Carlo Rovelli writes: According to tradition, in the year 450 BCE, a man embarked on a 400-mile sea voyage from Miletus in Anatolia to Abdera in Thrace, fleeing a prosperous Greek city that was suddenly caught up in political turmoil. It was to be a crucial journey for the history of knowledge. The traveller’s name was Leucippus; little is known about his life, but his intellectual spirit proved indelible. He wrote the book The Great Cosmology, in which he advanced new ideas about the transient and permanent aspects of the world. On his arrival in Abdera, Leucippus founded a scientific and philosophical school, to which he soon affiliated a young disciple, Democritus, who cast a long shadow over the thought of all subsequent times.
Together, these two thinkers have built the majestic cathedral of ancient atomism. Leucippus was the teacher. Democritus, the great pupil who wrote dozens of works on every field of knowledge, was deeply venerated in antiquity, which was familiar with these works. ‘The most subtle of the Ancients,’ Seneca called him. ‘Who is there whom we can compare with him for the greatness, not merely of his genius, but also of his spirit?’ asks Cicero.
What Leucippus and Democritus had understood was that the world can be comprehended using reason. They had become convinced that the variety of natural phenomena must be attributable to something simple, and had tried to understand what this something might be. They had conceived of a kind of elementary substance from which everything was made. Anaximenes of Miletus had imagined this substance could compress and rarefy, thus transforming from one to another of the elements from which the world is constituted. It was a first germ of physics, rough and elementary, but in the right direction. An idea was needed, a great idea, a grand vision, to grasp the hidden order of the world. Leucippus and Democritus came up with this idea.
The idea of Democritus’s system is extremely simple: the entire universe is made up of a boundless space in which innumerable atoms run. Space is without limits; it has neither an above nor a below; it is without a centre or a boundary. Atoms have no qualities at all, apart from their shape. They have no weight, no colour, no taste. ‘Sweetness is opinion, bitterness is opinion; heat, cold and colour are opinion: in reality only atoms, and vacuum,’ said Democritus. Atoms are indivisible; they are the elementary grains of reality, which cannot be further subdivided, and everything is made of them. They move freely in space, colliding with one another; they hook on to and push and pull one another. Similar atoms attract one another and join.
This is the weave of the world. This is reality. Everything else is nothing but a by-product – random and accidental – of this movement, and this combining of atoms. The infinite variety of the substances of which the world is made derives solely from this combining of atoms. [Continue reading…]
The universe is an astonishingly secretive place. Mysterious substances known as dark matter and dark energy account for some 95% of it. Despite huge effort to find out what they are, we simply don’t know.
We know dark matter exists because of the gravitational pull of galaxy clusters – the matter we can see in a cluster just isn’t enough to hold it together by gravity. So there must be some extra material there, made up by unknown particles that simply aren’t visible to us. Several candidate particles have already been proposed.
Scientists are trying to work out what these unknown particles are by looking at how they affect the ordinary matter we see around us. But so far it has proven difficult, so we know it interacts only weakly with normal matter at best. Now my colleague Benjamin Varcoe and I have come up with a new way to probe dark matter that may just prove successful: by using atoms that have been stretched to be 4,000 times larger than usual.
Steve Paulson writes: One gets the sense that Freeman Dyson has seen everything. It’s not just that at 92 he’s had a front row seat on scientific breakthroughs for the past century, or that he’s been friends and colleagues with many of the giants of 20th-century physics, from Hans Bethe and Wolfgang Pauli to Robert Oppenheimer and Richard Feynman. Dyson is one of the great sages of the science world. If you want to get a sense of where science has come from and where it might be headed, Dyson is your man.
Dyson grew up in England with a gift for numbers and calculating. During World War II, he worked with the British Royal Air Force to pinpoint bombing targets in Germany. After the war, he moved to the United States where he got to know many of the physicists who’d built the atomic bomb. Like a lot of scientists from that era, excitement over the bomb helped launch his career in physics, and later he dreamed of building a fleet of spaceships that would travel around the solar system, powered by nuclear bombs. Perhaps it’s no accident that Dyson became an outspoken critic of nuclear weapons during the Cold War.
For more than six decades, Princeton’s Institute for Advanced Study has been his intellectual home. Dyson has described himself as a fox rather than a hedgehog. He says scientists who jump from one project to the next have more fun. Though no longer an active scientist, he continues to track developments in science and technology. Dyson seems to be happy living in a universe filled with answered questions, and he likes the fact that physics has so far failed to unify the classical world of stars and the quantum world of atoms.
When I approached Dyson about an interview on the idea of the heroic in science, he responded, “I prefer telling stories to talking philosophy.” In the end, I got both stories and big ideas. Dyson isn’t shy about making sweeping pronouncements—whether on the archaic requirements of the Ph.D. system or the pitfalls of Big Science—but his manner is understated and his dry sense of humor is always just below the surface. [Continue reading…]
Brian Gallagher writes: In 1939, the year Edwin Hubble won the Benjamin Franklin award for his studies of “extra-galactic nebulae,” he paid a visit to an ailing friend. Depressed and interred at Las Encinas Hospital, a mental health facility, the friend, an actor and playwright named John Emerson, asked Hubble what — spiritually, cosmically — he believed in. In Edwin Hubble: Mariner of the Nebulae, Gale E. Christianson writes that Hubble, a Christian-turned-agnostic, “pulled no punches” in his reply. “The whole thing is so much bigger than I am,” he told Emerson, “and I can’t understand it, so I just trust myself to it, and forget about it.”
Even though he was moved by a sense of the universe’s immensity, it’s arresting to recall how small Hubble thought the cosmos was at the time. “The picture suggested by the reconnaissance,” he wrote in his 1937 book, The Observational Approach to Cosmology, “is a sphere, centred on the observer, about 1,000 million light-years in diameter, throughout which are scattered about 100 million nebulae,” or galaxies. “A suitable model,” he went on, “would be furnished by tennis balls, 50 feet apart, scattered through a sphere 5 miles in diameter.” From the instrument later named after him, the Hubble Space Telescope, launched in 1990, we learned from a series of pictures taken, starting five years later, just how unsuitable that model was.
The first is called the Hubble Deep Field, arguably “the most important image ever taken” according to this YouTube video. (I recommend watching it.) The Hubble gazed, for ten days, at an apparently empty spot in the sky, one about the size of a pinhead held up at arm’s length — a fragment one 24-millionth of the whole sky. The resulting picture had 3,000 objects, almost all of them galaxies in various stages of development, and many of them as far away as 12 billion light-years. Robert Williams, the former director of the Space Telescope Science Institute, wrote in the New York Times, “The image is really a core sample of the universe.” Next came the Ultra Deep Field, in 2003 (after a three-month exposure with a new camera, the Hubble image came back with 10,000 galaxies), then the eXtreme Deep Field, in 2012, a refined version of the Ultra that reveals galaxies that formed just 450 million years after the Big Bang. [Continue reading…]
“They,” as everybody knew, were the two massive black holes that, more than 1 billion years ago and in a remote corner of the cosmos, spiraled together and merged, making waves in the fabric of space and time. These “gravitational waves” rippled outward and, on Sept. 14, 2015, swept past Earth, strumming the ultrasensitive detectors of the Laser Interferometer Gravitational-Wave Observatory (LIGO). LIGO’s discovery, announced in February, triumphantly vindicated Albert Einstein’s 1916 prediction that gravitational waves exist. By tuning in to these tiny tremors in space-time and revealing for the first time the invisible activity of black holes — objects so dense that not even light can escape their gravitational pull — LIGO promised to open a new window on the universe, akin, some said, to when Galileo first pointed a telescope at the sky.
Already, the new gravitational-wave data has shaken up the field of astrophysics. In response, three dozen experts spent two weeks in August sorting through the implications at the Kavli Institute for Theoretical Physics (KITP) in Santa Barbara.[Continue reading…]
The Guardian reports: In the sleepy hillside town in al-Balqa, not far from the Jordan Valley, a grand project is taking shape. The Middle East’s new particle accelerator – the Synchrotron-Light for Experimental Science and Applications, or Sesame – is being built.
In a region racked by violence, extremism and the disintegration of nation states, Sesame feels a world apart; the meditative peace of the surrounding countryside belying the advanced stages of construction inside the site, which is due to be formally inaugurated next spring, with the first experiments taking place as early as this autumn.
It’s a miracle it got off the ground in the first place. Sesame’s members are Iran, Pakistan, Israel, Turkey, Cyprus, Egypt, the Palestinian Authority, Jordan and Bahrain. Iran and Pakistan do not recognise Israel, nor does Turkey recognise Cyprus, and everyone has their myriad diplomatic spats.
Iran, for example, continues to participate despite two of its scientists who were involved in the project, quantum physicist Masoud Alimohammadi and nuclear scientist Majid Shahriari, being assassinated in operations blamed on Israel’s Mossad.
“We’re cooperating very well together,” said Giorgio Paolucci, the scientific director of Sesame. “That’s the dream.” [Continue reading…]
The Guardian reports: China says it has launched the world’s first quantum satellite, a project Beijing hopes will enable it to build a coveted “hack-proof” communications system with potentially significant military and commercial applications.
Xinhua, Beijing’s official news service, said Micius, a 600kg satellite that is nicknamed after an ancient Chinese philosopher, “roared into the dark sky” over the Gobi desert at 1.40am local time on Tuesday, carried by a Long March-2D rocket.
“The satellite’s two-year mission will be to develop ‘hack-proof’ quantum communications, allowing users to send messages securely and at speeds faster than light,” Xinhua reported.
The Quantum Experiments at Space Scale, or Quess, satellite programme is part of an ambitious space programme that has accelerated since Xi Jinping became Communist party chief in late 2012.
“There’s been a race to produce a quantum satellite, and it is very likely that China is going to win that race,” Nicolas Gisin, a professor and quantum physicist at the University of Geneva, told the Wall Street Journal. “It shows again China’s ability to commit to large and ambitious projects and to realise them.”
The satellite will be tasked with sending secure messages between Beijing and Urumqi, the capital of Xinjiang, a sprawling region of deserts and snow-capped mountains in China’s extreme west.
Highly complex attempts to build such a “hack-proof” communications network are based on the scientific principle of entanglement. [Continue reading…]
Discover reports: What began as a bump has turned out to be nothing more than a statistical ghost.
Physicists at the International Conference on High Energy Physics in Chicago announced today that the much-discussed 750 GeV aberration in their data discovered by the Large Hadron Collider at the end of last year disappeared upon further testing.
“There is no excess seen in the 2016 data particularly around 750 GeV, confirms Bruno Lenzi, a physicist at CERN. “All over the mass range the data is consistent with the background only hypothesis.”
It was thought that the bump indicated the presence of a much larger particle new to physics, which could have held exciting implications for everything from the search for dark matter to quantum gravity. [Continue reading…]
Natalie Wolchover writes: In the same underground observatory in Japan where, 18 years ago, neutrinos were first seen oscillating from one “flavor” to another — a landmark discovery that earned two physicists the 2015 Nobel Prize — a tiny anomaly has begun to surface in the neutrinos’ oscillations that could herald an answer to one of the biggest mysteries in physics: why matter dominates over antimatter in the universe.
The anomaly, detected by the T2K experiment, is not yet pronounced enough to be sure of, but it and the findings of two related experiments “are all pointing in the same direction,” said Hirohisa Tanaka of the University of Toronto, a member of the T2K team who presented the result to a packed audience in London earlier this month.
“A full proof will take more time,” said Werner Rodejohann, a neutrino specialist at the Max Planck Institute for Nuclear Physics in Heidelberg who was not involved in the experiments, “but my and many others’ feeling is that there is something real here.”
The long-standing puzzle to be solved is why we and everything we see is matter-made. More to the point, why does anything — matter or antimatter — exist at all? The reigning laws of particle physics, known as the Standard Model, treat matter and antimatter nearly equivalently, respecting (with one known exception) so-called charge-parity, or “CP,” symmetry: For every particle decay that produces, say, a negatively charged electron, the mirror-image decay yielding a positively charged antielectron occurs at the same rate. But this cannot be the whole story. If equal amounts of matter and antimatter were produced during the Big Bang, equal amounts should have existed shortly thereafter. And since matter and antimatter annihilate upon contact, such a situation would have led to the wholesale destruction of both, resulting in an empty cosmos.
Somehow, significantly more matter than antimatter must have been created, such that a matter surplus survived the annihilation and now holds sway. The question is, what CP-violating process beyond the Standard Model favored the production of matter over antimatter? [Continue reading…]
The Washington Post reports: A lot of people deny climate change. Not many, though, deny gravity.
That’s why a recent animation released by NASA’s Jet Propulsion Laboratory — well, it came out in April, but people seem to be noticing it now — is so striking. Because it suggests the likely gravitational imprint of our changing climate on key features of the Earth in a way that’s truly startling.
The animation uses measurements from NASA’s squadron of GRACE satellites (Gravity Recovery and Climate Experiment), which detect changes in mass below them as they fly over the Earth, to calculate how the ocean changed from April 2002 until July 2013, based on corresponding changes in the mass of the continents. The resulting animation suggests the oceans gained mass overall, as seas rose, albeit with seasonal variations that result from water moving from the continents into the seas and back again.
But in key areas where glaciers have been melting — coastal Alaska, West Antarctica and, above all, Greenland — it suggests something very different happened. Here, the animation finds that the ocean actually fell, and in some places by as much as 50 millimeters (2 inches) over this short decadal span: [Continue reading…]
Brian Gallagher writes: It’s always a mistake to read,” Philip Marcus, a computational physicist and a professor in the mechanical engineering department at the University of California, Berkeley, tells me in a coffee shop near campus. “You learn too many things. That’s how I got really fascinated by fluid dynamics.”
It was 1978, and Marcus was in his first year of a post-doctoral position at Cornell focused on numerical simulations of solar convection and laboratory flows using spectral methods. But he had wanted to study cosmic evolution and general relativity; the problem, as Marcus told me, was that there was talk of no one seeing results of general relativity within their lifetime. As a result, “the field kind of collapsed on itself a little bit, and so everybody from general relativity was going to other fields.”
It was also in 1978 that Voyager 1 began to send up-close images of Jupiter back to Earth. When Marcus needed to, as he put it, “unwind, relax, whatever,” he would walk over to a special library, next to the astrophysics building, and marvel at Voyager’s images of the Great Red Spot. The storm had raged hundreds of millions of miles away since at least 1665, when it was first observed by Robert Hooke. “I realized that almost nobody in astronomy was trained in fluid dynamics, and I was,” he told me. “And I said, well, I’m in as good a position as anybody to start studying this.”
And he never stopped. Today, he is something of an expert on the solar system’s most famous storm. Sporting a mountain-biker’s build, he answered my questions with animation, often waving his hands around to clarify his concepts. He admitted this energy of his could encourage clumsiness. “People are leery of me,” he said. “If I walked into a laboratory, I would immediately break everything.” Thankfully, he explained, “I have the great fortune of having some wonderful friends who are experimentalists.” [Continue reading…]
The Guardian reports: Physicists have detected ripples in the fabric of spacetime that were set in motion by the collision of two black holes far across the universe more than a billion years ago.
The event marks only the second time that scientists have spotted gravitational waves, the tenuous stretching and squeezing of spacetime predicted by Einstein more a century ago.
The faint signal received by the twin instruments of the Laser Interferometer Gravitational Wave Observatory (LIGO) in the US revealed two black holes circling one another 27 times before finally smashing together at half the speed of light. [Continue reading…]
Adam Frank writes: Last month astronomers from the Kepler spacecraft team announced the discovery of 1,284 new planets, all orbiting stars outside our solar system. The total number of such “exoplanets” confirmed via Kepler and other methods now stands at more than 3,000.
This represents a revolution in planetary knowledge. A decade or so ago the discovery of even a single new exoplanet was big news. Not anymore. Improvements in astronomical observation technology have moved us from retail to wholesale planet discovery. We now know, for example, that every star in the sky likely hosts at least one planet.
But planets are only the beginning of the story. What everyone wants to know is whether any of these worlds has aliens living on it. Does our newfound knowledge of planets bring us any closer to answering that question?
A little bit, actually, yes. In a paper published in the May issue of the journal Astrobiology, the astronomer Woodruff Sullivan and I show that while we do not know if any advanced extraterrestrial civilizations currently exist in our galaxy, we now have enough information to conclude that they almost certainly existed at some point in cosmic history. [Continue reading…]
The Guardian reports: The universe is expanding faster than anyone had previously measured or calculated from theory. This is a discovery that could test part of Albert Einstein’s theory of relativity, a pillar of cosmology that has withstood challenges for a century.
Nasa and the European Space Agency jointly announced the universe is expanding 5% to 9% faster than predicted, a finding they reached after using the Hubble space telescope to measure the distance to stars in 19 galaxies beyond theMilky Way.
The rate of expansion did not match predictions based on measurements of radiation left over from the Big Bang that gave rise to the known universe 13.8bn years ago.
Physicist and lead author Adam Riess said: “You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right.
“But now the ends are not quite meeting in the middle and we want to know why.” [Continue reading…]
Dan Falk writes: Of the many counterintuitive features of quantum mechanics, perhaps the most challenging to our notions of common sense is that particles do not have locations until they are observed. This is exactly what the standard view of quantum mechanics, often called the Copenhagen interpretation, asks us to believe. Instead of the clear-cut positions and movements of Newtonian physics, we have a cloud of probabilities described by a mathematical structure known as a wave function. The wave function, meanwhile, evolves over time, its evolution governed by precise rules codified in something called the Schrödinger equation. The mathematics are clear enough; the actual whereabouts of particles, less so. Until a particle is observed, an act that causes the wave function to “collapse,” we can say nothing about its location. Albert Einstein, among others, objected to this idea. As his biographer Abraham Pais wrote: “We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.”
But there’s another view — one that’s been around for almost a century — in which particles really do have precise positions at all times. This alternative view, known as pilot-wave theory or Bohmian mechanics, never became as popular as the Copenhagen view, in part because Bohmian mechanics implies that the world must be strange in other ways. In particular, a 1992 study claimed to crystalize certain bizarre consequences of Bohmian mechanics and in doing so deal it a fatal conceptual blow. The authors of that paper concluded that a particle following the laws of Bohmian mechanics would end up taking a trajectory that was so unphysical — even by the warped standards of quantum theory — that they described it as “surreal.”
Nearly a quarter-century later, a group of scientists has carried out an experiment in a Toronto laboratory that aims to test this idea. And if their results, first reported earlier this year, hold up to scrutiny, the Bohmian view of quantum mechanics — less fuzzy but in some ways more strange than the traditional view — may be poised for a comeback.
Bohmian mechanics was worked out by Louis de Broglie in 1927 and again, independently, by David Bohm in 1952, who developed it further until his death in 1992. (It’s also sometimes called the de Broglie–Bohm theory.) As with the Copenhagen view, there’s a wave function governed by the Schrödinger equation. In addition, every particle has an actual, definite location, even when it’s not being observed. Changes in the positions of the particles are given by another equation, known as the “pilot wave” equation (or “guiding equation”). The theory is fully deterministic; if you know the initial state of a system, and you’ve got the wave function, you can calculate where each particle will end up.
That may sound like a throwback to classical mechanics, but there’s a crucial difference. Classical mechanics is purely “local” — stuff can affect other stuff only if it is adjacent to it (or via the influence of some kind of field, like an electric field, which can send impulses no faster than the speed of light). Quantum mechanics, in contrast, is inherently nonlocal. The best-known example of a nonlocal effect — one that Einstein himself considered, back in the 1930s — is when a pair of particles are connected in such a way that a measurement of one particle appears to affect the state of another, distant particle. The idea was ridiculed by Einstein as “spooky action at a distance.” But hundreds of experiments, beginning in the 1980s, have confirmed that this spooky action is a very real characteristic of our universe.
In the Bohmian view, nonlocality is even more conspicuous. The trajectory of any one particle depends on what all the other particles described by the same wave function are doing. And, critically, the wave function has no geographic limits; it might, in principle, span the entire universe. Which means that the universe is weirdly interdependent, even across vast stretches of space. The wave function “combines — or binds — distant particles into a single irreducible reality,” as Sheldon Goldstein, a mathematician and physicist at Rutgers University, has written. [Continue reading…]
Philip Ball writes: Have you heard the one about the biologist, the physicist, and the mathematician? They’re all sitting in a cafe watching people come and go from a house across the street. Two people enter, and then some time later, three emerge. The physicist says, “The measurement wasn’t accurate.” The biologist says, “They have reproduced.” The mathematician says, “If now exactly one person enters the house then it will be empty again.”
Hilarious, no? You can find plenty of jokes like this — many invoke the notion of a spherical cow — but I’ve yet to find one that makes me laugh. Still, that’s not what they’re for. They’re designed to show us that these academic disciplines look at the world in very different, perhaps incompatible ways.
There’s some truth in that. Many physicists, for example, will tell stories of how indifferent biologists are to their efforts in that field, regarding them as irrelevant and misconceived. It’s not just that the physicists were thought to be doing things wrong. Often the biologists’ view was that (outside perhaps of the well established but tightly defined discipline of biophysics) there simply wasn’t any place for physics in biology.
But such objections (and jokes) conflate academic labels with scientific ones. Physics, properly understood, is not a subject taught at schools and university departments; it is a certain way of understanding how processes happen in the world. When Aristotle wrote his Physics in the fourth century B.C., he wasn’t describing an academic discipline, but a mode of philosophy: a way of thinking about nature. You might imagine that’s just an archaic usage, but it’s not. When physicists speak today (as they often do) about the “physics” of the problem, they mean something close to what Aristotle meant: neither a bare mathematical formalism nor a mere narrative, but a way of deriving process from fundamental principles.
This is why there is a physics of biology just as there is a physics of chemistry, geology, and society. But it’s not necessarily “physicists” in the professional sense who will discover it. [Continue reading…]