[Detour] LIGO | If two black holes collide in the universe, do they make a sound?

Summary

A short written summary of the episode — not the full transcript. Press play above for the whole thing.

“Who’s the smartest person who ever lived?”

“Probably Einstein.”

In 1936 Einstein submitted a paper arguing that gravitational waves do not exist. The journal sent it to an anonymous reviewer, who found a math error. Einstein was furious and pulled the paper. Then his assistant checked with the reviewer and came back and said the mistake was real. The paper ran later, elsewhere, with the opposite conclusion.

“Wait, Einstein got fact-checked?”

Being wrong in public is the job.

We drove out through the eastern Washington desert to see it. There is nothing out there, which is the point. LIGO is two concrete arms in an L, two and a half miles in each direction. The engineers had to build up the ground at the far end of each arm, because the laser has to travel straight for four kilometers and the Earth curves almost a meter away underneath it.

It is also the quietest instrument on the planet. A truck on a highway five miles off is louder than what it listens for. So are waves on the Oregon coast.

“My heartbeat would wreck the experiment?”

Your heartbeat is too loud for it. Before LIGO, this was the Hanford site, where the country made plutonium for nuclear weapons. Same emptiness, opposite purpose.

Rahul Kumar, a detector engineer with Caltech, led the tour and was precise. LIGO is not measuring mirrors moving. It is measuring the space between the mirrors stretching and squeezing. The mirrors are along for the ride.

Then the part that takes patience. Rainer Weiss at MIT worked out how you would build such a machine, obstacle by obstacle, and published the blueprint in 1972, when most physicists thought detection was hopeless. Construction started in 1994. The detector took data from 2002 and found nothing for years. From 2010 to 2015 they pulled it apart and rebuilt it ten times more sensitive. On September 14, 2015, before it was officially in science mode, the signal arrived. Everyone assumed it was fake, because the team had spent years secretly injecting fake signals to keep itself honest. They spent weeks trying to prove it was a truck. Louisiana had caught it seven milliseconds before Hanford, which is what light would do. Einstein died in 1955 and never knew.

Big worked out that if neutron star collisions forge gold, Little’s earrings may have come from space. He is not going to let her forget it.

“I have like fifty more questions.”

Then let’s go find a scientist.