Listening to spacetime: how gravitational waves opened a new kind of astronomy
Barry Barish explains how LIGO measures a stretch smaller than a thousandth of a proton and calls the result a new kind of astronomy, Michelle Thaller explains what gravitational waves reveal, and Brian Keating recounts the hunt for gravitational waves from cosmic inflation. Together they show how ripples in space became a tool for observing the universe, from black holes to its first moments.
What are gravitational waves? Show answer
Tiny ripples in space and time set off by violent events such as two black holes colliding; they offer a way besides light to observe the universe.
What kind of motion produces gravitational waves, according to Barish? Show answer
A quadrupole moment, which comes from objects orbiting each other, such as two black holes.
How did Feynman's thought experiment settle whether the waves are real? Show answer
A bar with rings on it would heat up from friction as a wave passed, so the waves had to carry energy and had to be real.
How does LIGO detect a passing wave? Show answer
A laser is split down two four-kilometer arms of equal length so the returning beams cancel; a wave stretches one arm and squeezes the other, so they no longer cancel.
How small is the distortion LIGO measures? Show answer
About one part in 10 to the 21, about 10 to the minus 18 meters over four kilometers, which Barish puts at a thousandth the size of a proton.
What change finally made LIGO's 2015 detection possible? Show answer
Rebuilding the detector with several changes, including active seismic isolation, which Barish says turned out to be key.
Why does Barish say LIGO's future is so open? Show answer
It is limited by technology, not by science, so each better laser or better isolation from the Earth brings more discoveries.
What does a detector ten times more sensitive gain? Show answer
It sees ten times farther, covering a thousand times more volume, and seeing farther means seeing further back in time.
Why can't light show us the universe's earliest moments? Show answer
The universe was too dense and opaque until about 400,000 years after the Big Bang; gravitational waves were not blocked that way.
How did Keating's team look for gravitational waves from inflation? Show answer
With BICEP, a small telescope at the South Pole that looked for their B-mode polarization imprint on the cosmic microwave background.
What went wrong with the BICEP2 announcement in 2014? Show answer
It was announced before peer review, and the signal turned out to come from aligned galactic dust, which Keating treats as a lesson in confirmation bias.