A Twitter thread by Emily Calandrelli.

Hi, hello - I'M AT LIGO (!!!!)
And THIS CHAMBER is where the first gravitational waves were detected.

@LIGO = Laser Interferometer Gravitational-Wave Observatory

A little 🧵about this engineering MARVEL.

First, what are gravitational waves?

These are ripples of the fabric in space time.

They're caused by catastrophic events like two black holes merging, stars exploding, etc.

They stretch space time in one direction and smoosh it in the other.

How do you measure them?

LIGO has two long beams shaped like an "L". They shoot a laser down the beam and have it bounce back. Because we know the speed of light, we can tell if the beam stretched/squished. (more complex than this, but basically)

Sounds simple - but this is one of the GREATEST ENGINEERING MARVELS OF ALL TIME.

Here's the accuracy LIGO lasers had to achieve: They could measure the distance b/n here and Alpha Centauri (4+ light-years away) to an accuracy smaller than the width of a human hair 😱

To achieve this they had to:
1) Create one of the largest extreme vacuum systems IN THE WORLD.

Why? Because air molecules distort and disturb light and they needed that laser beam to fly perfectly straight. This beam tube hasn't really seen air since the TURN OF THE CENTURY.

1a) the FOUR KILOMETER arms are fun to yell in.

2) Account for the curvature of the Earth

Those 4km arms are SO LONG that they had to account for the curvature of the friggin Earth. That beam needs to fly perfectly straight, so they had to design the beam tubes accordingly.

3) The mirrors used are probably the smoothest mirrors EVER CREATED. That laser beam needs to bounce off the mirrors perfectly - so there can't be any imperfections (even at a nanoscale!)

Fun Fact - b/c the mirrors work for an *infrared* laser, our eyes can see through them.

4) Cancel out ambient shakes and wiggles - think humans/wildlife, trains/cars, earthquakes/oceans. All of these can create false detections.

4a) They "listen" for sound near the instrument and then play the inverse sound wave to cancel it out (like noise cancelling headphones)

4b) they also have this cool pendulum system to protect the instruments from shakes and wiggles

5) create TWO LIGO facilities located 3000km apart - One in Louisiana and one in Washington. They need this to A) verify that one detection at one facility wasn't an error and B) to help locate WHERE the wave came from in the universe

In summary, @LIGO had to have:

1) EXTREMELY large Vacuum system
2) 2 large 4km arms where they accounted for the Earth's curve
3) Smoothest mirrors EVER
4) Complex noise/vibration cancelling
5) Two facilities 3000km apart


It was the largest project the @NSF had ever funded (at the time).

But one LIGO physicist pointed out that a single Space Shuttle launch ($450 million) cost more than building LIGO. Today, though, NSF has spent over $1billion on LIGO. Anyway, everything is relative!

Making gravitational waves even cooler - one LIGO physicist noted:

If the cosmic microwave background (created 380,000 years after the Big Bang) is like a baby picture of the universe then gravitational waves (created fractions of a second after Big Bang) is like the ULTRASOUND

Also LIGO scientists sometimes need to carefully baby crawl under the laser tube and I think that is marvelous.

In summary, @LIGO proved Einstein right and opened up an entirely new way to "see" the universe and I was so lucky to visit there for #XplorationOuterSpace (@XplorStation) - check out the full segment when Season 6 premieres this Fall. THIS SEASON IS GOING TO BE SO GOOD

Ok one last thing on @LIGO

Did you know that YOU can get notified when LIGO detects gravitational wave candidates? (They're about 1/week now!)

Apps ->

Android/iOS: Chirp: https://play.google.com/store/apps/details?id=org.laserlabs.chirp&hl=en_US …
iOS: Gravitational Wave Events: https://apps.apple.com/us/app/gravitational-wave-events/id1441897107 …