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  • richardmitnick 12:52 pm on December 28, 2018 Permalink | Reply
    Tags: , Dark Energy, , Scientists propose a new model with dark energy and our universe riding on an expanding bubble in an extra dimension, ,   

    From phys.org: “Our universe: An expanding bubble in an extra dimension” 

    physdotorg
    From phys.org

    December 28, 2018
    Uppsala University

    1
    In their article, the scientists propose a new model with dark energy and our universe riding on an expanding bubble in an extra dimension. Credit: Suvendu Giri

    Uppsala University researchers have devised a new model for the universe – one that may solve the enigma of dark energy. Their new article, published in Physical Review Letters, proposes a new structural concept, including dark energy, for a universe that rides on an expanding bubble in an additional dimension.

    We have known for the past 20 years that the universe is expanding at an ever accelerating rate. The explanation is the “dark energy” that permeates it throughout, pushing it to expand. Understanding the nature of this dark energy is one of the paramount enigmas of fundamental physics.

    It has long been hoped that string theory will provide the answer. According to string theory, all matter consists of tiny, vibrating “stringlike” entities. The theory also requires there to be more spatial dimensions than the three that are already part of everyday knowledge. For 15 years, there have been models in string theory that have been thought to give rise to dark energy. However, these have come in for increasingly harsh criticism, and several researchers are now asserting that none of the models proposed to date are workable.

    In their article, the scientists propose a new model with dark energy and our universe riding on an expanding bubble in an extra dimension. The whole universe is accommodated on the edge of this expanding bubble. All existing matter in the universe corresponds to the ends of strings that extend out into the extra dimension. The researchers also show that expanding bubbles of this kind can come into existence within the framework of string theory. It is conceivable that there are more bubbles than ours, corresponding to other universes.

    The Uppsala scientists’ model provides a new, different picture of the creation and future fate of the universe, while it may also pave the way for methods of testing string theory.

    See the full article here .

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    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

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  • richardmitnick 2:33 pm on November 28, 2018 Permalink | Reply
    Tags: , , , , , Dark Energy, , ,   

    From physicsworld.com: “Cosmic expansion rate remains a mystery despite new measurement” 

    physicsworld
    From physicsworld.com

    21 Nov 2018

    1
    Galaxy far away: an image taken by the Dark Energy Camera. (Courtesy: Fermilab)

    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

    A new value for the Hubble constant – the expansion rate of the universe — has been calculated by an international group of astrophysicists. The team used primordial distance scales to study more than 200 supernovae observed by telescopes in Chile and Australia. The new result agrees well with previous values of the constant obtained using a specific model of cosmic expansion, while disagreeing with more direct observations from the nearby universe – so exacerbating a long-running disagreement between cosmologists and astronomers.

    The Hubble constant is calculated by looking at distant celestial objects and determining how fast they are moving away from Earth. A plot of the speeds of the objects versus their distance from Earth falls on a straight line, the slope of which is the Hubble constant.

    Obtaining an object’s speed is straightforward and involves measuring the redshift of the light it emits, but quantifying its distance is much more complicated. Historically, this has been done using a “distance-ladder”, whereby progressively greater length scales are measured by using one type of “standard candle” to calibrate the output of another standard candle. The distance to stars known as Cepheid variables (one type of standard candle) is first established via parallax, and that information is used to calibrate the output of type Ia supernovae (another type of standard candle) located in galaxies containing Cepheids. The apparent brightness of other supernovae can then be used to work out distances to galaxies further away.

    Large discrepancy

    This approach has been refined over the years and has most recently yielded a Hubble constant of 73.5 ± 1.7 kilometres per second per magaparsec (one megaparsec being 3.25 million light-years). That number, however – obtained by starting close to Earth and moving outwards – is at odds with calculations of the Hubble constant that take the opposite approach — moving inwards from the dawn of time. The baseline in that latter case comes from length scales of temperature fluctuations in the radiation dating back to just after the Big Bang, known as the cosmic microwave background. The cosmic expansion rate at that time is extrapolated to the present day by assuming that the universe’s growth has accelerated under the influence of a particular kind of dark energy. Using the final results from the European Space Agency’s Planck satellite, a very different Hubble constant of 67.4 ± 0.5 is obtained.

    ESA/Planck 2009 to 2013

    To try to resolve the problem by using an alternative approach, scientists have in recent years created what is known as an “inverse distance ladder”. This also uses the cosmic microwave background as a starting point, but it calculates the expansion rate at a later time – about 10 billion years after the Big Bang – when the density fluctuations imprinted on the background radiation had grown to create clusters of galaxies distributed within “baryon acoustic oscillations”. The oscillations are used to calibrate the distance to supernovae – present in the galaxies – thanks to the fact that the oscillations lead to a characteristic separation between galaxies of 147 megaparsecs.

    In the latest work, the Dark Energy Survey collaboration draws on galaxy data from the Sloan Digital Sky Survey as well as 207 newly-studied supernovae captured by the Dark Energy Camera mounted on the 4-metre Víctor M Blanco telescope in Chile. Using spectra obtained mainly at the similarly-sized Anglo-Australian Telescope in New South Wales, the collaboration calculates a value for the Hubble constant of 67.8 ± 1.3 – so agreeing with the Planck value while completely at odds with the conventional distance ladder.


    AAO Anglo Australian Telescope near Siding Spring, New South Wales, Australia, Altitude 1,100 m (3,600 ft)

    Siding Spring Mountain with Anglo-Australian Telescope dome visible near centre of image at an altitude of 1,165 m (3,822 ft)

    Fewer assumptions

    “The key thing with these results,“ says team member Ed Macaulay of the University of Portsmouth in the UK, “is that the only physics you need to assume is plasma physics in the early universe. You don’t need to assume anything about dark energy.”

    Adam Riess, an astrophysicist at the Space Telescope Science Institute in Baltimore, US who studies the distance-ladder, says that the new work “adds more weight” to the disparity in values of the Hubble constant obtained from the present and early universe.

    Cosmic Distance Ladder, skynetblogs


    Dark Energy Camera Enables Astronomers a Glimpse at the Cosmic Dawn. CREDIT National Astronomical Observatory of Japan

    (Indeed, the distance-ladder itself has gained independent support from expansion rates calculated using gravitational lensing.) He reckons that the similarity between the Planck and Dark Energy Survey results means that redshifts out to z=1 (going back about 8 billion years) are “probably not where the tension develops” and that the physics of the early universe might be responsible instead.

    Chuck Bennett of Johns Hopkins University, who led the team on Planck’s predecessor WMAP, agrees. He points to a new model put forward by his Johns Hopkins colleagues Marc Kamionkowski, Vivian Poulin and others that adds extra dark energy to the universe very early on (before rapidly decaying). This model, says Bennett, “proves that it is theoretically possible to find cosmological solutions to the Hubble constant tension”.

    Macaulay is more cautious. He acknowledges the difficulty of trying to find an error, reckoning that potential systematic effects in any of the measurements “are about ten times smaller” than the disparity. But he argues that more data are needed before any serious theoretical explanations can be put forward. To that end, he and his colleagues are attempting to analyse a further 2000 supernovae observed by the Dark Energy Camera, although they are doing so without the aid of (costly) spectroscopic analysis. Picking out the right kind of supernovae and then working out their redshift “will be very difficult,” he says, “and not something that has been done with this many supernovae before”.

    A preprint describing the research is available on arXiv.

    See the full article here .


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  • richardmitnick 1:39 pm on November 13, 2018 Permalink | Reply
    Tags: , , , , Dark Energy, , ,   

    From Symmetry: “Gravitational lenses” 

    Symmetry Mag
    From Symmetry

    11/13/18
    Jim Daley

    Gravitational Lensing NASA/ESA

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova [Could not pass this one up.]

    Predicted by Einstein and discovered in 1979, gravitational lensing helps astrophysicists understand the evolving shape of the universe.

    On March 29, 1979, high in the Quinlan Mountains in the Tohono O’odham Nation in southwestern Arizona, a team of astronomers at Kitt Peak National Observatory was scanning the night sky when they saw something curious in the constellation Ursa Major: two massive celestial objects called quasars with remarkably similar characteristics, burning unusually close to one another.

    Kitt Peak National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft)

    The astronomers—Dennis Walsh, Bob Carswell and Ray Weymann—looked again on subsequent nights and checked whether the sight was an anomaly caused by interference from a neighboring object. It wasn’t. Spectroscopic analysis confirmed the twin images were actually both light from a single quasar 8.7 billion light-years from Earth. It appeared to telescopes on Kitt Peak to be two bodies because its light was distorted by a massive galaxy between the quasar and Earth. The team had made the first discovery of a gravitational lens.

    Since then, gravitational lenses have given us remarkable images of the cosmos and granted cosmologists a powerful means to unravel its mysteries.

    “Lensing is one of the primary tools we use to learn about the evolution of the universe,” says Mandeep Gill, an astrophysicist at Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), Stanford. By observing the gravitational lensing and redshift of galaxy clusters, he explains, cosmologists can determine both the matter content of the universe and the speed at which the universe is expanding.

    Gravitational lensing was predicted by Einstein’s theory of general relativity. General relativity posited that massive objects like the sun actually bend the fabric of spacetime around them. Like a billiard ball sinking into a stretched-out rubber sheet, a massive object creates a depression around it; it’s called a “gravity well.” Light passing through a gravity well bends with its curves.

    When an object is really immense—such as a galaxy or galaxy cluster—it can bend the path of passing light dramatically. Astronomers call this “strong lensing.”

    Strong lensing can have remarkable effects. A distant light source arranged in a straight line with a massive body and Earth—a configuration called a syzygy—can appear as a halo around the lensing body, an effect known as an “Einstein ring.” And light from one quasar in the constellation Pegasus bends so much by the time it reaches Earth that it looks like four quasars instead. Astronomers call this phenomenon a “quad lens,” and they’ve named the quasar in Pegasus “the Einstein Cross.”

    Most gravitational lensing events are not so dramatic. Any mass will curve the spacetime around it, causing slight distortions to passing light. While this weak lensing is not apparent from a single observation, taking an average from many light sources allows observers to detect weak lensing effects as well.

    Weak gravitational lensing NASA/ESA Hubble

    The overall distribution of matter in the universe has a lensing effect on light from distant galaxies, a phenomenon known as “cosmic shear.”

    “A cosmic shear measurement is incredibly meticulous as the effect is so small, but it holds a wealth of information about how the structure in the universe has evolved with time,” says Alexandra Amon, an observational cosmologist at KIPAC who specializes in weak lensing.

    Strong and weak gravitational lensing are both important tools in the study of dark matter and dark energy, the invisible stuff that together make up 96 percent of the universe. There is not enough visible mass in the universe to cause all of the gravitational lensing that astronomers see; scientists think most of it is caused by invisible dark matter.

    Fritz Zwicky discovered Dark Matter when observing the movement of the Coma Cluster.

    Fritz Zwicky from http:// palomarskies.blogspot.com

    Coma cluster via NASA/ESA Hubble

    But most of the real work was done by Vera Rubin a Woman in STEM

    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science)


    Vera Rubin measuring spectra, worked on Dark Matter (Emilio Segre Visual Archives AIP SPL)


    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970. https://home.dtm.ciw.edu

    And how all of that matter moves and changes over time is thought to be affected by a mysterious “force” (scientists aren’t really sure what it is) pushing our universe to expand at an accelerating pace: dark energy.

    Studying gravitational lensing can help astrophysicists track the universe’s growth.

    “Strong gravitational lensing can give you a lot of cosmology—from time delays,” Gill says. “From a very far away quasar, you can get multiple images that have followed different light paths. Because they’ve followed different paths, they will get to you at different times. And that time delay depends on the geometry of the universe.”

    The Dark Energy Survey is one of several experiments using gravitational lensing to study dark matter and dark energy. DES scientists are using the Cerro Tololo Inter-American Observatory in Chile to perform a 5000-square-degree survey of the southern sky. Along with other measurements, DES is searching for weak lensing and cosmic shear effects of dark matter on distant objects.

    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

    The Large Synoptic Survey Telescope, currently under construction in Chile, will also assess how dark matter is distributed in the universe by looking for gravitational lenses, among other things.

    “The LSST will see first light in the next couple of years,” Amon says. “As this telescope charts the southern sky every few nights, it’s going to bombard us with data—literally too much to handle—so a lot of the work right now is building pipelines that can analyze it.”

    Astronomers expect LSST to find 100 times more galaxy-scale strong gravitational lens systems than are currently known.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    “The ongoing lensing surveys—that is, the Kilo-Degree Survey, Hyper Suprime-Cam and Dark Energy Survey—are doing high-precision and high-quality analyses, but they are really training grounds compared to what we will be able to do with LSST,” Amon says. “We are stepping up from measuring the shapes of tens of millions of galaxies to a billion galaxies, building the largest, deepest map of the Southern sky over 10 years.”

    Surprisingly, these enormous studies of cosmic distortions may bring the make-up of our universe into focus.

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 1:50 pm on October 18, 2018 Permalink | Reply
    Tags: , , , , Dark Energy, , , ,   

    From Symmetry: “Five mysteries the Standard Model can’t explain” 

    Symmetry Mag
    From Symmetry

    10/18/18
    Oscar Miyamoto Gomez

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.


    Standard Model of Particle Physics from Symmetry Magazine

    Our best model of particle physics explains only about 5 percent of the universe.

    The Standard Model is a thing of beauty. It is the most rigorous theory of particle physics, incredibly precise and accurate in its predictions. It mathematically lays out the 17 building blocks of nature: six quarks, six leptons, four force-carrier particles, and the Higgs boson. These are ruled by the electromagnetic, weak and strong forces.

    “As for the question ‘What are we?’ the Standard Model has the answer,” says Saúl Ramos, a researcher at the National Autonomous University of Mexico (UNAM). “It tells us that every object in the universe is not independent, and that every particle is there for a reason.”

    For the past 50 years such a system has allowed scientists to incorporate particle physics into a single equation that explains most of what we can see in the world around us.

    Despite its great predictive power, however, the Standard Model fails to answer five crucial questions, which is why particle physicists know their work is far from done.

    1
    Illustration by Sandbox Studio, Chicago with Ana Kova

    1. Why do neutrinos have mass?

    Three of the Standard Model’s particles are different types of neutrinos. The Standard Model predicts that, like photons, neutrinos should have no mass.

    However, scientists have found that the three neutrinos oscillate, or transform into one another, as they move. This feat is only possible because neutrinos are not massless after all.

    “If we use the theories that we have today, we get the wrong answer,” says André de Gouvêa, a professor at Northwestern University.

    The Standard Model got neutrinos wrong, but it remains to be seen just how wrong. After all, the masses neutrinos have are quite small.

    Is that all the Standard Model missed, or is there more that we don’t know about neutrinos? Some experimental results have suggested, for example, that there might be a fourth type of neutrino called a sterile neutrino that we have yet to discover.

    2
    Illustration by Sandbox Studio, Chicago with Ana Kova

    2. What is dark matter?

    Scientists realized they were missing something when they noticed that galaxies were spinning much faster than they should be, based on the gravitational pull of their visible matter. They were spinning so fast that they should have torn themselves apart. Something we can’t see, which scientists have dubbed “dark matter,” must be giving additional mass—and hence gravitional pull—to these galaxies.

    Dark matter is thought to make up 27 percent of the contents of the universe. But it is not included in the Standard Model.

    Scientists are looking for ways to study this mysterious matter and identify its building blocks. If scientists could show that dark matter interacts in some way with normal matter, “we still would need a new model, but it would mean that new model and the Standard Model are connected,” says Andrea Albert, a researcher at the US Department of Energy’s SLAC National Laboratory who studies dark matter, among other things, at the High-Altitude Water Cherenkov Observatory in Mexico. “That would be a huge game changer.”

    HAWC High Altitude Cherenkov Experiment, located on the flanks of the Sierra Negra volcano in the Mexican state of Puebla at an altitude of 4100 meters(13,500ft), at WikiMiniAtlas 18°59′41″N 97°18′30.6″W. searches for cosmic rays

    3
    Illustration by Sandbox Studio, Chicago with Ana Kova

    3. Why is there so much matter in the universe?

    Whenever a particle of matter comes into being—for example, in a particle collision in the Large Hadron Collider or in the decay of another particle—normally its antimatter counterpart comes along for the ride. When equal matter and antimatter particles meet, they annihilate one another.

    Scientists suppose that when the universe was formed in the Big Bang, matter and antimatter should have been produced in equal parts. However, some mechanism kept the matter and antimatter from their usual pattern of total destruction, and the universe around us is dominated by matter.

    The Standard Model cannot explain the imbalance. Many different experiments are studying matter and antimatter in search of clues as to what tipped the scales.

    4
    Illustration by Sandbox Studio, Chicago with Ana Kova

    4. Why is the expansion of the universe accelerating?

    Before scientists were able to measure the expansion of our universe, they guessed that it had started out quickly after the Big Bang and then, over time, had begun to slow. So it came as a shock that, not only was the universe’s expansion not slowing down—it was actually speeding up.

    The latest measurements by the Hubble Space Telescope and the European Space Agency observatory Gaia indicate that galaxies are moving away from us at 45 miles per second. That speed multiplies for each additional megaparsec, a distance of 3.2 million light years, relative to our position.

    This rate is believed to come from an unexplained property of space-time called dark energy, which is pushing the universe apart. It is thought to make up around 68 percent of the energy in the universe. “That is something very fundamental that nobody could have anticipated just by looking at the Standard Model,” de Gouvêa says.

    5
    Illustration by Sandbox Studio, Chicago with Ana Kova

    5. Is there a particle associated with the force of gravity?

    The Standard Model was not designed to explain gravity. This fourth and weakest force of nature does not seem to have any impact on the subatomic interactions the Standard Model explains.

    But theoretical physicists think a subatomic particle called a graviton might transmit gravity the same way particles called photons carry the electromagnetic force.

    “After the existence of gravitational waves was confirmed by LIGO, we now ask: What is the smallest gravitational wave possible? This is pretty much like asking what a graviton is,” says Alberto Güijosa, a professor at the Institute of Nuclear Sciences at UNAM.

    More to explore

    These five mysteries are the big questions of physics in the 21st century, Ramos says. Yet, there are even more fundamental enigmas, he says: What is the source of space-time geometry? Where do particles get their spin? Why is the strong force so strong while the weak force is so weak?

    There’s much left to explore, Güijosa says. “Even if we end up with a final and perfect theory of everything in our hands, we would still perform experiments in different situations in order to push its limits.”

    “It is a very classic example of the scientific method in action,” Albert says. “With each answer come more questions; nothing is ever done.”

    See the full article here .


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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:16 am on September 14, 2018 Permalink | Reply
    Tags: , , , , Dark Energy, , Dark matter clusters could reveal nature of dark energy,   

    From Horizon The EU Research and Innovation Magazine: “Dark matter clusters could reveal nature of dark energy” 

    1

    From Horizon The EU Research and Innovation Magazine

    10 September 2018
    Jon Cartwright

    1
    Gravitational lensing in galaxy clusters such as Abell 370 are helping scientists to measure the dark matter distribution. Image credit – NASA, ESA, the Hubble SM4 ERO Team and ST-ECF

    Scientists are hoping to understand one of the most enduring mysteries in cosmology by simulating its effect on the clustering of galaxies.

    That mystery is dark energy – the phenomenon that scientists hypothesise is causing the universe to expand at an ever-faster rate. No-one knows anything about dark energy, except that it could be, somehow, blowing pretty much everything apart.

    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

    Meanwhile, dark energy has an equally shady cousin – dark matter.

    Dark Matter Research

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LUX Dark matter Experiment at SURF, Lead, SD, USA

    ADMX Axion Dark Matter Experiment, U Uashington

    This invisible substance appears to have been clustering around galaxies, and preventing them from spinning themselves apart, by lending them an extra gravitational pull.

    Such a clustering effect is in competition with dark energy’s accelerating expansion. Yet studying the precise nature of this competition might shed some light on dark energy.

    ‘Many dark energy models are already ruled out with current data,’ said Dr Alexander Mead, a cosmologist at the University of British Columbia in Vancouver, Canada, who is working on a project called Halo modelling. ‘Hopefully in future we can rule more out.’

    Gravitational lensing

    Currently, the only way dark matter can be observed is by looking for the effects of its gravitational pull on other matter and light. The intense gravitational field it produces can cause light to distort and bend over large distances – an effect known as gravitational lensing.

    By mapping the dark matter ​in distant parts of the cosmos, scientists can work out how much dark matter clustering there is – and in principle how that clustering is being affected by dark energy.

    The link between gravitational lensing and dark matter clustering is not straightforward, however. To interpret the data from telescopes, scientists must refer to detailed cosmological models – mathematical representations of complex systems.

    Dr Mead is developing a clustering model that he hopes will have enough accuracy to distinguish between different dark-energy hypotheses.

    ‘An analogy I like a lot is with turbulence. In turbulent fluid flow you can talk about currents and eddies, which are nice words, but the reality of how fluid in a pipe goes from flowing calmly to flowing in a turbulent fashion is extremely complicated.’

    _________________________________________

    ‘If dark energy turns out to be a dynamical phenomenon this will have a profound implication not only on cosmology, but on our understanding of fundamental physics.’

    Dr Pier Stefano Corasaniti, Paris Observatory, France
    _________________________________________

    Fifth force

    One of the more exotic theories is that dark energy is the result of a hitherto undetected fifth force, in addition to nature’s four known forces – gravity, electromagnetism, and the strong and weak nuclear forces inside atoms.

    A more common hypothesis for dark energy, however, is known as the cosmological constant, which was put forward by Albert Einstein as part of his general theory of relativity. It is often believed to describe an all-pervading sea of virtual particles that are continually popping into and out of existence throughout the universe.

    One way to rule out the cosmological constant hypothesis, of course, is to prove that dark energy is not constant at all. This is the goal of Dr Pier Stefano Corasaniti of the Paris Observatory in France, who – in a project called EDECS – is approaching dark-matter clustering from a different direction.

    Instead of attempting to model clustering from gravitational lensing data, he is beginning specifically with a dynamical – that is, not constant – hypothesis of dark energy, and trying to predict how dark matter would cluster if this was the case.

    Pushing the limits

    There are, in principle, infinite ways dark energy can vary in space and time, although many theories have already been ruled out by existing observations. Dr Corasaniti is focussing his simulations on types of dynamical dark energy that push at the edges of these observational limits, paving the way for tests with future experiments.

    The simulations, which trace the evolution of numerous, ‘N-body’ dark matter particles, require supercomputers running for long periods of time, processing several petabytes (one thousand million million bytes) of data.

    ‘We have run among the largest cosmological N-body simulations ever realised,’ Dr Corasaniti said.

    Dr Corasaniti’s simulations predict that the way dark energy evolves over time ought to affect dark matter clustering. This, in turn, alters the efficiency with which galaxies form in ways that would not be the case with constant dark energy.

    The predictions his models are making could be tested with the help of forthcoming telescopes such as the Large Synoptic Survey Telescope in Chile and the Square Kilometre Array in Australia and South Africa, as well as by satellite missions such as Euclid (EUropean Cooperation for LIghtning Detection) and WFIRST (Wide Field Infrared Survey Telescope).

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    SKA Square Kilometer Array


    SKA South Africa

    ESA/Euclid spacecraft

    NASA/WFIRST

    ‘If dark energy turns out to be a dynamical phenomenon this will have a profound implication not only on cosmology, but on our understanding of fundamental physics,’ said Dr Corasaniti.

    See the full article here .


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  • richardmitnick 12:21 pm on September 13, 2018 Permalink | Reply
    Tags: , Dark Energy, Lambda leads the way, , , , The Cosmic Landscape   

    From Stanford University: “Lambda leads the way” 

    Stanford University Name
    From Stanford University

    September 13, 2018
    Ker Than

    1
    Most physicists think that dark energy, the cosmological constant, and lambda all refer to a repulsive energy infused in empty space itself. (Image credit: Eric Nyquist)

    The discovery of dark energy in the 1990s marked a time of reckoning for string theorists: Either their theory had to account for the newfound force that was pushing space-time apart or they had to admit that string theory may never describe the universe we actually live in. This story is part 4 of a five-part series.

    In 1998, astronomers hunting halfway across the universe for the ebbing light of exploded stars announced they had discovered evidence that the universe’s expansion is speeding up and not, as had been suspected since 1929, slowing down.

    The realization came as “a thunderbolt to physicists, something so shocking that we are still reeling from the impact,” Leonard Susskind wrote in his book The Cosmic Landscape.

    Leonard Susskind by Linda Cicero-Stanford News Service

    “Physicists everywhere were asking, ‘Is the experiment wrong?’” Renata Kallosh recalled.

    But with every passing year, new experiments confirmed the results: Expansion is accelerating, not slowing down. For those results to be true, an elusive force that physicists had come to refer to as “dark energy” must be real.

    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

    Einstein had predicted the existence of dark energy in 1917 when he applied his general theory of relativity to the structure of space-time. He needed a hypothetical force to prevent the universe from collapsing, so he invented a repulsive, space-filling energy that he called the cosmological constant, or lambda. When astronomers discovered in the 1920s that the universe is expanding, Einstein realized that lambda was no longer necessary and he scrapped the idea, calling it his “biggest blunder.”

    But Einstein may have been too hard on himself. Today, most physicists think that dark energy, the cosmological constant and lambda all refer to a repulsive energy infused in empty space itself. Quantum mechanics predicts that the spontaneous creation and annihilation of ghostly “virtual particles” generates an anti-gravitational force whose influence grows with the age and size of the universe.

    When astronomers were able to measure lambda experimentally, they found it had a positive but bewilderingly tiny value that was about a trillion trillion trillion trillion trillion trillion trillion trillion trillion trillion times weaker than theory predicted. The Nobel Prize-winning physicist Steven Weinberg called this humiliating mismatch between observation and theory “the bone in our throat.”

    Equally perplexing, lambda’s tiny value lay just within the narrow range able to support life. If it were much larger, the universe would expand too quickly for galaxies and stars to form; much smaller, and creation would collapse back into a point.

    “Theoretical physics was upside down because of this experimental discovery,” Kallosh said. “We had no explanation whatsoever.”

    The cosmological constant problem

    The first tentative steps toward resolving what came to be known as the “cosmological constant problem” were taken in 2000 by theorists Joseph Polchinski of the University of California, Santa Barbara, and Raphael Bousso, a Stanford postdoc and a former student of Stephen Hawking. The pair published a paper showing that string theory could give rise to an enormous number of unique vacuum states – vastly more than previously thought. “The vacuum state is what remains if you remove all of the particles from the universe,” Andrei Linde explained. “The properties of a vacuum determine what its particles will look like and what the physics of their interactions will be if it were populated.”

    _______________________________________
    “Theoretical physics was upside down because of this experimental discovery. We had no explanation whatsoever.”
    —Renata Kallosh
    Professor of Physics
    _______________________________________

    Each vacuum described, in essence, a potential universe with its own singular take on particles and forces. “It was already known that string theory had lots of solutions,” Susskind said, “but their paper showed that it could have a vast number, and among them could be solutions that had these rare traits like a very low cosmological constant.”

    But despite offering tantalizing hints of string theory universes that could accommodate dark energy, Polchinski and Bousso, who is now at the University of California, Berkeley, stopped short of actually finding one. “They had a correct but imprecise collection of arguments for this diversity,” Susskind said. “They had no real examples of it.”

    In search of de Sitter

    The first reasonably concrete example was discovered by theoretical physicist Eva Silverstein, a professor at the Stanford Institute for Theoretical Physics who was motivated by dark energy’s discovery to search for a mechanism that could create a so-called “de Sitter” solution to string theory. De Sitter solutions (named after the Dutch astronomer Willem de Sitter) represent expanding universes with a positive cosmological constant similar to our own. Silverstein wanted to know if a solution existed in string theory that was compatible with the universe that astronomers actually observe. If none could be found, then string theorists had been wasting their time building castles in the air.

    Up to that point, string theorists had focused on solutions for universes with a negative lambda called anti-de Sitter space-time. “De Sitter solutions are more complex, and until the discovery of dark energy, no one bothered,” Silverstein said. “Some even argued that de Sitter solutions weren’t possible in string theory, and it remains a complicated subject. But these ‘no go’ arguments did not consider the leading contributions to the potential energy in string theory.”

    In 2001, Silverstein published a paper in which she proposed a mechanism for combining various ingredients from string theory – extra dimensions, orientifolds, fluxes and so on – in specific ways to create a de Sitter model. She also predicted that any de Sitter solutions would need to contain certain features. She argued, for example, that the path to positive lambda was indirect and would require making a negative contribution first. “One thing I pointed out early on is that negative contributions to the potential energy, in the right place to produce a local dip in it, would be needed,” Silverstein said, “and that this role could be played by orientifolds, which are defects in string theory’s extra dimensions that have a controlled amount of negative energy.”

    3
    Shamit Kachru, Renata Kallosh and Andrei Linde are three of the four authors of an influential paper that came to be known as KKLT. The paper helped lay the groundwork for the String Theory Landscape. (Image credit: L.A. Cicero)

    KKLT

    Early in 2003, Kallosh and Linde received an email from Shamit Kachru, who had been visiting the string theorist Sandip Trivedi in India. The quartet of physicists was engaged in a long-distance brainstorming session and Kachru’s message contained the kernel of an idea that had come to him during a flight layover in New Delhi.

    When Kallosh plotted data that Kachru had sent, up popped on her computer a chart with the same potential energy dip that Silverstein had predicted. However, this dip had been generated using different string theory ingredients and assumptions. “I knew we were onto something then,” Kallosh said.

    Later that year, the four of them published their results in a famous paper that would come to be known simply as KKLT (after the authors’ last initials). KKLT described a class of de Sitter solutions that incorporated a certain symmetry, called supersymmetry, that many physicists were expecting to see confirmed in particle collider experiments.

    “KKLT was a very important paper,” said particle physicist Savas Dimopoulos, the Hamamoto Family Professor in the School of Humanities and Sciences. “We don’t see supersymmetric particles in nature, so if symmetry did exist in the early universe, it’s been broken. What KKLT did was point out a breaking mechanism.”

    KKLT was also important for psychological reasons. “It was written by members from different parts of the physics community,” Kachru said. “Renata was a supergravity person, Andrei was an inflation person, and Sandip and I were more mathematical string theorists. All of us were saying that this kind of solution of string theory, which allows accelerated expansion due to dark energy, is something to take seriously.”

    For these reason, KKLT’s mathematical model, or “construction,” grabbed physicists’ attention in a way that earlier ones had not. Among those affected were Michael Douglas and Frederik Denef, both at Rutgers University at the time, who used the KKLT construction to famously calculate that there might exist as many as 10500 unique “vacua,” or possible universes, with a small cosmological constant. (For perspective, the total number of particles in the observable universe is estimated to be about 1090.)

    Around the same time, Susskind published a paper of his own expanding upon his colleagues’ findings. “I was more of a cheerleader than anything else,” Susskind said. “My paper was really just saying, ‘Hey guys, are you paying attention to this? This is happening.’”

    Susskind is also credited with naming the emerging concept within string theory of countless hypothetical universes with varying properties: He called it the “anthropic Landscape of string theory,” or the “String Theory Landscape” for short. “The Landscape doesn’t refer to a real place,” Susskind said. “It’s a scientific term borrowed from biology and physics that refers to an energy landscape with lots of hills and valleys. In string theory, the Landscape is incredibly rich, and our universe lies in one of the rare, habitable, low-lying valleys.”

    _______________________________________

    “In string theory, the Landscape is incredibly rich, and our universe lies in one of the rare, habitable, low-lying valleys.”
    —Leonard Susskind, Professor of Physics
    _______________________________________

    Susskind also reminded his fellow physicists that they already knew of a mechanism that could generate the tremendous diversity of universes predicted by string theory. This “natural candidate” had been pointed out by Bousso and Polchinski years earlier.

    Recalling his collaboration with Bousso in 2000, Polchinski, who died in February 2018, wrote in his memoir: “But when Bousso came back a few months later … he had added an important part of the story, the cosmology that allowed the theory to explore all these states. It was just Linde’s eternal chaotic inflation. … I had always assumed that such a thing would not be part of string theory, but in fact it arose quite naturally.”

    A Rube Goldberg construction

    If the measure of a theory’s beauty is the ratio of how many things it explains to how many assumptions it makes to explain them, then the constructions by Silverstein and KKLT are not pretty. Their authors rummaged through string theory’s pantry for exotic ingredients and combined them in wildly creative ways to concoct their imaginary universes. The KKLT construction in particular, Susskind said, was made up of “jury-rigged, Rube Goldberg contraptions” – a reference to the American inventor famous for his cartoon sketches of gadgets that performed simple tasks in convoluted ways.

    But the contrived nature of the de Sitter constructions mattered less to theorists than the fact that they existed at all. In a theory where infinite solutions are possible, Susskind argued, “simplicity and elegance are not considerations.” In all their long years of searching, KKLT and its kin were the clearest signs physicists had ever found that string theory could produce universes roughly resembling our own. The constructions the Stanford theorists produced gave powerful support to physicists’ hope that a mathematical version of our cosmos lay hidden somewhere within string theory’s labyrinthine equations and infinite solutions, and that – with ingenuity, luck and perhaps a late-night revelation or two – it might one day be found.

    See the full article here .


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    Leland and Jane Stanford founded the University to “promote the public welfare by exercising an influence on behalf of humanity and civilization.” Stanford opened its doors in 1891, and more than a century later, it remains dedicated to finding solutions to the great challenges of the day and to preparing our students for leadership in today’s complex world. Stanford, is an American private research university located in Stanford, California on an 8,180-acre (3,310 ha) campus near Palo Alto. Since 1952, more than 54 Stanford faculty, staff, and alumni have won the Nobel Prize, including 19 current faculty members

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  • richardmitnick 8:15 am on September 5, 2018 Permalink | Reply
    Tags: A Type IV civilization would be undetectable to us, A Type V master race that would function like gods able to harness energy not only from this universe but all universes in all dimensions, , At 100000 times the energy usage we have now we’d have access to 10¹⁷ watts of energy as a Type I civilization, , , Dark Energy, Dyson ring and Dyson bubble, , Micro-scale developed by John D. Barrow, , Physicist Michio Kaku, The Kardashev scale designed by astrophysicist Nikolai Kardashev, The trick for a galactic species would be the constraints of the laws of physics, These feats are very sci-fi and as far as we know impossible to accomplish. But then again we’re a lowly Type 0 civilization with no idea what may lie ahead, To colonize all the stars we could use self-replicating robots that would assemble and maintain the Dyson swarms, We’re a Type Zero Civilization   

    From Medium: “We’re a Type Zero Civilization” 

    From Medium

    Aug 11, 2018
    Updated 9.5.18
    Ella Alderson

    When will we move up the scale?

    1
    Image: Juanmrgt/iStock/Getty Images Plus

    The Kardashev scale, designed by astrophysicist Nikolai Kardashev, was created to assess how advanced a civilization is by taking into consideration multiple factors, including population growth, technology, and energy demands. The idea is that the more advanced the people are, the higher and more complex their energy usage will be. When we first appeared on Earth 200,000 years ago, for example, our species was few in number, and the extent of our energy source was, really, just fire. We now number in the billions and use a combination of wind, solar, and nuclear energy sources, though our main energy supply comes from fossil fuels (it really seems like we just moved on to burning bigger and badder things). The International Energy Agency estimates that each year our societies use an estimated 17.37 terrawatt-hours.

    All of this may sound fairly advanced — we’ve come a long way from just using logs to fuel our everyday lives. Yet in reality, we’re really quite primitive compared to where we could be. We still get the majority of our energy from dead plants and animals, a source that will eventually run out sooner or later, and which is helping destroy our planet in the process.

    So where do we place on the Kardashev scale? We’re a zero: 0.72, to be more exact. Here’s what we need to move forward.

    Type I

    To become a Type I civilization we would have to harness all the available energy of our home planet at 100% efficiency. This means capturing the energy of every wave, every beam of sunlight, and every bit of fossil fuel we can dig up. To do that without rendering the entire planet uninhabitable, we’d have to use nuclear fusion. And to create all the energy we need via this method, we would require 280 k/s of hydrogen and helium every second, or 89 billion grams of hydrogen per year. You can gather more than that from one square km of ocean water.

    With this ability to harness all energy from Earth also comes the ability to control all of the planet’s natural forces, including volcanoes, geothermal vents, earthquakes, and climate. At 100,000 times the energy usage we have now, we’d have access to 10¹⁷ watts of energy as a Type I civilization. Consider, for example, the ability to control a hurricane. One such storm can release the power of hundreds of hydrogen bombs.

    While controlling the weather may sound very fantastical, physicist Michio Kaku theorizes that we’ll reach Type I status in the next 100–200 years, as we continue to grow in population at about 3% per year.

    2
    Dyson ring concept drawing (Source: Vedexent/Wikipedia)
    3
    Dyson bubble concept drawing (Source: PNG Crusade Bot/Wikipedia)/CC BY 2.5

    After we’ve been able to harness all the energy from our home planet, we’ll move on to harnessing all the energy of our home star, the sun. One way of doing this is to build a Dyson swarm around the star, or a group of panels capable of reflecting light into small solar power plants which could then send those light beams to Earth for our use. Similar to the work of controlling the forces here on Earth, we’d be able to control the star as well, including the manipulation of solar flares. Another way to get enough energy for a Type II civilization would be to build a fusion reactor on a huge scale or to use a reactor to essentially drain the hydrogen from a nearby gas giant, like Jupiter.

    At this point we’re a few thousand years into the future and using 10²⁶ watts of energy. A stellar civilization capable of gathering energy on this scale has become immune to extinction.

    Type III

    We’ve gone from controlling all the energy of our home planet to our home star and, now, our galaxy. Take the Dyson swarm proposed above and extend it to cover all 100 billion stars of the Milky Way. A civilization this advanced, and with access to this many resources, would truly be a master race, having at their disposal 10³⁶ watts of energy. Hundreds of thousands, even millions of years of evolution would mean that we as a race would look very different, both biologically and in terms of merging with our technology in becoming cyborgs or even fully robotic.

    To colonize all the stars we could use self-replicating robots that would assemble and maintain the Dyson swarms, though it’s likely we’ll have found a new energy source by then. This could include tapping into the energy of the black hole at the center of the Milky Way, or even using gamma ray bursts. Another possibility, though they have been yet undetected, would be to find a white hole and to use the energy that emanates from it.

    The trick for a galactic species would be the constraints of the laws of physics — how can they be united when their colonies are light years away? They’d have to find a way to move at the speed of light or, even better, create wormholes to other locations.

    Kardashev ended the scale here because he didn’t believe it could go any further, stating that any civilizations beyond Type III would be too advanced to even fathom. But other astronomers have since extended the scale to include Type IV and Type V.

    Type IV and V

    A Type IV civilization would be undetectable to us. It would be able to harness the entire energy of the universe and move across all of space, appearing as nothing more than a work of nature. Some speculate that giant voids in space, like the one 1.8 billion light years across and missing 90% of its galaxies, could be proof of a civilization making use of the universe. But a civilization this advanced might not even harness energy as we know it anymore, choosing instead to move into more exotic substances, like dark energy. They might also live inside black holes, controlling 10⁴⁶ watts of energy. These feats are very sci-fi and, as far as we know, impossible to accomplish. But then again we’re a lowly Type 0 civilization with no idea what may lie ahead.

    It gets even more fantastical when one considers a Type V master race that would function like gods, able to harness energy not only from this universe, but all universes in all dimensions. Its energy usage and access to knowledge would be incomprehensible.

    Micro-scale

    The micro-dimensional mastery extension to the Kardashev scale was proposed by John D. Barrow, a scientist who decided to take civilization ranking in the opposite direction, choosing instead to base his scale on how small a people’s control could reach. This scale is outlined differently:

    Type I-minus: controlling matter at the observable level, that is, being to manipulate things we can see and touch.

    Type II-minus: controlling genes

    Type III-minus: controlling molecules

    Type IV-minus: controlling atoms

    Type V-minus: controlling protons

    Type VI-minus: controlling elementary particles, like quarks

    Type Omega-minus: controlling fundamental elements of spacetime

    Whether using the original or micro version, the beautiful thing about the Kardashev scale is that it’s not just full of fascinating and alien concepts; it’s also a blueprint for where we could go if our species could just make it the next 100 years. Will the human race emerge from our planet and thrive in the universe just as we emerged from Africa and grew to thrive around the world?

    See the full article here .

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  • richardmitnick 5:17 pm on August 20, 2018 Permalink | Reply
    Tags: , , , , , Dark Energy, , , , , The scientific theories battling to explain the universe   

    From CNN: “The scientific theories battling to explain the universe” 

    1
    From CNN

    August 17, 2018
    1
    FNAL’s Don Lincoln

    In human history, there have been many interesting and epic feuds — the Hatfields and McCoys, Bette Davis and Joan Crawford, or the Notorious B.I.G and Tupac. Many of us love to read in tabloids or history books about the salacious details of how the bad blood came to be.

    Just like these human characters, scientific theories can also fall into disagreement, causing just as much drama in the science world.

    Recently, a group of scientists claimed to have found a fatal tension between two of the scientific community’s most mind-blowing theories: superstrings and dark energy. If the authors are correct, one of the two theories is in trouble.

    Superstring theory is a candidate theory of everything, with the operative word being “candidate,” meaning it is not yet accepted by the scientific community. It tries to explain all observed phenomena of the universe with a single principle. At its core, it predicts that the smallest building blocks of the cosmos aren’t the familiar atoms and protons, neutrons, and electrons; nor are the smallest building blocks the even-smaller quarks and lepton that my colleagues and I have discovered. Instead, superstring theory suggests that the very smallest building blocks of all are tiny and vibrating “strings.”

    These strings can vibrate in different ways — essentially different notes — with each note looking like one of the known subatomic particles. Waxing slightly poetic, superstring theory explains the universe as a vast and cosmic symphony.

    The other popular theory, called dark energy, is quite different. Astronomers have long known that the universe is expanding. For decades, we thought we understood that, because gravity is an attractive force, this expansion would slow over the lifetime of the universe. It was therefore a surprise when, in 1998, astronomers discovered that not only was the expansion of the universe not slowing down — it was speeding up.

    To explain this observation, astronomers added a type of energy — called dark energy — to Einstein’s equations describing the behavior of gravity. Dark energy is an energy field that permeates the entire universe. And, because the expansion of the universe is accelerating, dark energy must exist and it must be positive. The reason we know that is simple. If the dark energy didn’t exist or was negative, the expansion of the universe would be slowing down.

    So, what is it about these two theories that has caused such a conflict?

    In a nutshell, it’s hard to make a superstring theory with positive energy and yet the accelerating expansion of the universe demands it. If one theory is completely accurate it means that a key aspect of the other is wrong. And, on the face of it, things look bad for superstring theory. This is because while dark energy is still a theory, the accelerating expansion of the universe is not. Thus, dark energy is probably true, while superstring theory still remains only a conjecture.

    But there’s a reason that scientists aren’t rushing to media platforms to spread the news that superstring theory has been disproved.

    It’s because superstring theory is fiendishly complex. Aside from the prediction of subatomic vibrating strings, it also predicts that there are more dimensions of space than our familiar three. In fact, the theory predicts that there are nine in total — 10 if you include time. You’d think that this would be a fatal flaw of the theory, but these additional dimensions are thought to be invisibly small.

    Since these extra dimensions (if they exist) are smaller than our best instrumentation can detect, we don’t know what their shapes are, and scientists must consider all possibilities. But there are a lot of possibilities. In fact, there are more configurations than there are atoms in a million universes just like ours. It’s a crazy big number.

    So, what conclusion can we draw?

    With so many possible configurations, it would seem that superstring theory could predict just about anything, yet the scientists who pointed out the theories’ disagreement are making the bold claim that none of these configurations result in the existence of a positive and constant energy (aka, the theory of dark energy).

    And all the data recorded so far have made scientists feel relatively confident that dark energy not only exists, but is also both positive and nearly constant, making it seem likely that, if only one of these theories can be true, it’s dark energy for the win. Still, it’s premature to make any conclusions about the superstrings. It’s possible that scientists are not right about the nature of dark energy and they are using powerful instruments like the Dark Energy Survey to refine their measurements.

    The bottom line is that physicists are going to have to take this new idea seriously. It’s not quite a WWE cage match, but it’s going to be fun to watch these theories fight it out.

    See the full article here .

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  • richardmitnick 9:20 am on August 14, 2018 Permalink | Reply
    Tags: , , , , Dark Energy, DECam at the Blanco telescope, , ,   

    From Fermi National Accelerator Lab: “Mapping the universe in 3-D: Fermilab contributes to the Dark Energy Spectroscopic Instrument” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    August 13, 2018
    Jordan Rice

    In 1998, scientists discovered that the universe’s expansion is accelerating. Physicists don’t know how or why the universe is accelerating outward, but they gave the mysterious force behind this phenomenon a name: dark energy.

    Scientists know a great deal about the effects of dark energy, but they don’t know what it is. Cosmologists approximate that 68 percent of the universe’s total energy must be made of the stuff. One way to get a better handle on dark energy and its effects is to create detailed maps of the universe, plotting its expansion. Scientists, engineers and technicians are currently building the Dark Energy Spectroscopic Instrument, or DESI, to do just that.

    DESI will help create the largest 3-D map of galaxies to date, one that will span a third of the entire sky, stretch back 11 billion light-years, and record approximately 35 million galaxies and quasars.

    LBNL/DESI Dark Energy Spectroscopic Instrument for the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, Ariz, USA

    It will measure the spectra of light emanating from galaxies to determine their distances from Earth. Other surveys have created maps that locate galaxies’ lateral positions in the sky, but scientists using DESI will be able to take more precise measurements of their distance from us, creating high-resolution, 3-D maps.

    DESI is currently being installed at the Mayall 4-Meter Telescope at Kitt Peak National Observatory in Tucson, Arizona. Once installation is complete, it will run for five years.


    Mayall telescope interior

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    The DESI project is managed at the U.S. Department of Energy’s Lawrence Berkley National Laboratory (Berkeley Lab) in California, and the U.S. DOE’s Fermilab is contributing to the ambitious effort with specialty systems for collecting and analyzing the galactic light.

    “The collaborative effort to build DESI is an example of how science draws on expertise from multiple institutions toward a common goal, one that humanity is always moving toward: understanding the fundamentals of our universe,” said Berkeley Lab’s Michael Levi, DESI project director.

    One of the largest pieces Fermilab is contributing is the DESI corrector barrel. Fermilab collaborators designed, built and tested the barrel, which is roughly the size of a telephone booth. It plays a critical role: holding DESI’s six giant lenses in perfect alignment. To ensure spot-on precision, the barrel is designed so that the lenses are accurately positioned to within the width of a human hair. Collaborators at University College London recently finished installing the lenses in the barrel, and the whole ensemble will soon be lifted onto the telescope.

    “The barrel needs to be extremely precise,” said Gaston Gutierrez, Fermilab scientist managing the corrector barrel construction. “If there is any misalignment of the lenses, the error will be highly magnified, and the images will be blurred.”

    Fermilab also designed and built large structures that will support a cage surrounding the barrel. These were delivered to the Mayall in April, and their installation has begun.

    To convert the light from galaxies into digital information for analysis, DESI will use high-tech versions of the familiar components in typical hand-held cameras — charge coupled devices, or CCDs. Fermilab packaged and tested these sensitive devices before delivering them to Tucson.

    The job of collecting the galactic light belongs to DESI’s 5,000 fiber-optic cables, which will help record the spectra of each galaxy. For roughly 20 minutes, each one of the fibers will aim at a single galaxy and record its spectrum. Then the telescope will move to a new position in the sky, and all 5,000 fibers will be moved to point at new galaxies. Fermilab is developing the software that tells the instrument where in the sky to point those fibers. Without this automation, DESI would not be able to measure the millions of objects it plans to study.

    To fully understand the spectra that DESI will collect, scientists need to keep detailed information about the instrument and telescope status. In addition to the DESI barrel, Fermilab is creating an electronic logbook and a database to store the instrument control systems operational data. These will be used to keep track of the information on the systems required to operate DESI, such as how to read the CCDs, direct the telescope and ensure the apparatus for recording the spectra is working properly.

    2
    Fermilab is developing the software that tells DESI where in the sky to point its 5,000 fiber-optic cables, a fraction of which are shown here. Photo: Lawrence Berkeley National Laboratory

    DESI’s predecessor, called the Dark Energy Camera (DECam), is currently mounted on Chile’s Victor Blanco telescope, the sister telescope of the Mayall.

    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

    In 2012, researchers and technicians completed DECam’s construction for use in the five-year Dark Energy Survey, hosted by Fermilab. The same scientists who designed DECam are bringing their expertise and knowledge to DESI.

    The Dark Energy Survey and DECam serve as stepping stones to DESI. The DESI project will improve our understanding of the nature of dark energy by using the Dark Energy Survey’s results as a baseline. DECam’s data will also help DESI find the galaxies so the latter can take more precise spectra measurements to determine the galaxy’s redshift: The farther away a galaxy is from us, the more its light is stretched and shifted in the direction of redder (longer) wavelengths, by the expansion of the universe.

    “For the Dark Energy Survey, we are just taking images, but for DESI we are pointing fibers at galaxies and measuring spectra,” said Fermilab’s Brenna Flaugher, project manager of DES and one of the leading scientists for DESI. “So, it is sort of the next level of resolution in redshift.”

    DESI’s final pieces are planned to be installed by April 2019, with first light planned for May of that year.

    “DESI will help us understand the nature of dark energy,” Flaugher said. “And that will lead to a better understanding of the evolution of our universe.”

    Work on DESI is supported by DOE’s Office of Science along with several international partners.

    See the full article here .


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    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.


    FNAL/MINERvA

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    Dark Energy Camera [DECam], built at FNAL

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  • richardmitnick 12:47 pm on August 10, 2018 Permalink | Reply
    Tags: , , , , , Dark Energy, Dark Energy Survey Reveals Stellar Streams,   

    From AAS NOVA: “Dark Energy Survey Reveals Stellar Streams” 

    AASNOVA

    From AAS NOVA

    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

    Over billions of years, globular clusters and dwarf galaxies orbiting the Milky Way have been torn apart and stretched out by tidal forces. The disruption of these ancient stellar populations results in narrow trails of stars called stellar streams. These stellar streams can help us understand how the Milky Way halo was constructed and what our galaxy’s dark matter distribution is like — but how do we find them?

    1
    Along with cosmological simulations, like the Millennium Simulation pictured here, stellar streams can help us understand how dark matter is distributed in galaxies like the Milky Way. [Max Planck Institute for Astrophysics]

    On the Trail of Tidal Streams

    Understanding how our galaxy came to look the way it does is no easy task. Trying to discern the structure and formation history of the outer reaches of the Milky Way from our vantage point on Earth is a bit like trying to see the forest for the trees — while also trying to learn how old the forest is and where the trees came from!

    One way to do so is to search for the stellar streams that form when globular clusters and dwarf galaxies are disrupted and torn apart by our galaxy. Stellar streams tend to be faint, diffuse, and obscured by foreground stars, which makes them tricky to observe. Luckily, recent data releases from the Dark Energy Survey are perfectly suited to the task.

    Dark Energy Survey Brings Faint Stars to Light

    Nora Shipp (University of Chicago) and collaborators analyzed three years of data from the Dark Energy Survey in search of these stellar streams. The Dark Energy Survey is well-suited for stellar-stream hunts since it covers a wide area (5,000 square degrees of the southern sky) and can observe objects as faint as 26th magnitude.

    Shipp and collaborators use a matched-filter technique to pinpoint the old, low-metallicity stars that belong to stellar streams. This method uses the modeled properties of stars of a certain age — synthetic isochrones — to identify stars within a background stellar stream with minimal contamination from foreground stars.

    Using their matched filters, the authors found 15 stellar streams, 11 of which had never been seen before. They then estimated the age, metallicity, and distance modulus for each stream — all critical to understanding how the individual streams fit into the larger picture of galactic structure.

    3
    A closer look at the stellar streams in the first quadrant of the surveyed area. Top: Density map of stars with a distance modulus of 15.4. Bottom: Stars with a distance modulus of 17.5. [Adapted from Shipp et al. 2018]

    Reconstructing the Galactic Halo

    These 11 newly discovered stellar streams will greatly enhance our understanding of the history of the galactic halo. Spectroscopy can help clarify the ages of these structures, while kinematic studies can help us understand if and how these structures are associated.

    Future work may also help us discern the origin of the streams; the stark dichotomy in the mass-to-light ratios of the stellar streams discovered in this work hints that it may be possible to link some streams to globular clusters and others to dwarf galaxies. Look for this and more exciting results from galactic archaeologists in the future!

    Citation

    N. Shipp et al 2018 ApJ 862 114. doi:10.3847/1538-4357/aacdab

    Related journal articles
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    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    AAS Mission and Vision Statement

    The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

    The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
    The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
    The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
    The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
    The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

    Adopted June 7, 2009

     
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