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  • richardmitnick 11:07 am on July 18, 2019 Permalink | Reply
    Tags: , , Birth of the Moon, Nautilus, , , Replicating the forces that generate new planets, Sarah T. Stewart, ,   

    From Nautilus: Women in STEM-“She Rewrote the Moon’s Origin Story” Sarah T. Stewart 

    Nautilus

    From Nautilus

    July 18, 2019
    Brian Gallagher

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    Nautilus

    2
    Fire When Ready: In her lab, Sarah T. Stewart (above) tries to replicate the forces that generate new planets. She employs “light gas guns, essentially cannons,” she says, to fire disks—at eight kilometers per second—toward minerals, vaporizing them, to generate the pressures and temperatures needed for planet formation. John D. & Catherine T. MacArthur Foundation.

    Fifty years ago, in the Oval Office, Richard Nixon made what he called the “most historic phone call ever.” Houston had put him through to the men on the moon. “It’s a great honor and privilege for us to be here,” Neil Armstrong said, “representing not only the United States but men of peace of all nations, and with interest and a curiosity and a vision for the future.” The Apollo missions—a daring feat of passion and reason—weren’t just for show. In reaching the moon in 1969, fulfilling John F. Kennedy’s promise seven years earlier to go there not because it would be easy, but hard, humanity tested its limits—as well as the lunar soil.

    The samples the astronauts brought back to Earth have revolutionized our understanding of the moon’s origins, leading scientists to imagine new models of how our planet, and its companion, emerged. One of those scientists is Sarah T. Stewart, a planetary physicist at the University of California, Davis. Last year she won a MacArthur Foundation Fellowship, unofficially known as the “genius grant,” for her work on the origin of Earth’s moon. Her theory upends one held for decades.

    Stewart’s bold vision grows out a love for science planted in high school in O’Fallon, Illinois. “I had phenomenal math and physics teachers,” she said. “So when I went to college, I wanted to be a physics major.” At Harvard, where she studied astronomy and physics, “I met amazing scientists, and that sparked a whole career.” She earned her Ph.D. at Caltech.

    Nautilus spoke to Stewart last year about the scientific significance of the Apollo lunar landings, as well as how her laboratory experiments, which replicate the pressures and temperatures of planetary collisions, informed her model of the moon’s birth.

    How significant were the Apollo moon landings to science?

    This July marks the 50th anniversary of the Apollo moon landing. The rock samples that the Apollo missions brought back basically threw out every previous idea for the origin of the moon. Before the Apollo results were in, a Russian astronomer named Viktor Safronov had been developing models of how planets grow. He found that they grow into these sub- or proto-planet-size bodies that would then collide. A couple of different groups then independently proposed that a giant impact made a disc around the Earth that the moon accreted from. Over the past 50 years, that model became quantitative, predictive. Simulations showed that the moon should be made primarily out of the object that struck the proto-Earth. But the Apollo mission found that the moon is practically a twin of the Earth, particularly its mantle, in major elements and in isotopic ratios: The different weight elements are like fingerprints, present in the same abundances. Every single small asteroid and planet in the solar system has a different fingerprint, except the Earth and the moon. So the giant impact hypothesis was wrong. It’s a lesson in how science works—the giant impact hypothesis hung on for so long because there was no alternative model that hadn’t already been disproven.

    How is your proposal for the moon’s birth different?

    We changed the giant impact. And by changing it we specifically removed one of the original constraints. The original giant impact was proposed to set the length of day of the Earth, because angular momentum—the rotational equivalent of linear momentum—is a physical quantity that is conserved: If we go backwards in time, the moon comes closer to the Earth. At the time the moon grew, the Earth would have been spinning with a five-hour day. So all of the giant impact models were tuned to give us a five-hour day for the Earth right after the giant impact. What we did was say, “Well, what if there were a way to change the angular momentum after the moon formed?” That would have to be through a dynamical interaction with the sun. What that means is that we could start the Earth spinning much faster—we were exploring models where the Earth had a two- to three-hour day after the giant impact.

    What did a faster-spinning Earth do to your models?

    The surprising new thing is that when the Earth is hot, vaporized, and spinning quickly, it isn’t a planet anymore. There’s a boundary beyond which all of the Earth material cannot physically stay in an object that rotates altogether—we call that the co-rotation limit. A body that exceeds the co-rotation limit forms a new object that we named a synestia, a Greek-derived word that is meant to represent a connected structure. A synestia is a different object than a planet plus a disc. It has different internal dynamics. In this hot vaporized state, the hot gas in the disc can’t fall onto the planet, because the planet has an atmosphere that’s pushing that gas out. What ends up happening is that the rock vapor that forms a synestia cools by radiating to space, forms magma rain in the outer parts of the synestia, and that magma rain accretes to form the moon within the rock vapor that later cools to become the Earth.

    How did you the idea of a synestia come about?

    In 2012, Matija Ćuk and I published a paper that was a high-spin model for the origin of the moon. We changed the impact event, but we didn’t realize that after the impact, things were completely different. It just wasn’t anything we ever extracted from the simulations. It wasn’t until two years later when my student Simon Lock and I were looking at different plots, plots we had never made before out of the same simulations, that we realized that we had been interpreting what happened next incorrectly. There was a bonafide eureka moment where we’re sitting together talking about how the disc would evolve around the Earth after the impact, and realizing that it wasn’t a standard disc. These synestias have probably been sitting in people’s computer systems for quite some time without anyone ever actually identifying them as something different.

    Was the size of the synestia beyond the moon’s current orbit?

    It could have been bigger. Exactly how big it was depends on the energy of the event and how fast it was spinning. We don’t have precise constraints on that to make the moon because a range of synestias could make the moon.

    How long was the Earth in a synestia state?

    The synestia was very large, but it didn’t last very long. Because rock vapor is very hot, and where we are in the solar system is far enough away from the sun that our mean temperature is cooler than rock vapor, the synestia cooled very quickly. So it could last a thousand years or so before looking like a normal planet again. Exactly how long it lasts depends on what else is happening in the solar system around the Earth. In order to be a long lived object it would need to be very close to the star.

    What was the size of the object that struck proto-Earth?

    We can’t tell, because a variety of mass ratios, impact angles, impact velocities can make a synestia that has enough mass and angular momentum in it to make our moon. I don’t know that we will ever know for sure exactly what hit us. There may be ways for us to constrain the possibilities. One way to do that is to look deep in the Earth for clues about how large the event could have been. There are chemical tracers from the deep mantle that indicate that the Earth wasn’t completely melted and mixed, even by the moon-forming event. Those reach the surface through what are called ocean island basalts, sometimes called mantle plumes, from near the core-mantle boundary, up through the whole mantle to the surface. It could be that that could be used as a constraint on being too big. Because the Earth and the moon are very similar in the mantles of the two bodies, that can be used to determine what is too small of an event. That would give us a range that can probably be satisfied by a number of different impact configurations.

    How much energy does it take to form a synestia?

    Giant impacts are tremendously energetic events. The energy of the event, in terms of the kinetic energy of the impact, is released over hours. The power involved is similar to the power, or luminosity, of the sun. We really cannot think of the Earth as looking anything like the Earth when you’ve just dumped the energy of the sun into this planet.

    How common are synestias?

    We actually think that synestias should happen quite frequently during rocky planet formation. We haven’t looked at the gas giant planets. There are some different physics that happen with those. But for growing rocky bodies like the Earth, we attempted to estimate the statistics of how often there should be synestias. And for Earth-mass bodies anywhere in the universe probably, the body is a synestia at least once while it’s growing. The likelihood of making a synestia goes up as the bodies become larger. Super-Earths also should have been a synestia at some point.

    You say that all of the pressures and temperatures reached during planet formation are now accessible in the laboratory. First, give us a sense of the magnitude of those pressures and temperatures, and then tell us how accessing them in labs is possible.

    The center of the Earth is at several thousand degrees, and has hundreds of gigapascals of pressure—about three million times more pressure than the surface. Jupiter’s center is even hotter. The center-of-Jupiter pressures can be reached temporarily during a giant impact, as the bodies are colliding together. A giant impact and the center of Jupiter are about the limits of the pressures and temperatures reached during planet formation: so tens of thousands of degrees, and a million times the pressure of the Earth. To replicate that, we need to dump energy into our rock or mineral very quickly in order to generate a shockwave that reaches these amplitudes in pressure and temperature. We use major minerals in the Earth, or rocky planets—so we’ve studied iron, quartz, forsterite, enstatite, and different alloy compositions of those. Other people have studied the hydrogen helium mixture for Jupiter, and ices for Uranus and Neptune. In my lab we have light gas guns, essentially cannons. And, using compressed hydrogen, we can launch a metal flyer plate—literally a thin disk—to almost eight kilometers per second. We can reach the core pressures in the Earth, but I can’t reach the range of giant impacts or the center of Jupiter in my lab. But the Sandia Z machine, which is a big capacitor that launches metal plates using a magnetic force, can reach 40 kilometers per second. , which is a big capacitor that launches metal plates using a magnetic force, can reach 40 kilometers per second.

    Sandia Z machine

    And with the National Ignition Facility laser at Lawrence Livermore National Lab, we can reach the pressures at the center of Jupiter.


    National Ignition Facility at LLNL

    What happens to the flyer plates when they’re shot?

    The target simply gets turned to dust after being vaporized and then cooling again. They’re very destructive experiments. You have to make real time measurements—of the wave itself and how fast it’s traveling—within tens of nanoseconds. That we can translate to pressure. My group has spent a lot of time developing ways to measure temperature, and to find phase boundaries. The work that led to the origin of the moon was specifically studying what it takes to vaporize Earth materials, and to determine the boiling points of rocks. We needed to know when it would be vaporized in order to calculate when something would become a synestia.

    How do you use your experimental results?

    What runs in our code is a simplified version of a planet. With our experiments we can simulate a simplified planet to infer the more complicated chemical system. Once we’ve determined the pressure-temperature of the average system, you can ask more detailed questions about the multi-component chemistry of a real planet. In the moon paper that was published last year, there’s two big sections. One that does the simplified modeling of the giant impact—it gives us the pressure-temperature range in the synestia. Then another that looks at the chemistry of the system that starts at these high pressures and temperatures and cools, but now using a more realistic model for the Earth.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 3:09 pm on June 20, 2019 Permalink | Reply
    Tags: "The Spirit of the Inquisition Lives in Science", Bohm refused to name anyone that the McCarthyists should investigate., Bohm's communist associations coupled with the national security implications of his Ph.D. work made him a target for Senator Joe McCarthy, By 1950 Bohm was working with Einstein at Princeton where his past came back to haunt him. Early in his Ph.D. studies he had joined a trade union and briefly a couple of communist groups., In 1570 Jerome was arrested by the Inquisition., It might have been Jerome’s pronouncement that a loving God couldn’t possibly condemn devout Jews or Muslims., Jerome Cardano was Europe’s pre-eminent inventor physician astrologer and mathematician in the 16th century., Jerome told his academic colleagues that many of his best ideas came from a spirit that visited him at night., Nautilus, One of the many conditions of Jerome's eventual release under house arrest was that he could never discuss the reason for his initial detention., Or maybe it was his writings considering “whether there is one universe or more or an infinity of them., Other conditions of Jerome’s release included that he could no longer teach or publish—which may explain why he fell into obscurity and you are only just learning about him now., The spirit of the Inquisition has never been fully extinguished; wherever the powerful are threatened by progress they will suppress debate. Science has not escaped this phenomenon., The United States authorities then confiscated his passport and he was forced to apply for Brazilian citizenship, There are a number of examples even within this small area of physics but perhaps none is more resonant of Jerome’s experience than the story of David Bohm.   

    From Nautilus: “The Spirit of the Inquisition Lives in Science” 

    Nautilus

    From Nautilus

    June 20, 2019
    Michael Brooks

    I’ve been talking to Jerome Cardano for years now. What’s more, he talks back to me—in a voice that often drips with gentle mockery. He clearly thinks my sanity is as precarious as his always was.

    Jerome was Europe’s pre-eminent inventor, physician, astrologer, and mathematician in the 16th century. He created the first theory of probability, and discovered the square root of a negative number, something we now call the imaginary number and an essential part of our understanding of how the universe holds together. He invented the mechanical gimbal that was to make the printing press possible. His idea led to the “Cardan joint” that takes the rotary power in the driveshaft of your car’s engine and allows it to be transmitted to the front and rear axles. He pioneered the experimental method of research in areas as diverse as medical cures for deafness and hernia, cryptography, and speaking with the dead (forgive him, his were not strictly scientific times).

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    SKEPTIC ASTROLOGER: Jerome Cardano, pictured in this rendering, was convinced stars and planets exerted some influence on people. But as a rational thinker, he was conflicted. “A man is a fool who attaches too much meaning to insignificant events,” he wrote.

    My obsession with Jerome has taken me over. I’ve been schooled in quantum physics and trained to think rationally, dissecting facts and ideas dispassionately. And here I am constantly carrying on imaginary conversations with a 16th-century astrologer. Perhaps the most amusing aspect of this is that Jerome is not remotely humbled by talking to someone from the future. On the contrary, he feels he has earned such visitations through his earnest attempts to discern the truth about how the universe works.

    He’s not altogether wrong about this. I was first drawn to Jerome by a simple statement in his autobiography: He told his academic colleagues that many of his best ideas came from a spirit that visited him at night. He knows this is an odd claim, but he also sees himself as a pioneering visionary who would be worth the attention of celestial beings. He even writes in one of his books that, on his death, “The earth will not cover me over, but I will be snatched up to high heaven and live in distinction in the learned mouths of men.” This is precisely why he is willing to take so many intellectual risks: He doesn’t worry about being taken seriously on Earth when he already feels he is taken seriously in the heavens.

    There is a neat payoff to this hubris. Jerome’s belief that a visiting spirit holds secrets that are yet to be revealed to humans means he also appreciates there is a lot that is still hidden from him. Jerome is aware that he doesn’t have all the information required to understand the universe, and I find his acknowledged ignorance engaging. As an observer of science, I’m fascinated by the gaps—known and unknown—in our understanding of the universe. There are plenty of gaps in Jerome’s understanding too, but he seems more aware of his evidential gaps than do many of the scientists I meet.

    If only more of Jerome’s contemporaries—particularly those running the Catholic Inquisition—had shown a similar humility, we might know more about him. In 1570, Jerome was arrested by the Inquisition. We don’t know exactly why, because one of the many conditions of his eventual release under house arrest was that he could never discuss the reason for his initial detention. The charge could have been that he once presented the Pope with a horoscope of Christ. It might have been Jerome’s pronouncement that a loving God couldn’t possibly condemn devout Jews or Muslims. Or maybe it was his writings considering “whether there is one universe, or more, or an infinity of them.” After all, that was among the questions that pushed the Inquisition to burn Giordano Bruno at the stake two decades later.

    Other conditions of Jerome’s release included that he could no longer teach or publish—which may explain why he fell into obscurity and you are only just learning about him now. But despite Jerome’s life story being relatively unfamiliar today, his experiences of what happens when people reject orthodoxy are not. The spirit of the Inquisition has never been fully extinguished; wherever the powerful are threatened by progress, they will suppress debate. Science has not escaped this phenomenon. Even something as fundamental as quantum mechanics, built on the twin pillars of probability and imaginary numbers that Jerome erected, has been stunted by censure. There are a number of examples even within this small area of physics, but perhaps none is more resonant of Jerome’s experience than the story of David Bohm.

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    David Joseph Bohm (December 20, 1917 – October 27, 1992) was an American scientist who has been described as one of the most significant theoretical physicists of the 20th century and who contributed unorthodox ideas to quantum theory, neuropsychology and the philosophy of mind.

    During the latter part of World War II, when Bohm was a graduate student at the University of California, Berkeley, J. Robert Oppenheimer recruited him into the newly formed effort to build an atomic bomb. Bohm’s contributions to the Manhattan Project were so valuable that they were immediately classified and Bohm was shut out. Even though Oppenheimer was his Ph.D. supervisor, Bohm was not allowed to write his own Ph.D. thesis. He only got his Ph.D. after insisting that Oppenheimer vouch for the quality of his work.

    By 1950, Bohm was working with Einstein at Princeton, where his past came back to haunt him. Early in his Ph.D. studies he had joined a trade union and, briefly, a couple of communist groups. Those communist associations, coupled with the national security implications of his Ph.D. work, made him a target for Senator Joe McCarthy’s crusade against un-American activities.

    Bohm refused to answer questions, and refused to name anyone that the McCarthyists should investigate. He was arrested. By the time he was acquitted, he had been suspended from Princeton. In 1951, unemployable in the United States, Bohm took a job in Brazil. The United States authorities then confiscated his passport and he was forced to apply for Brazilian citizenship. It was as a Brazilian that he traveled to England and began a long career as a professor of theoretical physics at Birkbeck College in London. There, he successfully applied for a British passport. Then, in 1986, he won back his American citizenship in a legal battle with the U.S. government.

    Nothing in that long and painful saga distracted David Bohm from physics. He made significant contributions in a variety of areas, but it is for his interpretation of quantum physics that he is best known. In 1952, Bohm published a seminal paper that is now seen as a complementary, but independently derived, version of work begun decades before—and then abandoned—by the French aristocrat and physicist Louis de Broglie.

    De Broglie first mentioned it in his 1924 dissertation. He brought it up again when he gave a talk in October 1927, at the same meeting where Albert Einstein and Niels Bohr had their famous debates over quantum theory. In his talk, he spoke about the théorie de l’onde pilote—pilot wave theory.

    It deals with the “double slit experiment,” where quantum objects such as photons seem to have two different locations at once before this anomaly is resolved at the photon detector. Bohr’s view (now central to the “Copenhagen” interpretation of quantum theory) was that the objects have no definite position or momentum until they hit the detector. According to de Broglie, though, each photon fired at the double slit exists as a real object. He suggested it has a definite position and momentum at all times. What you can’t know is the initial position.

    And since the initial position would be what you combine with the momentum to give you the final position, you can’t know the final position in advance, explaining the apparently random outcomes of each measurement.

    Because it is a real object, with a well-defined position, the photon can pass through only one of the slits. However, its trajectory is guided by a “pilot wave,” in much the same way that a ferry entering a treacherous harbor is guided by a pilot boat. This pilot wave is also real and has properties that are a reflection of the “wave function” in the theory described by the Schrödinger equation.

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    MAKING WAVES: A simulated image of the double-slit experiment, in which the wave function of atomic particles pass through two slits at once. David Bohm’s idea of an undetectable pilot wave was criticized, but the physicist who survived the McCarthy witch hunts was not put off. Alexandre Gondran

    Because of this link to the Schrödinger equation’s wave function, although the particle will only pass through one of the slits, there is still a final distribution of particles determined by an interfering wave. That means the major consequence of interference—the strange clumping at certain points on the target and absence at others—will occur.

    Eventually, de Broglie abandoned his idea and fell in with Bohr, becoming what we would now call a Copenhagenist. It wasn’t that the pilot wave theory was particularly flawed; it was just that Bohr was probably too powerful and charismatic a figure to resist. So the pilot wave theory sank.

    In 1952, however, it resurfaced in the hands of David Bohm. Bohm’s idea of an invisible, undetectable pilot wave was roundly criticized, but a man who had survived the McCarthy witch hunts was not easily put off. Having overcome the most heinous character assassination of the era, he could take a little heat. And so he stuck to his guns, suggesting we needed to look at quantum experiments in a different way. In a 1952 paper, published in Physical Review, he said, “the history of scientific research is full of examples in which it was very fruitful indeed to assume that certain objects or elements might be real, long before any procedures were known which would permit them to be observed directly.” In other words, why shouldn’t there be an as-yet-undiscovered pilot wave?

    “Of course, we must avoid postulating a new element for each new phenomenon,” Bohm continued. “But an equally serious mistake is to admit into the theory only those elements which can now be observed … In fact, the better a theory is able to suggest the need for new kinds of observations and to predict their results correctly, the more confidence we have that this theory is likely to be good representation of the actual properties of matter and not simply an empirical system especially chosen in such a way as to correlate a group of already known facts.”

    So far, so good, perhaps. But there are two problems. The first is that, in order to get the predictions right about the interference effect and the ultimate distribution of the photons at the detector, you have to work backward from the final result.

    The second problem is that Bohm’s pilot wave is odd—in a way that physicists call “nonlocal.” This means that the properties and future state of our photon are not determined solely by the conditions and actions in its immediate vicinity. The photon’s pilot wave and the photon’s wave function are linked to the wave function of the much, much larger system in which they sit—the wave function of the whole universe, effectively. So our photon can be instantaneously affected by something that happens half a universe away.

    Many physicists—most physicists—are not happy about allowing this nonlocal action. After all, such action is prohibited by Einstein’s special theory of relativity, which says an influence can’t travel faster than the speed of light.

    On the plus side, it does give us an explanation for the relativity-breaking entanglement-based phenomena that Einstein derided as “spooky action at a distance.” And it’s not clear that accepting Bohmian mechanics is any worse than shoehorning entanglement into a relativity-friendly physics. Many fine physicists are certainly happy to talk in terms of Bohmian mechanics. I attended a conference in Vienna where an experimenter called Aephraim Steinberg explained his experimental results from a Bohm-eyed view; this, he says, is the easiest way to think about it. What Steinberg presented was a picture showing the trajectories of photons as they pass through the double slit apparatus. In the Copenhagen interpretation, remember, this is impossible because the photons have no meaningful existence before they are detected. Without an existence, they can’t logically have a trajectory.

    The de Broglie-Bohm interpretation of quantum physics, as it is now known, is not popular. Only one venerated physicist has ever really championed it: John Bell, the Irishman who came up with the first definitive test for the existence of entanglement. Here’s what Bell had to say:

    “While the founding fathers agonized over the question ‘particle’ or ‘wave’, de Broglie in 1925 proposed the obvious answer ‘particle’ and ‘wave.’ Is it not clear from the smallness of the scintillation on the screen that we have to do with a particle? And is it not clear, from the diffraction and interference patterns, that the motion of the particle is directed by a wave? De Broglie showed in detail how the motion of a particle, passing through just one of two holes in screen, could be influenced by waves propagating through both holes. And so influenced that the particle does not go where the waves cancel out, but is attracted to where they cooperate. This idea seems to me so natural and simple, to resolve the wave-particle dilemma in such a clear and ordinary way, that it is a great mystery to me that it was so generally ignored.”

    Bell felt de Broglie-Bohm was a better bet than anything the Copenhagenists had to offer. They had elevated the issue of measurement to the status where it was fundamental to the subject without ever making clear what it actually entailed. “The concept of ‘measurement’ becomes so fuzzy on reflection,” Bell said, “that it is quite surprising to have it appearing in physical theory at the most fundamental level … does not any analysis of measurement require concepts more fundamental than measurement? And should not the fundamental theory be about these more fundamental concepts?”

    Bell is widely venerated. Go to quantum physics conferences and his name comes up again and again, with some people quoting from his writings as if from scripture. He has the advantage, from the fame perspective, of having died suddenly and relatively young. A cerebral hemorrhage took him out of the blue in 1990, aged just 62. But even his influence is not enough. When it comes to quantum interpretations, the Copenhagenists appear to have won the day. For now, at least.

    As I have said to Jerome many times as we discuss this deplorable situation, the Copenhagen interpretation can’t last. It doesn’t give us an answer to the question “why” when we see the results from the double-slit experiment; it refuses to explain anything about what reality looks like. Steven Weinberg has called it “clearly unsatisfactory.” Murray Gell-Mann, who died in May, said the Copenhagen interpretation has survived for so long only because “Niels Bohr brainwashed a whole generation of theorists.” The phrase made Jerome chuckle. “That’s a nice way of putting it,” he said. “All doubts and questions rinsed away in a flow of appealing nonsense.” He shook his head and laughed again. “I suspect my entire life has been a struggle against having my brain washed.”

    Fortunately, the brainwashed generation is passing: Copenhagen doesn’t dominate like it used to. Just as Jerome’s inventions and creations ultimately survived the strictures of the Inquisition, Bohm’s ideas are also still alive, despite some of the “killer blows” they are reputed to have suffered. There are other options, too. The many-worlds interpretation, where quantum events occur in separate realities, is growing in popularity. This is more appealing to Jerome; he always liked the dangerous idea of a plurality of worlds.

    In the end, we can be reasonably confident that none of our current interpretations of quantum theory are right. The most likely scenario is we, like Jerome, don’t have all the information necessary to make a correct inference about the nature of reality. The point, though, is to keep trying. Why wouldn’t we? As Jerome said, “There is nothing better than a mind that understands everything.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 10:10 am on April 28, 2019 Permalink | Reply
    Tags: , , , , , , , Jupiter's Europa moon, , Nautilus, OPAG-Outer Planet Assessment Group   

    From Nautilus: “Why Europa Is the Place to Go for Alien Life” 

    Nautilus

    From Nautilus

    April 18, 2019
    Corey S. Powell

    1
    This image shows a view of the trailing hemisphere of Jupiter’s ice-covered satellite, Europa, in approximate natural color. Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. The bright feature containing a central dark spot in the lower third of the image is a young impact crater some 50 kilometers (31 miles) in diameter. This crater has been provisionally named “Pwyll” for the Celtic god of the underworld. Europa is about 3,160 kilometers (1,950 miles) in diameter, or about the size of Earth’s moon. This image was taken on September 7, 1996, at a range of 677,000 kilometers (417,900 miles) by the solid state imaging television camera onboard the Galileo spacecraft during its second orbit around Jupiter. The image was processed by Deutsche Forschungsanstalt fuer Luftund Raumfahrt e.V., Berlin, Germany. NASA/JPL/DLR.

    NASA/Galileo 1989-2003

    I have seen the future of space exploration, and it looks like a cue ball covered with brown scribbles. I am talking about Europa, the 1,940-mile-wide, nearly white, and exceedingly smooth satellite of Jupiter. It is an enigmatic world that is, in many ways, almost a perfect inversion of Earth. It is also one of the most plausible places to look for alien life. If it strikes you that those two statements sound rather contradictory—why yes, they do. And therein lies the reason why Europa just might be the most important world in the solar system right now. The Europa Clipper spacecraft is scheduled to launch in 2023 to probe the mysterious moon, according to NASA’s 2020 budget proposal.

    NASA/Europa Clipper annotated

    The unearthly aspects of Europa are literally un-earthly : This is an orb sculpted from water ice, not from rock. It has ice tectonics in place of shifting continents, salty ocean in place of mantle, and vapor plumes in place of volcanoes. The surface scribbles may be dirty ocean material that leaked up through the icy equivalent of an earthquake fault.

    From a terrestrial perspective, Europa is built all wrong, with its solid crust up top and water down below. From the perspective of alien life, though, that might be a perfectly dandy arrangement. Beneath its frozen crust, Europa holds twice as much liquid water as exists in all of our planet’s oceans combined. Astrobiologists typically flag water as life’s number-one requirement; well, Europa is drowning in it. Just below the ice line, conditions might resemble the environment on the underside of Antarctic ice sheets. At the bottom of its buried ocean, Europa may have an active system of hydrothermal vents. Both of these are vibrant habitats on Earth.

    Adding a new twist to the story, Europa’s water may sometimes escape its icy confines. On at least four occasions, the Hubble Space Telescope has detected what appear to be large plumes of water vapor erupting from Europa. That detection has confirmed and expanded on the scientific ideas about what makes Europa such a dynamic world. Europa travels in a slightly oval orbit around Jupiter, causing it to get alternately squeezed and stretched by the giant planet’s gravity. The flexing creates intense friction inside the satellite and generates enough heat to maintain a warm ocean beneath Europa’s frozen outer shell. The presence of a plume suggests that the stretching of Europa also opens and closes a network of fissures that allow buried water to erupt as geysers.

    If the geysers consist of ocean water shooting all the way through the crust, they could carry traces of aquatic life with them. And if the plumes rise high enough, a future spacecraft could fly right through them, sniffing for biochemicals.

    2
    SIGNS FROM BELOW: Salty seawater appears to have breached Europa’s frozen exterior, creating a network of red-brown streaks. Perhaps traces of aquatic life were carried along in the process? This scene is 100 miles wide. NASA/JPL-Caltech/SETI Institute

    You can see why people were giddy at a 2015 OPAG meeting held at NASA’s Ames Research Center. A regular forum for geeking out about ice worlds, the OPAG gatherings—short for Outer Planet Assessment Group—feel halfway between the corporate swarm of a MacWorld expo and a vinyl record fair. They are where true believers mingle with the newbies, showing off the latest science, kicking around speculative ideas, and developing strategies for exploration. With each new bit of data, they have grown increasingly convinced that Europa, not Mars, is the place to go to search for alien life. Finding the plume on Europa was another shot of adrenaline. The room went fervently silent as Lorenz Roth of Sweden’s Royal Institute of Technology, calling in via a fuzzy phone line, reported on the latest search for a recurrence of such water eruptions (no luck yet, alas).

    Another significant piece of news was hanging over the OPAG meeting: The discovery that Europa has plate tectonics, like Earth and unlike any other world we know of. Tectonics describes a process in which the crust moves about and cycles back and forth into the interior. Louise Prockter of Johns Hopkins University’s Applied Physics Laboratory co-discovered this style of activity on Europa by painstakingly reconstructing old images from the Galileo spacecraft, which circled Jupiter from 1995 to 2003. (Analysis of other Galileo data suggests the probe flew right past a Europan water plume in 1997, but scientists didn’t realize it at the time.)

    As Prockter explained to me at the meeting, a mobile crust potentially does two important things. It cycles surface ice, along with all the compounds it develops during exposure to the sun, down into the dark ocean; that chemical flow could be crucial for supplying the ocean with nutrients. The motion of the crust also brings ocean material up to the surface, where prying human eyes can seek clues about the Europan ocean without actually drilling down into it.

    Bolstered by these discoveries, the cult of Europa has now escaped the confines of the OPAG meetings. A successful mission to Europa would bring into focus the incredible ice-and-ocean environment of Europa. It would also help scientists understand ice worlds in general. Icy moons, dwarf planets, and giant asteroids are the norm in the vast outer zone of the solar system, and if they repeat the pattern of Europa they may contain much of the solar system’s habitable real estate. There is good reason to think that ice worlds are similarly abundant around other stars as well. Putting all of these new ideas together suggests that the Milky Way may collectively contain tens of billions of life-friendly iceboxes.

    But if these stunning extrapolations seem to suggest that scientists are starting to get a handle on how Europa works, allow me to suggest otherwise. Europa is still largely a big, icy ball of confusion.

    3
    Under the Ice: An artist’s conception of Europa (foreground), Jupiter (right) and Jupiter’s innermost large moon, Io (middle), shows salts bubbling up from Europa’s liquid ocean to reach its frozen surface. NASA/JPL-Caltech.

    Almost everything we know about the surface of Europa comes from NASA’s Galileo mission, which reached Jupiter in 1995. During its eight-year mission, Galileo mapped most of Europa, but at a crude resolution of about one mile per pixel. For comparison, today’s best Mars images show features as small as three feet. Elizabeth “Zibi” Turtle of the Hopkins Applied Physics Lab promises that the camera on NASA’s upcoming Europa probe will achieve a similar level of clarity. Until then, imagine trying to navigate using a map that doesn’t show anything smaller than one mile and you will get a sense of how far the Europa scientists have to go.

    What’s more, at a very basic level, planetary scientists still do not have a good handle on how geology (or maybe we should say “glaciology?”) works in frozen settings. Ice, you see, is not just ice. Robert Pappalardo of NASA’s Jet Propulsion Laboratory, the ponytail-wielding mission scientist for the agency’s upcoming Europa probe, spelled out some of the complexities to me. On Europa, surface temperatures on a warm day at the equator might rise up to -210 degrees Fahrenheit; at the poles, the lows plunge to -370 degrees Fahrenheit. Under those conditions, water is properly thought of as a mineral, and ice has approximately the consistency of concrete. In many ways it is remarkably similar to rock in how it fractures, faults, and shatters. But even in such a deep freeze, surface ice can sublimate—evaporate directly from solid to gas—in a way that rock does not. Icy material tends to boil off from darker, warmer regions and collect on lighter, cooler ones, producing an exotic kind of weathering that rearranges the landscape without any wind or rain.

    All sorts of other things are happening on the surface of Europa. Jupiter has a huge, potent magnetic field that bombards its satellite with radiation: about 500 rem per day on average, which you can more easily judge as a dose strong enough to make you sick in one hour and to kill you in 24. That radiation quickly breaks down any organic compounds, greatly complicating the search for life, but produces all kinds of other complex chemistry. A lab experiment at the Jet Propulsion Laboratory suggests that the colors of Europa’s streaks are produced by irradiated ocean salts. These and other fragmented molecules, along with a steady rain of organic material delivered by comet impacts, could be used as energy sources for life when they circulate back down into the ocean, where any living things would be well protected.

    The movement of Europa’s crust—its icy outer shell—is another broad area of mystery. On ice worlds, Pappalardo notes, water takes on the role of magma and hot rock deep below the surface, but once again ice and rock are not quite the same. Warm ice turns soft, almost slushy, under high pressure and slowly flows. There could be complicated circulation patterns contained entirely within the crust, which is perhaps 10 to 15 miles thick (or maybe more or less; that is yet another mystery that the Europa mission will investigate). Pools of liquid water might exist trapped within the shell, cut off from the underlying ocean. Plumes of water at the surface might not originate directly from the ocean; it is possible that they come from these intermediate lakes, analogous to the largely unexplored Lake Vostok in Antarctica.

    At the OPAG meeting, seemingly narrow arguments about the circulation of ice sparked colorful debates about prospects for life on Europa and, by extension, on the myriad other ice worlds out there. Britney Schmidt of Georgia Tech wondered if the active geology (glaciology) on Europa occurs entirely within the crust. If material does not circulate at all between surface and ocean, Europa is sealed tight. Life could not get any fresh chemicals from up above, and if it somehow manages to survive anyway we might never know unless we find a way to dig a hole all the way through. Several researchers at OPAG suggested that meaningful answers will require a surface lander; one energetic audience member repeatedly argued for sending an impactor—a high-speed bowling ball, essentially—to smack the surface and shake loose any possible buried microbes.

    As for the Europan ocean itself, that runs even deeper into what you might call aqua incognita . If the surface truly is streaked with salts, as the recent experiments indicate, that suggests a mineral-rich ocean in which waters interact vigorously with a rocky seafloor at the bottom. A likely source of such interaction is a network of hydrothermal vents powered by Europa’s internal heat; such vents could provide chemical energy to sustain Europan life, as they do on Earth. But how much total hydrothermal activity goes on? Are the acidity and salinity conducive to life? How much organic material is down there? The scientists egged each other on with provocative questions that, as yet, have no answers.

    When (or if) we will find out will depend, in large part, on how much of Europa’s inner nature is evident from the outside. The conversations at OPAG sometimes devolved into something resembling a college existential argument: If an alien swims in Europa’s ocean and nobody is able to see it, is it really alive?

    The Europa faithful have been waiting a long time for a mission that would wipe away those kinds of arguments, or at least ground them in hard data. That wait has been full of whipsaw swings between optimism and disappointment. NASA’s planned Europa Orbiter got a green light in 1999, only to be cancelled in 2002. The agency rebounded with a proposal for an even more ambitious, nuclear-propelled Jupiter Icy Moons Orbiter, which looked incredible until it got delayed and finally cancelled in 2006. A proposed joint venture with the European Space Agency never even got that far, though the Europeans are going ahead with their part of the project, which will send a probe to Ganymede, another one of Jupiter’s icy moons, in 2030.

    The Europa Clipper, outfitted with scientific instruments that include cameras and spectrometers, will swoop repeatedly past the moon and produce images that determine its composition. There is a chance the Europa mission will include a lander. Funding does not exist yet, but Adam Steltzner—the hearty engineer who figured out how to land the two-ton Curiosity rover safely on Mars—assures me that from a technical standpoint it would not be difficult to design a small probe equipped with rockets to allow a soft touchdown on Europa. There it could drill into the surface and search for possible organic material that has not been degraded by the radiation blasts from Jupiter.

    What you won’t see, the OPAG boffins all sadly agreed, is one of those cool Europa submarines that show up on the speculative “future mission concept” NASA web pages. Getting a probe into Lake Vostok right here on Earth has proven a daunting challenge. Drilling through 10 miles or more of Europan ice and exploring an alien ocean by remote control is something we still don’t know how to do, and certainly not with any plausible future NASA budget.

    No matter. Even the no-frills version of NASA’s current Europa plan will unleash a flood of information about how ice worlds work, and about how likely they are to support life. If the answers are as exciting as many scientists hope—and as I strongly expect—it will bolster the case for future missions to Titan, Enceladus, and some of Europa’s other beckoning cousins. It will reshape the search for habitable worlds around other stars as well. Right now astronomers are mostly focused on finding other Earthlike planets, but maybe that is not where most of the action is. Perhaps most of the life in the universe is locked away, safe but almost undetectable, beneath shells of ice.

    Whether or not Europa is home to alien organisms, it will tell us about the range of what life can be, and where it can be. That one icy moon will help cure science of its rocky-planet chauvinism. Hey, who you calling cue ball?

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 12:32 pm on April 18, 2019 Permalink | Reply
    Tags: "When Beauty Gets in the Way of Science", , , , , Nautilus, , , , , ,   

    From Nautilus: “When Beauty Gets in the Way of Science” 

    Nautilus

    From Nautilus

    April 18, 2019
    Sabine Hossenfelder

    Insisting that new ideas must be beautiful blocks progress in particle physics.

    When Beauty Gets in the Way of Science. Nautilus

    The biggest news in particle physics is no news. In March, one of the most important conferences in the field, Rencontres de Moriond, took place. It is an annual meeting at which experimental collaborations present preliminary results. But the recent data from the Large Hadron Collider (LHC), currently the world’s largest particle collider, has not revealed anything new.

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    Forty years ago, particle physicists thought themselves close to a final theory for the structure of matter. At that time, they formulated the Standard Model of particle physics to describe the elementary constituents of matter and their interactions.

    Standard Model of Particle Physics (LATHAM BOYLE AND MARDUS OF WIKIMEDIA COMMONS)

    After that, they searched for the predicted, but still missing, particles of the Standard Model. In 2012, they confirmed the last missing particle, the Higgs boson.

    CERN CMS Higgs Event

    CERN ATLAS Higgs Event

    The Higgs boson is necessary to make sense of the rest of the Standard Model. Without it, the other particles would not have masses, and probabilities would not properly add up to one. Now, with the Higgs in the bag, the Standard Model is complete; all Pokémon caught.

    1
    HIGGS HANGOVER: After the Large Hadron Collider (above) confirmed the Higgs boson, which validated the Standard Model, it’s produced nothing newsworthy, and is unlikely to, says physicist Sabine Hossenfelder.Shutterstock

    The Standard Model may be physicists’ best shot at the structure of fundamental matter, but it leaves them wanting. Many particle physicists think it is simply too ugly to be nature’s last word. The 25 particles of the Standard Model can be classified by three types of symmetries that correspond to three fundamental forces: The electromagnetic force, and the strong and weak nuclear forces. Physicists, however, would rather there was only one unified force. They would also like to see an entirely new type of symmetry, the so-called “supersymmetry,” because that would be more appealing.

    2
    Supersymmetry builds on the Standard Model, with many new supersymmetric particles, represented here with a tilde (~) on them. ( From the movie “Particle fever” reproduced by Mark Levinson)

    Oh, and additional dimensions of space would be pretty. And maybe also parallel universes. Their wish list is long.

    It has become common practice among particle physicists to use arguments from beauty to select the theories they deem worthy of further study. These criteria of beauty are subjective and not evidence-based, but they are widely believed to be good guides to theory development. The most often used criteria of beauty in the foundations of physics are presently simplicity and naturalness.

    By “simplicity,” I don’t mean relative simplicity, the idea that the simplest theory is the best (a.k.a. “Occam’s razor”). Relying on relative simplicity is good scientific practice. The desire that a theory be simple in absolute terms, in contrast, is a criterion from beauty: There is no deep reason that the laws of nature should be simple. In the foundations of physics, this desire for absolute simplicity presently shows in physicists’ hope for unification or, if you push it one level further, in the quest for a “Theory of Everything” that would merge the three forces of the Standard Model with gravity.

    The other criterion of beauty, naturalness, requires that pure numbers that appear in a theory (i.e., those without units) should neither be very large nor very small; instead, these numbers should be close to one. Exactly how close these numbers should be to one is debatable, which is already an indicator of the non-scientific nature of this argument. Indeed, the inability of particle physicists to quantify just when a lack of naturalness becomes problematic highlights that the fact that an unnatural theory is utterly unproblematic. It is just not beautiful.

    Anyone who has a look at the literature of the foundations of physics will see that relying on such arguments from beauty has been a major current in the field for decades. It has been propagated by big players in the field, including Steven Weinberg, Frank Wilczek, Edward Witten, Murray Gell-Mann, and Sheldon Glashow. Countless books popularized the idea that the laws of nature should be beautiful, written, among others, by Brian Greene, Dan Hooper, Gordon Kane, and Anthony Zee. Indeed, this talk about beauty has been going on for so long that at this point it seems likely most people presently in the field were attracted by it in the first place. Little surprise, then, they can’t seem to let go of it.

    Trouble is, relying on beauty as a guide to new laws of nature is not working.

    Since the 1980s, dozens of experiments looked for evidence of unified forces and supersymmetric particles, and other particles invented to beautify the Standard Model. Physicists have conjectured hundreds of hypothetical particles, from “gluinos” and “wimps” to “branons” and “cuscutons,” each of which they invented to remedy a perceived lack of beauty in the existing theories. These particles are supposed to aid beauty, for example, by increasing the amount of symmetries, by unifying forces, or by explaining why certain numbers are small. Unfortunately, not a single one of those particles has ever been seen. Measurements have merely confirmed the Standard Model over and over again. And a theory of everything, if it exists, is as elusive today as it was in the 1970s. The Large Hadron Collider is only the most recent in a long series of searches that failed to confirm those beauty-based predictions.

    These decades of failure show that postulating new laws of nature just because they are beautiful according to human standards is not a good way to put forward scientific hypotheses. It’s not the first time this has happened. Historical precedents are not difficult to find. Relying on beauty did not work for Kepler’s Platonic solids, it did not work for Einstein’s idea of an eternally unchanging universe, and it did not work for the oh-so-pretty idea, popular at the end of the 19th century, that atoms are knots in an invisible ether. All of these theories were once considered beautiful, but are today known to be wrong. Physicists have repeatedly told me about beautiful ideas that didn’t turn out to be beautiful at all. Such hindsight is not evidence that arguments from beauty work, but rather that our perception of beauty changes over time.

    That beauty is subjective is hardly a breakthrough insight, but physicists are slow to learn the lesson—and that has consequences. Experiments that test ill-motivated hypotheses are at high risk to only find null results; i.e., to confirm the existing theories and not see evidence of new effects. This is what has happened in the foundations of physics for 40 years now. And with the new LHC results, it happened once again.

    The data analyzed so far shows no evidence for supersymmetric particles, extra dimensions, or any other physics that would not be compatible with the Standard Model. In the past two years, particle physicists were excited about an anomaly in the interaction rates of different leptons. The Standard Model predicts these rates should be identical, but the data demonstrates a slight difference. This “lepton anomaly” has persisted in the new data, but—against particle physicists’ hopes—it did not increase in significance, is hence not a sign for new particles. The LHC collaborations succeeded in measuring the violation of symmetry in the decay of composite particles called “D-mesons,” but the measured effect is, once again, consistent with the Standard Model. The data stubbornly repeat: Nothing new to see here.

    Of course it’s possible there is something to find in the data yet to be analyzed. But at this point we already know that all previously made predictions for new physics were wrong, meaning that there is now no reason to expect anything new to appear.

    Yes, null results—like the recent LHC measurements—are also results. They rule out some hypotheses. But null results are not very useful results if you want to develop a new theory. A null-result says: “Let’s not go this way.” A result says: “Let’s go that way.” If there are many ways to go, discarding some of them does not help much.

    To find the way forward in the foundations of physics, we need results, not null-results. When testing new hypotheses takes decades of construction time and billions of dollars, we have to be careful what to invest in. Experiments have become too costly to rely on serendipitous discoveries. Beauty-based methods have historically not worked. They still don’t work. It’s time that physicists take note.

    And it’s not like the lack of beauty is the only problem with the current theories in the foundations of physics. There are good reasons to think physics is not done. The Standard Model cannot be the last word, notably because it does not contain gravity and fails to account for the masses of neutrinos. It also describes neither dark matter nor dark energy, which are necessary to explain galactic structures.

    So, clearly, the foundations of physics have problems that require answers. Physicists should focus on those. And we currently have no reason to think that colliding particles at the next higher energies will help solve any of the existing problems. New effects may not appear until energies are a billion times higher than what even the next larger collider could probe. To make progress, then, physicists must, first and foremost, learn from their failed predictions.

    So far, they have not. In 2016, the particle physicists Howard Baer, Vernon Barger, and Jenny List wrote an essay for Scientific American arguing that we need a larger particle collider to “save physics.” The reason? A theory the authors had proposed themselves, that is natural (beautiful!) in a specific way, predicts such a larger collider should see new particles. This March, Kane, a particle physicist, used similar beauty-based arguments in an essay for Physics Today. And a recent comment in Nature Reviews Physics about a big, new particle collider planned in Japan once again drew on the same motivations from naturalness that have already not worked for the LHC. Even the particle physicists who have admitted their predictions failed do not want to give up beauty-based hypotheses. Instead, they have argued we need more experiments to test just how wrong they are.

    Will this latest round of null-results finally convince particle physicists that they need new methods of theory-development? I certainly hope so.

    As an ex-particle physicist myself, I understand very well the desire to have an all-encompassing theory for the structure of matter. I can also relate to the appeal of theories such a supersymmetry or string theory. And, yes, I quite like the idea that we live in one of infinitely many universes that together make up the “multiverse.” But, as the latest LHC results drive home once again, the laws of nature care heartily little about what humans find beautiful.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 9:45 am on April 14, 2019 Permalink | Reply
    Tags: "The Day Feynman Worked Out Black-Hole Radiation on My Blackboard", , , , , , Nautilus,   

    From Nautilus: “The Day Feynman Worked Out Black-Hole Radiation on My Blackboard” 

    Nautilus

    From Nautilus

    Apr 11, 2019

    The amazing image of a black hole unveiled Wednesday, along with data from the Event Horizon Telescope, may not substantiate Stephen Hawking’s famous theory that radiation, an example of spontaneous emission at the quantum level, is emitted by a black hole.

    The first image of a black hole, Messier 87 Credit Event Horizon Telescope Collaboration, via NSF 4.10.19

    But the news did remind us of a story that physicist and writer Alan Lightman told Nautilus: Richard Feynman came up with the idea for spontaneous emission before Hawking. Here is Lightman in his own words:

    1
    After a few minutes, Richard Feynman had worked out the process of spontaneous emission, which is what Stephen Hawking became famous for a year later.Wikicommons

    “One day at lunch in the Caltech cafeteria, I was with two graduate students, Bill Press and Saul Teukolsky, and Feynman. Bill and Saul were talking about a calculation they had just done. It was a theoretical calculation, purely mathematical, where they looked at what happens if you shine light on a rotating black hole. If you shine it at the right angle, the light will bounce off the black hole with more energy than it came in with. The classical analogue is a spinning top. If you throw a marble at the top at the right angle, the marble will bounce off the top with more velocity than it came in with. The top slows down and the energy, the increased energy of the marble, comes from the spin of the top. As Bill and Saul were talking, Feynman was listening.

    We got up from the table and began walking back through the campus. Feynman said, ‘You know that process you’ve described? It sounds very much like stimulated emission.’ That’s a quantum process in atomic physics where you have an electron orbiting an atom, and a light particle, a photon, comes in. The two particles are emitted and the electron goes to a lower energy state, so the light is amplified by the electron. The electron decreases energy and gives up that extra energy to sending out two photons. Feynman said, ‘What you’ve just described sounds like stimulated emission. According to Einstein, there’s a well-known relationship between stimulated emission and spontaneous emission.’

    Spontaneous emission is when you have an electron orbiting an atom and it just emits a photon all by itself, without any light coming in, and goes to a lower energy state. Einstein had worked out this relationship between stimulated and spontaneous emission. Whenever you have one, you have the other, at the atomic level. That’s well known to graduate students of physics. Feynman said that what Bill and Saul were describing sounded like simulated emission, and so there should be a spontaneous emission process analogous to it.

    We’d been wandering through the campus. We ended up in my office, a tiny little room, Bill, Saul, me, and Feynman. Feynman went to the blackboard and began working out the equations for spontaneous emission from black holes. Up to this point in history, it had been thought that all black holes were completely black, that a black hole could never emit on its own any kind of energy. But Feynman had postulated, after listening to Bill and Saul talk at lunch, that if a spinning black hole can emit with light coming in, it can also emit energy with nothing coming in, if you take into account quantum mechanics.

    After a few minutes, Feynman had worked out the process of spontaneous emission, which is what Stephen Hawking became famous for a year later. Feynman had it all on my blackboard. He wasn’t interested in copying down what he’d written. He just wanted to know how nature worked, and he had just learned that isolated black holes are capable of emitting energy when you take into account quantum effects. After he finished working it out, he brushed his hands together to get the chalk dust off them, and walked out of the office.

    After Feynman left, Bill and Saul and I were looking at the blackboard. We were thinking it was probably important, not knowing how important. Bill and Saul had to go off to some appointment, and so they left the office. A little bit later, I left. But that night I realized this was a major thing that Feynman had done and I needed to hurry back to my office and copy down the equations. But when I got back to my office in the morning, the cleaning lady had wiped the blackboard clean.”

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 6:10 pm on April 11, 2019 Permalink | Reply
    Tags: , , , , , , Nautilus, , , ,   

    From Nautilus: “First Black-Hole Image: It’s Not Looks That Count” 

    Nautilus

    From Nautilus

    Apr 11, 2019
    Sabine Hossenfelder

    1
    FIRST LOOK: The Event Horizon Telescope measures wavelength in the millimeter regime, too long to be seen by eye, but ideally suited to the task of imaging a black hole: The gas surrounding the black hole is almost transparent at this wavelength and the light travels to Earth almost undisturbed. Since we cannot see light of such wavelength by eye, the released telescope image shows the observed signal shifted into the visible range.Event Horizon Telescope Collaboration.

    “The Day Feynman Worked Out Black-Hole Radiation on My Blackboard”
    2
    After a few minutes, Richard Feynman had worked out the process of spontaneous emission, which is what Stephen Hawking became famous for a year later.Wikicommons.

    The Italian 14th-century painter, Giotto di Bondone, when asked by the Pope to prove his talent, is said to have swung his arm and drawn a perfect circle. But geometric perfection is limited by the medium. Inspect a canvas closely enough, and every circle will eventually appear grainy. If perfection is what you seek, don’t look at man-made art, look at the sky. More precisely, look at a black hole.

    Looking at a black hole is what the Event Horizon Telescope has done for the past 12 years. Yesterday, the collaboration released the long-awaited results from its first full run in April 2017. Contrary to expectation, their inaugural image is not, as many expected, Sagittarius A*, the black hole at the center of the Milky Way. Instead, it is the supermassive black hole in the elliptic galaxy Messier 87, about 55 million light-years from here. This black hole weighs in at 6.5 billion times the mass of our sun, and is considerably larger than the black hole in our own galaxy [1,000 times the size of SGR A*]. So, even though the Messier 87 black hole is a thousand times farther away than Sagittarius A*, it still appears half the size in the sky.

    The Event Horizon Telescope (EHT) is not less remarkable than the objects it observes. With a collaboration of 200 people, the EHT uses not a single telescope, but a global network of nine telescopes. Its sites, from Greenland to the South Pole and from Hawaii to the French Alps, act in concert as one. Together, the collaboration commands a telescope the size of planet Earth, staring at a tiny patch in the northern sky that contains the Messier-87 black hole.

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM 30m Radio telescope, on Pico Veleta in the Spanish Sierra Nevada,, Altitude 2,850 m (9,350 ft)


    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Mauna Kea, Hawaii, USA, Altitude 4,080 m (13,390 ft)

    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile [recently added]

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL [recently added]

    Future Array/Telescopes

    NOEMA (NOrthern Extended Millimeter Array) will double the number of its 15 meter antennas of its predecessor from six to twelve, located in the French Alpes on the wide and isolated Plateau de Bure at an elevation of 2550 meters

    NSF CfA Greenland telescope


    Greenland Telescope

    ARO 12m Radio Telescope, Kitt Peak National Observatory, Arizona, USA, Altitude 1,914 m (6,280 ft)


    ARO 12m Radio Telescope

    In theory, black holes are regions of space where the gravitational pull is so large that everything, including light, becomes trapped for eternity. The surface of the trapping region is called the “event horizon.” It has no substance; it is a property of space itself. In the simplest case, the event horizon is a sphere—a perfect sphere, made of nothing.

    In reality, it’s complicated. Astrophysicists have had evidence for the existence of black holes since the 1990s, but so far all observations have been indirect—inferred from the motion of visible stars and gas, leaving doubt as to whether the dark object really possesses the defining event horizon. It turned out difficult to actually see a black hole. Trouble is, they’re black. They trap light. And while Stephen Hawking proved that black holes must emit radiation due to quantum effects, this quantum glow is far too feeble to observe.

    But much like the prisoners in Plato’s cave, we can see black holes by observing the shadows they cast. Black holes attract gas from their environment. This gas collects in a spinning disk, and heats up as it spirals into the event horizon, pushing around electric charges. This gives rise to strong magnetic fields that can create a “jet,” a narrow, directed stream of particles leaving the black hole at almost the speed of light. But whatever strays too close to the event horizon falls in and vanishes without a trace.

    At the same time black holes bend rays of light, bend them so strongly, indeed, that looking at the front of a black hole, we can see part of the disk behind it. The light that just about manages to escape reveals what happens nearby the horizon. It is an asymmetric image that the astrophysicists expect, brighter on the side of the black hole where the material surrounding it moves toward us, and darker where it moves away from us. The hot gas combined with the gravitational lensing creates the unique observable signature that the EHT looks out for.

    The experimental challenge is formidable. The network’s telescopes must synchronize their data-taking using atomic clocks. Weather conditions must be favorable at all locations simultaneously. Once recorded, the amount of data is so staggeringly large, it must be shipped on hard disks to central locations for processing.

    The theoretical challenges are not any lesser. Black holes bend light so much that it can wrap around the horizon multiple times. The resulting image is too complicated to capture in simple equations. Though the math had been known since the 1920s, it wasn’t until 1978 that physicists got a first glimpse of what a black hole would actually look like. In that year, the French astrophysicist Jean-Pierre Luminet programmed the calculation on an IBM 7040 using punchcards. He drew the image by hand.

    Today, astrophysicists use computers many times more powerful to predict the accretion of gas onto the black hole and how the light bends before reaching us. Still, the partly turbulent motion of the gas, the electric and magnetic fields created by it, and the intricacies of the particle’s interactions are not fully understood.

    The EHT’s observations agree with expectation. But this result is more than just another triumph of Einstein’s theory of general relativity. It is also a triumph of the astronomers’ resourcefulness. They joined hands and brains to achieve what they could not have done separately. And while their measurement settles a long-standing question—yes, black holes really do have event horizons!—it is also the start of further exploration. Physicists hope that the observations will help them understand better the extreme conditions in the accretion disk, the role of magnetic fields in jet formation, and the way supermassive black holes affect galaxy formation.

    When the Pope received Giotto’s circle, it was not the image itself that impressed him. It was the courtier’s report that the artist produced it without the aid of a compass. This first image of a black hole, too, is remarkable not so much for its appearance, but for its origin. A black sphere, spanning 40 billion kilometers, drawn on a background of hot gas by the greatest artist of all: Nature herself.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 9:38 am on March 27, 2019 Permalink | Reply
    Tags: , , , , Nautilus, , Snowball Earth   

    From Nautilus: “Glaciers May Have Covered the Entire Planet—Twice” 

    Nautilus

    From Nautilus

    Mar 26, 2019
    Laura Poppick

    1
    Ancient rocks suggest that ice entirely covered our planet on at least two occasions. Those events may help explain the rise of complex life that followed. Photo Illustration by pryzmat / Shutterstock.

    The Earth has endured many changes in its 4.5-billion-year history, with some tumultuous twists and turns along the way. One especially dramatic episode appears to have come between 700 million and 600 million years ago, when scientists think ice smothered the entire planet, from the poles to the equator—twice in quick succession.

    Drawing on evidence across multiple continents, scientists say these Snowball Earth events may have paved the way for the Cambrian explosion of life that followed—the period when complex, multicellular organisms began to diversify and spread across the planet.

    When Caltech geologist Joe Kirschvink coined the term Snowball Earth in 1989—merging ideas that some geologists, climate physicists and planetary chemists had been thinking about for decades—many earth scientists were skeptical that these cataclysmic events could really have occurred. But with mounting evidence in support of the theory and new data that help pin down the timing of events, more scientists have warmed up to the idea.

    Paul Hoffman, a geologist at the University of Victoria in British Columbia, has helped pioneer Snowball Earth research over the past 25 years. Among other things, he amassed 50 months’ worth of fieldwork in Namibia, where he gathered evidence of ancient glacial activity in rocks that are interspersed with limestone. Since limestone tends to form in the warmest parts of the ocean, this sandwich-like pattern supports the idea that glaciers covered all of the Earth, cold as well as warm spots, during Snowball Earth episodes. Knowable spoke with Hoffman, who recounts his life work in the Annual Review of Earth and Planetary Sciences, about the evolution of the Snowball Earth theory and what questions remain. This conversation has been edited for length and clarity.

    3
    Snowologist: Paul Hoffman says he is still doing fieldwork in Namibia, as a 77-year-old. “It’s just a large and fascinating problem,” he said. “It’s hard to pull myself away.”
    Illustration by James Provost / Creative Commons.

    What did the planet look like during Snowball Earth?

    The name describes its appearance from outer space—a glistening white ball. The ice surface is mostly coated with frost and tiny ice crystals that settled out of the cold dry air, which is far below freezing everywhere. Gale-force winds howl in low latitudes. Beneath the floating ice shelf, a dark and briny ocean is continually stirred by tides and turbulent eddies generated by geothermal heat slowly entering from the ocean floor.

    What tipped off geologists to the possibility of a Snowball Earth?

    Geologists were struggling to understand what they saw in the geologic record—that not too long before the first appearance of complex life, there was unmistakable evidence of glaciation even in the warmest areas of the Earth. Geologists had a very difficult time understanding how this was possible.

    The deposits that glaciers leave behind are very distinctive. They look like cement that has been dumped out of a cement truck. These Snowball ice sheets would have flowed from the continents out onto the ocean, so we have a lot of deposits that formed in the marine environment where you get what are known as dropstones: pebbles or boulders that are out of place. Very often, you see structures related to the impact, as if the stone was somehow dropped and then plunked into the underlying sediment. It’s difficult to imagine what, other than floating ice, could have possibly transported this debris; trees, which can carry soil and stones out to sea in their roots, had not yet evolved.

    3
    A Seafloor Embrace: A glacial dropstone from Namibia, in rocks that date to the second Snowball Earth. The stone was likely carried and dropped by a floating ice shelf, and when it plunked into seafloor sediment below, that sediment folded around it. (Penny [upper right] shown for scale.)Courtesy of Paul Hoffman.

    How did you start studying Snowball Earth?

    I had known about the hypothesis since even before I was interested in working on the problem myself. Joe Kirschvink at Caltech told me about it a few months after he had the idea in 1989, but he never did anything more with it at that time. I liked it because I like ideas, but there was a credibility gap, so before our work, the hypothesis was dormant.

    The biggest problem was that because the conditions were so different from any other time in Earth’s history, we didn’t understand the implications of the hypothesis well enough to know whether any given bit of geologic evidence was either for or against it. We had to have climate models to see what actually happens under Snowball conditions, and that modeling, developed later, has been extremely important.

    My main contribution was making the case that it was a credible scientific hypothesis by arguing, from different disciplines within geoscience, that there was a lot of geological evidence consistent with the predictions. As I often like to say, new ideas or hypotheses are like small children: It’s best not to judge them too early because you don’t know what they are going to be like as adults. Very often, the problem with new ideas is not that they are wrong, but that they are incomplete.

    What triggered the runaway growth of ice on Earth?

    That’s the “why” question and that’s maybe the most difficult one. I don’t think there is a consensus on this. There are a number of factors that contributed, and it is useful to look at this in two ways. First of all, what was the general condition that made for a colder climate and therefore made the Earth more susceptible to this runaway ice growth phenomenon? And then what was the immediate trigger that tipped it over the edge?

    4
    Snowball Earth Snooping: On a field expedition with Paul Hoffman in 2002, geoscientists Galen Halverson (now at McGill University) and Matthew Hurtgen (now at Northwestern University) collect carbonate rocks from a mountainside in northeastern Svalbard, Norway. The carbonate rocks rest directly above glacial deposits from the second Snowball Earth event. This juxtaposition of carbonates—which form only in warm parts of the ocean—and glacial rocks supports the theory that ice covered the entire planet during the Snowball Earth episodes. Courtesy of Paul Hoffman.

    When the Snowball events occurred, the supercontinent Rodinia was in the process of breaking up. A supercontinent is a state in which all of the continents are clustered together in one group. The reason why people think there is a connection there is that the breakup of a supercontinent would increase rainfall in the continental areas, and that would increase the weathering of crustal rocks. The weathering of rocks actually consumes carbon dioxide, so that would lead to less carbon dioxide in the atmosphere and therefore a colder climate.

    As for what actually caused the immediate trigger, attention has focused in recent years on a sequence of very large volcanic eruptions that occurred in what is now the high arctic of Canada. These eruptions occurred around 717 million and 719 million years ago. When you get fire fountains—lava that comes out of one place over a period of weeks or months—you get a strong thermal upwelling in the atmosphere from the heating effect of that lava. These upwellings can loft sulfur aerosols into the stratosphere where they hang around for a significant amount of time. These sulfur gas particles reflect incoming solar radiation and have a strong cooling effect. Because of the coincidence in timing between these eruptions and the onset of the first and longer of the two Snowball Earths, it’s been postulated that that may have been the immediate trigger.

    What did life on Snowball Earth look like, and how did it change as a consequence of runaway ice growth?

    There were certainly bacteria and there were also algae and unicellular primitive animals, or protists.

    There is also evidence that the first multicellular animals originated at this time, probably something like sponges. Why is a matter of speculation: There are a number of ideas on this, but they are difficult to test. One idea is that on Snowball Earth, ecosystems may have been more isolated from one another and this might be a situation that would be helpful for evolving new forms of life, and particularly forms of life that are altruistic—ones with cells that find that there is an advantage in working together rather than working individually. So more isolation of different ecosystems might have allowed certain ecosystems that had a higher proportion of these multicellular altruists to establish a foothold.

    How was the Snowball theory received by other geologists?

    I underestimated how emotional people would get about it and how wedded people were to the idea that the Earth has never really been greatly different than it is today. In the 19th century, people had a difficult time believing that most of northern Europe and North America were covered by an ice sheet only 20,000 years ago. That was as hard for a 19th-century geologist to accept as Snowball Earth has been for 20th-century geologists.

    For a long time we had a lot of evidence for glaciation at low latitude and in the warmest parts of the Earth, but we didn’t really have a good idea of the dates of these events. It was sort of embarrassing. But between 2010 and 2014 that situation dramatically changed. We now have pretty precise estimates from two very different dating techniques, and it’s impressive that they are giving highly consistent results. Working out the timescale [GeoScienceWorld] has caused a majority of geologists working on the problem to now accept the Snowball hypothesis.

    Alternative theories have arisen over the years, including what is called the Slushball theory—a less extreme version of Snowball Earth. How does pinning down the dates help sort out these alternative theories?

    In the Slushball scenario, carbon dioxide would start building up very quickly, so the glaciation would be short-lived and the ice would retreat gradually. This is not what we see in the geologic record. We now know that the first Snowball lasted for 58 million years and that is completely inconsistent with the Slushball idea. Also, we see the Snowball glaciations terminate extremely abruptly and they are followed by clear evidence of a complete and abrupt climate reversal, a very hot period. That is not explained by the Slushball model.

    I don’t think there are any other alternatives that satisfy the evidence.

    4
    It Was a Seafloor in Another Life: Hoffman has spent a cumulative 50 months collecting evidence of Snowball Earth in the desert mountain ranges of Namibia. The landscape shown here is comprised of an ancient seafloor punctuated with dropstones—sporadically placed stones that researchers believe were carried by ice floating out at sea.Courtesy of Paul Hoffman.

    What other questions about Snowball Earth remain?

    The dating has created a new set of problems. One thing the dating revealed was that the two Snowball Earths occurred in rapid succession and were very unequal in duration. The first one lasted 58 million years [PNAS] and the second one only lasted 5 million to 15 million years. So we don’t know why there is this great disparity in how long the glaciations lasted. And why was it that there was just this short interval between the two? There’s only about 10 million years when there was no ice at all and then suddenly the planet went back into Snowball Earth. So why two in rapid succession? And why wasn’t there a third one or a fourth one? These are new questions that have arisen as a result of our understanding of the timing.

    Could Snowball Earth return?

    I don’t think we are in a very good position to say whether or not it’s likely to happen in the future. The future is a long time. We can say it is not going to happen in the next several tens of thousands of years.

    Why study Earth history?

    The history of our planet is one of the greatest stories. Because we live here and we are dependent on this place, it is very important to understand that the Earth has not always been the way it is today. Snowball Earth is an example of the kinds of amazing things that the Earth has been through that we would never have suspected if we didn’t investigate the geologic record.

    Dealing with Snowball Earth has been fantastic—it’s been the most intense learning experience of my life, and I never anticipated that it would be accepted in my lifetime.

    And you’re still at it, after 25 years?

    I’m still doing fieldwork in Namibia, as a 77-year-old. It’s just a large and fascinating problem. It’s hard to pull myself away.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 11:00 am on February 7, 2019 Permalink | Reply
    Tags: Abraham (Avi) Loeb, , , , , Black Hole Initiative, Black Hole Institute, , , Infrared results beautifully complemented by observations at radio wavelengths, , Nautilus, , S-02, , , The development of high-resolution infrared cameras revealed a dense cluster of stars at the center of the Milky Way   

    From Nautilus: “How Supermassive Black Holes Were Discovered” 

    Nautilus

    From Nautilus

    February 7, 2019
    Mark J. Reid, CfA SAO

    Astronomers turned a fantastic concept into reality.

    An Introduction to the Black Hole Institute

    Fittingly, the Black Hole Initiative (BHI) was founded 100 years after Karl Schwarzschild solved Einstein’s equations for general relativity—a solution that described a black hole decades before the first astronomical evidence that they exist. As exotic structures of spacetime, black holes continue to fascinate astronomers, physicists, mathematicians, philosophers, and the general public, following on a century of research into their mysterious nature.

    Pictor A Blast from Black Hole in a Galaxy Far, Far Away

    This computer-simulated image of a supermassive black hole at the core of a galaxy. Credit NASA, ESA, and D. Coe, J. Anderson

    The mission of the BHI is interdisciplinary and, to that end, we sponsor many events that create the environment to support interaction between researchers of different disciplines. Philosophers speak with mathematicians, physicists, and astronomers, theorists speak with observers and a series of scheduled events create the venue for people to regularly come together.

    As an example, for a problem we care about, consider the singularities at the centers of black holes, which mark the breakdown of Einstein’s theory of gravity. What would a singularity look like in the quantum mechanical context? Most likely, it would appear as an extreme concentration of a huge mass (more than a few solar masses for astrophysical black holes) within a tiny volume. The size of the reservoir that drains all matter that fell into an astrophysical black hole is unknown and constitutes one of the unsolved problems on which BHI scholars work.

    We are delighted to present a collection of essays which were carefully selected by our senior faculty out of many applications to the first essay competition of the BHI. The winning essays will be published here on Nautilus over the next five weeks, beginning with the fifth-place finisher and working up to the first-place finisher. We hope that you will enjoy them as much as we did.

    —Abraham (Avi) Loeb
    Frank B. Baird, Jr. Professor of Science, Harvard University
    Chair, Harvard Astronomy Department
    Founding Director, Black Hole Initiative (BHI)

    In the 1700s, John Michell in England and Pierre-Simon Laplace in France independently thought “way out of the box” and imagined what would happen if a huge mass were placed in an incredibly small volume. Pushing this thought experiment to the limit, they conjectured that gravitational forces might not allow anything, even light, to escape. Michell and Laplace were imagining what we now call a black hole.

    Astronomers are now convinced that when massive stars burn through their nuclear fuel, they collapse to near nothingness and form a black hole. While the concept of a star collapsing to a black hole is astounding, the possibility that material from millions and even billions of stars can condense into a single supermassive black hole is even more fantastic.

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Yet astronomers are now confident that supermassive black holes exist and are found in the centers of most of the 100 billion galaxies in the universe.

    How did we come to this astonishing conclusion? The story begins in the mid-1900s when astronomers expanded their horizons beyond the very narrow range of wavelengths to which our eyes are sensitive. Very strong sources of radio waves were discovered and, when accurate positions were determined, many were found to be centered on distant galaxies. Shortly thereafter, radio antennas were linked together to greatly improve angular resolution.

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    CfA Submillimeter Array Mauna Kea, Hawaii, USA,4,207 m (13,802 ft) above sea level

    These new “interferometers” revealed a totally unexpected picture of the radio emission from galaxies—the radio waves did not appear to come from the galaxy itself, but from two huge “lobes” symmetrically placed about the galaxy. Figure One shows an example of such a “radio galaxy,” named Cygnus A. Radio lobes can be among the largest structures in the universe, upward of a hundred times the size of the galaxy itself.

    2
    Figure One: Radio image of the galaxy Cygnus A. Dominating the image are two huge “lobes” of radio emitting plasma. An optical image of the host galaxy would be smaller than the gap between the lobes. The minimum energy needed to power some radio lobes can be equivalent to the total conversion of 10 million stars to energy! Note the thin trails of radio emission that connect the lobes with the bright spot at the center, where all of the energy originates. NRAO/AUI

    How are immense radio lobes energized? Their symmetrical placement about a galaxy clearly suggested a close relationship. In the 1960s, sensitive radio interferometers confirmed the circumstantial case for a relationship by discovering faint trails, or “jets,” tracing radio emission from the lobes back to a very compact source at the precise center of the galaxy. These findings motivated radio astronomers to increase the sizes of their interferometers in order to better resolve these emissions. Ultimately this led to the technique of Very Long Baseline Interferometry (VLBI), in which radio signals from antennas across the Earth are combined to obtain the angular resolution of a telescope the size of our planet!

    GMVA The Global VLBI Array

    Radio images made from VLBI observations soon revealed that the sources at the centers of radio galaxies are “microscopic” by galaxy standards, even smaller than the distance between the sun and our nearest star.

    When astronomers calculated the energy needed to power radio lobes they were astounded. It required 10 million stars to be “vaporized,” totally converting their mass to energy using Einstein’s famous equation E = mc2! Nuclear reactions, which power stars, cannot even convert 1 percent of a star’s mass to energy. So trying to explain the energy in radio lobes with nuclear power would require more than 1 billion stars, and these stars would have to live within the “microscopic” volume indicated by the VLBI observations. Because of these findings, astronomers began considering alternative energy sources: supermassive black holes.

    Given that the centers of galaxies might harbor supermassive black holes, it was natural to check the center of our Milky Way galaxy for such a monster. In 1974, a very compact radio source, smaller than 1 second of arc (1/3600 of a degree) was discovered there. The compact source was named Sagittarius A*, or Sgr A* for short, and is shown at the center of the right panel of Figure 2. Early VLBI observations established that Sgr A* was far more compact than the size of our solar system. However, no obvious optical, infrared, or even X-ray emitting source could be confidently identified with it, and its nature remained mysterious.

    3
    Figure Two: Images of the central region of the Milky Way. The left panel shows an infrared image. The orbital track of star S2 is overlaid, magnified by a factor of 100. The orbit has period of 16 years, requires an unseen mass of 4 million times that of the sun, and the gravitational center is indicated by the arrow. The right panel shows a radio image. The point-like radio source Sgr A* (just below the middle of the image) is precisely at the gravitational center of the orbiting stars. Sgr A* is intrinsically motionless at the galactic center and, therefore, must be extremely massive.Left panel: R. Genzel; Right panel: J.-H. Zhao

    Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group

    Andrea’s Favorite star SO-2

    Andrea Ghez, astrophysicist and professor at the University of California, Los Angeles, who leads a team of scientists observing S2 for evidence of a supermassive black hole UCLA Galactic Center Group

    SGR A and SGR A* from Penn State and NASA/Chandra

    SGR A* , the supermassive black hole at the center of the Milky Way. NASA’s Chandra X-Ray Observatory

    Meanwhile, the development of high-resolution infrared cameras revealed a dense cluster of stars at the center of the Milky Way. These stars cannot be seen at optical wavelengths, because visible light is totally absorbed by intervening dust. However, at infrared wavelengths 10 percent of their starlight makes its way to our telescopes, and astronomers have been measuring the positions of these stars for more than two decades. These observations culminated with the important discovery that stars are moving along elliptical paths, which are a unique characteristic of gravitational orbits. One of these stars has now been traced over a complete orbit, as shown in the left panel of Figure Two.

    Many stars have been followed along partial orbits, and all are consistent with orbits about a single object. Two stars have been observed to approach the center to within the size of our solar system, which by galaxy standards is very small. At this point, gravity is so strong that stars are orbiting at nearly 10,000 kilometers per second—fast enough to cross the Earth in one second! These measurements leave no doubt that the stars are responding to an unseen mass of 4 million times that of the sun. Combining this mass with the (astronomically) small volume indicated by the stellar orbits implies an extraordinarily high density. At this density it is hard to imagine how any type of matter would not collapse to form a black hole.

    The infrared results just described are beautifully complemented by observations at radio wavelengths. In order to identify an infrared counterpart for Sgr A*, the position of the radio source needed to be precisely transferred to infrared images. An ingenious method to do this uses sources visible at both radio and infrared wavelengths to tie the reference frames together. Ideal sources are giant red stars, which are bright in the infrared and have strong emission at radio wavelengths from molecules surrounding them. By matching the positions of these stars at the two wavebands, the radio position of Sgr A* can be transferred to infrared images with an accuracy of 0.001 seconds of arc. This technique placed Sgr A* precisely at the position of the gravitational center of the orbiting stars.

    How much of the dark mass within the stellar orbits can be directly associated with the radio source Sgr A*? Were Sgr A* a star, it would be moving at over 10,000 kilometers per second in the strong gravitational field as other stars are observed to do. Only if Sgr A* is extremely massive would it move slowly. The position of Sgr A* has been monitored with VLBI techniques for over two decades, revealing that it is essentially stationary at the dynamical center of the Milky Way. Specifically, the component of Sgr A*’s intrinsic motion perpendicular to the plane of the Milky Way is less than one kilometer per second. By comparison, this is 30 times slower than the Earth orbits the sun. The discovery that Sgr A* is essentially stationary and anchors the galactic center requires that Sgr A* contains over 400,000 times the mass of the sun.

    Recent VLBI observations have shown that the size of the radio emission of Sgr A* is less than that contained within the orbit of Mercury. Combining this volume available to Sgr A* with the lower limit to its mass yields a staggeringly high density. This density is within a factor of less than 10 of the ultimate limit for a black hole. At such an extreme density, the evidence is overwhelming that Sgr A* is a supermassive black hole.

    These discoveries are elegant for their directness and simplicity. Orbits of stars provide an absolutely clear and unequivocal proof of a great unseen mass concentration. Finding that the compact radio source Sgr A* is at the precise location of the unseen mass and is motionless provides even more compelling evidence for a supermassive black hole. Together they form a simple, unique demonstration that the fantastic concept of a supermassive black hole is indeed a reality. John Michell and Pierre-Simon Laplace would be astounded to learn that their conjectures about black holes not only turned out to be correct, but were far grander than they ever could have imagined.

    Mark J. Reid is a senior astronomer at the Center for Astrophysics, Harvard & Smithsonian. He uses radio telescopes across the globe simultaneously to obtain the highest resolution images of newborn and dying stars, as well as black holes.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 10:01 am on November 8, 2018 Permalink | Reply
    Tags: , , , , Nautilus, Sarah Stewart, , The Woman Who Reinvented the Moon,   

    From Nautilus: Women in STEM- “The Woman Who Reinvented the Moon” Sarah Stewart 

    Nautilus

    From Nautilus

    November 8, 2018
    Brian Gallagher

    Sarah Stewart is living her ideal life—and it just got sweeter. The University of California, Davis planetary physicist recently won a MacArthur Foundation Fellowship, famously and unofficially known as the “genius grant,” for her work on the origin of Earth’s moon, upending a decades-old theory. She’s been awarded $625,000.

    “It’s an amazing concept to just say, ‘We’re going to give you the opportunity to do something, and we’re not going to tell you anything about what to do.’ That’s very unusual and freeing,” she told Nautilus, referring to the grant program. She was particularly thrilled by the recognition the award represents. The foundation speaks to several dozen of a candidate’s peers as a part of its vetting process. “What I really feel is appreciation for my colleagues,” she said. “That really touches me.”

    Nautilus spoke to Stewart during World Space Week, the theme of which, this year, is “Space Unites the World.” It compelled her to pen a poem, using the theme as a title. Nautilus asked Stewart about that, as well as how her laboratory experiments, which replicate the pressures and temperatures of planetary collisions, informed her model of the moon’s birth.

    1
    Sarah Stewart. John D. & Catherine T. MacArthur Foundation

    How can space bring us together?

    This World Space Week is happening at a time where the world seems to be highlighting divisions. And so I wrote what I wrote as a response to that. Space exploration and discovery of things that are surprising and new is a way to bring everyone together, and enjoy the profound beauty of nature. And I would like us to spend more time talking about the things that bring us together.

    Like the moon. Give us a brief history of its origin theories.

    Next year, 2019, is the 50th anniversary of the Apollo moon landing. The rock samples that the Apollo missions brought back basically threw out every previous idea for the origin of the moon. Before the Apollo results were in, a Russian astronomer named Viktor Safronov had been developing models of how planets grow. He found that they grow into these sub- or proto-planet-size bodies that would then collide. A couple of different groups then independently proposed that a giant impact made a disc around the Earth that the moon accreted from. Over the past 50 years, that model became quantitative, predictive. Simulations showed that the moon should be made primarily out of the object that struck the proto-Earth. But the Apollo mission found that the moon is practically a twin of the Earth, particularly its mantle, in major elements and in isotopic ratios: The different weight elements are like fingerprints, present in the same abundances. Every single small asteroid and planet in the solar system has a different fingerprint, except the Earth and the moon. So the giant impact hypothesis was wrong. It’s a lesson in how science works—the giant impact hypothesis hung on for so long because there was no alternative model that hadn’t already been disproven.

    How is your proposal for the moon’s birth different?

    We changed the giant impact. And by changing it we specifically removed one of the original constraints. The original giant impact was proposed to set the length of day of the Earth, because angular momentum—the rotational equivalent of linear momentum—is a physical quantity that is conserved: If we go backward in time, the moon comes closer to the Earth. At the time the moon grew, the Earth would have been spinning with a five-hour day. So all of the giant impact models were tuned to give us a five-hour day for the Earth right after the giant impact. What we did was say, “Well, what if there were a way to change the angular momentum after the moon formed?” That would have to be through a dynamical interaction with the sun. What that means is that we could start the Earth spinning much faster—we were exploring models where the Earth had a two- to three-hour day after the giant impact.

    What did a faster-spinning Earth do to your models?

    The surprising new thing is that when the Earth is hot, vaporized, and spinning quickly, it isn’t a planet anymore. There’s a boundary beyond which all of the Earth material cannot physically stay in an object that rotates altogether—we call that the co-rotation limit. A body that exceeds the co-rotation limit forms a new object that we named a synestia, a Greek-derived word that is meant to represent a connected structure. A synestia is a different object than a planet plus a disc. It has different internal dynamics. In this hot vaporized state, the hot gas in the disc can’t fall onto the planet, because the planet has an atmosphere that’s pushing that gas out. What ends up happening is that the rock vapor that forms a synestia cools by radiating to space, forms magma rain in the outer parts of the synestia, and that magma rain accretes to form the moon within the rock vapor that later cools to become the Earth.

    How did the idea of a synestia come about?

    In 2012, Matija Ćuk and I published a paper that was a high-spin model for the origin of the moon. We changed the impact event, but we didn’t realize that after the impact, things were completely different. It just wasn’t anything we ever extracted from the simulations. It wasn’t until two years later when my student Simon Lock and I were looking at different plots, plots we had never made before out of the same simulations, that we realized that we had been interpreting what happened next incorrectly. There was a bonafide eureka moment where we’re sitting together talking about how the disc would evolve around the Earth after the impact, and realizing that it wasn’t a standard disc. These synestias have probably been sitting in people’s computer systems for quite some time without anyone ever actually identifying them as something different.

    Was the size of the synestia beyond the moon’s current orbit?

    It could have been bigger. Exactly how big it was depends on the energy of the event and how fast it was spinning. We don’t have precise constraints on that to make the moon because a range of synestias could make the moon.

    How long was the Earth in a synestia state?

    The synestia was very large, but it didn’t last very long. Because rock vapor is very hot, and where we are in the solar system is far enough away from the sun that our mean temperature is cooler than rock vapor, the synestia cooled very quickly. So it could last 1,000 years or so before looking like a normal planet again. Exactly how long it lasts depends on what else is happening in the solar system around the Earth. In order to be a long lived object it would need to be very close to the star.

    What was the size of the object that struck proto-Earth?

    We can’t tell, because a variety of mass ratios, impact angles, impact velocities can make a synestia that has enough mass and angular momentum in it to make our moon. I don’t know that we will ever know for sure exactly what hit us. There may be ways for us to constrain the possibilities. One way to do that is to look deep in the Earth for clues about how large the event could have been. There are chemical tracers from the deep mantle that indicate that the Earth wasn’t completely melted and mixed, even by the moon-forming event. Those reach the surface through what are called ocean island basalts, sometimes called mantle plumes, from near the core-mantle boundary, up through the whole mantle to the surface. It could be that that could be used as a constraint on being too big. Because the Earth and the moon are very similar in the mantles of the two bodies, that can be used to determine what is too small of an event. That would give us a range that can probably be satisfied by a number of different impact configurations.

    How much energy does it take to form a synestia?

    Giant impacts are tremendously energetic events. The energy of the event, in terms of the kinetic energy of the impact, is released over hours. The power involved is similar to the power, or luminosity, of the sun. We really cannot think of the Earth as looking anything like the Earth when you’ve just dumped the energy of the sun into this planet.

    How common are synestias?

    We actually think that synestias should happen quite frequently during rocky planet formation. We haven’t looked at the gas giant planets. There are some different physics that happen with those. But for growing rocky bodies like the Earth, we attempted to estimate the statistics of how often there should be synestias. And for Earth-mass bodies anywhere in the universe probably, the body is a synestia at least once while it’s growing. The likelihood of making a synestia goes up as the bodies become larger. Super-Earths also should have been a synestia at some point.

    You say that all of the pressures and temperatures reached during planet formation are now accessible in the laboratory. First, give us a sense of the magnitude of those pressures and temperatures, and then tell us how accessing them in labs is possible.

    The center of the Earth is at several thousand degrees, and has hundreds of gigapascals of pressure—about 3 million times more pressure than the surface. Jupiter’s center is even hotter. The center-of-Jupiter pressures can be reached temporarily during a giant impact, as the bodies are colliding together. A giant impact and the center of Jupiter are about the limits of the pressures and temperatures reached during planet formation: so tens of thousands of degrees, and a million times the pressure of the Earth. To replicate that, we need to dump energy into our rock or mineral very quickly in order to generate a shockwave that reaches these amplitudes in pressure and temperature. We use major minerals in the Earth, or rocky planets—so we’ve studied iron, quartz, forsterite, enstatite, and different alloy compositions of those. Other people have studied the hydrogen helium mixture for Jupiter, and ices for Uranus and Neptune. In my lab we have light gas guns, essentially cannons. And, using compressed hydrogen, we can launch a metal flyer plate—literally a thin disk—to almost 8 kilometers per second. We can reach the core pressures in the Earth, but I can’t reach the range of giant impacts or the center of Jupiter in my lab. But the Sandia Z machine, which is a big capacitor that launches metal plates using a magnetic force, can reach 40 kilometers per second. And with the National Ignition Facility laser at Lawrence Livermore National Lab, we can reach the pressures at the center of Jupiter.

    Sandia Z machine

    National Ignition Facility at LLNL

    What happens to the flyer plates when they’re shot?

    The target simply gets turned to dust after being vaporized and then cooling again. They’re very destructive experiments. You have to make real time measurements—of the wave itself and how fast it’s traveling—within tens of nanoseconds. That we can translate to pressure. My group has spent a lot of time developing ways to measure temperature, and to find phase boundaries. The work that led to the origin of the moon was specifically studying what it takes to vaporize Earth materials, and to determine the boiling points of rocks. We needed to know when it would be vaporized in order to calculate when something would become a synestia.

    How do you use your experimental results?

    What runs in our code is a simplified version of a planet. With our experiments we can simulate a simplified planet to infer the more complicated chemical system. Once we’ve determined the pressure-temperature of the average system, you can ask more detailed questions about the multi-component chemistry of a real planet. In the moon paper that was published this year, there’s two big sections. One that does the simplified modeling of the giant impact—it gives us the pressure-temperature range in the synestia. Then another that looks at the chemistry of the system that starts at these high pressures and temperatures and cools, but now using a more realistic model for the Earth.

    What was it like to get a call from the MacArthur Foundation?

    It did come out of the blue. They called me in my office, and I answered the phone. There were three people on the other end, and they said they were from the MacArthur Foundation. I knew what it was, and I stopped listening, because it was such a nice surprise. To me it probably is just unreal at the moment, meaning it will probably take some time to really sink in.

    How did you come to study planetary physics?

    I had enjoyed science fiction, not thinking I was going to be a scientist. But while I was in high school I had phenomenal math and physics teachers. That really grabbed my interest, so when I went to college I wanted to be a physics major. I quickly learned that the astronomers very much welcomed undergraduate researchers because the work was very accessible to someone with undergraduate skills. I met amazing scientists, and that sparked a whole career.

    What would you be doing if you weren’t a scientist?

    That’s hard. Because it has been my ideal for a very long time. In college I did a lot of theater. More theater than homework. The best theatrical experience I had was directing Sweeney Todd. It was absolutely amazing. So I did watch with some envy as some of my friends pursued a theatrical life. That is something that you can be wistful about, except that that would have been a hard path.

    NASA is celebrating its 60th anniversary. What does that mean to you as a scientist studying space?

    It feels like we’ve learned so much over 60 years, because we’ve had our first visits to everything in the solar system now. But at the same time, we’re completely surprised every time we arrive at a new object. So in some ways we’re still in the youthful period in planetary science, where we’re trying to work out basic knowledge. That’s a very exciting time. We’re still on a very big growth curve.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
  • richardmitnick 2:23 pm on October 21, 2018 Permalink | Reply
    Tags: Are Black Holes Actually Dark Energy Stars?, , , , , , Nautilus   

    From Nautilus: “Are Black Holes Actually Dark Energy Stars?” 

    Nautilus

    From Nautilus

    Oct 15, 2018
    Jesse Stone

    1
    George Chapline believes that the Event Horizon Telescope will offer evidence that black holes are really dark energy stars. NASA.

    What does the supermassive black hole at the center of the Milky Way look like? Early next year, we might find out. The Event Horizon Telescope—really a virtual telescope with an effective diameter of the Earth—has been pointing at Sagittarius A* for the last several years.

    Event Horizon Telescope Array

    Arizona Radio Observatory
    Arizona Radio Observatory/Submillimeter-wave Astronomy (ARO/SMT)

    ESO/APEX
    Atacama Pathfinder EXperiment

    CARMA Array no longer in service
    Combined Array for Research in Millimeter-wave Astronomy (CARMA)

    Atacama Submillimeter Telescope Experiment (ASTE)
    Atacama Submillimeter Telescope Experiment (ASTE)

    Caltech Submillimeter Observatory
    Caltech Submillimeter Observatory (CSO)

    IRAM NOEMA interferometer
    Institut de Radioastronomie Millimetrique (IRAM) 30m

    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA
    James Clerk Maxwell Telescope interior, Mauna Kea, Hawaii, USA

    Large Millimeter Telescope Alfonso Serrano
    Large Millimeter Telescope Alfonso Serrano

    CfA Submillimeter Array Hawaii SAO
    Submillimeter Array Hawaii SAO

    ESO/NRAO/NAOJ ALMA Array
    ESO/NRAO/NAOJ ALMA Array, Chile

    South Pole Telescope SPTPOL
    South Pole Telescope SPTPOL

    NSF CfA Greenland telescope

    Greenland Telescope

    Future Array/Telescopes

    Plateau de Bure interferometer
    Plateau de Bure interferometer

    Most researchers in the astrophysics community expect that its images, taken from telescopes all over the Earth, will show the telltale signs of a black hole: a bright swirl of light, produced by a disc of gases trapped in the black hole’s orbit, surrounding a black shadow at the center—the event horizon. This encloses the region of space where the black-hole singularity’s gravitational pull is too strong for light to escape.

    But George Chapline, a physicist at the Lawrence Livermore National Laboratory, doesn’t expect to see a black hole. He doesn’t believe they’re real. In 2005, he told Nature that “it’s a near certainty that black holes don’t exist” and—building on previous work he’d done with physics Nobel laureate Robert Laughlin—introduced an alternative model that he dubbed “dark energy stars.” Dark energy is a term physicists use to describe a peculiar kind of energy that appears to permeate the entire universe.

    Dark energy depiction. Image: Volker Springle/Max Planck Institute for Astrophysics/SP)

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    It expands the fabric of spacetime itself, even as gravity attempts to bring objects closer together. Chapline believes that the immense energies in a collapsing star cause its protons and neutrons to decay into a gas of photons and other elementary particles, along with what he refers to as “droplets of vacuum energy.” These form a “condensed” phase of spacetime—much like a gas under enough pressure transitions to liquid—that has a much higher density of dark energy than the spacetime surrounding the star. This provides the pressure necessary to hold gravity at bay and prevent a singularity from forming. Without a singularity in spacetime, there is no black hole.

    The idea has found no support in the astrophysical community—over the last decade, Chapline’s papers on this topic have garnered only single-digit citations. His most popular paper in particle physics, by contrast, has been cited over 600 times. But Chapline suspects his days of wandering in the scientific wilderness may soon be over. He believes that the Event Horizon Telescope will offer evidence that dark energy stars are real.

    The idea goes back to a 2000 paper [International Journal of Modern Physics A], with Evan Hohlfeld and David Santiago, in which Chapline and Laughlin modeled spacetime as a Bose-Einstein condensate—a state of matter that arises when taking an extremely low-density gas to extremely low temperatures, near absolute zero. Chapline and Laughlin’s model is quantum mechanical in nature: General relativity emerges as a consequence of the way that the spacetime condensate behaves on large scales. Spacetime in this model also undergoes phase transformations when it gains or loses energy. Other scientists find this to be a promising path, too. A 2009 paper [Physical Review A] by a group of Japanese physicists stated that “[Bose-Einstein Condensates] are one of the most promising quantum fluids for” analogizing curved spacetime.

    Chapline and Laughlin argue that they can describe the collapsed stars that most scientists take to be black holes as regions where spacetime has undergone a phase transition. They find that the laws of general relativity are valid everywhere in the vicinity of the collapsed star, except at the event horizon, which marks the boundary between two different phases of spacetime.

    In the condensate model the event horizon surrounding a collapsed star is no longer a point of no return but instead a traversable, physical surface. This feature, along with the lack of a singularity that is the signature feature of black holes, means that paradoxes associated with black holes, like the destruction of information, don’t arise. Laughlin has been reticent to conjecture too far beyond his and Chapline’s initial ideas. He believes Chapline is onto something with dark energy stars, “but where we part company is in the amount of speculating we are willing to do about what ‘phase’ of the vacuum might be inside” what most scientists call black holes, Laughlin said. He’s holding off until experimental data reveals more about the interior phase. “I will then write my second paper on the subject,” he said.

    In recent years Chapline has continued to refine his dark energy star model in collaboration with several other authors, including Pawel Mazur of the University of South Carolina and Piotr Marecki of Leipzig University. He’s concluded that dark energy stars aren’t spherical or oblate, like black holes. Instead, they have the shape of a torus, or donut. In a rotating compact object, like a dark energy star, Chapline believes quantum effects in the spacetime condensate generate a large vortex along the object’s axis of rotation. Because the region inside the vortex is empty—think of the depression that forms at the center of whirlpool—the center of the dark energy star is hollow, like an apple without its core. A similar effect is observed when quantum mechanics is used to model rotating drops of superfluid. There too, a central vortex can form at the center of a rotating drop and, surprisingly, change its shape from a sphere to a torus.

    For Chapline, this strange toroidal geometry isn’t a bug of dark energy stars, but a feature, as it helps explain the origin and shape of astrophysical jets—the highly energetic beams of ionized matter that are generated along the axis of rotation of a compact object like a black hole. Chapline believes he’s identified a mechanism in dark energy stars that explains observations of astrophysical jets better than mainstream ones, which posit that energy is extracted from the accretion disk outside of a black hole and focused into a narrow beam along the black hole’s axis of rotation. To Chapline, matter and energy falling toward a dark energy star would make its way to the inner throat (the “donut hole”), where electrons orbiting the throat would, as in a Biermann Battery, generate magnetic fields powerful enough to drive the jets.

    Chapline points to recent experimental work where scientists, at the OMEGA Laser Facility at the University of Rochester, created magnetized jets using lasers to form a ring-like excitation on a flat surface.

    U Rochester Omega Laser facility

    Though the experiments were not conducted with dark energy stars in mind, Chapline believes it provides support for his theory since the ring-like excitation—Chapline calls it a “ring of fire”—is exactly what he would expect to happen along the throat of a dark energy star. He believes the ring could be the key to supporting the existence of dark energy stars. “This ought to eventually show up clearly” in the Event Horizon Telescope images, Chapline said, referring to the ring.

    3
    Black hole vs dark energy star: When viewed from the top down, a dark energy star has a central opening, the donut hole. Chapline believes that matter and energy rotating around the central opening (forming the “ring of fire”) is the source of the astrophysical jets observed by astronomers in the vicinity of what most believe to be black holes. No image credit.

    Chapline also points out that dark energy stars will not be completely opaque to light, as matter and light can pass into, but also out of, a dark energy star. A dark energy star won’t have a completely black interior—instead it will show a distorted image of any stars behind it. Other physicists, though, are skeptical that these kinds of deviations from conventional black hole models would show up in the Event Horizon Telescope data. Raul Carballo-Rubio, a physicist at the International School for Advanced Studies, in Trieste, Italy, has developed his own alternative model to black holes known as semi-classical relativistic stars. Speaking more generally about alternative black hole models Caraballo-Rubio said, “The differences [with black holes] that would arise in these models are too minute to be detected” by the Event Horizon Telescope.

    Chapline plans to discuss his dark energy star predictions in December, at the Kavli Institute for Theoretical Physics in Santa Barbara. But even if his predictions are confirmed, he said he doesn’t expect the scientific community to become convinced overnight. “I expect that for the next few years the [Event Horizon Telescope] people will be confused by what they see.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

     
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