The Laser Interferometer Gravitational-Wave Observatory (LIGO) is a huge installation measured in kilometers that is listening for wrinkles in space-time. Pulling this off is a true story of hardware and software hacking, and we were lucky to have Dr. Keith Thorne dive into those details with his newly published “Extreme Instruments for Extreme Astrophysics” keynote from the 2021 Hackaday Remoticon.
Gravity causes space-time to stretch — think back to the diagrams you’ve seen of a massive orb (a star or planet) sitting on a plane with grid lines drawn on it, the fabric of that plane being stretch downward from the mass of the orb. If you have two massive entities like black holes orbiting each other, they give off gravitational waves. When they collide and merge, they create a brief but very strong train of waves. Evidence of these events are what LIGO is looking for.
Rai Weiss had the idea to look for gravitational waves using laser interferometers in about 1967, but the available laser technology was too new to accomplish the feat. In an interferometer, a laser is shot through a beam splitter and one beam reflects out and back over a distance, and is then recombined with the other half using a photodetector to measure the intensity of light. As the distance in the long leg changes, the relative phase of the lasers shift, and the power detected will vary.
LIGO is not your desktop interferometer. It uses a 5 kW laser input. The 4 km legs of the interferometer bounce the light back and forth 1,000 times for an effective 4,000 km travel distance. These legs are kept under extreme vacuum and the mirrors are held exceptionally still. It’s worth it; the instrument can measure at a precision of 1/10,000 the diameter of a proton!
Continue reading “Keynote Video: Dr. Keith Thorne Explains The Extreme Engineering Of The LIGO Hardware”
It is my pleasure to announce that Keith Thorne has graciously agreed to deliver a keynote take at Hackaday Remoticon 2. Get your ticket now!
Keith is an astrophysicist and has worked on the Laser Interferometer Gravitational-Wave Observatory (LIGO) since 2008, literally looking for ripples in space-time that you know as gravitational waves. The effects of the phenomena are so subtle that detecting an event requires planet-scale sensors in the form of 4 km long interferometers placed in different parts of the United States whose readings can be compared against one another. A laser beam inside these interferometers bounces back and forth 300 times for a total travel distance of 1,200 km in which any interaction with gravitational waves will ever-so-slightly alter how the photons from the beam register.
The challenges of building, operating, and interpreting such a device are manifold. These interferometers are the highest precision devices ever devised, able to detect motion 1/10,000 of the diameter of a proton! To get there, the mirrors need to be cooled to 77 nano-Kelvins. Getting the most out of it is what Keith and the rest of the team specialize in. This has included things like hacking the Linux kernel to achieve a sufficient level of real-time digital control, and using “squeezed light” to improve detection sensitivity in frequencies where quantum mechanics is getting in the way. While the detectors were first run in 2015 & 2016, successfully observing three events, the work to better understand this phenomenon is ongoing and may include a third site in India, and a space-based detector in the future.
In getting to know Keith he mentioned that he is excited to speak to a conference packed with people who want to hear the gory technical details of this fantastic piece of hardware. I’m sure we’re all giddy to learn what he has to say. But if you’re someone who wants to work on a project like this, he tipped us off that there’s an active EE job posting for LIGO right now. Maybe you’ll end up doing the keynote at a future Hackaday conference.
Call for Proposals is Still Open!
We’re still on the hunt for great talks about hardware creation. True creativity is fed by a steady stream of inspiration. Be that inspiration by giving a talk about the kinds of things you’ve been working on!
Gravity is one of the more obvious forces in the universe, generally regarded as easily noticeable by the way apples fall from trees. However, the underlying mechanisms behind gravity are inordinately complex, and the subject of much study to this day.
A major component of this study is around the concept of gravitational waves. First posited by Henri Poincaré in 1905, and later a major component of Einstein’s general theory of relativity, they’re a phenomena hunted for by generations of physicists ever since. For the team at the Laser Interferometer Gravitational-wave Observatory, or LIGO, finding direct evidence of gravitational waves is all in a day’s work.
Continue reading “How The LIGO Observatory Detects Gravitational Waves”