The Daily Galaxy -Great Discoveries Channel, is an eclectic text and video presentation of news and original insights on science, space exploration and the environment and their reflections in popular culture (film, books, events). It provides news and original insights on science, space exploration, cosmology, astrobiology, and astrophysics.
The renowned British physicist, who died at 76, left behind a riddle that could eventually lead his successors to the theory of quantum gravity.
Hawking was something of a betting man, regularly entering into friendly wagers with his colleagues over key questions in theoretical physics. “I sensed when Stephen and I first met that he would enjoy being treated irreverently,” wrote John Preskill, a physicist at the California Institute of Technology, earlier today on Twitter. “So in the middle of a scientific discussion I could interject, ‘What makes you so sure of that, Mr. Know-It-All?’ knowing that Stephen would respond with his eyes twinkling: ‘Wanna bet?’”
And bet they did, writes Jennifer Ouellette in Quanta. In 1991, Hawking and Kip Thorne bet Preskill that information that falls into a black hole gets destroyed and can never be retrieved. Called the black hole information paradox, this prospect follows from Hawking’s landmark 1974 discovery about black holes — regions of inescapable gravity, where space-time curves steeply toward a central point known as the singularity. Hawking had shown that black holes are not truly black. Quantum uncertainty causes them to radiate a small amount of heat, dubbed “Hawking radiation.” They lose mass in the process and ultimately evaporate away. This evaporation leads to a paradox: Anything that falls into a black hole will seemingly be lost forever, violating “unitarity” — a central principle of quantum mechanics that says the present always preserves information about the past.
Hawking and Thorne argued that the radiation emitted by a black hole would be too hopelessly scrambled to retrieve any useful information about what fell into it, even in principle. Preskill bet that information somehow escapes black holes, even though physicists would presumably need a complete theory of quantum gravity to understand the mechanism behind how this could happen.
Physicists thought they resolved the paradox in 2004 with the notion of black hole complementarity. According to this proposal, information that crosses the event horizon of a black hole both reflects back out and passes inside, never to escape. Because no single observer can ever be both inside and outside the black hole’s horizon, no one can witness both situations simultaneously, and no contradiction arises. The argument was sufficient to convince Hawking to concede the bet. During a July 2004 talk in Dublin, Ireland, he presented Preskill with the eighth edition of Total Baseball: The Ultimate Baseball Encyclopedia, “from which information can be retrieved at will.”
Thorne, however refused to concede, and it seems he was right to do so. In 2012, a new twist on the paradox emerged. Nobody had explained precisely how information would get out of a black hole, and that lack of a specific mechanism inspired Joseph Polchinski and three colleagues to revisit the problem. Conventional wisdom had long held that once someone passed the event horizon, they would slowly be pulled apart by the extreme gravity as they fell toward the singularity. Polchinski and his co-authors argued that instead, in-falling observers would encounter a literal wall of fire at the event horizon, burning up before ever getting near the singularity.
It's rare that a scientist becomes a folk hero. But in China, Qian Xuesen draws crowds almost a decade after his death. Recruited from MIT, Qian joined Theodore von Karman's group at Caltech, including the founding of the NASA's Jet Propulsion Laboratory. Later, he returned to China made huge contributions to China's missile, space, and nuclear weapons program.
On a Saturday morning in a three-story museum here, writes Mara Hvistendahl in Science, tourists admire Qian's faded green sofa set, the worn leather briefcase he carried for 4 decades, and a picture of him shaking hands with opera star Luciano Pavarotti. They file past a relic from a turning point in Qian's life—and in China's rise as a superpower: a framed ticket from his 1955 voyage from San Francisco, California, to Hong Kong in China aboard the SS President Cleveland.
Once a professor at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, he had been accused of having communist sympathies in the heat of the Red Scare and placed under virtual house arrest. Upon his release, he and his family set sail for his motherland.
After arriving in China, Qian went on to spearhead the rapid ascent of the country's nuclear weapons program, an achievement that explains some of the adulation. But his legacy is still unfolding in a second area that could have great consequences for China—and for the world. Qian, who died in 2009 at the age of 97, helped lay the groundwork for China's modern surveillance state.
Early in his career, he embraced systems engineering—an interdisciplinary field focused on understanding the general properties common to all physical and societal systems, and using that knowledge to exert control. By mapping a system's dynamics and constraints, including any feedback loops, systems theorists learn how to intervene in it and shape outcomes. Since the field's founding in the 1950s, systems approaches have been applied to areas as varied as biology and transportation infrastructure.
In the West, systems engineering's heyday has long passed. But in China, the discipline is deeply integrated into national planning. The city of Wuhan is preparing to host in August the International Conference on Control Science and Systems Engineering, which focuses on topics such as autonomous transportation and the "control analysis of social and human systems." Systems engineers have had a hand in projects as diverse as hydropower dam construction and China's social credit system, a vast effort aimed at using big data to track citizens' behavior. Systems theory "doesn't just solve natural sciences problems, social science problems, and engineering technology problems," explains Xue Huifeng, director of the China Aerospace Laboratory of Social System Engineering (CALSSE) and president of the China Academy of Aerospace Systems Science and Engineering in Beijing. "It also solves governance problems."
The field has resonated with Chinese President Xi Jinping, who in 2013 said that "comprehensively deepening reform is a complex systems engineering problem." So important is the discipline to the Chinese Communist Party that cadres in its Central Party School in Beijing are required to study it. By applying systems engineering to challenges such as maintaining social stability, the Chinese government aims to "not just understand reality or predict reality, but to control reality," says Rogier Creemers, a scholar of Chinese law at the Leiden University Institute for Area Studies in the Netherlands.
Maybe we owe our existence to a vast looming shadow of unseen, broken worlds. If we can only ever wake up on rare and seemingly miraculous worlds—and it’s a big enough universe—we shouldn’t be surprised to find our past filled with miracles.
It’s something of a miracle that life on our planet has been left to evolve without fatal interruption for billions of years, writes Peter Brannen in today's Atlantic. Such a long unbroken chain of survival, however unlikely, is necessary for bags of mud and water like ourselves to eventually sit up, and just recently, to wonder how we got here. And like the bullet-riddled—but safe—planes, our planet has survived countless near-fatal blows. There have been volcanic apocalypses, body blows from supersonic space rocks the size of Mount Everest, and ice ages that might have frozen the planet almost to the tropics. Had any of these catastrophes been worse, we wouldn’t be here. But they couldn’t have been worse for precisely that reason.
As Anders Sandberg, a senior research fellow at University of Oxford’s Future of Humanity Institute and his coauthors Nick Bostrom and Milan Ćirković write, “The risks associated with catastrophes such as asteroidal/cometary impacts, supervolcanic episodes, and explosions of supernovas/gamma-ray bursts are based on their observed frequencies. As a result, writes Peter Brannen in today's Atlantic, the frequencies of catastrophes that destroy or are otherwise incompatible with the existence of observers are systematically underestimated.”
That is, our forecasts about the future could be blinded by our necessarily lucky past. Not only is it impossible to look back and find truly world-ending impact craters in our planet’s history—stranger still, it would be impossible to find these impacts in the rock record even if they struck planets like ours all the time. Existential hazards, even if they’re extremely likely, might hover just out of frame, concealed by our “anthropic shadow.”
“Maybe the universe is super dangerous and Earth-like planets are destroyed at a very high rate,” Sandberg says. “But if the universe is big enough, then when observers do show up on some very, very rare planets, they’ll look at the record of meteor impacts and disasters and say, ‘The universe looks pretty safe!’ But the problem is, of course, that their existence depends on them being very, very lucky. They’re actually living in an unsafe universe and next Tuesday they might get a very nasty surprise.”
"With Juno only about a third of the way through its primary mission, we are being presented with a whole new Jupiter that is shaking up our basic understanding of giant planets throughout the universe," said Scott Bolton, principal investigator of the mission and a coauthor of the Nature papers. "Surprisingly, the Jupiter we grew up knowing and loving, dressed in gorgeous colorful bands across its midsection, is now known to be beautiful down deep as well."
"Before Juno, scientists knew little about Jupiter's poles due to the Earth's perspective of the planet," he said. Previous spacecraft flew past the gas giant at an equatorial level, capturing wonderful views of the zones and belts but revealing little about its polar regions. "Turns out, Jupiter is hardly recognizable from a polar perspective."
In the year and a half NASA's Juno spacecraft has been orbiting Jupiter, the science team led by Southwest Research Institute's Dr. Scott Bolton has discovered that the orange and white bands that characterize Jupiter's outer atmosphere extend thousands of miles into the gas giant's atmosphere. The findings are part of a four-article collection about Juno science results in the March 8th edition of the journal Nature.
The four Nature articles focus on the structure of Jupiter's deep interior and the surprising discovery of clusters of cyclones encircling Jupiter's poles. One paper discusses Juno's unique orbit, and how the spacecraft's precise radio tracking system measures Jupiter's gravity field.
"This Juno system is so technically advanced that measurement capabilities have been improved by orders of magnitude in precision," Bolton said. This improved accuracy allowed scientists to detect an asymmetry in Jupiter's structure at depths near 3,000 km. "This asymmetry mirrors what we see in Jupiter's cloud layer, those colorful bands that blow across Jupiter." A second paper describes how these belts and zones manifest themselves as jet streams deep in Jupiter's atmosphere.
"This discovery surprised the entire team," Bolton said. "The Juno data show that what seemed like a weather pattern on Jupiter extends down well below the depth where sunlight penetrates, which means that something other than weather may be driving these forces.
"In total, Jupiter's jet streams contain about 1 percent of the gas giant's mass. That means a mass equivalent to about three Earths is moving around Jupiter in the form of jet streams," he continued. "That is a lot of atmosphere to be moving with jet streams. On Earth, our atmosphere is less than a millionth of Earth's mass!"
A third paper looks at how the symmetric layers of Jupiter work and reports that below the jet stream layer, Jupiter rotates as a rigid body. "Somehow Jupiter transitions from the jet stream layer that rotates like the top cloud layer to a rigid body deep inside where everything moves together," Bolton said. "The transition might have something to do with the creation of Jupiter's strong magnetic field."
Understanding the transition between the atmospheric layer and the more rigid layers that lie beneath will be revealed during the remainder of Juno's primary mission over the next couple of years. The fourth paper provided the first detailed look at how the familiar bands give way to giant cyclones organized in geometric patterns at both of Jupiter's poles.
Visible and infrared images obtained from above each pole during Juno's first five orbits reveal persistent polygonal patterns of large cyclones. In the north, eight circumpolar cyclones surround a single polar cyclone. In the south, one polar cyclone is encircled by five circumpolar cyclones
"These cyclones are huge with winds speeds as great as 220 miles per hour," Bolton said. "These novel features seem to exist in harmony, close together and persistent. They are surprisingly different from the single storm pattern that the Cassini spacecraft measured at Saturn's poles."
Launched in 2011, Juno arrived at Jupiter in 2016. Every 53 days, the spacecraft swings in close to the planet, studying its auroras and probing beneath the obscuring cloud cover to learn more about the planet's origins, structure, weather layer and magnetosphere.
Phytoplankton are microscopic plants whose growth in ocean surface waters supports ocean food webs and global marine fisheries. They are also key agents in the long-term removal of carbon dioxide (CO2). A team led by scientists from Scripps Institution of Oceanography at the University of California San Diego and the J. Craig Venter Institute has demonstrated that the excess carbon dioxide added to the atmosphere through the combustion of fossil fuels interferes with the health of phytoplankton (shown below) which form the base of marine food webs.
As reported in the March 14 edition of Nature, the team shows that a mechanism widely used by phytoplankton to acquire iron has a requirement for carbonate ions. Rising concentrations of atmospheric CO2 are acidifying the ocean and decreasing carbonate, and the team shows how this loss of carbonate affects the ability of phytoplankton to obtain enough of the nutrient iron for growth. Ocean acidification is poised to decrease the concentration of sea surface carbonate ions 50 percent by the end of this century.
The study reveals an unexpected twist to the theory of how iron controls the growth of phytoplankton. By showing how the loss of seawater carbonate hampers the ability of phytoplankton to grab onto iron, the authors show a direct connection between the effects of ocean acidification and the health of phytoplankton at the base of the marine food chain.
"Ultimately our study reveals the possibility of a 'feedback mechanism' operating in parts of the ocean where iron already constrains the growth of phytoplankton," said Jeff McQuaid, lead author of the study who made the discoveries as a PhD student at Scripps Oceanography. "In these regions, high concentrations of atmospheric CO2 could decrease phytoplankton growth, restricting the ability of the ocean to absorb CO2 and thus leading to ever higher concentrations of CO2 accumulating in the atmosphere."
"Studies investigating the effects of high CO2 on phytoplankton growth have shown mixed results to date. In some cases, certain phytoplankton seem to benefit from high CO2," added Andrew E. Allen, a biologist with a joint appointment at Scripps and JCVI who is senior author and initiator of the study. "Most of these studies, however, have been conducted under high-iron conditions. Our study uncovers a widespread cellular mechanism that suggests high CO2 might be particularly problematic for phytoplankton growth in low-iron regions of the ocean."
One consequence of acidification is a nearly one-for-one reduction in the concentration of carbonate ions for every molecule of CO2 that dissolves in the ocean. The concentration of atmospheric CO2 is predicted to double by the end of this century; thus, the concentration of carbonate ions at the surface of the ocean will nearly halve by the year 2100. While the negative influence of acidification on corals and shellfish is known, this is the first study to reveal a mechanism that affects life which forms the base of most marine food webs.
This study revises a key concept in oceanography that the growth of phytoplankton in vast areas of the ocean is regulated by the concentration of iron. In ocean regions that are high in dissolved nutrients like nitrogen and phosphorous, iron limitation results in low numbers of phytoplankton relative to amounts of available nutrients. Addition of iron to these areas causes phytoplankton, particularly diatoms, to grow. In the largest of these regions, the Southern Ocean, concentrations of available iron are below one trillionth of a gram per liter, approaching the limit supporting life.
Marine scientists have spent decades investigating how phytoplankton are able to grab such low concentrations of iron from seawater and internalize it.
"Understanding the mechanism of iron uptake is critical to develop meaningful predictions on how phytoplankton may respond to future ocean conditions, but this understanding has been elusive," said Adam Kustka, a trace metal physiologist and project collaborator from Rutgers University.
Clues began to emerge in 2008, when Allen discovered several iron-responsive genes in diatoms that had no known function. That same year, McQuaid was traveling around East Antarctica assisting in a survey of plankton in the Southern Ocean. DNA analysis of those samples revealed that one of Allen's iron genes was not only present in every sample of seawater, but every major phytoplankton group in the Southern Ocean seemed to have a copy.
"This gene, called ISIP2A, was one of the most abundantly transcribed genes in low-iron Southern Ocean, suggesting it had a really important role in the environment," said Allen.
Earlier studies suggested a transferrin-like protein, called phytotransferrin, was at work in the marine environment, but ISIP2A looked nothing like transferrin. It took the development of an entirely new discipline, synthetic biology, to help prove the team's hypothesis that ISIP2A was a type of transferrin. Synthetic biology is the fusion of biology and engineering, and in collaboration with scientists with the Venter Institute, the team developed methods to insert synthetic DNA into a marine diatom. The scientists deleted ISIP2A and replaced it with a synthetic gene for human transferrin, demonstrating that ISIP2A was a type of transferrin.
The team then initiated a study to investigate the evolutionary relationships of transferrin and phytotransferrin. To their surprise, the proteins were functional analogs whose ancient origins extend to the pre-Cambrian period of Earth history, predating the appearance of modern plants and animals.
"The appearance of phytotransferrin some 700 million years ago is consistent with a time in Earth's history marked by massive changes in ocean chemistry, and this ancient evolutionary history helps explain why no one has connected ISIP2A and transferrin," said Miroslav Oborník, a molecular evolutionary biologist from the University of South Bohemia and co-author on the paper.
In transferrin, iron and carbonate bind simultaneously, and neither can bind in the absence of the other. Such synergistic binding is unique among biological interactions. The research team hypothesized that diatom phytotransferrin uses a similar mechanism and that, as a result, reductions in carbonate ion could lead to reduced phytoplankton growth rates.
Using a number of biochemical methods, the researchers were able to independently manipulate pH along with the concentrations of iron and carbonate ion. As they pumped in increasing concentrations of CO2, the team showed that the ability of their diatom to grab onto iron decreased proportionally with the concentration of carbonate ions.
"Since carbonate and iron have to bind simultaneously, as carbonate concentrations drop, phytotransferrin is able to 'see' less iron," said McQuaid. "The total amount of iron isn't changing - rather the ability to grab onto it changes, and this ultimately influences the growth rate."
The Daily Galaxy via University of California - San Diego
The reaction among physicists yesterday to Hawking's death is "just profound shock and sadness,” says Malcolm Perry, a Cambridge theoretical physicist who was a student of Hawking’s in the early 1970s. “He was a truly extraordinary man,” says Roger Penrose, a theoretical physicist at the University of Oxford, UK, who in 1970 co-authored a seminal paper with Hawking on the nature of black holes.
“We set out to develop methods to transform the idea of a multiverse into a coherent testable scientific framework," says Thomas Hertog, a cosmologist at KU Leuven in Belgium and former student of Hawking who co-authored studies with him. “This was Hawking: to boldly go where Star Trek fears to tread.”
The Nature Video explores three of the seminal publications that shaped his career and his legacy.
Stephen Hawking: Three publications that shaped his career - YouTube
Observations of Ceres have detected recent variations in its surface, revealing that the only dwarf planet in the inner solar system is a dynamic body that continues to evolve and change. "This is the first direct detection of change on the surface of Ceres," said Andrea Raponi of the Institute of Astrophysics and Planetary Science in Rome.
NASA's Dawn mission has found recently exposed deposits that give us new information on the materials in the crust and how they are changing, according to two papers published March 14 in Science Advances that document the new findings.
Observations obtained by the visible and infrared mapping spectrometer (VIR) on the Dawn spacecraft previously found water ice in a dozen sites on Ceres. The new study revealed the abundance of ice on the northern wall of Juling Crater, a crater 12 miles (20 kilometers) in diameter. The new observations, conducted from April through October 2016, show an increase in the amount of ice on the crater wall.
Raponi led the new study, which found changes in the amount of ice exposed on the dwarf planet. "The combination of Ceres moving closer to the sun in its orbit, along with seasonal change, triggers the release of water vapor from the subsurface, which then condenses on the cold crater wall. This causes an increase in the amount of exposed ice. The warming might also cause landslides on the crater walls that expose fresh ice patches."
By combining chemical, geological and geophysical observations, the Dawn mission is producing a comprehensive view of Ceres. Previous data had shown Ceres has a crust about 25 miles (40 kilometers) thick and rich in water, salts and, possibly, organics.
In a second study, VIR observations also reveal new information about the variability of Ceres' crust, and suggest recent surface changes, in the form of newly exposed material.
Dawn previously found carbonates, common on the planet's surface, that formed within an ocean. Sodium carbonates, for example, dominate the bright regions in Occator Crater (shown at top of page), and material of similar composition has been found at Oxo Crater and Ahuna Mons.
This study, led by Giacomo Carrozzo of the Institute of Astrophysics and Planetary Science, identified 12 sites rich in sodium carbonates and examined in detail several areas of a few square miles that show where water is present as part of the carbonate structure. The study marks the first time hydrated carbonate has been found on the surface of Ceres, or any other planetary body besides Earth, giving us new information about the dwarf planet's chemical evolution.
Water ice is not stable on the surface of Ceres over long time periods unless it is hidden in shadows, as in the case of Juling. Similarly, hydrated carbonate would dehydrate, although over a longer timescale of a few million years.
"This implies that the sites rich in hydrated carbonates have been exposed due to recent activity on the surface," Carrozzo said.
The great diversity of material, ice and carbonates, exposed via impacts, landslides and cryovolcanism suggests Ceres' crust is not uniform in composition. These heterogeneities were either produced during the freezing of Ceres' original ocean - which formed the crust - or later on as a consequence of large impacts or cryovolcanic intrusions.
"Changes in the abundance of water ice on a short timescale, as well as the presence of hydrated sodium carbonates, are further evidence that Ceres is a geologically and chemically active body," said Cristina De Sanctis, VIR team leader at the Institute of Astrophysics and Planetary Science.
"Venus is like Earth in so many ways," explains Stephen Hawking. "A sort of kissing cousin. She's almost the same size as Earth, a touch closer to the Sun. And, she has an atmosphere that could crush a submarine."
Astrobiologist David Grinspoon believes that scientists should look at our neighboring planets to help understand the perils of global warming.“It seems that both Mars and Venus started out much more like Earth and then changed. They both hold priceless climate information for Earth."
In the second episode of the original documentary series Stephen Hawking's Favorite Places, the renowned physicist proposes that climate-science deniers take a trip to Venus, even offering to pay for their fare to view the ultimate results of their ignorance.
The conditions on Venus today, Hawking says, are almost impossible to comprehend. Planetary scientists say "start by imagining Hell and work up from there." At the surface, Venus roasts at more than 800 degrees Fahrenheit under a suffocating blanket of sulfuric acid clouds and a crushing atmosphere more than 90 times the pressure of Earth's that has flat-out crushed every probe we've sent to it.
Stephen Hawking Tells Climate Change Deniers To Take A Trip To Venus - YouTube
In the findings of a study conducted by the National Aeronautics and Space Administration (NASA) in 2002, it was suggested that Venus shared similar traits to the Earth and even had water around 4.5 billion years ago. However, as the planet increasingly warmed, more water vapor was in its atmosphere resulting to more heat being trapped which continued until its oceans completely evaporated.
Using rudimentary computer-generated imagery (CGI), Hawking can be seen traveling in a spaceship to Venus as he passed through clouds of sulfuric acid. However, he finds that the pressure on the planet is roughly 90 times that of the Earth "enough to crush a submarine," while the temperature is around 200 degrees. He explains that the Earth could find itself in a similar situation if greenhouse gases are not controlled.
Venus was created at about the same time as Earth, in about the same place, and it's roughly the same size - it would therefore have started with the same materials as us, drawn together from the same region of the planet forming dust left over from the sun. But Venus now has only 0.001% of our water content, and a couple of flybys by the Venus Express may have revealed the reason.
In 2008, the probe discovered hydrogen and oxygen streaming off the night side of the planet in a 2:1 ratio, which you might recognize as the ratio in H20. It seems that what little water Venus has left is being blasted apart in the atmosphere by the solar wind, a vast stream of charged particles blown out by the sun. Venus Express has passed by the dayside and measured almost three hundred kilograms of hydrogen a day being lost into space. It hasn't found any oxygen yet, but the search continues.
"Venus today has a thick atmosphere that contains very little water, but we think the planet started out with an ocean's worth of water," said John T. Clarke of Boston University.
Scientists are still trying to determine whether water existed on the surface of Venus or only high up the atmosphere, where temperatures were cooler. If the surface temperature stayed below the boiling point of water long enough, rivers might have once flowed on the planet. Venus may have even had ice.
The key to figuring out how much water Venus once had lies in how much hydrogen and deuterium, a heavier version of hydrogen, remain in the atmosphere. Both can combine with oxygen to make water, either in the familiar H2O form or the rarer hydrogen, deuterium and oxygen form, called HDO. (Very small amounts of D2O also form.)
Intense UV light from the sun has broken apart nearly all of the water molecules in Venus' atmosphere. Because the regular hydrogen atoms in the water are lighter, they escape into space more quickly than the heavier deuterium ones.
By comparing the amount of deuterium now in the atmosphere to the amount of hydrogen, researchers can estimate how much water disappeared from Venus and how quickly it happened.
Early estimates, made from data collected by NASA's 1978 Pioneer Venus spacecraft and other observations, indicated Venus could have had enough ancient water to cover the entire planet with 23 feet (7 meters) of liquid.
But it turns out that the amounts of hydrogen and deuterium can vary at different heights in Venus' atmosphere, which could change the calculations.
Data gathered from European Space Agency’s Venus Express is invaluable to climate scientists modeling Earth’s climate to predict its future.
Climate scientists believe that Venus experienced a runaway greenhouse effect as the Sun gradually heated up. Astronomers believe that the young Sun was dimmer than the present-day Sun by 30 percent. Over the last 4 thousand million years, it has gradually brightened. During this increase, Venus’s surface water evaporated and entered the atmosphere.
“Water vapor is a powerful greenhouse gas and it caused the planet to heat-up even more. This is turn caused more water to evaporate and led to a powerful positive feedback response known as the runaway greenhouse effect,” says Grinspoon.
As Earth warms in response to man-made greenhouse gases, it risks the same fate. Reconstructing the climate of the past on Venus can give scientists a better understanding of how close our planet is to such a catastrophe. However, determining when Venus passed the point of no return is not trivial.
The Daily Galaxy via NASA's Goddard Space Flight Center and ESA
Geneticist David Reich used to study the living, but now he studies the dead. The precipitating event came in the form of 40,000-year-old Neanderthal bones found in a Croatian cave. So well-preserved were the bones that they yielded enough DNA for sequencing, and it became Reich’s job in 2007 to analyze the DNA for signs that Neanderthals interbred with humans—a idea he was “deeply suspicious” of at the time.
To his surprise, writes Sarah Zhang in today's Atlantic, the DNA revealed that humans and Neanderthals did interbreed in their time together in Europe. Possibly even more than once. Today, surprisingly, the people carrying the most Neanderthal DNA are not in Europe but in East Asia—likely due to the patterns of ancient human migration in Eurasia in the thousands of years after Neanderthals died out.
All this painted a complicated but dynamic picture of human prehistory. Since the very beginning of our species, humans have been on the move; at times they replaced and at other times they mixed with the local population, first hominids like Neanderthals and later other humans.
Reich has since converted his lab at Harvard Medical School into a “factory” for studying ancient DNA. His new book, Who We Are and How We Got Here, charts the myriad ways the study of ancient DNA is lobbing bombs into the halls of established wisdom. In Europe, for example, ancient DNA is identifying waves of migrations into the continent, in which groups of people serially replaced, or nearly replaced, the local population.
This work is not without controversy, especially as these replacements can be difficult to explain. Reich once had German collaborators drop out of a study when the initial findings seemed to mirror too closely Nazi propaganda about the Aryan race. We discuss this and other aspects of his work below. Our conversation has been condensed and edited for clarity.
"My goal is simple: a complete understanding of the universe, why it is as it is and why it exists at all."
The image of Stephen Hawking – who has died aged 76 – in his motorized wheelchair, with head contorted slightly to one side and hands crossed over to work the controls, caught the public imagination, as a true symbol of the triumph of mind over matter.
As with the Delphic oracle of ancient Greece, physical impairment seemed compensated by almost supernatural gifts, which allowed his mind to roam the universe freely, upon occasion enigmatically revealing some of its secrets hidden from ordinary mortal view, writes Sir Roger Penrose in today's Guardian.
Of course, such a romanticized image can represent but a partial truth. Those who knew Hawking would clearly appreciate the dominating presence of a real human being, with an enormous zest for life, great humor, and tremendous determination, yet with normal human weaknesses, as well as his more obvious strengths. It seems clear that he took great delight in his commonly perceived role as “the No 1 celebrity scientist”; huge audiences would attend his public lectures, perhaps not always just for scientific edification.
The scientific community might well form a more sober assessment. He was extremely highly regarded, in view of his many greatly impressive, sometimes revolutionary, contributions to the understanding of the physics and the geometry of the universe.
Cosmology's brightest star Stephen Hawking dies aged 76 - YouTube
Hawking had been diagnosed shortly after his 21st birthday as suffering from an unspecified incurable disease, which was then identified as the fatal degenerative motor neurone disease amyotrophic lateral sclerosis, or ALS. Soon afterwards, rather than succumbing to depression, as others might have done, he began to set his sights on some of the most fundamental questions concerning the physical nature of the universe. In due course, he would achieve extraordinary successes against the severest physical disabilities. Defying established medical opinion, he managed to live another 55 years.
His background was academic, though not directly in mathematics or physics. His father, Frank, was an expert in tropical diseases and his mother, Isobel (nee Walker), was a free-thinking radical who had a great influence on him. He was born in Oxford and moved to St Albans, Hertfordshire, at eight. Educated at St Albans school, he won a scholarship to study physics at University College, Oxford. He was recognised as unusually capable by his tutors, but did not take his work altogether seriously. Although he obtained a first-class degree in 1962, it was not a particularly outstanding one.
He decided to continue his career in physics at Trinity Hall, Cambridge, proposing to study under the distinguished cosmologist Fred Hoyle. He was disappointed to find that Hoyle was unable to take him, the person available in that area being Dennis Sciama, unknown to Hawking at the time. In fact, this proved fortuitous, for Sciama was becoming an outstandingly stimulating figure in British cosmology, and would supervise several students who were to make impressive names for themselves in later years (including the future astronomer royal Lord Rees of Ludlow).
Sciama seemed to know everything that was going on in physics at the time, especially in cosmology, and he conveyed an infectious excitement to all who encountered him. He was also very effective in bringing together people who might have things of significance to communicate with one another.
When Hawking was in his second year of research at Cambridge, I (at Birkbeck College in London) had established a certain mathematical theorem of relevance. This showed, on the basis of a few plausible assumptions (by the use of global/topological techniques largely unfamiliar to physicists at the time) that a collapsing over-massive star would result in a singularity in space-time – a place where it would be expected that densities and space-time curvatures would become infinite – giving us the picture of what we now refer to as a “black hole”.
Such a space-time singularity would lie deep within a “horizon”, through which no signal or material body can escape. (This picture had been put forward by J Robert Oppenheimer and Hartland Snyder in 1939, but only in the special circumstance where exact spherical symmetry was assumed. The purpose of this new theorem was to obviate such unrealistic symmetry assumptions.) At this central singularity, Einstein’s classical theory of general relativity would have reached its limits.
Meanwhile, Hawking had also been thinking about this kind of problem with George Ellis, who was working on a PhD at St John’s College, Cambridge. The two men had been working on a more limited type of “singularity theorem” that required an unreasonably restrictive assumption. Sciama made a point of bringing Hawking and me together, and it did not take Hawking long to find a way to use my theorem in an unexpected way, so that it could be applied (in a time-reversed form) in a cosmological setting, to show that the space-time singularity referred to as the “big bang” was also a feature not just of the standard highly symmetrical cosmological models, but also of any qualitatively similar but asymmetrical model.
Image top of page: National Geographic Channels/Pau