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    ‘Flashes of Creation’ recounts the Big Bang theory’s origin story

    Flashes of CreationPaul HalpernBasic Books, $30

    The Big Bang wasn’t always a sure bet. For several decades in the 20th century, researchers wrestled with interpreting cosmic origins, or if there even was a beginning at all. At the forefront of that debate stood physicists George Gamow and Fred Hoyle: One advocated for an expanding universe that sprouted from a hot, dense state; the other for a cosmos that is eternal and unchanging. Both pioneered contemporary cosmology, laid the groundwork for our understanding of where atoms come from and brought science to the masses.

    In Flashes of Creation, physicist Paul Halpern recounts Gamow’s and Hoyle’s interwoven stories. The book bills itself as a “joint biography,” but that is a disservice. While Gamow and Hoyle are the central characters, the book is a meticulously researched history of the Big Bang as an idea: from theoretical predictions in the 1920s, to the discovery of its microwave afterglow in 1964, and beyond to the realization in the late 1990s that the expansion of the universe is accelerating.

    Although the development of cosmology was the work of far more than just two scientists, Halpern would be hard-pressed to pick two better mascots. George Gamow was an aficionado of puns and pranks and had a keen sense of how to explain science with charm and whimsy (SN: 8/28/18). The fiercely stubborn Fred Hoyle had a darker, more cynical wit, with an artistic side that showed through in science fiction novels and even the libretto of an opera. Both wrote popular science books — Gamow’s Mr Tompkins series, which explores modern physics through the titular character’s dreams, are a milestone of the genre — and took to the airwaves to broadcast the latest scientific thinking into people’s homes.

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    “Gamow and Hoyle were adventurous loners who cared far more about cosmic mysteries than social conventions,” Halpern writes. “Each, in his own way, was a polymath, a rebel, and a master of science communication.”

    While the Big Bang is now entrenched in the modern zeitgeist, it wasn’t always so. The idea can be traced to Georges Lemaître, a physicist and priest who proposed in 1927 that the universe is expanding. A few years later, he suggested that perhaps the cosmos began with all of its matter in a single point — the “primeval atom,” he called it. In the 1940s, Gamow latched on to the idea as way to explain how all the atomic elements came to be, forged in the “fireball” that would have filled the cosmos in its earliest moments. Hoyle balked at the notion of a moment of creation, convinced that the universe has always existed — and always will exist — in pretty much the same state we find it today. He even coined the term “Big Bang” as a put-down during a 1949 BBC radio broadcast. The elements, Hoyle argued, were forged in stars.

    As far as the elements go, both were right. “One wrote the beginning of the story of element creation,” Halpern writes, “and the other wrote the ending.” We now know that hydrogen and helium nuclei emerged in overwhelming abundance during the first few minutes following the Big Bang. Stars took care of the rest.

    Halpern treats Gamow and Hoyle with reverence and compassion. Re-created scenes provide insight into how both approached science and life. We learn how Gamow, ever the scientist, roped in physicist Niels Bohr to test ideas about why movie heroes always drew their gun faster than villains — a test that involved staging a mock attack with toy pistols. We sit in with Hoyle and colleagues while they discuss a horror film, Dead of Night, whose circular timeline inspired their ideas about an eternal universe.

    In the mid-20th century, two astronomers emerged as spokesmen for dueling ideas about the origin of the cosmos. George Gamow (left) was a passionate defender of the Big Bang theory, arguing that the universe evolved from a hot, dense state. Fred Hoyle (right) upheld the rival “steady state model,” insisting that the universe is eternal and unchanging.From left: AIP Emilio Segrè Visual Archives, George Gamow Collection; AIP Emilio Segrè Visual Archives, Clayton Collection

    And Halpern doesn’t shy away from darker moments, inviting readers to know these scientists as flawed human beings. Gamow’s devil-may-care attitude wore on his colleagues, and his excessive drinking took its toll. Hoyle, in his waning decades, embraced outlandish ideas, suggesting that epidemics come from space and that a dinosaur fossil had been tampered with to show an evolutionary link to birds. And he went to his grave in 2001 still railing against the Big Bang.

    Capturing the history of the Big Bang theory is no easy task, but Halpern pulls it off. The biggest mark against the book, in fact, may be its scope. To pull in all the other characters and side plots that drove 20th century cosmology, Gamow and Hoyle sometimes get forgotten about for long stretches. A bit more editing could have sharpened the book’s focus.

    But to anyone interested in how the idea of the Big Bang grew — or how any scientific paradigm changes — Flashes of Creation is a treat and a worthy tribute to two scientific mavericks.

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    Physicists’ devotion to symmetry has led them astray before

    Second of two parts

    Physicists have a lot in common with Ponce de León and U2’s Bono. After decades of searching, they aren’t getting any younger. And they still haven’t found what they’re looking for.

    In this case, the object of the physicists’ quest is SUSY. SUSY is not a real person or even a fountain relevant to aging in any way. It’s a mathematical framework based on principles of symmetry that could help physicists better explain the mysteries of the universe. Many experts believe that particles predicted by SUSY are the weakly interacting massive particles, or WIMPs, that supposedly make up the invisible “dark matter” lurking throughout the cosmos.

    So far, though, SUSY has been something of a disappointment. Despite multiple heroic searches, SUSY has remained concealed from view. Maybe it is a mathematical mirage.

    If SUSY does turn out to be a myth, it won’t be the first time that symmetry has led science on a wild WIMP chase. Reasoning from the symmetry of circular motion originally suggested the existence of a new form of matter out in space more than two millennia ago. Devotion to that symmetry blinded science to the true nature of the solar system and planetary motion for the next 19 centuries.

    You can blame Plato and Aristotle. In their day, ordinary matter supposedly consisted of four elements: earth, air, fire and water. Aristotle built an elaborate theory of motion based on those elements. He insisted that they naturally moved in straight lines; earth and water moving straight down (toward the center of the world), air and fire moving straight up. In the heavens, though, Aristotle noticed that motion appeared to be circular, as the stars rotated around the nighttime sky. “Our eyes tell us that the heavens revolve in a circle,” he wrote in On the Heavens. Since the known four elements all moved in a straight line, Aristotle deduced that the heavens must consist of a fifth element, called aether — absent on Earth but predominant in space.

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    Plato, on theoretical rather than observational grounds, had already insisted that circularity’s symmetry signified perfection, and therefore circular motion should be required in the heavens. And so for centuries, the assumption that celestial motion must be circular held a stranglehold on natural philosophers attempting to understand of the universe. As late as the 16th century, Copernicus was willing to depose Aristotle’s Earth from the middle of everything but still believed that the Earth and other planets revolved around the sun with a combination of circular motions. Another half century passed before Kepler established that planetary orbits are elliptical, not circular.

    Aristotle’s belief in an exotic form of matter in space is not so different from the picture scientists paint of the heavens today, albeit in a rather more rigorous and sophisticated theoretical way. Dark matter predominates in space, astronomers believe; it is inferred to exist from gravitational effects altering the motions of stars and galaxies. And physicists have determined that the dark matter cannot (for various noncircular reasons) be made of the same ordinary matter found on Earth.

    SUSY particles have long been one of the most popular proposals for the identity of this cosmic dark matter, based on more complicated notions of symmetry than those available to Plato and Aristotle. And since the onset of the 20th century, symmetry math has generated an astounding string of scientific successes. From Einstein’s relativity to the theory of elementary particles and forces, symmetry considerations now form the core of science’s understanding of nature.  

    These mathematical forms of symmetry are more elaborate examples of symmetry as commonly understood: a change that leaves things looking like they did before. A perfectly symmetric face looks the same when a mirror swaps left with right. A perfect sphere’s appearance is not altered when you rotate it to see the other side. Rotate a snowflake by any multiple of 60 degrees and you see the same snowflake.

    In a similar way, more sophisticated mathematical frameworks, known as symmetry groups, describe aspects of the physical world, such as time and space or the families of subatomic particles that make up matter or transmit forces. Symmetries in the equations of such math can even predict previously unknown phenomena. Symmetry in the equations describing subatomic particles, for instance, revealed that for each particle nature allowed an antimatter particle, with opposite electric charge.

    In fact, all the known ordinary matter and force particles fit neatly into the mathematical patterns described by symmetry groups. But none of those particles can explain the dark matter.

    SUSY particles as a dark matter possibility emerged in the 1970s and 1980s, when theorists proposed an even more advanced symmetry system. That math, called supersymmetry (hence SUSY), suggested the existence of a “super” partner particle for each known particle: a force-particle partner for every matter particle, and a matter-particle partner for every force particle. It was an elegant concept mathematically, and it solved (or at least ameliorated) some other vexing theoretical problems. Plus, of the super partner particles it predicted, the lightest one (whichever one that was) seemed likely to be a perfect dark matter WIMP.

    Alas, efforts to detect WIMPs (which should be hitting the Earth all the time) have almost all failed to find any. One experiment that did claim a WIMP detection seems to be on shaky ground — a new experiment, using the same method and materials, reports no such WIMP evidence. And attempts to produce SUSY particles in the world’s most powerful particle accelerator, the Large Hadron Collider, have also come up empty.

    Some physicists have therefore given up on SUSY. And perhaps supersymmetry has been as misleading as the Greek infatuation with circular motion. But the truth is that SUSY is not a theory that can be slain by a single experiment. It is a more nebulous mathematical notion, a framework within which many specific theories can be constructed.   

    “You can’t really kill SUSY because it’s not a thing,” physicist Patrick Stengel of the International Higher School of Advanced Studies in Trieste, Italy, said at a conference in Washington, D.C., in 2019. “It’s not an idea that you can kill. It’s basically just a framework for a bunch of ideas.”

    At the same conference, University of Texas at Austin physicist Katherine Freese pointed out that there was never any guarantee that the Large Hadron Collider would discover SUSY. “Even before the LHC got built, there were a lot of people who said, well, it might not go to a high enough energy,” she said.

    So SUSY may yet turn out to be an example of symmetry that leads physics to success. But just in case, physicists have pursued other dark matter possibilities. One old suggestion that has recently received renewed interest is a lightweight hypothetical particle called an axion (SN: 3/24/20).

    Of course, if axions do exist, symmetry fans could still rejoice — the motivation for proposing the axion to begin with was resolving an issue with yet another form of symmetry. More

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    The dark matter mystery deepens with the demise of a reported detection

    First of two parts

    In mystery stories, the chief suspect almost always gets exonerated before the end of the book. Typically because a key piece of evidence turned out to be wrong.

    In science, key evidence is supposed to be right. But sometimes it’s not. In the mystery of the invisible “dark matter” in space, evidence implicating one chief suspect has now been directly debunked. WIMPs, tiny particles widely regarded as prime dark matter candidates, have failed to appear in an experiment designed specifically to test the lone previous study claiming to detect them.

    For decades, physicists have realized that most of the universe’s matter is nothing like earthly matter, which is made mostly from protons and neutrons. Gravitational influences on visible matter (stars and galaxies) indicate that some dark stuff of unknown identity pervades the cosmos. Ordinary matter accounts for less than 20 percent of the cosmic matter abundance.

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    For unrelated reasons, theorists have also long suggested that nature possesses mysterious types of tiny particles predicted by a theoretical mathematical framework known as supersymmetry, or SUSY for short. Those particles would be massive by subatomic standards but would interact only weakly with other matter, and so are known as Weakly Interacting Massive particles, hence WIMPs.

    Of the many possible species of WIMPs, one (presumably the lightest one) should have the properties necessary to explain the dark matter messing with the motion of stars and galaxies (SN: 12/27/12). Way back in the last century, searches began for WIMPs in an effort to demonstrate their existence and identify which species made up the dark matter.

    In1998, one research team announced apparent success. An experiment called DAMA (for DArk MAtter, get it?), consisting of a particle detector buried under the Italian Alps, seemingly did detect particles with properties matching some physicists’ expectations for a dark matter signal.

    It was a tricky experiment to perform, relying on the premise that space is full of swarms of WIMPs. A detector containing chunks of sodium iodide should give off a flash of light when hit by a WIMP. But other particles from natural radioactive substances would also produce flashes of light even if WIMPs are a myth.

    So the experimenters adopted a clever suggestion proposed earlier by physicists Katherine Freese, David Spergel and Andrzej Drukier, known formally as an annual modulation test. But let’s just call it the June-December approach.

    As the Earth orbits the sun, the sun also moves, traveling around the Milky Way galaxy, carried by a spiral arm in the direction of the constellation Cygnus. If the galaxy really is full of WIMPs, the sun should be constantly plowing through them, generating a “WIMP wind.” (It’s like the wind you feel if you stick your head out of the window of a moving car.) In June, the Earth’s orbit moves it in the same direction as the sun’s motion around the galaxy — into the wind. But in December, the Earth moves the opposite direction, away from the wind. So more WIMPs should be striking the Earth in June than in December. It’s just like the way your car windshield smashes into more raindrops when driving forward than when going in reverse.

    As the sun moves through space, it should collide with dark matter particles called WIMPs, if they exist. When the Earth’s revolution carries it in the same direction as the sun, in summer, the resulting “WIMP wind” should appear stronger, with more WIMP collisions detected in June than in December.GEOATLAS/GRAPHI-OGRE, ADAPTED BY T. DUBÉ

    At an astrophysics conference in Paris in December 1998, Pierluigi Belli of the DAMA team reported a clear signal (or at least a strong hint) that more particles arrived in June than December. (More precisely, the results showed an annual modulation in frequency of light flashes, peaking around June with a minimum in December.) The DAMA data indicated a WIMP weighing in at 59 billion electron volts, roughly 60 times the mass of a proton.

    But some experts had concerns about the DAMA team’s data analysis. And other searches for WIMPs, with different detectors and strategies, should have found WIMPs if DAMA was right — but didn’t. Still, DAMA persisted. An advanced version of the experiment, DAMA/LIBRA, continued to find the June-December disparity.

    Perhaps DAMA was more sensitive to WIMPs than other experiments. After all, the other searches did not duplicate DAMA’s methods. Some used substances other than sodium iodide as a detecting material, or watched for slight temperature increases as a sign of a WIMP collision rather than flashes of light.

    For that matter, WIMPs might not be what theorists originally thought. DAMA initially reported 60 proton-mass WIMPs based on the belief that the WIMPs collided with iodine atoms. But later data suggested that perhaps the WIMPs were hitting sodium atoms, implying a much lighter WIMP mass — lighter than other experiments had been optimally designed to detect. Yet another possibility: Maybe trace amounts of the metallic element thallium (much heavier atoms than either iodine or sodium) had been the WIMP targets. But a recent review of that proposal found once again that the DAMA results could not be reconciled with the absence of a signal in other experiments.

    And now DAMA’s hope for vindication has been further dashed by a new underground experiment, this one in Spain. Scientists with the ANAIS collaboration have repeated the June-December method with sodium iodide, in an effort to reproduce DAMA’s results with the same method and materials. After three years of operation, the ANAIS team reports no sign of WIMPs.

    To be fair, the no-WIMP conclusion relies on a lot of seriously sophisticated technical analysis. It’s not just a matter of counting light flashes. You have to collect rigorous data on the behavior of nine different sodium iodide modules. You have to correct for the presence of rare radioactive isotopes generated by cosmic ray collisions while the modules were still under construction. And then the statistical analysis needed to discern a winter-summer signal difference is not something you should try at home (unless you’re fully versed in things like the least-square periodogram or the Lomb-Scargle technique). Plus, ANAIS it still going, with plans to collect two more years of data before issuing a final analysis. So the judgment on DAMA’s WIMPs is not necessarily final.

    Nevertheless, it doesn’t look good for WIMPs, at least for the WIMPs motivated by belief in supersymmetry.   

    Sadly for SUSY fans, searches for WIMPs from space are not the only bad news. Attempts to produce WIMPs in particle accelerators have also so far failed. Dark matter might just turn out to consist of some other kind of subatomic particle.

    If so, it would be a plot twist worthy of Agatha Christie, kind of like Poirot turning out to be the killer. For symmetry has long been physicists’ most reliable friend, guiding many great successes, from Einstein’s relativity theory to the standard model of particles and forces.

    Still, failure to find SUSY particles so far does not necessarily mean they don’t exist. Supersymmetry just might be not as simple as it first seemed. And SUSY particles might just be harder to detect than scientists originally surmised. But if supersymmetry does turn out not to be so super, scientists might need to reflect on the ways that faith in symmetry can lead them astray. More

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    Einstein’s theory of general relativity unveiled a dynamic and bizarre cosmos

    Albert Einstein’s mind reinvented space and time, foretelling a universe so bizarre and grand that it has challenged the limits of human imagination. An idea born in a Swiss patent office that evolved into a mature theory in Berlin set forth a radical new picture of the cosmos, rooted in a new, deeper understanding of gravity.
    Out was Newton’s idea, which had reigned for nearly two centuries, of masses that appeared to tug on one another. Instead, Einstein presented space and time as a unified fabric distorted by mass and energy. Objects warp the fabric of spacetime like a weight resting on a trampoline, and the fabric’s curvature guides their movements. With this insight, gravity was explained.
    Einstein presented his general theory of relativity at the end of 1915 in a series of lectures in Berlin. But it wasn’t until a solar eclipse in 1919 that everyone took notice. His theory predicted that a massive object — say, the sun — could distort spacetime nearby enough to bend light from its straight-line course. Distant stars would thus appear not exactly where expected. Photographs taken during the eclipse verified that the position shift matched Einstein’s prediction. “Lights all askew in the heavens; men of science more or less agog,” declared a New York Times headline.
    Even a decade later, a story in Science News Letter, the predecessor of Science News, wrote of “Riots to understand Einstein theory” (SN: 2/1/30, p. 79). Apparently extra police had to be called in to control a crowd of 4,500 who “broke down iron gates and mauled each other” at the American Museum of Natural History in New York City to hear an explanation of general relativity.

    By 1931, physicist Albert A. Michelson, the first American to win a Nobel Prize in the sciences, called the theory “a revolution in scientific thought unprecedented in the history of science.”
    But for all the powers of divination we credit to Einstein today, he was a reluctant soothsayer. We now know that general relativity offered much more than Einstein was willing or able to see. “It was a profoundly different way of looking at the universe,” says astrophysicist David Spergel of the Simons Foundation’s Flatiron Institute in New York City, “and it had some wild implications that Einstein himself didn’t want to accept.” What’s more, says Spergel (a member of the Honorary Board of the Society for Science, publisher of Science News), “the wildest aspects of general relativity have all turned out to be true.”
    What had been masquerading as a quiet, static, finite place is instead a dynamic, ever-expanding arena filled with its own riot of space-bending beasts. Galaxies congregate in superclusters on scales vastly greater than anything experts had considered before the 20th century. Within those galaxies reside not only stars and planets, but also a zoo of exotic objects illustrating general relativity’s propensity for weirdness, including neutron stars, which pack a fat star’s worth of mass into the size of a city, and black holes, which pervert spacetime so strongly that no light can escape. And when these behemoths collide, they shake spacetime, blasting out ginormous amounts of energy. Our cosmos is violent, evolving and filled with science fiction–like possibilities that actually come straight out of general relativity.
    “General relativity opened up a huge stage of stuff for us to look at and try out and play with,” says astrophysicist Saul Perlmutter of the University of California, Berkeley. He points to the idea that the universe changes dramatically over its lifetime — “the idea of a lifetime of a universe at all is a bizarre concept” — and the idea that the cosmos is expanding, plus the thought that it could collapse and come to an end, and even that there might be other universes. “You get to realize that the world could be much more interesting even than we already ever imagined it could possibly be.”

    General relativity has become the foundation for today’s understanding of the cosmos. But the current picture is far from complete. Plenty of questions remain about mysterious matter and forces, about the beginnings and the end of the universe, about how the science of the big meshes with quantum mechanics, the science of the very small. Some astronomers believe a promising route to answering some of those unknowns is another of general relativity’s initially underappreciated features — the power of bent light to magnify features of the cosmos.
    Today’s scientists continue to poke and prod at general relativity to find clues to what they might be missing. General relativity is now being tested to a level of precision previously impossible, says astrophysicist Priyamvada Natarajan of Yale ​University. “General relativity expanded our cosmic view, then gave us sharper focus on the cosmos, and then turned the tables on it and said, ‘now we can test it much more strongly.’ ” It’s this testing that will perhaps uncover problems with the theory that might point the way to a fuller picture.
    And so, more than a century after general relativity debuted, there’s plenty left to foretell. The universe may turn out to be even wilder yet.
    Ravenous beasts
    Just over a century after Einstein unveiled general relativity, scientists obtained visual confirmation of one of its most impressive beasts. In 2019, a global network of telescopes revealed a mass warping spacetime with such fervor that nothing, not even light, could escape its snare. The Event Horizon Telescope released the first image of a black hole, at the center of galaxy M87 (SN: 4/27/19, p. 6).
    In 2019, the Event Horizon Telescope Collaboration released this first-ever image of a black hole, at the heart of galaxy M87. The image shows the shadow of the monster surrounded by a bright disk of gas.Event Horizon Telescope Collaboration
    “The power of an image is strong,” says Kazunori Akiyama, an astrophysicist at the MIT Haystack Observatory in Westford, Mass., who led one of the teams that created the image. “I somewhat expected that we might see something exotic,” Akiyama says. But after looking at the first image, “Oh my God,” he recalls thinking, “it’s just perfectly matching with our expectation of general relativity.”
    For a long time, black holes were mere mathematical curiosities. Evidence that they actually reside out in space didn’t start coming in until the second half of the 20th century. It’s a common story in the annals of physics. An oddity in some theorist’s equation points to a previously unknown phenomenon, which kicks off a search for evidence. Once the data are attainable, and if physicists get a little lucky, the search gives way to discovery.
    In the case of black holes, German physicist Karl Schwarzschild came up with a solution to Einstein’s equations near a single spherical mass, such as a planet or a star, in 1916, shortly after Einstein proposed general relativity. Schwarzschild’s math revealed how the curvature of spacetime would differ around stars of the same mass but increasingly smaller sizes — in other words, stars that were more and more compact. Out of the math came a limit to how small a mass could be squeezed. Then in the 1930s, J. Robert Oppenheimer and Hartland Snyder described what would happen if a massive star collapsing under the weight of its own gravity shrank past that critical size — today known as the “Schwarzschild radius” — reaching a point from which its light could never reach us. Still, Einstein — and most others — doubted that what we now call black holes were plausible in reality.
    The term “black hole” first appeared in print in Science News Letter. It was in a 1964 story by Ann Ewing, who was covering a meeting in Cleveland of the American Association for the Advancement of Science (SN: 1/18/64, p. 39). That’s also about the time that hints in favor of the reality of black holes started coming in.
    Just a few months later, Ewing reported the discovery of quasars — describing them in Science News Letter as “the most distant, brightest, most violent, heaviest and most puzzling sources of light and radio waves” (SN: 8/15/64, p. 106). Though not linked to black holes at the time, quasars hinted at some cosmic powerhouses needed to provide such energy. The use of X-ray astronomy in the 1960s revealed new features of the cosmos, including bright beacons that could come from a black hole scarfing down a companion star. And the motions of stars and gas clouds near the centers of galaxies pointed to something exceedingly dense lurking within.  
    Quasars (one illustrated) are so bright that they can outshine their home galaxies. Though baffling when first discovered, these outbursts are powered by massive, feeding black holes.Mark Garlick/Science Source
    Black holes stand out among other cosmic beasts for how extreme they are. The largest are many billion times the mass of the sun, and when they rip a star apart, they can spit out particles with 200 trillion electron volts of energy. That’s some 30 times the energy of the protons that race around the world’s largest and most powerful particle accelerator, the Large Hadron Collider.
    As evidence built into the 1990s and up to today, scientists realized these great beasts not only exist, but also help shape the cosmos. “These objects that general relativity predicted, that were mathematical curiosities, became real, then they were marginal. Now they’ve become central,” says Natarajan.
    We now know supermassive black holes reside at the centers of most if not all galaxies, where they generate outflows of energy that affect how and where stars form. “At the center of the galaxy, they define everything,” she says.
    Though visual confirmation is recent, it feels as though black holes have long been familiar. They are a go-to metaphor for any unknowable space, any deep abyss, any endeavor that consumes all our efforts while giving little in return.
    Real black holes, of course, have given plenty back: answers about our cosmos plus new questions to ponder, wonder and entertainment for space fanatics, a lost album from Weezer, numerous episodes of Doctor Who, the Hollywood blockbuster Interstellar.
    For physicist Nicolas Yunes of the University of Illinois at Urbana-Champaign, black holes and other cosmic behemoths continue to amaze. “Just thinking about the dimensions of these objects, how large they are, how heavy they are, how dense they are,” he says, “it’s really breathtaking.”
    [embedded content]
    In 2019, scientists gave us the first real picture of the supermassive black hole at the center of galaxy M87. How? We explain.
    Spacetime waves
    When general relativity’s behemoths collide, they disrupt the cosmic fabric. Ripples in spacetime called gravitational waves emanate outward, a calling card of a tumultuous and most energetic tango.
    Einstein’s math predicted such waves could be created, not only by gigantic collisions but also by explosions and other accelerating bodies. But for a long time, spotting any kind of spacetime ripple was a dream beyond measure. Only the most dramatic cosmic doings would create signals that were large enough for direct detection. Einstein, who called the waves gravitationswellen, was unaware that any such big events existed in the cosmos.
    Gravitational waves ripple away from two black holes that orbit each other before merging (shown in this simulation). The merging black holes created a new black hole that’s much larger than those found in previous collisions.Deborah Ferguson, Karan Jani, Deirdre Shoemaker and Pablo Laguna/Georgia Tech, Maya Collaboration
    Beginning in the 1950s, when others were still arguing whether gravitational waves existed in reality, physicist Joseph Weber sunk his career into trying to detect them. After a decade-plus effort, he claimed detection in 1969, identifying an apparent signal perhaps from a supernova or from a newly discovered type of rapidly spinning star called a pulsar. In the few years after reporting the initial find, Science News published more than a dozen stories on what it began calling the “Weber problem” (SN: 6/21/69, p. 593). Study after study could not confirm the results. What’s more, no sources of the waves could be found. A 1973 headline read, “The deepening doubt about Weber’s waves” (SN: 5/26/73, p. 338).
    Weber stuck by his claim until his death in 2000, but his waves were never verified. Nonetheless, scientists increasingly believed gravitational waves would be found. In 1974, radio astronomers Russell Hulse and Joseph Taylor spotted a neutron star orbiting a dense companion. Over the following years, the neutron star and its companion appeared to be getting closer together by the distance that would be expected if they were losing energy to gravitational waves. Scientists soon spoke not of the Weber problem, but of what equipment could possibly pick up the waves. “Now, although they have not yet seen, physicists believe,” Dietrick E. Thomsen wrote in Science News in 1984 (SN: 8/4/84, p. 76).
    It was a different detection strategy, decades in the making, that would provide the needed sensitivity. The Advanced Laser Interferometry Gravitational-wave Observatory, or LIGO, which reported the first confirmed gravitational waves in 2016, relies on two detectors, one in Hanford, Wash., and one in Livingston, La. Each detector splits the beam of a powerful laser in two, with each beam traveling down one of the detector’s two arms. In the absence of gravitational waves, the two beams recombine and cancel each other out. But if gravitational waves stretch one arm of the detector while squeezing the other, the laser light no longer matches up.

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    The machines are an incredible feat of engineering. Even spacetime ripples detected from colliding black holes might stretch an arm of the LIGO detector by as little as one ten-thousandth of the width of a proton.
    When the first detection, from two colliding black holes, was announced, the discovery was heralded as the beginning of a new era in astronomy. It was Science News’ story of the year in 2016, and such a big hit that the pioneers of the LIGO detector won the Nobel Prize in physics the following year.
    Scientists with LIGO and another gravitational wave detector, Virgo, based in Italy, have by now logged dozens more detections (SN: 1/30/21, p. 30). Most of the waves have emanated from mergers of black holes, though a few events have featured neutron stars. Smashups so far have revealed the previously unknown birthplaces of some heavy elements and pointed to a bright jet of charged subatomic particles that could offer clues to mysterious flashes of high-energy light known as gamma-ray bursts. The waves also have revealed that midsize black holes, between 100 and 100,000 times the sun’s mass, do in fact exist — along with reconfirming that Einstein was right, at least so far.
    Researchers at two gravitational wave observatories, LIGO in the United States and Virgo in Italy (shown), have reported dozens of detections of black hole smashups, as well as neutron star mergers, in the last five years.The Virgo Collaboration
    Just five years in, some scientists are already eager for something even more exotic. In a Science News article about detecting black holes orbiting wormholes via gravitational waves, physicist Vítor Cardoso of Instituto Superior Técnico in Lisbon, Portugal, suggested a coming shift to more unusual phenomena: “We need to look for strange but exciting signals,” he said (SN: 8/29/20, p. 12).
    Gravitational wave astronomy is truly only at its beginnings. Improved sensitivity at existing Earth-based detectors will turn up the volume on gravitational waves, allowing detections from less energetic and more distant sources. Future detectors, including the space-based LISA, planned for launch in the 2030s, will get around the troublesome noise that interferes when Earth’s surface shakes.
    “Perhaps the most exciting thing would be to observe a small black hole falling into a big black hole, an extreme mass ratio inspiraling,” Yunes says. In such an event, the small black hole would zoom back and forth, back and forth, swirling in different directions as it followed wildly eccentric orbits, perhaps for years. That could offer the ultimate test of Einstein’s equations, revealing whether we truly understand how spacetime is warped in the extreme. More

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    Scientists can’t agree on how clumpy the universe is

    The universe is surprisingly smooth.
    A new measurement reveals that the universe is less clumpy than predicted, physicists report in a series of papers posted July 30 at The discrepancy could hint at something amiss with scientists’ understanding of the cosmos.
    To pin down the cosmic clumpiness, researchers studied the orientation of 21 million galaxies with the Kilo-Degree Survey at the Paranal Observatory in Chile. As light from those galaxies streams through the universe, its trajectory is bent by massive objects, a phenomenon called gravitational lensing. This lensing causes the elongated shapes of galaxies to appear slightly aligned, rather than oriented randomly.
    When combined with additional data from other sky surveys, that alignment quantifies how much the matter in the universe is clumped together. The researchers found that the universe is about 10 percent more homogenous, or smoother, than predicted based on light released just after the Big Bang, the cosmic microwave background. Previous results had hinted at the discrepancy, but the new measurement strengthens the case that the disagreement is not a fluke (SN: 7/30/19).
    If the measurement is correct, the mismatch could hint at a hole in the standard model of cosmology, the theory that describes how the universe has changed over time. When combined with a similar puzzle over how fast the universe is expanding (SN: 7/15/20), physicists are beginning to suspect that the universe is putting them­­­­­ on notice.
    “It’s a bit of a riddle,” says cosmologist Hendrik Hildebrandt of Ruhr-Universität Bochum in Germany, a coauthor of the studies. “Is [the universe] just telling us ‘You’re stupid and you didn’t do your measurement right,’ or … ‘Hey, I’m more complicated than you thought’?” More

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    ‘The End of Everything’ explores the ways the universe could perish

    The End of EverythingKatie MackScribner, $26
    Eventually, the universe will end. And it won’t be pretty.
    The universe is expanding at an accelerating clip, and that evolution, physicists expect, will lead the cosmos to a conclusion. Scientists don’t know quite what that end will look like, but they have plenty of ideas. In The End of Everything, theoretical astrophysicist Katie Mack provides a tour of the admittedly bleak possibilities. But far from being depressing, Mack’s account mixes a sense of reverence for the wonders of physics with an irreverent sense of humor and a disarming dose of candor.
    Some potential finales are violent: If the universe’s expansion were to reverse, the cosmos collapsing inward in a Big Crunch, extremely energetic swells of radiation would ignite the surfaces of stars, exploding them. Another version of the end is quieter but no less terrifying: The universe’s expansion could continue forever. That end, Mack writes, “like immortality, only sounds good until you really think about it.” Endless expansion would beget a state known as “heat death” — a barren universe that has reached a uniform temperature throughout (SN: 10/2/09). Stars will have burned out, and black holes will have evaporated until no organized structures exist. Nothing meaningful will happen anymore because energy can no longer flow from one place to another. In such a universe, time ceases to have meaning.
    Perhaps more merciful than the purgatory of heat death is the possibility of a Big Rip, in which the universe’s expansion accelerates faster and faster, until stars and planets are torn apart, molecules are shredded and the very fabric of space is ripped apart.

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    These potential endings are all many billions of years into the future — or perhaps much further off. But there’s also the possibility that the universe could end abruptly at any moment. That demise would not be a result of expansion or contraction, but due to a phenomenon called vacuum decay. If the universe turns out to be fundamentally unstable, a tiny bubble of the cosmos could convert to a more stable state. Then, the edge of that bubble would expand across the cosmos at the speed of light, obliterating anything in its path with no warning. In a passage a bit reminiscent of a Kurt Vonnegut story, Mack writes, “Maybe it’s for the best that you don’t see it coming.”
    Already known for her engaging Twitter personality, public lectures and popular science writing, Mack has well-honed scientific communication chops. Her evocative writing about some of the most violent processes in the universe, mixed with her obvious glee at the unfathomable grandness of it all, should both satisfy longtime physics fans and inspire younger generations of physicists.
    Reading Mack’s prose feels like learning physics from a brilliant, quirky friend. The book is sprinkled with plenty of informal quips: “I’m not going to sugarcoat this. The universe is frickin’ weird.” Readers will find themselves good-naturedly rolling their eyes at some of the goofy footnotes and nerdy pop-culture references. At the same time, the book delves deep into gritty physics details, thoroughly explaining important concepts like the cosmic microwave background — the oldest light in the universe — and tackling esoteric topics in theoretical physics. Throughout, Mack does an excellent job of recognizing where points of confusion might trip up a reader and offers clarity instead.
    Mack continues a long-standing tradition of playfulness among physicists. That’s how we got stuck with somewhat cheesy names for certain fundamental particles, such as “charm” and “strange” quarks, for example. But she also brings an emotional openness that is uncommon among scientists. Sometimes this is conveyed by declarations in all caps about how amazing the universe is. But other times, it comes when Mack makes herself vulnerable by leveling with the reader about how unnerving this topic is: “I’m trying not to get hung up on it … the end of this great experiment of existence. It’s the journey, I repeat to myself. It’s the journey.”
    Yes, this is a dark subject. Yes, the universe will end, and everything that has ever happened, from the tiniest of human kindnesses to the grandest of cosmic explosions, will one day be erased from the record. Mack struggles with what the inevitable demise of everything means for humankind. By contemplating the end times, we can refine our understanding of the universe, but we can’t change its fate.
    Buy The End of Everything from Science News is a participant in the Amazon Services LLC Associates Program. Please see our FAQ for more details. More

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    Despite a new measurement, the debate over the universe’s expansion rages on

    When it comes to the expansion rate of the universe, physicists have apparently agreed to disagree.
    Two types of measurements clash over how fast the cosmos is expanding (SN: 7/30/19). Now, a new estimate from the Atacama Cosmology Telescope, or ACT, further entrenches this disagreement.
    To tease out the properties of the universe, ACT observes light emitted shortly after the Big Bang, known as the cosmic microwave background. Those observations reveal that the universe is expanding a rate of about 67.9 kilometers per second for each megaparsec (about 3 million light-years), physicists report in two papers posted online and submitted to The number aligns with that of an earlier cosmic microwave background experiment called Planck (SN: 7/24/18).
    “As an independent experiment, we see the same thing,” says cosmologist Simone Aiola of the Flatiron Institute in New York City. Located in the Atacama Desert in Chile, ACT observes the cosmic microwave background with a higher resolution than Planck did.
    To measure the expansion of the universe, the Atacama Cosmology Telescope mapped out the cosmic microwave background (one portion shown). Colors represent differences in the polarization, the orientation of the light’s electromagnetic waves.ACT Collaboration
    Both ACT and Planck disagree with most estimates from objects that emitted their light more recently, such as exploding stars called supernovas and bright hearts of galaxies known as quasars. Those studies tend to indicate a faster expansion rate of around 74 kilometers per second per megaparsec.
    If no simple explanation can be found for the discrepancy, it could dramatically alter physicists’ understanding of the contents of the universe and how the cosmos changes over time. For example, dark energy, the shadowy stuff that causes the universe to expand at an accelerating rate, might behave differently than scientists thought.
    Some researchers had speculated that an unidentified source of experimental error in the Planck data could have accounted for the mismatch. But with the independent measurement from ACT, that explanation has gone out the window. That frees physicists to focus on other explanations, like potential issues with the supernova or quasar measurements, or the possibility of unexplained new physics phenomena.
    Now, says cosmologist Adam Riess of Johns Hopkins University and the Space Telescope Science Institute in Baltimore, “we can proceed without the niggling worries.” More