Thursday 18 February 2016

Einstein vindicated

Someone, ?Richard Feynman? claimed that there were only 12 people in the world who understood Quantum Electrodynamics QED.  He wrote the book QED: The Strange Theory of Light and Matter about it aNNyway.  I failed my Physics 'O' Level, so don't expect me to explain QED, or why, or indeed if, Einstein didn't believe it.  It's been like that with the News From LIGO which spilled briefly onto BBC/Sky/Fox/RTE news last week: gravitational waves had been discovered in a replicated experimental design that would have really gratified Albert Einstein.  I looked at the headlines and reckoned that a bear-of-little-brain like me wouldn't be able to really understand what had happened.  But, because of informed reading [original PDF in science-speak] and patient explanation by The Pharmacist, the 7 attendees at this week's Wexford Science Café [prév, prev] came away with a much better grasp of what had happened; and why it mattered.

Einstein predicted gravitational waves 100ish years ago but added that their force would be so staggeringly feeble that it would be impossible for any imaginable instrument to detect them.  There are four fundamental forces at play in our Universe and it has been the aspiration of GUT [Grand Unified Theory] and ToE [Theory of Everything] to integrate and reconcile them, so that we can understand their impact on the quarks-to-quasars universe of which we occupy the middle [nanometer to Astronomical Unit AU] ground.  Those forces are:
Relative strength
GUT appears to have sorted the relationships among weak+EM+strong forces to an extent that satisfies most normal physicsists.  The next [ToE] challenge is to show how gravity, the most feeble small-small tweaker of space-time, fits into the picture.  As gravity is what brings apples to earth, so we don't need ladders, it will clearly be advantageous to discover how it works. Einstein incorporated gravity into his theory of relativity and thought of the force being propagated as waves, at least partly because this is how electromagnetic stuff appeared to exist.  The whole story of whether light is particles (photons) or waves or both at the same time is a story for another blog and another time.

The Laser Interferometer Gravitational-Wave Observatory (LIGO) was the parity of esteem project that Physics required of the US government when 100$ of million$ were allocated to the Human Genome Project.  It was led by  Kip Thorne and Ronald Drever of Caltech and Rainer Weiss of MIT who herded 900 working scientists [269 collaborators bloboprev] in dozens of institutions into a huge collaborative effort.  44,000 crowd-sourced 'civilian' gophers also gave up CPU cycles on their computers to process the incoming data in the Einstein@Home project. Because gravitational waves are so tiny, you need a huge scaled-up instrument to detect the changes. Nothing that will fit on a lab-bench will do. It's not as big as the 27km circumference Large Hadron Collider LHC at CERN which discovered the Higgs Boson a tuthree years ago; LIGO is 'only' 4km in length.  Actually, it consists of two 4km tubes with mirrors at the end set at right-angles to each other sending out laser pulses on a regular basis and detecting changes in the wavelength when they come back.  Einstein and everyone else holds that the speed of light in a vacuum is the one universal constant at 300,000,000 m/s.  So if the laser pulse goes out along both arms at the same time and comes back down one arm with a delay andif the changes precisely matches certain theoretical predictions then the length of one arm has changed, and we might have witnessed a pulse of gravitational waves. The pulse would have to be either very massive or very close or both to get above the threshold for detection in the instrument.

That was the plan in 1992 and eventually 2 LIGOs were built in different parts of the country [L]. That duplication was a key element of the success because if the same event was detected at a distance of  3000km, then it's nothing to do with a truck delivering milk to the canteen or an earthquake or the temperature difference. The hunt began, patiently, in 2002 and nothing was picked up.  Improvements in technology led to the implementation of a $620 million upgrade which was completed in mid-September 2015. That's about 2x the cost of restoring a single small river in the same state as the Hanford site. About 1.3 billion years ago, in another galaxy far away,  two black holes, which had been waltzing/whizzing round each other for some time, finally took the plunge and disappeared up each other's darkness. These super-dense, super-massive gravitational sinks had a combined mass 65x that of our cosy Sun, and their coming together resulted in the most humongous >!bang!<. The explosion converted 3 solar masses from mass into pure energy at the rate of E = mc2 and the loss of mass resulted in a change of the local gravity. That sent a pulse - a gravity wave - out across the Universe which was detected at both Hanford and Livingston with a delay between them of a few milliseconds . . . just two days after the refurb-and-upgrade was completed at LIGO.  Phew! Imagine if they'd finished a few days later, missed that pulse and waited another 12 years to see nothing-at-all. Then again, with the universe is so big maybe these events happen every few days, but I doubt it.

Appropriate quotes:
From Feynman's book "What I am going to tell you about is what we teach our physics students in the third or fourth year of graduate school... It is my task to convince you not to turn away because you don't understand it. You see my physics students don't understand it... That is because I don't understand it. Nobody does.
From Niels Bohr: "Hvis man kan sætte sig ind i kvantemekanik uden at blive svimmel, har man ikke forstået noget af det." If you can fathom quantum mechanics without getting dizzy, you don't get it.
From Feynman's Messenger Lecture MIT 1964 "There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics."

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