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  • richardmitnick 9:12 am on May 12, 2019 Permalink | Reply
    Tags: , , , , Dark Energy, , Dark nature is observable only indirectly by its effects   

    From COSMOS Magazine: “Multiple measurements close in on dark energy” 

    Cosmos Magazine bloc

    From COSMOS Magazine

    06 May 2019
    Andrew Masterson

    Cerro Tololo Inter-American Observatory, located on Cerro Tololo in the Coquimbo Region of northern Chile, Altitude 2,207 m (7,241 ft)

    An extensive analysis of four different phenomena within the universe points the way to understanding the nature of dark energy, a collaboration between more than 100 scientists reveals.

    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

    Timeline of the Inflationary Universe WMAP

    The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our Universe. DES began searching the Southern skies on August 31, 2013.

    According to Einstein’s theory of General Relativity, gravity should lead to a slowing of the cosmic expansion. Yet, in 1998, two teams of astronomers studying distant supernovae made the remarkable discovery that the expansion of the universe is speeding up. To explain cosmic acceleration, cosmologists are faced with two possibilities: either 70% of the universe exists in an exotic form, now called dark energy, that exhibits a gravitational force opposite to the attractive gravity of ordinary matter, or General Relativity must be replaced by a new theory of gravity on cosmic scales.

    DES is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 400 scientists from over 25 institutions in the United States, Spain, the United Kingdom, Brazil, Germany, Switzerland, and Australia are working on the project. The collaboration built and is using an extremely sensitive 570-Megapixel digital camera, DECam, mounted on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory, high in the Chilean Andes, to carry out the project.

    Over six years (2013-2019), the DES collaboration used 758 nights of observation to carry out a deep, wide-area survey to record information from 300 million galaxies that are billions of light-years from Earth. The survey imaged 5000 square degrees of the southern sky in five optical filters to obtain detailed information about each galaxy. A fraction of the survey time is used to observe smaller patches of sky roughly once a week to discover and study thousands of supernovae and other astrophysical transients.

    Dark energy – the force that propels the acceleration of the expanding universe – is a mysterious thing. It’s nature, write telescope scientist Timothy Abbott from the Cerro Tololo Inter-American Observatory, in Chile, and colleagues, “is unknown, and understanding its properties and origin is one of the principal challenges in modern physics”.

    Indeed, there is a lot at stake. Current measurements indicate that dark energy can be smoothly incorporated into the theory of general relativity as a cosmological constant; but, the researchers note, those measurements are far from precise and incorporate a wide range of potential variations.

    “Any deviation from this interpretation in space or time would constitute a landmark discovery in fundamental physics,” they note.

    The heart of the problem, of course, is that dark nature is observable only indirectly, by its effects.

    These fall into two categories. First, it deforms galactic architectures through accelerating the expansion of the universe. Second, it suppresses growth in some parts of the cosmic structure.

    However, it is not the only force that can produce such results, and the danger thus always exists that what is assumed to be evidence of dark matter activity may in fact be something else altogether.

    Current approaches to measuring dark matter are problematic. All of them begin with the cosmic microwave background (CMB), the relic radiation that fills space, generated just 400,000 years after the Big Bang.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    At that point in the history of the universe the influence of dark matter was minimal. It increased significantly as spacetime expanded ever more and ever faster.

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    The second pillar for measuring it, thus, comprises observations of “low-redshift” phenomena – wavelengths stretched over vast distances, allowing calculations of conditions within the universe the past several billion years.

    Red shift and wave length shift-The Earliest Stars And Galaxies In The Universe Science at ESA

    Combining the two measurements and then extrapolating forwards to the present day, Abbott and colleagues note, “can be a powerful test of our models, but it requires precise, independent constraints from low-redshift experiments”.

    It follows, then, that any increase in the precision of low-redshift measurements will also increase the precision of dark energy calculations, reducing (or perhaps increasing) the chances that a previously undiscovered physics is in play in the universe.

    The researchers approach this challenge by invoking a combination of multiple observational probes for low-redshift phenomena – namely, those measuring Type Ia supernova light curves, fluctuations in the density of visible (or “baryonic”) matter, weak gravitational lensing, and galaxy clustering.

    To do this, they use the results of the Dark Energy Survey (DES), a collaboration of research institutions in the US, South America and Europe that studies observations made by the Victor M Blanco telescope in Chile, which is fitted with specialised instruments for dark energy detection.

    Presenting the first tranche of results from the survey, Abbott and colleagues reveal progress towards constraining the nature of dark energy.

    The DES findings, they report, absolutely – and independent of CMB-based research – rule out a universe in which dark energy doesn’t exist. They also report that the results suggest the universe is spatially flat, and derive a tighter constraint on the density of baryon matter.

    These results, they suggest, constrain the state of “of dark energy and its energy density in the Universe” … “to a precision that is almost a factor of three better than the 7 previous best single-experiment result from the CMB”.

    Further planned DES surveys, they conclude, will likely sharpen up knowledge of the impact of dark energy in the universe by orders of magnitude.

    The research is published in the journal Physical Review Letters.

    See the full article here .


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  • richardmitnick 3:43 pm on May 1, 2019 Permalink | Reply
    Tags: , , , , Dark Energy   

    From “Physics”: “Dark Energy Faces Multiple Probes” 

    Physics LogoAbout Physics

    Physics Logo 2

    From “Physics”

    May 1, 2019
    Nikhil Padmanabhan
    Department of Physics and Department of Astronomy
    Yale University

    The Dark Energy Survey has combined its analysis of four cosmological observables to constrain the properties of dark energy—paving the way for cosmological surveys that will run in the next decade.

    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

    1
    Figure 1: Area of the sky observed by the Dark Energy Survey in its 5-year mission. The different colors indicate different observation runs. SV: preliminary science verification run; Y1: year 1; Y2: year 2; SN fields: areas containing the supernovae used as standard candles to monitor the Universe’s expansion.

    One of the top goals in cosmology today is understanding the dark energy that is responsible for the accelerated expansion of the Universe. Is the dark energy consistent with the cosmological constant of general relativity—representing a constant energy density filling space homogenously? Or can we find deviations from general relativity on cosmological scales that suggest a more complex nature for gravity? Questions like these motivate the current and next generations of surveys that aim to map out ever larger volumes of the Universe, using a wide variety of probes to constrain the properties of dark energy. The Dark Energy Survey (DES) has now derived such constraints from the combined analysis of four canonical observables related to dark energy: supernovae, baryon acoustic oscillations, gravitational lensing, and galaxy clustering [1]. The resulting bounds confirm what we knew from previous studies, which focused on single probes. But the results indicate that this multiprobe approach could allow surveys in the 2020s to improve such constraints by orders of magnitude, possibly bringing us close to solving the dark energy puzzle.

    Measurements of dark energy traditionally come in two “flavors.” The first measures the geometric expansion of the Universe. It includes observations of supernovae and of baryon acoustic oscillations (BAO). Type Ia supernovae can be used as “standard candles”—their known brightness allows astronomers to estimate their distance. In the 1990s, measurements of the recession speed (or redshift) of supernovae as a function of distance led to the discovery that the expansion of the Universe was accelerating, upsetting predictions based on models of a matter-dominated Universe [2]. BAO are also related to spatial distances, but they serve instead as “standard rulers” that can calibrate cosmic lengths. BAO are fluctuations in the density of matter caused by acoustic waves in the primordial photon-baryon plasma of the early Universe. The length of the BAO standard rulers can be estimated from cosmic microwave background (CMB) measurements. By observing the angular size of the BAO rulers at different times, scientists can directly measure the geometric background expansion of the Universe.

    The second flavor of measurements focuses on dark energy’s effect on the growth rate of cosmic structures, both visible and dark. The accelerated expansion causes these structures to grow slower, as gravity has less time to pull in matter around over-dense regions. The growth suppression can be characterized by observing the distribution of matter. The DES traces the matter distribution through weak lensing—measurements of subtle, coherent distortions of the shapes of background galaxies due to the gravitational lensing of foreground matter. From such distortions, the distribution of foreground matter (which is mostly dark matter) can be inferred. The small magnitude of the weak-lensing effect makes it challenging to measure and susceptible to systematic observational errors, but a number of surveys, including the DES [3], were able to produce maps of the matter distribution using weak lensing.

    Another approach to measure structure-growth suppression is to trace out the matter distribution by mapping out the positions of visible galaxies. Measuring distances to galaxies requires determining their redshifts through spectroscopy. While the DES doesn’t have high-resolution spectroscopy capabilities, it partially addresses this challenge by imaging the sky through five spectral filters, acquiring low-resolution spectra that provide approximate measurements of distances to galaxies. These distance errors blur out the three-dimensional structure, but the resulting maps are still a powerful probe of gravitational structure formation. While these galaxy maps are less noisy than the weak-lensing maps, they are limited because we don’t know exactly how dark matter is distributed with respect to visible galaxies. However, the DES Collaboration has developed techniques based on correlating weak-lensing data with visible galaxy distributions, which allows it to use the higher signal-to-noise galaxy maps for cosmology.

    Imaging a large area of the Southern Sky (Fig. 1) with the 4-m Victor M. Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile, the DES Collaboration has, for the first time, combined all four dark energy probes in a single analysis. The primary results of this work are independent constraints on the cosmological densities of both dark matter and dark energy (Fig 2). The DES Collaboration also constrains the dark energy equation of state parameter ( w). As Fig. 2 shows, these constraints are not yet competitive with the best constraints derived from other experiments that combine galaxy surveys with CMB data. However, demonstrating the feasibility of a multiprobe approach within a single survey is, in my view, the most important aspect of the work, as it has several advantages over single-probe surveys. First, since all the probes derive from a single survey, calibrations and systematic errors can be consistently controlled across the multiple probes—a harder task for studies that compile data from separate experiments. Second, the Collaboration can uniformly apply the same blinding strategy—an analysis approach in which information is withheld from the researchers carrying out the analysis to reduce observer bias. Finally, the simultaneous characterization of the four probes allows the survey to carry out the cross-correlation analyses described above. While all of the above is, in principle, possible using separate experiments, in practice it is extremely challenging. What’s more, the richness of the data from a multiprobe analysis may inspire novel tests of gravity and dark energy that hadn’t been previously thought about.

    3
    Figure 2: Constraints on dark energy density (ΩΛ) and on matter density (Ωm). Gray contours are constraints from DES data on weak gravitational lensing, large-scale structure, supernovae, and BAO. Green contours are the best available constraints…Y. Guo et al., Phys. Rev. Lett. (2019)

    The results of the DES multiprobe analysis bode very well for the next decade of dark energy research. In the short term, we can expect the DES Collaboration to significantly improve on its constraints. The data analyzed in this work represent only a fraction of the overall data that the DES has already taken. The final dataset will have three times more data for the weak-lensing and galaxy-clustering measurements and include 10 times more supernovae. Statistically, this should yield a factor of 2–4 improvement in the constraints presented here. As constraints get tighter, tensions among different observables could potentially signal cracks in existing cosmological models. There are already intriguing disagreements between local measurements of the Hubble constant compared with its value inferred by CMB and BAO [4], as well as hints of disagreements on the amount of structure revealed by CMB and weak lensing [5]. The full DES analysis may help resolve these discrepancies, or possibly—and that would be even more exciting—exacerbate them.

    In the longer term, we can look forward to results from a number of similarly powerful ongoing surveys, and from even larger surveys planned over the next decade. These include photometric surveys like the DES (such as the Kilo-Degree Survey, the Hyper Suprime-Cam Survey, and the Large Synoptic Survey Telescope), spectroscopic surveys (the Extended Baryon Oscillation Spectroscopic Survey and surveys planned with the 4-m Multi-Object Spectroscopic Telescope and the Dark Energy Spectroscopic Instrument), two satellite missions that will combine both photometric and spectroscopic observations (the Euclid telescope and the Wide Field Infrared Survey Telescope), CMB measurements (the Simons Observatory and the Stage-4 CMB experiment), and surveys that use newer probes like the 21-cm hydrogen line and gravitational waves. The breadth of these programs ensures that the DES measurements are just the beginning of an exciting exploration of one of the most intriguing cosmological questions.

    5
    KiDS, the Kilo-Degree Survey, is a large optical imaging survey in the Southern sky, designed to tackle some of the most fundamental questions of cosmology and galaxy formation of today. Using the VLT Survey Telescope (VST), located at the ESO Paranal Observatory, KiDS will map 1500 square degrees of the night sky in four broad-band filters (u, g, r, i).

    NAOJ Subaru Hyper Suprime-Cam

    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.


    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018


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

    BOSS Spectrograph – SDSS-III

    ESA/Euclid spacecraft

    NASA/WFIRST

    This research is published in Physical Review Letters

    References

    T. M. C. Abbott et al., “Cosmological constraints from multiple probes in the Dark Energy Survey,” Phys. Rev. Lett. 122, 171301 (2019).
    A. G. Riess et al., “Observational evidence from supernovae for an accelerating universe and a cosmological constant,” Astron. J. 116, 1009 (1998); S. Perlmutter et al., “Discovery of a supernova explosion at half the age of the Universe,” Nature 391, 51 (1998); “Erratum: Discovery of a supernova explosion at half the age of the Universe,” 392, 311 (1998).
    M. A. Troxel et al., “Dark Energy Survey Year 1 results: Cosmological constraints from cosmic shear,” Phys. Rev. D 98 (2018).
    Wendy L. Freedman, “Cosmology at at crossroads: Tension with the Hubble Constant,” arXiv:1706.02739.
    H. Hildebrandt et al., “KiDS-450: cosmological parameter constraints from tomographic weak gravitational lensing,” Mon. Not. R. Astron. Soc. 465, 1454 (2016); E. van Uitert et al., “KiDS+GAMA: cosmology constraints from a joint analysis of cosmic shear, galaxy–galaxy lensing, and angular clustering,” 476, 4662 (2018); S. Joudaki et al., “KiDS-450 + 2dFLenS: Cosmological parameter constraints from weak gravitational lensing tomography and overlapping redshift-space galaxy clustering,” 474, 4894 (2017); C. Hikage et al., “Cosmology from cosmic shear power spectra with Subaru Hyper Suprime-Cam first-year data,” Publ. Astron. Soc. Jpn. 71, 43 (2019); C. Chang et al., “A unified analysis of four cosmic shear surveys,” Mon. Not. R. Astron. Soc. 482, 3696 (2018).

    See the full article here .

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    Physicists are drowning in a flood of research papers in their own fields and coping with an even larger deluge in other areas of physics. How can an active researcher stay informed about the most important developments in physics? Physics highlights a selection of papers from the Physical Review journals. In consultation with expert scientists, the editors choose these papers for their importance and/or intrinsic interest. To highlight these papers, Physics features three kinds of articles: Viewpoints are commentaries written by active researchers, who are asked to explain the results to physicists in other subfields. Focus stories are written by professional science writers in a journalistic style and are intended to be accessible to students and non-experts. Synopses are brief editor-written summaries. Physics provides a much-needed guide to the best in physics, and we welcome your comments (physics@aps.org).

     
  • richardmitnick 9:22 am on April 8, 2019 Permalink | Reply
    Tags: , and the Fate of Our Universe", , , , , Dark Energy, ,   

    From AAS NOVA: “Supernovae, Dark Energy, and the Fate of Our Universe” 

    AASNOVA

    From AAS NOVA

    5 April 2019
    Susanna Kohler

    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

    What’s the eventual fate of our universe? Is spacetime destined to continue to expand forever? Will it fly apart, tearing even atoms into bits? Or will it crunch back in on itself? New results from Dark Energy Survey supernovae address these and other questions.

    Uncertain Expansion

    1
    The evolution of the scale of our universe. Measurements suggest that the universe is currently expanding, but does dark energy behaves like a cosmological constant, resulting in continued accelerating expansion like now? Or might we instead be headed for a Big Rip or Big Crunch? [NASA/CXC/M. Weiss]

    At present, the fabric of our universe is expanding — and not only that, but the its expansion is accelerating. To explain this phenomenon, we invoke what’s known as dark energy — an unknown form of energy that exists everywhere and exerts a negative pressure, driving the expansion.

    Since this idea was first proposed, we’ve conducted decades of research to better understand what dark energy is, how much of it there is, and how it influences our universe.

    In particular, dark energy’s still-uncertain equation of state determines the universe’s ultimate fate. If the density of dark energy is constant in time, our universe will continue its current accelerating expansion indefinitely. If the density increases in time, the universe will end in the Big Rip — space will expand at an ever-increasing acceleration rate until even atoms fly apart. And if the density decreases in time, the universe will recollapse in the Big Crunch, ending effectively in a reverse Big Bang.

    Which of these scenarios is correct? We’re not sure yet. But there’s a project dedicated to finding out: the Dark Energy Survey (DES).

    The Hunt for Supernovae

    DES was conducted with the Dark Energy Camera at the Cerro Tololo Inter-American Observatory in Chile. After six years taking data, the survey officially wrapped up observations this past January.

    One of DES’s several missions was to make detailed measurements of thousands of supernovae. Type Ia supernovae explode with a prescribed absolute brightness, allowing us to determine their distance from observations. DES’s precise measurements of Type Ia supernovae allow us to calculate the expansion of the space between us and the supernovae, probing the properties of dark energy.

    Though DES scientists are still in the process of analyzing the tens of terabytes of data generated by the project, they recently released results from the first three years of data — including the first DES cosmology results based on supernovae.

    Refined Measurements

    2
    Constraints on the dark energy equation of state w from the DES supernova survey. Combining this data with constraints from the cosmic microwave background radiation suggest an equation of state consistent with a constant density of dark energy (w = –1). [Abbott et al. 2019]

    Using a sample of 207 spectroscopically confirmed DES supernovae and 122 low-redshift supernovae from the literature, the authors estimate the matter density of a flat universe to be Ωm = 0.321 ± 0.018. This means that only ~32% of the universe’s energy density is matter (the majority of which is dark matter); the remaining ~68% is primarily dark energy.

    From their observations, the DES team is also able to provide an estimate for the dark-energy equation of state w, finding that w = –0.978 ± 0.059. This result is consistent with a constant density of dark energy (w = –1), which would mean that our universe will continue to expand with its current acceleration indefinitely.

    These results are exciting, but they use only ~10% of the supernovae DES discovered over the span of its 5-year survey. This means that we can expect even further refinements to these measurements in the future, as the DES collaboration analyzes the remaining data!

    Citation

    “First Cosmology Results using Type Ia Supernovae from the Dark Energy Survey: Constraints on Cosmological Parameters,” T. M. C. Abbott et al 2019 ApJL 872 L30.
    https://iopscience.iop.org/article/10.3847/2041-8213/ab04fa/meta

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation

    See the full article here .


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    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

     
  • richardmitnick 7:18 am on March 13, 2019 Permalink | Reply
    Tags: "How Much Of The Unobservable Universe Will We Someday Be Able To See?", Dark Energy, , SDSS-Sloan Digital Sky Survey,   

    From Ethan Siegel: “How Much Of The Unobservable Universe Will We Someday Be Able To See?” 

    From Ethan Siegel

    Mar 12, 2019

    1
    Our deepest galaxy surveys can reveal objects tens of billions of light years away, but there are more galaxies within the observable Universe we still have yet to reveal. Most excitingly, there are parts of the Universe that are not yet visible today that will someday become observable to us. (SLOAN DIGITAL SKY SURVEY (SDSS))

    SDSS Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude2,788 meters (9,147 ft)

    As more time passes since the Big Bang, more of the Universe comes into view. But how much?

    Even though it’s been billions of years since the Big Bang, there’s a cosmic limit to how far we can observe the objects that occupy our Universe. The Universe has been expanding all this time, but that expansion rate is both finite and well-measured. If we were to calculate how far a photon emitted at the instant the Big Bang occurred could have traveled by today, we come up with the upper limit to how far we can see in any direction: 46 billion light-years.

    That’s the size of our observable Universe, which contains an estimated two trillion galaxies in various stages of evolutionary development. But beyond that, there ought to be much more Universe beyond the limits of what we can presently see: the unobservable Universe. Thanks to our best measurements of the part we can see, we’re finally figuring out what lies beyond, and how much of it we’ll someday be able to perceive and explore.

    2
    On a logarithmic scale, we can illustrate the entire Universe, going all the way back to the Big Bang. Although we cannot observe farther than this cosmic horizon which is presently a distance of 46.1 billion light-years away, there will be more Universe to reveal itself to us in the future. The observable Universe contains 2 trillion galaxies today, but as time goes on, more Universe will become observable to us. (WIKIPEDIA USER PABLO CARLOS BUDASSI)

    The Big Bang tells us that at some point in the distant past, the Universe was hotter, denser, and expanding much more rapidly than it is today. The stars and galaxies we see throughout the Universe in all directions only exist as they do because the Universe has expanded and cooled, allowing gravitation to pull matter into clumps. Over billions of years, gravitational growth has fueled generations of stars and the formation of galaxies, leading to the Universe we see today.

    Everywhere we look, in all directions, we see a Universe that tells us the same cosmic story. But part of that story is the fact that the farther away we look, the farther we’re looking back in time. The Universe hasn’t been around, forming stars and growing galaxies, forever. According to the Big Bang and the observations that support it, the Universe had a beginning.

    Inflationary Universe. NASA/WMAP


    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex Mittelmann Cold creation


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

    In the early stages after the Big Bang, the Universe was filled with a variety of ingredients, and it began with an incredibly rapid initial expansion rate. These two factors — the initial expansion rate and the gravitational effects of everything in the Universe — are the two head-to-head players in the ultimate cosmic race.

    On the one hand, the expansion works to push everything apart, stretching the fabric of space and driving the galaxies and the large-scale structure of the Universe apart. But on the other hand, gravitation attracts all forms of matter and energy, working to pull the Universe back together. Normal matter, dark matter, dark energy, radiation, neutrinos, black holes, gravitational waves and more all play a role in the expanding Universe.

    3
    The relative importance of different energy components in the Universe at various times in the past. Note that when dark energy reaches a number near 100% in the future, the energy density of the Universe (and, therefore, the expansion rate) will remain constant arbitrarily far ahead in time. Owing to dark energy, distant galaxies are already speeding up in their apparent recession speed from us, and have been since the dark energy density was half of the total matter density, 6 billion years ago. (E. SIEGEL)

    The expansion rate began large, but has been decreasing as the Universe expands. There’s a simple reason for this: as the Universe expands, its volume increases, and therefore the energy density goes down. As the density drops, so does the expansion rate. Light that was once too far away from us to be seen can now catch up to us.

    This fact carries with it a huge implication for the Universe: over time, galaxies that were once too distant to be revealed to us will spontaneously come into view. It may have been 13.8 billion years since the Big Bang occurred, but with the expansion of the Universe, there are objects as far away as 46.1 billion light-years whose light is just reaching us.

    4
    An illustration of how redshifts work in the expanding Universe. As a galaxy gets more and more distant, it must travel a greater distance and for a greater time through the expanding Universe. In a dark-energy dominated Universe, this means that individual galaxies will appear to speed up in their recession from us, but that there will be distant galaxies whose light is just reaching us for the first time today. (LARRY MCNISH OF RASC CALGARY CENTER, VIA CALGARY.RASC.CA/REDSHIFT.HTM)

    All told, if we were to add up all the galaxies that exist within this volume of space, we’d find there are a whopping two trillion of them within our observable Universe. As enormous as this number is, it’s still finite, and our observations don’t reveal an edge in space in any direction we look.

    The amount of time that’s passed since the Big Bang, the speed of light, and the ingredients in our Universe determine the limit of what’s observable. Any farther than that, and even something moving at the speed of light since the moment of the hot Big Bang will not have had sufficient time to reach us.

    But all of this will change in time. As the years and aeons tick by, light that was unable to reach us will finally catch up to our eyes, revealing more of the Universe than we’ve ever seen before.

    You might think that if we waited for an arbitrarily long amount of time, we’d be able to see an arbitrarily far distance, and that there would be no limit to how much of the Universe would become visible.

    But in a Universe with dark energy, that simply isn’t the case. As the Universe ages, the expansion rate doesn’t drop to lower and lower values, approaching zero. Instead, there remains a finite and important amount of energy intrinsic to the fabric of space itself. As time goes on in a Universe with dark energy, the more distant objects will appear to recede from our perspective faster and faster. Although there’s still more Universe out there to discover, there’s a limit to how much of it will ever become observable to us.

    5
    The different possible fates of the Universe, with our actual, accelerating fate shown at the right. After enough time goes by, the acceleration will leave every bound galactic or supergalactic structure completely isolated in the Universe, as all the other structures accelerate irrevocably away. We can only look to the past to infer dark energy’s presence and properties, which require at least one constant, but its implications are larger for the future. (NASA & ESA)

    Based on the expansion rate, the amount of dark energy we have, and the present cosmological parameters of the Universe, we can calculate what we call the future visibility limit: the maximum distance we’ll ever be able to observe [The Astrophysical Journal]. Right now, in a 13.8 billion year old Universe, our current visibility limit is 46 billion light-years. Our future visibility limit is approximately 33% greater: 61 billion light-years. There are galaxies out there, right now, whose light is on the way to our eyes, but has not had the opportunity to reach us yet.

    If we were to add up all the galaxies in the parts of the Universe that we’ll someday see but cannot yet access today, we might be shocked to learn that there are more yet-to-be-revealed galaxies than there are galaxies in the visible Universe. There are an additional 2.7 trillion galaxies waiting to show us their light, on top of the 2 trillion we can already access.

    6
    The observable Universe might be 46 billion light years in all directions from our point of view, but there’s certainly more unobservable Universe, perhaps even an infinite amount, just like ours, beyond that. Over time, we’ll be able to see a bit, but not a lot, more of it. (FRÉDÉRIC MICHEL AND ANDREW Z. COLVIN, ANNOTATED BY E. SIEGEL)

    Compared to what the future holds for us, we’re presently only seeing 43% of the galaxies that we’ll someday be able to observe. Beyond our observable Universe lies the unobservable Universe, which ought to look just like the part we can see. The way we know that is through observations of the cosmic microwave background [CMB] and the large-scale structure of the Universe.

    CMB per ESA/Planck


    ESA/Planck 2009 to 2013

    If the Universe were finite in size, had an edge to it, or its properties began to change as we looked to greater distances, our measurements of these phenomena would reveal it. The observed spatial flatness of the Universe tells us that it is neither positively nor negatively curved to a precision of 99.6%, meaning that if it curves back on itself, the unobservable Universe is at least 250 times as large as the presently visible part.

    7
    The magnitudes of the hot and cold spots, as well as their scales, indicate the curvature of the Universe. To the best of our capabilities, we measure it to be perfectly flat. Baryon acoustic oscillations and the CMB, together, provide the best methods of constraining this, down to a combined precision of 0.4%. (SMOOT COSMOLOGY GROUP / LBNL)

    We will never be able to see anything close to those extraordinary distances. The future visibility limit will take us to distances that are presently 61 billion light-years away, but no farther. It will reveal slightly more than twice the volume of the Universe we can observe today. The unobservable Universe, on the other hand, must be at least 23 trillion light years in diameter, and contain a volume of space that’s over 15 million times as large as the volume we can observe.

    8
    The simulated large-scale structure of the Universe shows intricate patterns of clustering that never repeat. But from our perspective, we can only see a finite volume of the Universe, which appears uniform on the largest scales. (V. SPRINGEL ET AL., MPA GARCHING, AND THE MILLENIUM SIMULATION)

    At the same time that we ponder the Universe beyond our observational limits, however, it’s worth remembering how little of that Universe we can actually access or visit. All that we’re looking forward to viewing is based on light that was already emitted many billions of years ago: close to the Big Bang in time. As it stands today, even if we left right now at the speed of light, we wouldn’t be able to reach nearly all of the galaxies throughout space.

    Dark energy is causing the Universe to not only expand, but for distant galaxies to speed up in their apparent recession from us. Although there are a total of 4.7 trillion galaxies that we will someday be able to observe out to a distance of 61 billion light-years, the limit of what we can reach today is much more modest.

    9
    The observable (yellow, containing 2 trillion galaxies) and reachable (magenta, containing 66 billion galaxies) portions of the Universe, which are what they are thanks to the expansion of space and the energy components of the Universe. Beyond the yellow circle is an even larger (imaginary) one containing 4.7 trillion galaxies, the maximum portion of the Universe that will be accessible to us in the far future. (E. SIEGEL, BASED ON WORK BY WIKIMEDIA COMMONS USERS AZCOLVIN 429 AND FRÉDÉRIC MICHEL)

    Only those galaxies within approximately 15 billion light-years, or a quarter of the radius at the future visibility limit, can be reached today, which equates to about 66 billion galaxies only. This is only 1.4% of the total number of galaxies that will ever become visible to us. In other words, in the future, we will have a total of 4.7 trillion galaxies to view. Most of them will only ever appear to us as they were in the very distant past, and most of them will never get to see us as we are today. Of all those galaxies we’ll someday see, 4.634 trillion of them are already forever unreachable, even at the speed of light.

    You might notice an interesting occurrence: the future visibility limit is exactly equal to the reachable limit (of 15 billion light-years) added to the current visibility limit (of 46 billion light-years). This no coincidence; the light that will ultimately reach us is right at that reachable limit today, after journeying 46 billion light-years since the Big Bang. Someday far in the future, it will arrive at our eyes. With each moment that passes, we come ever closer to our ultimate cosmic viewpoint, as the light from the last galactic holdouts continues on its inevitable journey towards us in the expanding Universe.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 7:01 pm on February 25, 2019 Permalink | Reply
    Tags: A disturbance in the Force, Adam Riess [High-Z Supernova Search Team] Saul Perlmutter [Supernova Cosmology Project] and Brian Schmidt [High-Z Supernova Search Team]shared the Nobel Prize in physics awarded in 2011 for proving th, As space expands it carries galaxies away from each other like the raisins in a rising cake. The farther apart two galaxies are the faster they will fly away from each other. The Hubble constant simpl, , , Axions? Phantom energy? Astrophysicists scramble to patch a hole in the universe- rewriting cosmic history in the process, , , Dark Energy, Dark energy might be getting stronger and denser leading to a future in which atoms are ripped apart and time ends, , , The Hubble constant- named after Edwin Hubble the Mount Wilson astronomer who in 1929 discovered that the universe is expanding, Thus far there is no evidence for most of these ideas, Under the influence of dark energy the cosmos is now doubling in size every 10 billion years   

    From The New York Times: “Have Dark Forces Been Messing With the Cosmos?” 

    New York Times

    From The New York Times

    Feb. 25, 2019
    Dennis Overbye

    1
    Brian Stauffer

    Axions? Phantom energy? Astrophysicists scramble to patch a hole in the universe, rewriting cosmic history in the process.

    There was, you might say, a disturbance in the Force.

    Long, long ago, when the universe was only about 100,000 years old — a buzzing, expanding mass of particles and radiation — a strange new energy field switched on. That energy suffused space with a kind of cosmic antigravity, delivering a not-so-gentle boost to the expansion of the universe.

    Then, after another 100,000 years or so, the new field simply winked off, leaving no trace other than a speeded-up universe.

    So goes the strange-sounding story being promulgated by a handful of astronomers from Johns Hopkins University. In a bold and speculative leap into the past, the team has posited the existence of this field to explain an astronomical puzzle: the universe seems to be expanding faster than it should be.

    The cosmos is expanding only about 9 percent more quickly than theory prescribes. But this slight-sounding discrepancy has intrigued astronomers, who think it might be revealing something new about the universe.

    And so, for the last couple of years, they have been gathering in workshops and conferences to search for a mistake or loophole in their previous measurements and calculations, so far to no avail.

    “If we’re going to be serious about cosmology, this is the kind of thing we have to be able to take seriously,” said Lisa Randall, a Harvard theorist who has been pondering the problem.

    At a recent meeting in Chicago, Josh Frieman, a theorist at the Fermi National Accelerator Laboratory in Batavia, Ill., asked: “At what point do we claim the discovery of new physics?”

    Now ideas are popping up. Some researchers say the problem could be solved by inferring the existence of previously unknown subatomic particles. Others, such as the Johns Hopkins group, are invoking new kinds of energy fields.

    Adding to the confusion, there already is a force field — called dark energy — making the universe expand faster. And a new, controversial report suggests that this dark energy might be getting stronger and denser, leading to a future in which atoms are ripped apart and time ends.

    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

    Thus far, there is no evidence for most of these ideas. If any turn out to be right, scientists may have to rewrite the story of the origin, history and, perhaps, fate of the universe.

    Or it could all be a mistake. Astronomers have rigorous methods to estimate the effects of statistical noise and other random errors on their results; not so for the unexamined biases called systematic errors.

    As Wendy L. Freedman, of the University of Chicago, said at the Chicago meeting, “The unknown systematic is what gets you in the end.”

    2
    Edwin Hubble in 1949, two decades after he discovered that the universe is expanding.CreditBoyer/Roger Viollet, via Getty Images

    Hubble trouble

    Generations of great astronomers have come to grief trying to measure the universe. At issue is a number called the Hubble constant, named after Edwin Hubble, the Mount Wilson astronomer who in 1929 discovered that the universe is expanding.

    Edwin Hubble looking through a 100-inch Hooker telescope at Mount Wilson in Southern California

    Mt Wilson 100 inch Hooker Telescope, perched atop the San Gabriel Mountains outside Los Angeles, CA, USA, Mount Wilson, California, US, Altitude 1,742 m (5,715 ft)

    As space expands, it carries galaxies away from each other like the raisins in a rising cake. The farther apart two galaxies are, the faster they will fly away from each other. The Hubble constant simply says by how much.

    But to calibrate the Hubble constant, astronomers depend on so-called standard candles: objects, such as supernova explosions and certain variable stars, whose distances can be estimated by luminosity or some other feature. This is where the arguing begins.

    Standard Candles to measure age and distance of the universe NASA

    Until a few decades ago, astronomers could not agree on the value of the Hubble constant within a factor of two: either 50 or 100 kilometers per second per megaparsec. (A megaparsec is 3.26 million light years.)

    But in 2001, a team using the Hubble Space Telescope, and led by Dr. Freedman, reported a value of 72. For every megaparsec farther away from us that a galaxy is, it is moving 72 kilometers per second faster.

    NASA/ESA Hubble Telescope

    More recent efforts by Adam G. Riess, of Johns Hopkins and the Space Telescope Science Institute, and others have obtained similar numbers, and astronomers now say they have narrowed the uncertainty in the Hubble constant to just 2.4 percent.

    But new precision has brought new trouble. These results are so good that they now disagree with results from the European Planck spacecraft, which predict a Hubble constant of 67.

    ESA/Planck 2009 to 2013

    4
    Workers with the European Planck spacecraft at the European Space Agency spaceport in Kourou, French Guiana, in 2009.CreditESA – S. Corvaja

    The discrepancy — 9 percent — sounds fatal but may not be, astronomers contend, because Planck and human astronomers do very different kinds of observations.

    Planck is considered the gold standard of cosmology. It spent four years studying the cosmic bath of microwaves [CMB] left over from the end of the Big Bang, when the universe was just 380,000 years old.

    CMB per ESA/Planck

    But it did not measure the Hubble constant directly. Rather, the Planck group derived the value of the constant, and other cosmic parameters, from a mathematical model largely based on those microwaves.

    In short, Planck’s Hubble constant is based on a cosmic baby picture. In contrast, the classical astronomical value is derived from what cosmologists modestly call “local measurements,” a few billion light-years deep into a middle-aged universe.

    What if that baby picture left out or obscured some important feature of the universe?

    ‘Cosmological Whac-a-Mole’

    And so cosmologists are off to the game that Lloyd Knox, an astrophysicist from the University of California, Davis, called “cosmological Whac-a-Mole” at the recent Chicago meeting: attempting to fix the model of the early universe, to make it expand a little faster without breaking what the model already does well.

    One approach, some astrophysicists suggest, is to add more species of lightweight subatomic particles, such as the ghostlike neutrinos, to the early universe. (Physicists already recognize three kinds of neutrinos, and argue whether there is evidence for a fourth variety.) These would give the universe more room to stash energy, in the same way that more drawers in your dresser allow you to own more pairs of socks. Thus invigorated, the universe would expand faster, according to the Big Bang math, and hopefully not mess up the microwave baby picture.

    A more drastic approach, from the Johns Hopkins group, invokes fields of exotic anti-gravitational energy. The idea exploits an aspect of string theory, the putative but unproven “theory of everything” that posits that the elementary constituents of reality are very tiny, wriggling strings.

    String theory suggests that space could be laced with exotic energy fields associated with lightweight particles or forces yet undiscovered. Those fields, collectively called quintessence, could act in opposition to gravity, and could change over time — popping up, decaying or altering their effect, switching from repulsive to attractive.

    The team focused in particular on the effects of fields associated with hypothetical particles called axions. Had one such field arisen when the universe was about 100,000 years old, it could have produced just the right amount of energy to fix the Hubble discrepancy, the team reported in a paper late last year. They refer to this theoretical force as “early dark energy.”

    “I was surprised how it came out,” said Marc Kamionkowski, a Johns Hopkins cosmologist who was part of the study. “This works.”

    The jury is still out. Dr. Riess said that the idea seems to work, which is not to say that he agrees with it, or that it is right. Nature, manifest in future observations, will have the final say.

    Dr. Knox called the Johns Hopkins paper “an existence proof” that the Hubble problem could be solved. “I think that’s new,” he said.

    Dr. Randall, however, has taken issue with aspects of the Johns Hopkins calculations. She and a trio of Harvard postdocs are working on a similar idea that she says works as well and is mathematically consistent. “It’s novel and very cool,” Dr. Randall said.

    So far, the smart money is still on cosmic confusion. Michael Turner, a veteran cosmologist at the University of Chicago and the organizer of a recent airing of the Hubble tensions, said, “Indeed, all of this is going over all of our heads. We are confused and hoping that the confusion will lead to something good!”

    Doomsday? Nah, nevermind

    Early dark energy appeals to some cosmologists because it hints at a link to, or between, two mysterious episodes in the history of the universe. As Dr. Riess said, “This is not the first time the universe has been expanding too fast.”

    The first episode occurred when the universe was less than a trillionth of a trillionth of a second old. At that moment, cosmologists surmise, a violent ballooning propelled the Big Bang; in a fraction of a trillionth of a second, this event — named “inflation” by the cosmologist Alan Guth, of M.I.T. — smoothed and flattened the initial chaos into the more orderly universe observed today. Nobody knows what drove inflation.

    The second episode is unfolding today: cosmic expansion is speeding up. But why? The issue came to light in 1998, when two competing teams of astronomers asked whether the collective gravity of the galaxies might be slowing the expansion enough to one day drag everything together into a Big Crunch.

    To great surprise, they discovered the opposite: the expansion was accelerating under the influence of an anti-gravitational force later called dark energy. The two teams won a Nobel Prize.

    Studies of Universe’s Expansion Win Physics Nobel

    By DENNIS OVERBYE OCT. 4, 2011

    3
    From left, Adam Riess [High-Z Supernova Search Team], Saul Perlmutter [Supernova Cosmology Project] and Brian Schmidt [High-Z Supernova Search Team]shared the Nobel Prize in physics awarded Tuesday. Credit Johns Hopkins University; University Of California At Berkeley; Australian National University

    Dark energy comprises 70 percent of the mass-energy of the universe. And, spookily, it behaves very much like a fudge factor known as the cosmological constant, a cosmic repulsive force that Einstein inserted in his equations a century ago thinking it would keep the universe from collapsing under its own weight. He later abandoned the idea, perhaps too soon.

    Under the influence of dark energy, the cosmos is now doubling in size every 10 billion years — to what end, nobody knows.

    Early dark energy, the force invoked by the Johns Hopkins group, might represent a third episode of antigravity taking over the universe and speeding it up. Perhaps all three episodes are different manifestations of the same underlying tendency of the universe to go rogue and speed up occasionally. In an email, Dr. Riess said, “Maybe the universe does this from time-to-time?”

    If so, it would mean that the current manifestation of dark energy is not Einstein’s constant after all. It might wink off one day. That would relieve astronomers, and everybody else, of an existential nightmare regarding the future of the universe. If dark energy remains constant, everything outside our galaxy eventually will be moving away from us faster than the speed of light, and will no longer be visible. The universe will become lifeless and utterly dark.

    But if dark energy is temporary — if one day it switches off — cosmologists and metaphysicians can all go back to contemplating a sensible tomorrow.

    “An appealing feature of this is that there might be a future for humanity,” said Scott Dodelson, a theorist at Carnegie Mellon who has explored similar scenarios [Physical Review D].

    The phantom cosmos

    But the future is still up for grabs.

    Far from switching off, the dark energy currently in the universe actually has increased over cosmic time, according to a recent report in Nature Astronomy. If this keeps up, the universe could end one day in what astronomers call the Big Rip, with atoms and elementary particles torn asunder — perhaps the ultimate cosmic catastrophe.

    This dire scenario emerges from the work of Guido Risaliti, of the University of Florence in Italy, and Elisabeta Lusso, of Durham University in England. For the last four years, they have plumbed the deep history of the universe, using violent, faraway cataclysms called quasars as distance markers.

    Quasars arise from supermassive black holes at the centers of galaxies; they are the brightest objects in nature, and can be seen clear across the universe. As standard candles, quasars aren’t ideal because their masses vary widely. Nevertheless, the researchers identified some regularities in the emissions from quasars, allowing the history of the cosmos to be traced back nearly 12 billion years. The team found that the rate of cosmic expansion deviated from expectations over that time span.

    One interpretation of the results is that dark energy is not constant after all, but is changing, growing denser and thus stronger over cosmic time. It so happens that this increase in dark energy also would be just enough to resolve the discrepancy in measurements of the Hubble constant.

    The bad news is that, if this model is right, dark energy may be in a particularly virulent and — most physicists say — implausible form called phantom energy. Its existence would imply that things can lose energy by speeding up, for instance. Robert Caldwell, a Dartmouth physicist, has referred to it as “bad news stuff.”

    As the universe expands, the push from phantom energy would grow without bounds, eventually overcoming gravity and tearing apart first Earth, then atoms.

    The Hubble-constant community responded to the new report with caution. “If it holds up, this is a very interesting result,” said Dr. Freedman.

    Astronomers have been trying to take the measure of this dark energy for two decades. Two space missions — the European Space Agency’s Euclid and NASA’s Wfirst — have been designed to study dark energy and hopefully deliver definitive answers in the coming decade. The fate of the universe is at stake.

    ESA/Euclid spacecraft

    NASA/WFIRST

    In the meantime, everything, including phantom energy, is up for consideration, according to Dr. Riess.

    “In a list of possible solutions to the tension via new physics, mentioning weird dark energy like this would seem appropriate,” he wrote in an email. “Heck, at least their dark energy goes in the right direction to solve the tension. It could have gone the other way and made it worse!”

    See the full article here .

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  • richardmitnick 1:32 pm on February 14, 2019 Permalink | Reply
    Tags: , , , , Dark Energy, , , , The Kavli Institute for the Physics and Mathematics of the Universe   

    From The Kavli Institute for the Physics and Mathematics of the Universe: “New Map of Dark Matter Puts the Big Bang Theory on Trial” 

    KavliFoundation

    From The Kavli Institute for the Physics and Mathematics of the Universe

    Kavli IPMU
    Kavli IMPU

    The prevailing view of the universe has just passed a rigorous new test, but the mysteries of dark matter and dark energy remain frustratingly unsolved.

    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

    A NEW COSMIC MAP was unveiled in August, plotting where the mysterious substance called dark matter is clumped across the universe.

    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

    To immense relief—and frustration—the map is just what scientists had expected. The distribution of dark matter agrees with our current understanding of a universe born with certain properties in a Big Bang, 13.8 billion years ago.

    But for all the map’s confirmatory power, it still tells us little about the true identity of dark matter, which acts as an invisible scaffold for galaxies and cosmic structure. It also does not explain an even bigger factor shaping the cosmos, known as dark energy, an enigmatic force seemingly pushing the universe apart at ever greater speeds. Tantalizingly, however, a small discrepancy between the new findings and previous observations of the early universe might just crack open the door for new physics.

    To discuss these issues, The Kavli Foundation turned to three scientists involved in creating this new cosmic map, compiled by the Dark Energy Survey.

    Adam Hadhazy, Fall 2017

    The participants were:

    SCOTT DODELSON – is a cosmologist and the head of the Department of Physics at Carnegie Mellon University. He is one of the lead scientists behind the Dark Energy Survey’s new map of cosmic structure, which he worked on at the Fermi National Accelerator Laboratory and as a professor at the Kavli Institute for Cosmological Physics at the University of Chicago.

    3
    Map of dark matter made from gravitational lensing measurements of 26 million galaxies in the Dark Energy Survey. The map covers about 1/30th of the entire sky and spans several billion light years in extent. Red regions have more dark matter than average, blue regions less dark matter. Image credit: Chihway Chang/Kavli Institute for Cosmological Physics at the University of Chicago/DES Collaboration.

    RISA WECHSLER – is an associate professor of physics at Stanford University and the SLAC National Accelerator Laboratory, as well as a member of the Kavli Institute for Particle Astrophysics and Cosmology. A founder of the Dark Energy Survey, Wechsler is also involved in two next-generation projects that will delve even deeper into the dark universe.
    GEORGE EFSTATHIOU – is a professor of astrophysics and the former director of the Kavli Institute for Cosmology at the University of Cambridge. Along with his work on the Dark Energy Survey, Efstathiou is a science team leader for the European Space Agency’s Planck spacecraft, which between 2009 and 2013 created a detailed map of the early universe.

    The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.

    THE KAVLI FOUNDATION: The Dark Energy Survey just confirmed that matter as we know it makes up only four percent of the universe. That means 96 percent is stuff we can neither see nor touch, and we have pretty much no idea what it really is. Why are these new findings actually good news?

    RISA WECHSLER: It does seem very strange that the results are good news, right? Forty years ago, nobody would’ve guessed that we apparently live in a universe in which most of the matter is stuff that doesn’t interact with us, and most of the energy is not even matter! It’s still super mind-blowing.

    But we’ve kept making increasingly precise measurements of the universe, and that’s where the Dark Energy Survey results come in. They are the most precise measurements of the density of matter and how it’s clumped in the local universe. In the past, we have measured the density of matter in the young, distant universe. So the Dark Energy Survey is really allowing us to test our understanding of the universe’s evolution, which we’ve formalized as the standard model of Big Bang cosmology, in a totally new way.

    Still, it’s certainly possible that we may have something wrong.

    SCOTT DODELSON: These data, along with precise measurements taken by other projects, might start showing small hints of disagreement, or tension, as we call it, with our current understanding of how the universe began and is now actually expanding at increasing speeds.

    As Risa just said, we’re not sure our current way of thinking is correct because it essentially requires us to make stuff up, namely dark matter and dark energy. It could be that we really are just a month away from a scientific revolution that will upend our whole understanding about cosmology and does not require these things.

    GEORGE EFSTATHIOU: Those measurements of the matter and energy in the young, distant universe that Risa referred to were obtained just a few years ago, when a different program called Planck looked at the relic radiation of the Big Bang, which we call the cosmic microwave background [CMB, see below]. Although the Planck spacecraft’s measurements support the model we’re talking about, one is always uneasy having to postulate things, like dark matter and dark energy, that have not been observed. That’s why the Dark Energy Survey is very important—it can stringently test our knowledge about the birth of the universe by comparing it to the actual structure of the modern-day and young universe.

    TKF: The Dark Energy Survey kicked off four years ago, so you’ve been waiting a long time for these results to come in. What was your initial reaction?

    DODELSON: It was the most amazing experience of my scientific career. On July 7, 2017, a date I will always remember, we had 50 people join a conference call. No one knew what the data were going to say because they were blinded, which guards against accidentally biasing the results to be something you “want” them to be. Then one of the leaders of the lensing analysis, Michael Troxel, ran a computer script on the data, unblinding it, and shared his screen with everybody on the call. We all got to see our results compared to Planck’s. They were in such close agreement, independently of each other. We all just gasped and then clapped.

    WECHSLER: I was on that conference call, too. It was really exciting. I’ve been working on this survey since we wrote the first proposal in 2004, so it felt like a culmination.

    TKF: In 2013, Planck gave us a highly accurate “baby” picture of the universe.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Now we have a highly precise picture of the universe in a later epoch. George, you were a leader on the Planck mission. What do you see when you look at these two different snapshots in time?

    EFSTATHIOU: The “baby” picture is consistent with a universe mostly made of dark matter and dark energy. It is also consistent with the idea that the universe underwent an exponential expansion in its earliest moments, known as inflation.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    Alan Guth’s notes:
    5

    So how does the baby picture extrapolate to the modern, “grown up” universe? As the new Dark Energy Survey results show, the pictures are remarkably consistent.

    DODELSON: We’re all astonished that these two pictures agree to the extent they do. Here’s an example. Let’s say you bought Berkshire Hathaway stock in 1970. Say it was $10 a share then and today it’s $250,000 a share. If you were to predict back then that today it would be $250,000, plus or minus $1,000, people would’ve thought you were nuts. But basically, that’s what we’ve done. When the universe was very young, only 380,000 years old, it was also very “smooth.” Matter was so evenly distributed. Today though—more than 13 billion years later—matter in the cosmos is highly, highly clumped in galaxies, stars, planets and other objects. This is what one would anticipate with cosmic expansion, and with the Dark Energy Survey, we’ve been able to confirm the prediction of this cosmic unevenness to a remarkable degree.

    WECHSLER: What’s really helped us make the precise measurements with Dark Energy Survey is that for the first time, we’re looking over a much larger area, about one-thirtieth, of the sky. That’s three or four times larger than the largest dark matter map we have ever made before. We are also able to make that map essentially over half the age of the universe, from now until about seven billion years ago, by collecting light shining from distant galaxies. So we’re able to tell this story over half of the universe’s history, and it remains consistent throughout.

    There are some small disagreements with the Planck results, but I don’t think we should be too worried yet about them.

    EFSTATHIOU: It would’ve been very interesting if the results had significantly increased the tension with the cosmological standard model, which is the foundation for understanding why, beginning with the Big Bang, the universe is undergoing an accelerated expansion. Some previous surveys had suggested that there might be a problem, though I thought that these results were questionable. In my view, one should rely on the data and not be alarmed if our theories disagree with observations. The universe is what it is.

    TKF: Yet a Nature News story characterized George’s view on the discrepancies as “worrisome.”

    EFSTATHIOU: Well, yes, there have been some claims of tension between the clumping measured in the local universe and Planck’s observations of the distant universe. Some other observations have suggested that the late-time, local universe is expanding at a faster rate than expected from Planck.

    If we were able to say convincingly that there was a real problem posed by any of these individual pieces of data, then we’d have to abandon our standard model of cosmology. We would need new physics, and the sort of physics that we would need would be in the exotic territory, overturning decades of otherwise independently supported physical laws. So it’s a big deal.

    In the past, these sorts of tensions have come and gone. When we wrote the 2013 Planck papers, the results then were in tension with most of astrophysics. Then two years later, some of these tensions had disappeared, and now in 2017, they’ve reemerged. So these things come and go. We need to set a high threshold for our science before launching into explanations based on new physics.

    TKF: It almost sounds like, “if it ain’t broke yet, don’t fix it.”

    EFSTATHIOU: We need to be sure it’s broke before fixing it.

    WECHSLER: I agree with George. There’s a very high bar to show you really understand all of the potential sources of error before taking the big leap of abandoning our current, well-evidenced conception about the universe. I don’t think we’re there yet. It means that we should be really excited about the continuing Dark Energy Survey, as well as all the other upcoming surveys and projects.

    TKF: Indeed, these new results are based on a year’s-worth of measurements out of a total of five years. What might we expect after four more years of data have been crunched?

    WECHSLER: With four times more data, our map of dark matter will be even more precise. I also expect there will be improvements in our analysis methods. There will also be a bunch of other new things that the Dark Energy Survey should discover, including new dwarf galaxies around our Milky Way galaxy that we’ve long thought must be there but couldn’t find. There’s lots more to look forward to!

    DODELSON: The increased precision Risa just talked about will enable us to hit the standard model of cosmology as hard as it’s ever been hit. Disproving the current model will revolutionize the way we think about the universe, so that’s the most exciting thing that I can imagine happening.

    TKF: How are astrophysicists extending the hunt for dark matter and dark energy? Risa, let’s start with you, because you are closely involved in two next-generation “dark universe” projects.

    WECHSLER: With the Dark Energy Spectroscopic Instrument, or DESI [pronounced “DEZ-ee”], we’ll be getting what we call spectra, or detailed observations of the light from about 35 million galaxies and quasars, which are galaxies that appear extra bright because their central black holes are actively devouring matter.

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018

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

    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)

    That’s about 10 times more spectra data than we’ve collected from all instruments, so you can imagine that will be really transformative. With DESI, we will be able to independently measure the universe’s expansion rate and how fast its structure of matter and dark matter grow, both of which are influenced by dark energy. Then when you compare those measurements, you get a precise test of the physics governing the universe. DESI will start in 2019 using a telescope in Arizona.

    The other major new instrument I’m working on is the Large Synoptic Survey Telescope, LSST.

    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.

    It will make observations just like the Dark Energy Survey, but at substantially higher precision. In fact, it will cover about four times more area, and the billions of galaxies it sees will be much deeper and farther away. LSST will be a new observatory, being built in Chile right now, and it’s scheduled to begin in about 2022.

    DODELSON: My guess is that both projects will raise new scientific questions. We’ve already seen that with the Dark Energy Survey. Questions shift over time and evolve, so I’m not sure we know what the most exciting thing we’re going to learn from LSST or DESI is.

    EFSTATHIOU: One of my hopes for Planck was that the standard model of cosmology would break and it didn’t. But wouldn’t it be absolutely great for cosmology and for physics if this happened? So we should plug away and see. Maybe we’ll be lucky.

    TKF: If you had to place a bet on what dark matter and dark energy actually are, where would you put your chips?

    DODELSON: We’re living in an era of cognitive dissonance. There is all this cosmological evidence for the existence of dark matter, but over the last 30 years, we’ve run all these experiments and haven’t found it. My bet is that we’re looking at things all wrong. Someone who’s 8 years old today is going to come around and figure out how to make sense of all the data without evoking mysterious new substances.

    EFSTATHIOU: What odds are you giving on that, Scott?

    DODELSON: I’m betting $2,000 of George’s money. [Laughter]

    EFSTATHIOU: I wouldn’t put a bet on any specific candidate for the dark matter. But I bet that dark energy is the cosmological constant, a fudge factor invented by Einstein describing the density of energy in a vacuum.

    WECHSLER: I’m basically with George on this one. I think if Scott’s right, that’ll be wonderful—but that definitely isn’t where I would place my money.

    I think it’s very likely that 15 years from now, we will just then be measuring that dark energy is caused by this cosmological constant. We will be able to shrink the error bars and find that our present model still works.

    On dark matter, I think it’s much less clear. For a long time, the most popular candidate was this thing called the WIMP, or a Weakly Interacting Massive Particle. That idea is still popular and totally possible, but a lot of the particles that could be that kind of dark matter are already ruled out. The other really compelling candidate is a subatomic particle called the axion. People are just getting to a place where they’re able to start searching for these particles that we think are going to be extremely difficult to detect. It’s also possible that dark matter might surprise us, that it’s some new kind of particle that we don’t have the techniques to look for yet.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Kavli IPMU (Kavli Institute for the Physics and Mathematics of the Universe) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
  • richardmitnick 10:28 am on January 29, 2019 Permalink | Reply
    Tags: , , , , , Dark Energy, Quasars are brilliant enough to be seen from a universe less than a billion years old making them prime targets for reaching earlier epochs, , , Two decades ago astronomers discovered that the universe was not only expanding but accelerating in its expansion, Type Ia supernovae have long been the brightest of standard candles, What Quasar Cosmology Can Teach Us About Dark Energy   

    From Sky & Telescope: “What Quasar Cosmology Can Teach Us About Dark Energy” 

    SKY&Telescope bloc

    From Sky & Telescope

    January 28, 2019
    Monica Young

    Astronomers have found a way to turn quasars into standard candles, with potentially far-reaching implications for the nature of mysterious dark energy.

    Standard Candles to measure age and distance of the universe NASA

    National Science Foundation (NASA, JPL, Keck Foundation, Moore Foundation, related) — Funded BICEP2 Program; modifications by E. Siegel.

    Two decades ago astronomers discovered that the universe was not only expanding but accelerating in its expansion. They dubbed the cause of this acceleration dark energy, but what that actually is remains as ineffable now as it was then.

    The weird repulsive force has left its fingerprints on the earliest photons we can see, the ones emitted as part of the cosmic microwave background (CMB), when the infant universe was only 370,000 years old. Yet dark energy only began to dominate expansion as the universe entered middle age, after 9 billion years or so.

    Now, Guido Risaliti (University of Florence and INAF-Astrophysical Observatory of Arcetri, Italy) and Elisabeta Lusso (Durham University, UK) are using quasars to probe the cosmology of our universe’s relatively unexplored adolescence. The results, appearing in the January 28th Nature Astronomy, promise to reveal dark energy’s true nature.

    The leading explanation for dark energy has long been the cosmological constant, also known as vacuum energy. This energy inherent to empty space arises from quantum theory, which says that even when space appears empty of particles, it’s actually filled with quantum fields. These fields exert a negative pressure that counteracts the attractive force of gravity. However, calculations of vacuum energy overpredict the measured dark energy density by an astounding 120 orders of magnitude (that’s a 1 followed by 120 zeroes!). That the cosmological constant remains the favorite theory speaks to how little we understand dark energy — and how difficult the measurements involved are.

    Studying the universe at any age starts with gauging cosmological distance — the farther we look, the further back in time we see­­ ­— but we can’t just roll out a tape measure to the stars. Enter standard candles, objects for which we can measure an intrinsic luminosity. By comparing how bright a standard candle appears to be with how bright it really is, we can determine its distance without knowing anything about cosmology.

    Type Ia supernovae have long been the brightest of standard candles. Observations of these detonating white dwarfs led to the Nobel-winning discovery of accelerating expansion announced back in 1998. The supernovae extended our reach to when the universe was a third of its current age. That’s a pretty good tape measure! Nevertheless, it only probes the era when dark energy began to dominate the universe’s expansion. To see farther back, and probe the era when dark energy overtook matter, astronomers need something even more luminous.

    Quasars as Standard Candles

    2
    Understanding the physics of quasar accretion disks (blue-white) and X-ray-emitting coronae (yellow) can help astronomers use quasars as standard candles.
    NASA / CXC / M. Weiss.

    What’s more luminous than an exploding star? A gas-guzzling supermassive black hole would do the trick. After all, quasars are brilliant enough to be seen from a universe less than a billion years old, making them prime targets for reaching earlier epochs.

    Unfortunately, quasars also exhibit a bewildering variety of forms — astronomers have long thought they were anything but standard. Case in point: Astronomers have known for the past 30 years that more visibly luminous quasars emit relatively fewer X-rays, but there was too much variance from one quasar to another to pin down any one quasar’s intrinsic brightness.

    Risaliti and Lusso realized that this relation between the emission of X-rays and visible light must arise from the physics of quasar accretion disks. The disk itself emits visible light, while a hot, gaseous corona emits the X-rays. The two are intertwined by straightforward physics; it’s just that previously, contaminants had been mucking things up. So for this study, Risaliti and Lusso removed any sources where disk emission is obscured (by dust or gas) or contaminated (by emission from a fast-flowing black hole jet). Their careful selection results in a much tighter, more useful relation. Using data from the Sloan Digital Sky Survey and the XMM-Newton, Chandra, and Swift space telescopes, the duo then apply the relation to turn 1,600 quasars into standard candles.

    SDSS 2.5 meter Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    ESA/XMM Newton

    NASA/Chandra X-ray Telescope

    NASA Neil Gehrels Swift Observatory

    3
    The history of the universe shows a crucial time when the expansion switched from decelerating to accelerating. But the future still hangs in the balance, depending on the behavior of dark energy. If dark energy increases, everything will be torn apart; if it changes direction, the cosmos could end in a big crunch.
    NASA / CXC / M.Weiss

    The quasars help Risaliti and Lusso fill in the gap along the cosmic timeline, looking back to an adolescent universe only a billion years old. From this data, the team finds that dark energy is actually increasing over cosmic time.

    The results appear to rule out the cosmological constant, which predicts a constant energy density. That’s a bit of a relief given that vacuum energy overpredicts the observations so badly. (Did I mention the 120 orders of magnitude?) Evolving dark energy may also help resolve an ongoing tension between measurements of the universe’s current expansion rate.

    Nevertheless, the results are unsettling from a philosophical standpoint: If dark energy density really does increase over time, then so does the repulsive force it exerts, potentially ending our universe in a Big Rip.

    Too Early To Tell

    Let’s not give up on the universe just yet, though. Phil Hopkins (Caltech), who wasn’t involved in the study, urges caution in interpreting its results. The relation that Lusso and Risaliti use to turn quasars into standard candles may itself evolve over time, making those quasars not so standard. For example, if quasars slow their gas-guzzling as mergers become less frequent, that might change the shape of the relation between the emission of X-rays and visible light. “[The relation] only needs to evolve a little bit to explain these observations,” he adds.

    That said, Hopkins agrees the results are interesting and worth following up with even bigger and better samples. The authors also note that other studies probing the adolescent universe are forthcoming. The bar is high these days for disproving the standard cosmological model, and only time and additional study will tell if this is the method that will do it.

    See the full article here .
    See also from Chandra here.

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    Stem Education Coalition

    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 9:26 am on January 29, 2019 Permalink | Reply
    Tags: , , , , , Dark Energy   

    From CERN: “Colliders join the hunt for dark energy” 

    Cern New Bloc

    Cern New Particle Event

    CERN New Masthead

    From CERN

    24 January 2019

    1
    Dark analysis

    It is 20 years since the discovery that the expansion of the universe is accelerating, yet physicists still know precious little about the underlying cause. In a classical universe with no quantum effects, the cosmic acceleration can be explained by a constant that appears in Einstein’s equations of general relativity, albeit one with a vanishingly small value. But clearly our universe obeys quantum mechanics, and the ability of particles to fluctuate in and out of existence at all points in space leads to a prediction for Einstein’s cosmological constant that is 120 orders of magnitude larger than observed. “It implies that at least one, and likely both, of general relativity and quantum mechanics must be fundamentally modified,” says Clare Burrage, a theorist at the University of Nottingham in the UK.

    With no clear alternative theory available, all attempts to explain the cosmic acceleration introduce a new entity called dark energy (DE) that makes up 70% of the total mass-energy content of the universe.

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

    It is not clear whether DE is due to a new scalar particle or a modification of gravity, or whether it is constant or dynamic. It’s not even clear whether it interacts with other fundamental particles or not, says Burrage. Since DE affects the expansion of space–time, however, its effects are imprinted on astronomical observables such as the cosmic microwave background and the growth rate of galaxies, and the main approach to detecting DE involves looking for possible deviations from general relativity on cosmological scales.

    Unique environment

    Collider experiments offer a unique environment in which to search for the direct production of DE particles, since they are sensitive to a multitude of signatures and therefore to a wider array of possible DE interactions with matter. Like other signals of new physics, DE (if accessible at small scales) could manifest itself in high-energy particle collisions either through direct production or via modifications of electroweak observables induced by virtual DE particles.

    Last year, the ATLAS collaboration at the LHC [below]carried out a first collider search for light scalar particles that could contribute to the accelerating expansion of the universe. The results demonstrate the ability of collider experiments to access new regions of parameter space and provide complementary information to cosmological probes.

    Unlike dark matter, for which there exists many new-physics models to guide searches at collider experiments, few such frameworks exist that describe the interaction between DE and Standard Model (SM) particles.

    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.

    However, theorists have made progress by allowing the properties of the prospective DE particle and the strength of the force that it transmits to vary with the environment. This effective-field-theory approach integrates out the unknown microscopic dynamics of the DE interactions.

    The new ATLAS search was motivated by a 2016 model by Philippe Brax of the Université Paris-Saclay, Burrage, Christoph Englert of the University of Glasgow, and Michael Spannowsky of Durham University. The model provides the most general framework for describing DE theories with a scalar field and contains as subsets many well-known specific DE models – such as quintessence, galileon, chameleon and symmetron. It extends the SM lagrangian with a set of higher dimensional operators encoding the different couplings between DE and SM particles. These operators are suppressed by a characteristic energy scale, and the goal of experiments is to pinpoint this energy for the different DE–SM couplings. Two representative operators predict that DE couples preferentially to either very massive particles like the top quark (“conformal” coupling) or to final states with high-momentum transfers, such as those involving high-energy jets (“disformal” coupling).

    Signatures

    “In a big class of these operators the DE particle cannot decay inside the detector, therefore leaving a missing energy signature,” explains Spyridon Argyropoulos of the University of Iowa, who is a member of the ATLAS team that carried out the analysis. “Two possible signatures for the detection of DE are therefore the production of a pair of top-anti­top quarks or the production of high-energy jets, associated with large missing energy. Such signatures are similar to the ones expected by the production of supersymmetric top quarks (“stops”), where the missing energy would be due to the neutralinos from the stop decays or from the production of SM particles in association with dark-matter particles, which also leave a missing energy signature in the detector.”

    The ATLAS analysis, which was based on 13 TeV LHC data corresponding to an integrated luminosity of 36.1 fb–1, re-interprets the result of recent ATLAS searches for stop quarks and dark matter produced in association with jets. No significant excess over the predicted background was observed, setting the most stringent constraints on the suppression scale of conformal and disformal couplings of DE to normal matter in the context of an effective field theory of DE. The results show that the characteristic energy scale must be higher than approximately 300 GeV for the conformal coupling and above 1.2 TeV for the disformal coupling.

    The search for DE at colliders is only at the beginning, says Argyropoulos. “The limits on the disformal coupling are several orders of magnitudes higher than the limits obtained from other laboratory experiments and cosmological probes, proving that colliders can provide crucial information for understanding the nature of DE. More experimental signatures and more types of coupling between DE and normal matter have to be explored and more optimal search strategies could be developed.”

    With this pioneering interpretation of a collider search in terms of dark-energy models, ATLAS has become the first experiment to probe all forms of matter in the observable universe, opening a new avenue of research at the interface of particle physics and cosmology. A complementary laboratory measurement is also being pursued by CERN’s CAST experiment [below], which studies a particular incarnation of DE (chameleon) produced via interactions of DE with photons.

    But DE is not going to give up its secrets easily, cautions theoretical cosmologist Dragan Huterer at the University of Michigan in the US. “Dark energy is normally considered a very large-scale phenomenon, but you may justifiably ask how the study of small systems in a collider can say anything about DE. Perhaps it can, but in a fairly model-dependent way. If ATLAS finds a signal that departs from the SM prediction it would be very exciting. But linking it firmly to DE would require follow-up work and measurements – all of which would be very exciting to see happen.”

    LHC signatures of scalar dark energy
    https://journals.aps.org/prd/abstract/10.1103/PhysRevD.94.084054

    See the full article here.


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Meet CERN in a variety of places:

    Quantum Diaries
    QuantumDiaries

    Cern Courier

    THE FOUR MAJOR PROJECT COLLABORATIONS

    ATLAS
    CERN ATLAS New
    ALICE

    CERN/ALICE Detector


    CMS
    CERN CMS New

    LHCb
    CERN LHCb New II

    LHC

    CERN map

    CERN LHC Grand Tunnel

    CERN LHC particles

    OTHER PROJECTS AT CERN

    CERN AEGIS

    CERN ALPHA

    CERN ALPHA


    CERN ALPHA-g Detector

    CERN ALPHA-g Detector


    CERN AMS

    CERN ACACUSA

    CERN ASACUSA

    CERN ATRAP

    CERN ATRAP

    CERN AWAKE

    CERN AWAKE

    CERN CAST

    CERN CAST Axion Solar Telescope

    CERN CLOUD

    CERN CLOUD

    CERN COMPASS

    CERN COMPASS

    CERN DIRAC

    CERN DIRAC

    CERN GBAR

    CERN GBAR

    CERN ISOLDE

    CERN ISOLDE

    CERN LHCf

    CERN LHCf

    CERN NA62

    CERN NA62

    CERN NTOF

    CERN TOTEM

    CERN UA9

    CERN Proto Dune

    CERN Proto Dune

     
  • 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.

     
  • 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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    Please help promote STEM in your local schools.


    Stem Education Coalition

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics

     
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