Space/Time/Gravity: A century later, the last prophecy of Einstein’s general theory of relativity is fulfilled
- J Brooks Spector
- Life, etc
- 12 Feb 2016 01:11 (South Africa)
A massive research project involving many hundreds of scientists around the world appears to have nailed down the heretofore unproved missing final element of Einstein’s general theory of relativity. It is, without doubt, a very massive bit of research. J. BROOKS SPECTOR looks at the announcement.
This discovery is more important than who says what about whom in South Carolina in their upcoming primary election. It is even more important than the unpleasantnesses in South Africa’s parliament and whatever was in Jacob Zuma’s State of the Nation Speech. Arguably, it is more important than anything else that has taken place place on Earth right about now. And what was this thing? Why it was, finally, the detection of gravity waves in the universe.
Nearly fifty years ago, when this writer was still in university, he took one of those courses designed to explore physics for non-science majors, taught by University of Maryland professor Joseph Weber. Besides guiding students like this writer to better appreciate the beauty of modern physics and how it is studied, Prof Weber was also engaged in the kind of research that sometimes could set less visionary people’s tongues clucking and heads shaking. The professor was trying to discover one of the basic forces holding the universe together – just as Albert Einstein had predicted a hundred years ago, with his theory of general relativity.
In Prof Weber’s case, he had constructed massive aluminum cylinders, suspended them in a giant laboratory, and was using the minute changes in their physical location to ascertain the presence of Einstein’s predicted force. At the time the writer was in his class, Weber had just claimed to have found that mysterious force - but no other researcher had been able to duplicate his work in finding this force – then or up to now, well, almost now.
This Thursday, however, a broad international team of researchers, using a different method than the one tried by Prof Weber, announced they had confirmed the presence of those impossible-to-find gravitational waves – explaining that they had found the key signature of gravity waves in a billion-plus year old sound – in what one of the researchers said was 261.625565 hertz (or middle C for the non-musical) - of two black holes coming together and warping the very fabric of the space time continuum. Cue that spooky music from The Twilight Zone?
As the New York Times described this astonishing moment in science, “A team of physicists who can now count themselves as astronomers announced on Thursday that they had heard and recorded the sound of two black holes colliding a billion light-years away, a fleeting chirp that fulfilled the last prophecy of Einstein’s general theory of relativity. That faint rising tone, physicists say, is the first direct evidence of gravitational waves, the ripples in the fabric of space-time that Einstein predicted a century ago. And it is a ringing (pun intended) confirmation of the nature of black holes, the bottomless gravitational pits from which not even light can escape, which were the most foreboding (and unwelcome) part of his theory. More generally, it means that scientists have finally tapped into the deepest register of physical reality, where the weirdest and wildest implications of Einstein’s universe become manifest.” Hopefully the reader is now beginning to be convinced that this announcement is more important than what was happening in Cape Town’s parliamentary precinct – or in Columbia, South Carolina, for that matter.
In this newly announced discovery, researchers at two locations in the US – one in the state of Washington and the other in Louisiana, called the LIGO, the Laser Interferometer Gravitational-Wave Observatory, as well as a horde of others around the world engaged with it in various capacities – say they detected some of those elusive gravity waves via LIGO’s two L-shaped radio antennas on 14 September 2015. The waves are described as being fifty times more powerful than all the stars in the universe put together and the sounds detected – converted to audible sound - rose to middle C before abruptly ceasing. This sound – assuming others can verify their work – will become one of the most famous sounds in human history – together with Alexander Graham Bell’s “Watson, come here I want you”, Thomas Edison’s recording of “Mary Had a Little Lamb”, those first chirps broadcast from Sputnik, Al Jolson’s voice in the first talkie, The Jazz Singer, and the modem handshake song.
Szabolcs Marka, a Columbia University scientist and a LIGO researcher described the work in some untypical superlatives, saying, “I think this will be one of the major breakthroughs in physics for a long time. Everything else in astronomy is like the eye,” he said, alluding to the many optical telescopes that have been the core of astronomical research that have given scientists increasing access to the broad range of the electromagnetic spectrum and an increasing ability to look ever more deeply into space and back in time. Marka added, “Finally, astronomy grew ears. We never had ears before.”
Gabriela Gonzales, project spokeswoman from Louisiana State University told the media exultantly, “We are all over the moon and back. Einstein would be very happy, I think.” The LIGO group, working with a team from Europe, the Virgo Collabortion, is publishing their research in Physical Review Letters in a paper with a staggering one thousand co-authors named. This kind of broad international participation in research, with research published quickly online has become a growing feature of scientific work generally. (In South Africa, the recent pathbreaking work with homo Naledi was released in a similarly speedy manner on the Internet – and the papers for that discovery had dozens of international collaborators as well.)
The New York Times explained that lead researchers Kip Thorne of the California Institute of Technology, Rainer Weiss of the Massachusetts Institute of Technology, and Ronald Drever, formerly of Caltech and now retired in Scotland, had bet their careers (just as Joseph Weber had done all those years ago) on being able to measure that most ineffable of Einstein’s revolutionary ideas. With the discovery announced, Thorne told reporters via email, “Until now, we scientists have only seen warped space-time when it’s calm. It’s as though we had only seen the ocean’s surface on a calm day but had never seen it roiled in a storm, with crashing waves.” The two black holes that LIGO had focused on had created a storm “in which the flow of time speeded, then slowed, then speeded. A storm with space bending this way, then that,” he said.
For America’s National Science Foundation, the governmental research body that had funded this adventure to the tune of a cool $1.1 billion over four decades, this announcement comes as good news in pushing back criticism of their spending on a project in which many had insisted the sources of those gravity waves were neither plentiful enough nor loud enough to be worth the trouble of doing this long-term hunt. The NSF’s director, France Cordova crowed, “It’s been decades, through a lot of different technological innovations,” and his organization’s advisory board had “really scratched their heads on this one.”
Now that the research has gone public, other scientists not directly engaged in the project used similarly unscientific language to speak about the work. Janna Levin said she “was freaking out” the work, and Robert Garisto, the editor of the journal where the research has been published told the media he had gotten “goose bumps” as he first read the LIGO research paper when it was submitted.
But what is all this fuss about? Back when Einstein first announced his theory of general relativity, he had created a revolutionary rethink of the basic rules governing space and time – a framework that had been in place since Isaac Newton’s day, more than two centuries earlier. Newton’s framework had been the commonly held understanding for every scientist once he first described them – until Einstein came along. As the New York Times explained, “Instead, Einstein said, matter and energy distort the geometry of the universe in the way a heavy sleeper causes a mattress to sag, producing the effect we call gravity. A disturbance in the cosmos could cause space-time to stretch, collapse and even jiggle, like a mattress shaking when that sleeper rolls over, producing ripples of gravity: gravitational waves.
“Einstein was not quite sure about these waves. In 1916, he told Karl Schwarzschild, the discoverer of black holes, that gravitational waves did not exist, then said they did. In 1936, he and his assistant Nathan Rosen set out to publish a paper debunking the idea before doing the same flip-flop again. According to the equations physicists have settled on, gravitational waves would compress space in one direction and stretch it in another as they traveled outward.”
When the writer had been in his physics for dummies class, Weber’s work had made headlines when he used those two metre-long aluminum cylinders to resonate like a tuning fork when the detected those gravity waves. While no one else was able to duplicate Weber’s work, it inspired others to try other ways to track down Einstein’s predicted gravity waves.
And then, a decade after Weber’s work, University of Massachusett radio astronomers Joseph Taylor Jr. and Russell Hulse discovered a pair of neutron stars, ultra dense leftovers from two dead stars, orbiting one another. One of them was a pulsar that shot out a periodic beam of electromagnetic radiation. The New York Times explained that in timing these pulses, the two men “determined that the stars were losing energy and falling closer together at precisely the rate that would be expected if they were radiating gravitational waves.” Just incidentally, the two scientists received the Nobel Prize for Physics for their work – something that may now bode well for the fortunes of those LIGO scientists, if not all one thousand of the full team, at least the leaders.
In one of those surprising moments in scientific research, Thorne and Weiss first met when they coincidentally happened to be in the same hotel conference room during a scientific gathering in Washington, DC. Thorne was already well known in his field, but he was then on the hunt for some new research areas. The two men stayed up all night, trying out ideas on how to carry out some tests of general relativity and how best to hunt down those gravity waves. Thorne and Weiss, in association with other researchers, tried out various ideas to capture the unseen waves and when they sought to explain the ideas for testing their theories, Weiss says “everybody thought we were out of our minds.” Well, Columbus also had trouble at first finding a rich sponsor. With dollars in hand, the NSF forced the Thorne/Weiss duo and another team to merge their work but the research did not move particularly smoothly until a single director was appointed to honcho the whole project.
Describing the early work, the Times noted, “The first version of the experiment, known as Initial LIGO, started in 2000 and ran for 10 years, mostly to show that it could work on the scale needed. There are two detectors: one in Hanford, Wash., the other in Livingston, La. Hunters once shot up the outside of one of the antenna arms in Louisiana, and a truck crashed into one of the arms in Hanford. In neither case was the experiment damaged. Over the last five years, the entire system was rebuilt to increase its sensitivity to the point where the team could realistically expect to hear something.
“LIGO’s antennas are L-shaped, with perpendicular arms 2.5 miles long. Inside each arm, cocooned in layers of steel and concrete, runs the world’s largest bottle of nothing, a vacuum chamber a couple of feet wide containing 2.5 million gallons of empty space. At the end of each arm are mirrors hanging by glass threads, isolated from the bumps and shrieks of the environment better than any Rolls-Royce ever conceived.
“Thus coddled, the lasers in the present incarnation, known as Advanced LIGO, can detect changes in the length of one of those arms as small as one ten-thousandth the diameter of a proton — a subatomic particle too small to be seen by even the most powerful microscopes — as a gravitational wave sweeps through. Even with such extreme sensitivity, only the most massive and violent events out there would be loud enough to make the detectors ring. LIGO was designed to catch collisions of neutron stars, which can produce the violent flashes known as gamma ray bursts. As they got closer together, these neutron stars would swing around faster and faster, hundreds of times a second, vibrating space-time geometry with a rising tone that would be audible in LIGO’s vacuum-tube ‘sweet spot.’ ” In fact, the system was only barely fully calibrated when a loud signal was picked up by it. “Data was streaming, and then ‘bam,’ ” said Caltech professor David Reitze, the head of the LIGO Laboratory that built and runs the detectors. The signal was first heard at the Louisiana site, and then seven seconds later at the Washington site. The computers heard it early in the morning while the research team was asleep. Weiss, on vacation, checked in and said of this signal, “It was waving hello. It was amazing. The signal was so big, I didn’t believe it.” But the frequency for the sound, the chirp, was too low for the neutron stars they thought they were listening for, and after some real number crunching, they determined it was from a death dance of two enormous black holes in an imaginably distant part of the galaxy. One was 36 times a massive as our sun and the other, smaller, was “only” 29 times as big. Moving at half the speed of light, they were circling each other 250 times a second. And then, unimaginably, those two black holes merged into a single thing, in a fifth of a second (a billion-plus years ago). The sound was from the low octaves on a piano right to middle C - a ping from a massive implosion transmitted clear across the universe. Three solar masses’ worth of energy, converted into gravitational waves in an unseen cataclysm before there was life on Earth. That energy would have been roughly equivalent to around a billion trillion stars the size of our Sun – but it moved those massive LIGO detectors an impossibly tiny four one-thousandths of the diameter of your standard, garden variety proton. And you, gentle reader, wanted to read about a badly delivered speech in Cape Town or squabbles in South Carolina. Isn’t this so much more exciting? DM
Photo: Albert Einstein in 1921 (Wikimedia Commons)
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- J Brooks Spector
- Life, etc