As reported by Mariëtte Le Roux of The Times of Israel, February 11, 2016 (bold in original):
Great excitement rippled through the physics world Thursday at the announcement that gravitational waves have been detected after a 100-year search.As reported by Kerry Sheridan of The Times of Israel, February 11, 2016 (bold in original):
Here’s what it means.
Q: What are gravitational waves?
A: Albert Einstein predicted gravitational waves in his general theory of relativity a century ago. Under this theory, space and time are interwoven into something called “spacetime” — adding a fourth dimension to our concept of the Universe, in addition to our 3D perception of it.
Einstein predicted that mass warps space-time through its gravitational force. A common analogy is to view space-time as a trampoline, and mass as a bowling ball placed on it. Objects on the trampoline’s surface will “fall” towards the centre — representing gravity.
When objects with mass accelerate, such as when two black holes spiral towards each other, they send waves along the curved space-time around them at the speed of light, like ripples on a pond.
The more massive the object, the larger the wave and the easier for scientists to detect.
Gravitational waves do not interact with matter and travel through the Universe completely unimpeded.
The strongest waves are caused by the most cataclysmic processes in the Universe — black holes coalescing, massive stars exploding, or the very birth of the Universe some 13.8 billion years ago.
Q: Why is the detection of gravitational waves important?
A: It ended the search for proof of a key prediction in Einstein’s theory, which changed the way that humanity perceived key concepts like space and time.
Detectable gravitational waves open exciting new avenues in astronomy — allowing measurements of faraway stars, galaxies and black holes based on the waves they make.
Indirectly, it also adds to the evidence that black holes — never directly observed — do actually exist.
So-called primordial gravitational waves, the hardest kind to detect and not implicated in Thursday’s announcement, would boost another leading theory of cosmology, that of “inflation” or exponential expansion of the infant Universe.
Primordial waves are theorised to still be resonating throughout the Universe today, though feebly.
If they are found, they would tell us about the energy scale at which inflation ocurred, shedding light on the Big Bang itself.
Q: Why are gravitational waves they so elusive?
A: Einstein himself doubted gravitational waves would ever be detected given how small they are.
Ripples emitted by a pair of merging black holes, for example, would stretch a one-million-kilometre (621,000-mile) ruler on Earth by less than the size of an atom.
Waves coming from tens of millions of lightyears away would deform a four-kilometre light beam such as those used at the Advanced Laser Interferometer Gravitational Wave Observatory (LIGO) by about the width of a proton.
Q: How have we looked for them?
A: Before now, gravitational waves had only been detected indirectly.
In 1974, scientists found that the orbits of a pair of neutron stars in our galaxy, circling a common centre of mass, were getting smaller at a rate consistent with a loss of energy through gravitational waves.
That discovery earned the Nobel Physics Prize in 1993. Experts say the first direct detection of gravitational waves is likely to be bestowed the same honour.
After American physicist Joseph Weber built the first aluminium cylinder-based detectors in the 1960s, decades of effort followed using telescopes, satellites and laser beams.
Earth- and space-based telescopes have been trained on cosmic microwave background, a faint glow of light left over from the Big Bang, for evidence of it being curved and stretched by gravitational waves.
Using this method, American astrophysicists announced two years ago they had identified gravitational waves using a telescope called BICEP2, stationed at the South Pole. But they later had to admit they made an error.
Another technique involves detecting small changes in distances between objects.
Gravitational waves passing through an object distort its shape, stretching and squeezing it in the direction the wave is travelling, leaving a telltale, though miniscule, effect.
Detectors such as LIGO at the centre of Thursday’s news, and its sister detector Virgo in Italy, are designed to pick up such distortions in laser light beams.
At LIGO, scientists split the light into two perpendicular beams that travel over several kilometres to be reflected by mirrors back to the point where they started.
Any difference in length upon their return would point to the influence of gravitational waves.
Sources: European Space Agency, Institute of Physics, LIGO, Nature.
The wave that made history snuck up on them.As reported by Joe Dyke of Agence France-Presse, February 11, 2016 (bold in original):
David Shoemaker will never forget the date — September 14, 2015 — when he woke up to a message alerting him that an underground detector had spotted a 1.3-billion-year-old ripple in the fabric of space-time.
A gravitational wave — predicted to exist a century ago by Albert Einstein — had been glimpsed directly for the first time by a pair of US-based detectors.
“It is seared in my brain,” said Shoemaker, a top scientist at the Massachusetts Institute of Technology (MIT) and head of the Advanced LIGO Project, an international effort to uncover evidence of gravitational waves.
Such waves are a measure of strain in space, an effect of the motion of large masses that stretches the fabric of space-time — a way of viewing space and time as a single, interweaved continuum.
The “chirp,” as Shoemaker described the long-awaited wave, had arrived while he was asleep.
But since the data analysis works in quasi-real-time, scientists watching the data stream early in the work day in Europe saw it immediately.
Two black holes spiraling into each other became a single black hole, and the joining of these two giants curved the fabric of space-time around them, ever so briefly.
“When the signal finally got to the Earth on September 14 we knew within three minutes that our instruments had seen something really different,” said Shoemaker.
“I was sitting at home, with a cup of coffee in my hand and opening up my email at around 7 am,” he told AFP.
An instant message had arrived from a close colleague in Germany.
The message said: “I think we are in trouble now,” he recalled.
But Shoemaker, a leading scientist in the search for gravitational waves since the early 1980s, did not leap out his chair or shout expletives.
He just took a deep breath.
“My immediate reaction was, ‘That’s fascinating. Let’s see what the instruments did wrong.'”
Taken by surprise
In fact, the team had only just turned on the pair of underground detectors — one in Louisiana and one in Washington state — for a series of final checks before formally starting the observation experiment, which would run from mid September until January.
“It was just at the beginning of this run, when we were all ready to go — to press the button to start the observing run — that the gravitational wave was observed,” he said.
“So it was a very exciting moment for us and it took us perfectly by surprise.”\
Immediately, Shoemaker and colleagues began running through a checklist of possible failures.
One by one, they ruled out electromagnetic storms, lighting strikes, earthquakes, or interference by people near sensitive parts of the instruments.
Furthermore, the timing matched up.
The detector in Hanford, Washington picked up the signal 7.1 milliseconds after the Livingston, Louisiana instrument, some 1,800 miles (3,000 kilometers) away.
“The travel time of light between the two instruments is 10 milliseconds,” said Shoemaker.
“And if the two signals had arrived 11 milliseconds apart, we would have simply said, ‘Nope. It’s two instrumental defects that happened at the same time.’
“But it happened within 7.1 milliseconds, which is a perfectly plausible delay between the two.”
Weeks of tests
After many tests, the LIGO team’s discovery was confirmed.
“It took weeks before we were really gaining confidence that it was a true gravitational wave event, before I could admit to myself that something had been seen,” Shoemaker said.
“But, you know, eventually, joy sets in.”
The LIGO work is vastly different from that done by US astrophysicists who announced in 2014 they had detected the first ripples from the Big Bang, then months later admitted their indirect, telescope-based findings were premature and could not be confirmed.
Shoemaker and colleagues are using different equipment to hunt for much smaller, shorter waves, on the order of milliseconds or seconds. In other words, the kinds of gravitational waves that happen all the time, but had never before been observed.
“This is the first time there has ever been a direct detection of the gravitational waveform,” Shoemaker said.
“And that makes it a magical thing.”
It took a century, but the theory from Albert Einstein handwritten neatly on paper that is now yellowing has finally been vindicated.
Israeli officials on Thursday offered a rare look at the documents where Einstein presented his ideas on gravitational waves, a display that coincided with the historic announcement that scientists had glimpsed the first direct evidence of his theory.
“Einstein devised this with pen and paper, but it took humanity 100 years to develop the tools to catch a glimpse of it,” said Roni Grosz, curator of the Albert Einstein Archives at Jerusalem’s Hebrew University, pointing to two pages.
One was the first document in which Einstein fully presented his theory of gravitational waves, while the other was a page from his 46-page theory of relativity, written in 1916 and 1915 respectively.
They were written neatly in German, with corrections made within the text.
The theory of gravitational waves was developed by the German physicist 100 years ago.
In a landmark discovery for physics and astronomy, international scientists announced in Washington on Thursday that they had glimpsed the first direct evidence of gravitational waves, or ripples in space-time.
Einstein’s theory states that mass warps space and time, much like placing a bowling ball on a trampoline.
Other objects on the surface will “fall” towards the centre — a metaphor for gravity in which the trampoline is space-time.
Gravitational waves do not interact with matter and travel through the universe completely unimpeded.
It was a central pillar of Einstein’s theory of gravity, but had never been proven.
“(The discovery) is a very moving moment,” Grosz said, wearing a tie with a picture of Einstein and his familiar bushy hair. “A smile from heaven after exactly 100 years.”
‘A new window’
Einstein himself doubted gravitational waves would ever be detected given how tiny they are.
Barak Kol, head of physics at the Hebrew University, explained the size of their impact can be as small as “one thousandths of the nucleus of an atom”.
Kol, who had worked on trying to prove the theory, said the discovery was a historic day for scientists and those concerned with Einstein’s legacy.
“It is the end of a part of the journey that took 100 years since it started with the idea of one person,” he said.
“(But) it will open a new window to the universe. It will enable us to see processes in the universe.”
He added that, as with other major scientific discoveries, it was likely to lead to many developments that “we cannot predict...”
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