A CELESTIAL event in the 5th century BC could be the earliest documented sighting of Halley’s comet – and it marked a turning point in the history of astronomy.
According to ancient authors, from Aristotle onwards, a meteorite the size of a “wagonload” crashed into northern Greece sometime between 466 and 468 BC. The impact shocked the local population and the rock became a tourist attraction for 500 years.
The accounts describe a comet in the sky when the meteorite fell. This has received little attention, but the timing corresponds to an expected pass of Halley’s comet, which is visible from Earth every 75 years or so.
Philosopher Daniel Graham and astronomer Eric Hintz of Brigham Young University in Provo, Utah, modelled the path that Halley’s comet would have taken, and compared this with ancient descriptions of the comet (Journal of Cosmology, vol 9, p 3030). For example, the comet was said to be visible for 75 days, accompanied by winds and shooting stars, and in the western sky when the meteorite fell.
The researchers show that Halley’s comet would have been visible for a maximum of 82 days between 4 June and 25 August 466 BC. From 18 July onwards, a time of year characterised in this region by strong winds, it was in the western sky. At around this time, the Earth was moving under the comet’s tail, so its debris field would have made shooting stars.
None of this proves the comet’s identity, but Graham says such major comet sightings are rare, so Halley must be a “strong contender”. Previously, the earliest known sighting of Halley was made by Chinese astronomers in 240 BC. If Graham and Hintz are correct, the Greeks saw it three orbits and more than two centuries earlier.
The researchers’ analysis reveals this moment to be a crucial turning point in the history of astronomy. Plutarch wrote in the 1st century AD that a young astronomer called Anaxagoras predicted the meteorite’s fall to Earth, which has puzzled historians because such events are essentially random occurrences.
After studying what was said about Anaxagoras, Graham concludes that he should be recognised as “the star of early Greek astronomy”. Rather than predicting a particular meteorite, he reckons Anaxagoras made a general statement that rocks might fall from the sky.
At this time, says Graham, everyone thought that celestial bodies such as the moon and planets were fiery, lighter-than-air objects. But after observing a solar eclipse in 478 BC, Anaxagoras concluded that they were heavy, rocky lumps, held aloft by a centrifugal force. This implied that solar eclipses occurred when the moon blocked the light from the sun. It also meant that if knocked from position, such a rock might crash to Earth.
“When the meteorite fell, no one could deny it,” says Graham. “The headline was ‘Anaxagoras was right’.”
Did Halley’s comet play a role? It is always possible that the comet might have nudged a near-Earth asteroid from its course and sent it hurtling towards northern Greece. From that point on, the idea of rocks in the sky was accepted, and the Greeks had a new understanding of the cosmos.
P ≠ NP? It’s Bad News for the Power of Computing
August 11, 2010
Has the biggest question in computer science been solved? On 6 August, Vinay Deolalikar , a mathematician at Hewlett-Packard Labs in Palo Alto, California, sent out draft copies of a paper titled simply “P ≠ NP”
This terse assertion could have profound implications for the ability of computers to solve many kinds of problem. It also answers one of the Clay Mathematics Institute’s seven Millennium Prize problems, so if it turns out to be correct Deolalikar will have earned himself a prize of $1 million.
The P versus NP question concerns the speed at which a computer can accomplish a task such as factorising a number. Some tasks can be completed reasonably quickly—in technical terms, the running time is proportional to a polynomial function of the input size—and these tasks are in class P.
If the answer to a task can be checked quickly then it is in class NP.
So if P = NP, every problem that can be checked quickly can also be completed quickly. That outcome would have huge repercussions for Internet security, where the difficulty of factorising very large numbers is the primary means by which our data is kept safe from hackers.
Though scientists have been studying them for years, atoms are only now ready for their first close-up portrait.
WASHINGTON — For the first time, physicists have photographed the structure of an atom down to its electrons.
The pictures, soon to be published in the journal Physical Review B, show the detailed images of a single carbon atom’s electron cloud, taken by Ukrainian researchers at the Kharkov Institute for Physics and Technology in Kharkov, Ukraine.
This is the first time scientists have been able to see an atom’s internal structure directly. Since the early 1980s, researchers have been able to map out a material’s atomic structure in a mathematical sense, using imaging techniques.
Quantum mechanics states that an electron doesn’t exist as a single point, but spreads around the nucleus in a cloud known as an orbital. The soft blue spheres and split clouds seen in the images show two arrangements of the electrons in their orbitals in a carbon atom. The structures verify illustrations seen in thousands of chemistry books because they match established quantum mechanical predictions.
David Goldhaber-Gordon, a physics professor at Stanford University in California, called the research remarkable.
“One of the advantages [of this technique] is that it’s visceral,” he said. “As humans we’re used to looking at images in real space, like photographs, and we can internalize things in real space more easily and quickly, especially people who are less deep in the physics.”
To create these images, the researchers used a field-emission electron microscope, or FEEM. They placed a rigid chain of carbon atoms, just tens of atoms long, in a vacuum chamber and streamed volts through the sample. The atom at the tip of the chain emitted electrons onto a surrounding phosphor screen, rendering an image of the electron cloud around the nucleus.
Field emitting electron microscopes have been a staple of scientists’ probing the very small since the 1930s. Up to this point, the microscopes were only able to reveal the arrangement of atoms in the sample.
The sharper a sample’s pointed tip inside the vacuum chamber, the greater the resolution of the final image on the screen said Igor Mikhailovskij, one of the paper’s authors. In the last year, physicists learned to manipulate carbon atoms into chains. With the tip of the sample now just a single atom wide, the microscope was able to resolve the electron’s orbitals. The Kharkov researchers are the first to produce real images of the electrons of a single atom, making the predictions of quantum mechanics visible. While tools like the scanning tunneling microscope already map the structure of electrons in a sample of many atoms, “it’s always good to have complementary approaches,” Goldhaber-Gordon said. “Sometimes something puzzling in one view becomes crystal clear in the other view. Each one gets you a step closer to a full understanding.” Goldhaber-Gordon also pointed out that the technique may not be widely applicable because the high resolution was due to the sample’s specific structure. “At the moment it’s more important for displaying quantum mechanics very directly than for learning new things about materials,” he said. “But that could change if [the Ukrainian team] develop new capabilities.”
May 19–On Aug. 24, 79 A.D., Italy’s Mount Vesuvius exploded, burying the Roman towns of Herculaneum and Pompeii under tons of super-heated ash, rock and debris in one of the most famous volcanic eruptions in history. Thousands died. But somehow, hundreds of papyrus scrolls survived — sort of — in a villa at Herculaneum thought to have been owned at one time by Julius Caesar’s father-in-law.
The scrolls contained ancient philosophical and learned writings. But they were so badly damaged — literally turned to carbon by the volcanic heat — that they crumbled when scholars first tried to open them centuries later. The remaining scrolls, stored away in Italy and France, haven’t been read — or even unrolled — since 79 AD. Now, a computer scientist from the University of Kentucky hopes that modern digital technology will allow him to peer inside two of the fragile scrolls — without physically opening them — and unlock secrets they have held for almost 2,000 years.
Brent Seales, the Gill professor of engineering in UK’s computer science department, will use an X-Ray CT scanning system to collect interior images of the scrolls’ rolled-up pages. Then, he and his colleagues hope to digitally “unroll” the scrolls on a computer screen so scholars can read them. “It will be a challenge because today these things look more like charcoal briquets than scrolls,” Seales said last week. “But we’re using a non-invasive scanning system, based on medical technology, that lets you slice through an object and develop a three-dimensional data set without having to open it, just as you would do a CT scan on a human body.” The two scrolls that Seales and his team will work on are stored at the French National Academy in Paris. The UK group will spend July working there.
Their system was developed at UK through the EDUCE project, or Enhanced Digital Unwrapping for Conservation and Exploration, which Seales launched through a grant from the National Science Foundation.
Experts say that if the UK system works as well as hoped, it could provide a safe new way to decipher and preserve more scrolls from Herculaneum, as well as other ancient books, manuscripts and documents that are too fragile to be opened.
“No one has yet really figured out a way to open them,” says Roger Macfarlane, a professor of classics at Brigham Young University who also has worked on scrolls from Herculaneum. “If Brent is successful it would be a huge, potentially monumental step forward.” Seales admits that there are hurdles, the biggest being the carbon-based ink thought to have been used on the scrolls. He says that since the papyrus in the scrolls was turned to carbon by the fury of Vesuvius, it might be impossible to visually separate the writing from the pages, even with powerful computer programs.
“The open question is, will we be able to read the writing?” Seales said. “There is a chance that we won’t be able to do it with our current machine, and that we’ll have to re-engineer some things. But if that’s the case, that’s what we will do.” Seales, who is from Buffalo, N.Y., grew up with two passions: computers and the humanities. His double major in undergraduate school was computer science and violin. While working on computer imaging in graduate school, Seales became interested in how that technology might be used to digitally preserve old manuscripts and documents.
By the early 1990s, he was developing systems to read old records that were crumpled and wrinkled with age. As a result, he joined an international computer team that digitized the oldest known complete text of Homer’s Iliad, which is stored in Venice, Italy. The project, ultimately completed at UK’s Center for Visualization and Virtual Environments, produced new digital images, bringing to life sections of the text from the 10th century B.C. that previously were little more than ink smudges.
Developing a method to virtually unroll and copy ancient documents too delicate for normal handling was the next step. This is the system that Seales and his colleagues will use on the Herculaneum scrolls.
If it works, what will they find? The best guess is that the scrolls contain writings by Philodemus, a Roman writer and Epicurean philosopher born about 110 B.C. Philodemus is not considered a classical thinker of the first rank, but he was a contemporary of Cicero. He taught Virgil and is thought to have influenced the Roman poet Horace.
Philodemus also was a friend of Lucius Calpurnius Piso — the father-in-law of Julius Caesar — who at one time owned that luxurious villa at Herculaneum.
The mansion had passed to other hands, however, when it and Herculaneum were buried during the eruption of 79 AD. Afterward, Herculaneum lay hidden for 1,600 years, until excavators stumbled upon it in 1709.
The villa itself was not uncovered until the mid-1700s. Inside its library, investigators found what they first thought to be lumps of coal but that turned out to be papyrus scrolls — about 1,800 in all — fused into blackened cylinders by furious volcanic heat. The building became known as the Villa of the Papyri.
According to Seales, the scrolls did not burn because the building so was completely encased in ash and lava that no oxygen was available to feed any flames.
Ironically, experts say that the papyrus, made of plant material, almost certainly would have decomposed over the last 2,000 years had it not been sealed in what amounted to an airtight vault.
What survived was incredibly fragile. Many scrolls simply crumbled when early researchers tried to open them. A Vatican priest eventually developed a way of opening a few scrolls, but it was slow and produced mixed results. Most were never unrolled.
The majority of the scrolls ultimately went to a library in Naples. But Napoleon had several shipped to France when he took over Italy after 1800. Among these scrolls are the two that the UK team plans to investigate.
Seales describes the process as resembling a “virtual colonoscopy,” a medical test for colon cancer.
“In a colonoscopy, you’re interested in whether there’s cancerous activity on the wall of the colon,” he said. “So you can imagine locating that in a scan, then flattening it out and manipulating it to see what you can see. We’ll be doing a similar sort of thing.” According to Seales, many experimental scans probably will be necessary, plus much additional computer work afterward, to produce clear images.
Members of the UK group won’t touch the fragile materials. All handling will be done by conservators at the French National Academy.
Macfarlane, the Brigham Young University scholar, predicted that if Seales’ team is successful, other Herculaneum scrolls probably also will be made available for scanning. Those could contain works by other ancient writers, more important than Philodemus, perhaps by Epicurus, who founded one of the major philosophies of ancient Greece, Macfarlane said.
“If Brent does unlock the door to reading these scrolls that are still hiding text, there will be a lot of excitement,” he said.
Seales sees other potential applications for the system, including deciphering otherwise unreadable written materials for homeland security purposes. But, he also admits that there are other ancient tests he’d like to examine.
“There are pieces of the Dead Sea scrolls that still haven’t been opened yet,” he said. “I’ve talked with some members of teams that work with those materials, and I’d love to see what more we could wring out of them.
Possible site of free will found in brain
Free will, or at least the place where we decide to act, is sited in a part of the brain called the parietal cortex, new research suggests.
When a neurosurgeon electrically jolted this region in patients undergoing surgery, they felt a desire to, say, wiggle their finger, roll their tongue or move a limb. Stronger electrical pulses convinced patients they had actually performed these movements, although their bodies remained motionless.
“What it tells us is there are specific brain regions that are involved in the consciousness of your movement,” says Angela Sirigu (pdf format), a neuroscientist at the CNRS Cognitive Neuroscience Centre in Bron, France, who led the study.
Sirigu’s team, including neurosurgeon Carmine Mottolese, performed the experiments on seven patients undergoing brain surgery to remove tumours.
In all but one case, the cancers were located far from the parietal cortex and other areas that Mottolese stimulated. One patient’s tumour sat near the parietal cortex, but did not interfere with the experiments, Sirigu says.
And because the patients were awake during the surgery, they could answer questions.
Religion might not be the only reason people buy into creationism and intelligent design, psychological experiments suggest. No matter what their religious beliefs, college-educated adults frequently agree with purpose-seeking yet false explanations of natural phenomena – finches diversified in order to survive, for instance. “The very fact of belief in purpose itself might lead you to favour intelligent design,” says Deborah Kelemen, a psychologist at Boston University, who led the study Kelemen has documented the same kind of erroneous thinking – called promiscuous teleology – in young children. Seven and eight-year olds agree with teleological statements such as “Rocks are jagged so animals can scratch themselves” and “Birds exist to make nice music”. These mistakes diminish as kids take more science classes and learn causal explanations for natural events.
To see whether education erases teleological tendencies or whether they instead represent our brain’s default mode, Kelemen and colleague Evelyn Rosset presented 230 university students with various teleological statements, such as:
• Earthworms tunnel underground to aerate the soil
• Mites live on skin to consume dead skin cells
• The Sun makes light so that plants can photosynthesise
• Earthquakes happen because tectonic plates must align
Students saw a sentence flash onto a computer screen and had either 5 or 3.2 seconds to answer true or false. A third group had no time limit.
To make sure students were paying attention and could read quickly, the researchers threw in some obviously true statements: “Flowers wilt because they get dehydrated” or “People buy vacuums because they suck up dirt”, for example.
IF WE ever establish contact with intelligent aliens living on a planet around a distant star, we would expect some problems communicating with them. As we are many light years away, our signals would take many years to reach them, so there would be no scope for snappy repartee. There could be an IQ gap and the aliens might be built from quite different chemistry. Yet there would be much common ground too. They would be made of similar atoms to us. They could trace their origins back to the big bang 13.7 billion years ago, and they would share with us the universe’s future. However, the surest common culture would be mathematics. Mathematics has been the language of science for thousands of years, and it is remarkably successful. In a famous essay, the great physicist Eugene Wigner wrote about the “unreasonable effectiveness of mathematics”. Most of us resonate with the perplexity expressed by Wigner, and also with Einstein’s dictum that “the most incomprehensible thing about the universe is that it is comprehensible”. We marvel at the fact that the universe is not anarchic – that atoms obey the same laws in distant galaxies as in the lab. The aliens would, like us, be astonished by the patterns in our shared cosmos and by the effectiveness of mathematics in describing those patterns. Mathematics can point the way towards new discoveries in physics too. Most famously, British theorist Paul Dirac used pure mathematics to formulate an equation that led to the idea of antimatter several years before the first antiparticle was found in 1932. So will physicists’ luck hold as they aim to probe still deeper levels of structure in the cosmos? Are limits set by the intrinsic capacity of our brains? Can computers offer insights, rather than just crunch numbers? These are some of the questions that exercise me. The precedents are encouraging. The two big breakthroughs in physics in the 20th century owed much to mathematics. The first was the formulation of quantum theory in the 1920s, of which Dirac was one of the great pioneers. The theory tells us that, on the atomic scale, nature is intrinsically fuzzy. Nonetheless, atoms behave in precise mathematical ways when they emit and absorb light, or link together to make molecules.
We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they? The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them. That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes. Smith uses this idea to derive a minimum density of civilizations below which contact is improbable within a given volume of space. The calculation depends on factors such as the lifetime of a civilization and the distance that it might be possible to communicate over and it produces some interesting scenarios: “Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilization in the galactic neighborhood to reach a minimum density.” So if there are only 200 advanced civilizations in our galaxy, the chances are that they’ll never notice each other. Of course, we’ve no way of knowing how many advanced civilizations are out there. But this kind of thinking could, for the first time, put a limit on the number that could be out there: less than 200 perhaps?
It also has significant implications for Fermi’s line of thinking.
Would it be too early to say the paradox has been solved?
ΕΞΩΓΗΙΝΟΙ πολιτισμοί ευφυών πλασμάτων υπάρχουν και μπορεί μάλιστα να είναι χιλιάδες, ανακοίνωσε ένας επιστήμονας στο Εδιμβούργο. Η ανακάλυψη, τα τελευταία χρόνια, άνω των 330 πλανητών εκτός του ηλιακού μας συστήματος επαναπροσδιόρισε τον αριθμό των μορφών ζωής που είναι στατιστικά πιθανό να υπάρχουν στο Διάστημα. Οι επιστήμονες υπολογίζουν τώρα ότι υπάρχουν τουλάχιστον 361 ευφυείς πολιτισμοί στον γαλαξία μας, ενώ ο αριθμός τους μπορεί να φθάνει και τις 38.000. Μολονότι οι ερευνητές ανακοινώνουν συχνά συνολικές εκτιμήσεις για την πιθανότητα να υπάρχει στο σύμπαν ευφυής ζωή πέραν των ανθρώπων, η διαδικασία αυτή βρίθει εικασιών. «Υπολογίζουμε την άγνοιά μας», λέει ο Ντάνκαν Φόργκαν, ερευνητής του Πανεπιστημίου του Εδιμβούργου που έκανε τον υπολογισμό, ο οποίος δημοσιεύεται στη Διεθνή Επιθεώρηση Αστροβιολογίας. Προχώρησε στην προσομοίωση ενός γαλαξία ο οποίος μοιάζει με τον δικό μας και ανέπτυξε ηλιακά συστήματα βάσει όσων γνωρίζουμε σήμερα από τους λεγόμενους εξωπλανήτες που έχουμε ανακαλύψει στη γαλαξιακή γειτονιά μας. Στη συνέχεια βάσει αυτών των προσομοιώσεων εξωγήινων κόσμων ανέπτυξε διαφορετικά σενάρια. Σύμφωνα με το πρώτο σενάριο, είναι δύσκολο να σχηματιστεί ζωή, αλλά εύκολο να αναπτυχθεί: στην περίπτωση αυτή, θα υπήρχαν στον γαλαξία 361 ευφυείς πολιτισμοί. Σύμφωνα με ένα δεύτερο σενάριο, η ζωή σχηματίστηκε εύκολα, αλλά δυσκολεύτηκε να αναπτύξει ευφυΐα. Υπό αυτές τις συνθήκες, ο Φοργκαν υπολόγισε ότι θα υπήρχαν 31.513 άλλες μορφές ζωής. Με το τελευταίο σενάριο εξέτασε την πιθανότητα να πέρασε η ζωή από τον έναν πλανήτη στον άλλον μέσω συγκρούσεων αστεροειδών- μια δημοφιλής θεωρία για την προέλευση της ζωής στη Γη. Η προσέγγιση αυτή έδειξε ότι θα υπήρχαν 37.964 ευφυείς πολιτισμοί.
Repulsive quantum effect finally measured
A quantum effect that causes objects to repel one another – first predicted almost 50 years ago – has at last been seen in the lab. According to Harvard physicist Federico Capasso, a member of the group who measured the effect, it could be used to lubricate future nanomachines. The team detected the weak repulsive force when they brought together a thin sheet of silica and a small gold-plated bead, about half the diameter of a human hair. The force is an example of the Casimir effect, generated by all-pervasive quantum fluctuations.
The simplest way to imagine the Casimir force in action is to place two parallel metal plates in a vacuum. Thanks to the odd quantum phenomenon, these become attracted to one another. It happens because even a vacuum is actually fizzing with a quantum field of particles, constantly popping in and out of existence. They can even fleetingly interact with and push on the plates. However, the small space between the two plates restricts the kind of particles that can appear, so the pressure from behind the plates overwhelms that from between them. The result is an attractive force that gums up nanoscale machines. (To learn more about the Casimir force see Under pressure from quantum foam.) Capasso says that the Casimir force needn’t be an enemy. “Micromechanics at some point will have to contend with these forces – or make use of them.”
In 1961, Russian theorists calculated that in certain circumstances, the Casimir effect could cause objects to repel one another – a scenario Capasso’s team have finally created experimentally. The team achieved this by adding a fluid, bromobenzene, to the setup. The Casimir attraction between the liquid and the silica plate is stronger than that between the gold bead and the silica, so the fluid forces its way around the bead, pushing it away from the plate. The effect is akin to the buoyancy we experience in the macro world – where objects less dense than water are held up by the liquid around them. But in this case the bromobenzene is less dense than the solid bead. “You could call it quantum buoyancy,” Capasso told New Scientist. The force he measured was feeble – amounting to just a few tens of piconewtons – but that is still enough to buoy up nanoscale objects.
“The next experiment we want to do is use a TV camera to track the motion of one of these spheres, then we should be able to see easily whether you have levitation.” Harnessing the repulsive Casimir force could provide a kind of lubrication to solve the problem of nanomachines becoming gummed up by the better-known attractive version, says Capasso. In theory you could instead use a liquid denser than the components to buoy them up, but that wouldn’t be practical. “These gizmos are usually made of metal, so you would have to use mercury,” he explains. Quantum buoyancy bearings could be used to build delicate sensors, such as a floating “nanocompass” to detect small-scale magnetic fields.