighboring galaxy getting sucked in a black hole). Until just a couple years ago (2015), it was impossible to measure gravitational waves. That is, until over 1000 researchers from more than 86 institutions came together and established the Light Interferometer Gravitational-wave Observatory (or LIGO, for short). There, they experimentally detected gravitational waves for the first time. 

The team used lasers that they beamed into two different perpendicular directions, one went north and the other one west. The mirrors were carefully positioned so that they were EXACTLY the same distance from the source. The effect of the gravitational waves that were reaching earth caused the mirrors to expand in one direction, and contract in the other. This effect was so weak that the net change in location was less than 1/1000th of an atom! But the LIGO team had carefully, painstakingly, accounted for every possible source of experimental noise which would drown out such a vanishingly small signal. And in the end, they found it. Two identical experiments at different parts of the country observe consistent results and now we have a way to directly observe how gravity warps spacetime.

 

photo credit: https://www.ligo.caltech.edu/assets/ligo_default_social_image-fa8a65b147c61b5147e1d43f9e7afc98.jpg