LIGO construction and welding

Tom's primary illustrative case for the section "where is the best engineering at MIT done?" — used to make the point that the physics department, not engineering proper, hosts MIT's most ambitious engineering project. Tom focuses on the surveying-precision challenge (1–2 cm over 4 km, accounting for earth curvature) as engineering achievement.

Where is the best engineering at MIT done? And which department? Course 3? Nope. Course 5? Nope. The physics department. If you go look — usually, I mean, if you're a nuclear engineer you might say, Al Couture over here is the fusion reactor, that's part of the nuclear engineering department. It is. But it's also part of the physics department. If you go to the largest National Science Foundation project ever — about a billion-dollar project, a partnership between Caltech and MIT, started almost thirty years ago — I've actually asked the retired chief scientist if he would come in and give a lecture: the LIGO project. Laser Interferometer Gravitational-Wave Observatory. They're trying to measure the most accurate measurement ever made — one part in 10 to the 23rd — and measure gravity waves from space. A billion-dollar project. They have two Michelson interferometers — these are the 90-degree ones — you send the lasers with a laser, and then you get the beating frequency coming back if the two of them shorten in length. The engineering that goes into it to align those four-kilometer legs — they have two of them in Livingston, Louisiana, and two of them up in Hanford, Washington. People propose putting others on the moon, and putting some in Australia, because the more, it's like astrophysical telescopes. This is a telescope of the sort — it's trying to measure length due to gravity waves coming from space, and they would verify Einstein's general theory of relativity and someone would win a Nobel Prize.

Most precise measurement ever attempted (10^-18 cm target). Tom's consulting role 15 years prior (~1997) on stainless steel welding for the 4-km vacuum tubes; surface treatments to prevent hydrogen outgassing; wave GPS surveying for mirror alignment.

Tom's role welding the 4-foot diameter beam tubes, and Ray Weiss's hand-written explanation of the 10⁻²³/√Hz measurement target. Used as the canonical "sublime" extreme of precision measurement. Tom also uses it to make the point that the best engineering at MIT is sometimes done in the School of Science.

But I want to give you a case study on the most accurate measurement ever attempted: the laser interferometric gravitational observatory. LIGO. It's a joint MIT-Caltech project. Back in 1992, Ray Weiss, a scientist in the MIT physics department who had started as a technician and then got his PhD in physics, proposed to the National Science Foundation, together with two people from Caltech, what has become the largest NSF project in terms of cost ever attempted. They built two interferometers.