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  • richardmitnick 12:05 pm on May 23, 2017 Permalink | Reply
    Tags: , Bubble chamber, Dark Matter, FNAL PICO, , ,   

    From FNAL: “Sleuths use bubbles to look for WIMPs” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    May 22, 2017
    Dan Garisto

    Invisible, imperceptible and yet far more common than ordinary matter, dark matter makes up an astounding 85 percent of the universe’s mass. Physicists are slowly but steadily tracking down the nature of this unidentified substance. The latest result from the PICO experiment places some of the best limits yet on the properties of certain types of dark matter.

    PICO searches for WIMPs (weakly interacting massive particles), a hypothesized type of dark matter particle that would interact only rarely, which makes them difficult to find.

    1
    FNAL PICO. 6,800 feet underground, PICO-60 is installed into its pressure vessel, which sits in a water tank. Photo: Dan Baxter

    In this extreme cosmic game of “Where’s Waldo?” the newest, most technologically complex detectors are usually considered the most promising. Many of these dark matter experiments rely on hundreds if not thousands of electrical channels and require racks of computer servers just to store the data they collect.

    But PICO relies on a simple phenomenon and a fairly low-key detector: bubbles, and a bubble chamber. At its core, PICO’s apparatus is simply a glass jar filled with fluid in which bubbles can form and be monitored by a video camera.

    Reinventing the bubble

    PICO had its beginnings in 2005 as a collaboration between the University of Chicago and the U.S. Department of Energy’s Fermilab. (The experiment started under a different name, COUPP, and later merged with the PICASSO experiment to form PICO.) In the experiment’s early days, much of Fermilab scientists’ work was devoted simply to developing bubble chamber technology. Because while the bubble chamber was hardly new — it was invented in 1952 — the technology had also been out of use for 20 years.

    Bubble chambers are designed to convert the energy deposited by a subatomic particle into a bubble that can be observed. In a liquid such as room temperature water, particle collisions do nothing noticeable. To achieve sensitivity to particles, the fluid inside bubble chambers is heated to just above its boiling point, so the slightest disruption could tip the fluid to a boiling state, creating a bubble.

    “You can actually watch the chamber and see the bubble form,” said Fermilab physicist Hugh Lippincott, a collaborator on PICO. In typical particle physics experiments, information about particle interactions is given solely through computer interfaces. In PICO, the interactions are visible to the naked eye as bubbles.

    “It’s great to press your face up against the glass and just … pop!” said Fermilab physicist Andrew Sonnenschein, also a collaborator on PICO.

    If WIMPs exist, they should occasionally interact with fluid in PICO’s bubble chamber, creating a certain number of bubbles every year.

    It was a return to old-school, low-tech particle physics when Fermilab collaborators began engineering the PICO bubble chamber, which is installed 2 kilometers underground at the Canadian laboratory SNOLAB.

    SNOLAB, Sudbury, Ontario, Canada.

    Bubble chambers of decades past had been used to track millions of charged particles such as protons and electrons, which would leave long, winding tracks in the fluid.

    “Old bubble chambers had a great run, but it ended in the ’80s,” Sonnenschein said. “They were too slow to keep up with experiments that had much larger data rates.”

    As a result, bubble chambers were phased out when modern particle colliders such as Fermilab’s Tevatron and CERN’s Large Hadron Collider took over. Using complex electronics, detectors at these colliders were able to collect millions of times more data than bubble chambers.

    FNAL Tevatron

    FNAL/Tevatron map


    FNAL/Tevatron DZero detector


    FNAL/Tevatron CDF detector

    LHC

    CERN/LHC Map

    CERN LHC Tunnel

    CERN LHC particles

    In fact, bubble chambers had been out of commission for so long that PICO’s founders had to go back to the drawing board, return to some of the papers of the original bubble chamber pioneers, and effectively reinvent the technology for detecting dark matter.

    “After the early bubble chamber designers figured out how to make them work to track high-energy particles with trails of bubbles, the basic ingredients of the recipe didn’t change. We’re looking for low-energy particles that make only single bubbles, so many things are different,” Sonnenschein said.

    The new design to allow bubble chambers to detect dark matter still preserves many of the elements from older bubble chamber detectors.

    “The thing that makes PICO interesting is that we’re using a relatively simple detector design compared to the other dark matter experiments,” said Dan Baxter, a Northwestern University graduate student and Fermilab fellow who was PICO’s latest run coordinator.

    Unlike traditional charged-particle-detecting bubble chambers, PICO’s bubble chamber is designed to look for elusive, neutrally charged WIMPs that might take years to make an appearance.

    “It’s using it in a different way,” Lippincott said. “In the old days, you would never expect to use a bubble chamber by just letting it sit there without anything happening.”

    3
    PICO-60’s inner vessel is cleaned to remove even microscopic particles. Photo: Dan Baxter

    A WIMPy bubble

    The weak force that governs WIMPs lives up to its name. For comparison, it’s about 10,000 times weaker than the electromagnetic force. Particles that interact through the weak force, such as WIMPs and neutrinos, don’t interact often, making them hard to capture. But even a slow-moving WIMP can deposit enough energy to be visible in a detector.

    By carefully calibrating heat and pressure in PICO’s bubble chamber fluid, scientists were able to make the detector sensitive only to the interactions from massive particles like WIMPs. PICO researchers were able to avoid much of the standard background, such as signals from electrons and gamma rays, that plague other dark matter detectors.

    Mastering the technology to do this took years. Predecessors to PICO started off as little more than test tubes filled with a few teaspoons of liquid. Gradually, the vessels grew larger. Then researchers added sound monitoring to their detectors to capture the “pops” from bubbles created by WIMPs.

    “We see a sound chirp,” Sonnenschein said, referring to the bubbles popping. “It turns out that if you look at the frequency content of the sound chirp and the amplitude, you can tell the difference between different kinds of particle interactions.”

    If a WIMP created a bubble, PICO would be able to not only see evidence of dark matter, but hear it as well. Using this acoustic technology, researchers were able to effectively veto bubbles that could not have been created by WIMPs, allowing them to eliminate background.

    As it turns out, PICO did not see any bubbles from WIMPs, so they were able to place limits on both WIMP masses and the likelihood that they will interact with matter — two factors that influence the number of bubbles WIMPs produce.

    Placing limits on these factors — mass and interaction rate — can tell physicists where they should look next for dark matter.

    Where no bubble has gone before

    “We don’t know what dark matter is, and so there’s a lot of theories about what it could be and about how it could interact with normal matter,” Baxter said.

    The variety of theories calls for a variety of different experiments. Other experiments search for different sources of dark matter, such as particles called axions or sterile neutrinos. PICO’s search for WIMPs has a specific focus on so-called spin-dependent WIMPs.

    “We don’t know what the WIMPs are,” Lippincott said. “But broadly speaking their interactions with normal matter would fall into two categories: one that isn’t sensitive to the spin of the nucleus, and one that is.”

    Spin, like charge, is an intrinsic quantity carried by particles and atomic nuclei. PICO looks primarily for WIMP interactions that are sensitive to the spin of the nucleus. To boost their resolution of these interactions, the researchers use a fluid with a liquid containing fluorine, which has a relatively large nuclear spin. With this method, PICO increased their ability to see spin-sensitive WIMPs by a factor of 17.

    Essentially, PICO’s result is that these spin-sensitive WIMPs, if they exist, must interact extremely infrequently — otherwise PICO would have seen more bubbles.

    This result, which is by far the best yet for spin-sensitive WIMPs interacting with protons, does not rule out the existence of WIMPs. There are many other places left to still look for dark matter, but thanks to PICO, fewer places for it to hide.

    The PICO collaboration currently has a proposal in to the Canada Foundation for Innovation to build the next generation of PICO chamber, and physicists like Lippincott and Sonnenschein remain optimistic because of the technology’s potential to scale up.

    “They’re pretty cheap once the engineering is done, mainly because they’re very simple mechanically. The fiddly bits are not very fiddly,” Lippincott said. “There’s a good chance that bubble chambers will continue to play a role in the hunt for dark matter.”

    PICO comprises about 50 physicists at 20 institutions in the Canada, Europe, India, Mexico and the United States and receives support from the U.S. Department of Energy Office of Science and National Science Foundation.

    See the full article here .

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    Fermilab Campus

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

     
  • richardmitnick 8:26 pm on May 21, 2017 Permalink | Reply
    Tags: , Dark Matter, Interactions.org, Laboratori Nazionali del Gran Sasso - INFN, , ,   

    From interactions.org: “XENON1T, the most sensitive detector on Earth searching for WIMP dark matter, releases its first result” 

    Interactions.org

    Laboratori Nazionali del Gran Sasso – INFN

    18 May 2017
    Contact:

    XENON spokesperson
    Prof. Elena Aprile, Columbia University, New York, US.
    Tel. +39 3494703313
    Tel. +1 212 854 3258
    age@astro.columbia.edu

    INFN spokesperson
    Roberta Antolini
    + 39 0862 437216
    Roberta.antolini@lngs.infn.it

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in the Abruzzo region of central Italy

    INFN Gran Sasso ICARUS, since moved to FNAL

    “The best result on dark matter so far! … and we have just started!”

    This is how scientists behind XENON1T, now the most sensitive dark matter experiment world-wide, hosted in the INFN Laboratori Nazionali del Gran Sasso, Italy, commented on their first result from a short 30-day run presented today to the scientific community.

    XENON1T at Gran Sasso

    Dark matter is one of the basic constituents of the Universe, five times more abundant than ordinary matter. Several astronomical measurements have corroborated the existence of dark matter, leading to a world-wide effort to observe directly dark matter particle interactions with ordinary matter in extremely sensitive detectors, which would confirm its existence and shed light on its properties. However, these interactions are so feeble that they have escaped direct detection up to this point, forcing scientists to build detectors that are more and more sensitive. The XENON Collaboration, that with XENON100 led the field for years in the past, is now back on the frontline with XENON1T. The result from a first short 30-day run shows that this detector has a new record low radioactivity level, many orders of magnitude below surrounding materials on Earth. With a total mass of about 3200 kg, XENON1T is at the same time the largest detector of this type ever built. The combination of significantly increased size with much lower background implies an excellent discovery potential in the years to come.

    The XENON Collaboration consists of 135 researchers from the US, Germany, Italy, Switzerland, Portugal, France, the Netherlands, Israel, Sweden and the United Arab Emirates. The latest detector of the XENON family has been in science operation at the LNGS underground laboratory since autumn 2016. The only things you see when visiting the underground experimental site now are a gigantic cylindrical metal tank, filled with ultra-pure water to shield the detector at his center, and a three-story-tall, transparent building crowded with equipment to keep the detector running, with physicists from all over the world. The XENON1T central detector, a so-called Liquid Xenon Time Projection Chamber (LXeTPC), is not visible. It sits within a cryostat in the middle of the water tank, fully submersed, in order to shield it as much as possible from natural radioactivity in the cavern. The cryostat allows keeping the xenon at a temperature of -95°C without freezing the surrounding water.

    The mountain above the laboratory further shields the detector, preventing it to be perturbed by cosmic rays. But shielding from the outer world is not enough since all materials on Earth contain tiny traces of natural radioactivity. Thus extreme care was taken to find, select and process the materials making up the detector to achieve the lowest possible radioactive content. Laura Baudis, professor at the University of Zürich and professor Manfred Lindner from the Max-Planck-Institute for Nuclear Physics in Heidelberg emphasize that this allowed XENON1T to achieve record “silence”, which is necessary to listen with a larger detector much better for the very weak voice of dark matter.

    A particle interaction in liquid xenon leads to tiny flashes of light. This is what the XENON scientists are recording and studying to infer the position and the energy of the interacting particle and whether it might be dark matter or not. The spatial information allows to select interactions occurring in the central 1 ton core of the detector. The surrounding xenon further shields the core xenon target from all materials which already have tiny surviving radioactive contaminants. Despite the shortness of the 30-day science run the sensitivity of XENON1T has already overcome that of any other experiment in the field, probing un-explored dark matter territory.

    “WIMPs did not show up in this first search with XENON1T, but we also did not expect them so soon!” says Elena Aprile, Professor at Columbia University and spokesperson of the project. “The best news is that the experiment continues to accumulate excellent data which will allow us to test quite soon the WIMP hypothesis in a region of mass and cross-section with normal atoms as never before. A new phase in the race to detect dark matter with ultra-low background massive detectors on Earth has just began with XENON1T. We are proud to be at the forefront of the race with this amazing detector, the first of its kind.”

    Further information:
    http://www.xenon1t.org
    http://www.lngs.infn.it

    See the full article here .

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  • richardmitnick 7:47 am on May 21, 2017 Permalink | Reply
    Tags: , , , , Dark Matter,   

    From Universe Today: “Are There Dark Matter Galaxies? ft. Sarah Pearson from Space with Sarah” 

    universe-today

    Universe Today

    20 May , 2017
    Fraser Cain

    One of the things I love about astronomy is how it’s rapidly changing and evolving over time. Every day there are new discoveries, and advancements in theories that take us incrementally forward in our understanding of the Universe.

    One of the best examples of this is dark matter; mysterious and invisible but a significant part of the Universe and accounting for the vast majority of mass out there.

    It was first theorized almost 100 years ago when astronomers surveyed the total mass of distant galaxy clusters and found that the visible mass we can see must be just a fraction of the total material in the clusters. When you add up the stars and gas, galaxies move and rotate in ways that indicate there’s a huge halo of invisible matter surrounding it.

    Some of the best evidence came from Vera Rubin and Kent Ford in the 60s and 70s, when they measured the rotational velocity of edge-on spiral galaxies. They estimated that there must be about 6 times as much dark matter as regular matter.


    Sarah Pearson from Space with Sarah

    1
    This NASA Hubble Space Telescope image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689

    See the full article here .

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  • richardmitnick 9:41 pm on May 18, 2017 Permalink | Reply
    Tags: , , , , Dark Matter, , ,   

    From Nautilus: “The Physicist Who Denies Dark Matter” Revised and Improved from post of 2017/03/01 

    Nautilus

    Nautilus

    May 18, 2017
    Oded Carmeli

    4
    Mordehai Milgrom. Cosmos on Nautilus

    Maybe Newtonian physics doesn’t need dark matter to work.

    He is one of those dark matter people,” Mordehai Milgrom said about a colleague stopping by his office at the Weizmann Institute of Science. Milgrom introduced us, telling me that his friend is searching for evidence of dark matter in a project taking place just down the hall.

    “There are no ‘dark matter people’ and ‘MOND people,’ ” his colleague retorted.

    7
    http://www.astro.umd.edu/~ssm/mond/

    “I am ‘MOND people,’” Milgrom proudly proclaimed, referring to Modified Newtonian Dynamics, his theory that fixes Newtonian physics instead of postulating the existence of dark matter and dark energy—two things that, according to the standard model of cosmology, constitute 95.1 percent of the total mass-energy content of the universe.

    This friendly incident is indicative of (“Moti”) Milgrom’s calmly quixotic character. There is something almost misleading about the 70-year-old physicist wearing shorts in the hot Israeli summer, whose soft voice breaks whenever he gets excited. Nothing about his pleasant demeanor reveals that this man claims to be the third person to correct Newtonian physics: First Max Planck (with quantum theory), then Einstein (with relativity), now Milgrom.

    This year marks Milgrom’s 50th year at the Weizmann.


    Weizmann Institute Campus

    I visited him there to learn more about how it feels to be a science maverick, what he appreciates about Thomas Kuhn’s The Structure of Scientific Revolutions, and why he thinks dark matter and dark energy don’t exist.

    1
    NASA

    What inspired you to dedicate your life to the motion of stars?

    I remember very vividly the way physics struck me. I was 16 and I thought: Here is a way to understand how things work, far beyond the understanding of my peers. It wasn’t a long-term plan. It was a daily attraction. I simply loved physics, the same way other people love art or sports. I never dreamed of one day making a major discovery, like correcting Newton.

    I had a terrific physics teacher at school, but when you study textbook material, you’re studying done deals. You still don’t see the effort that goes into making breakthrough science, when things are unclear and advances are made intuitively and often go wrong. They don’t teach you that at school. They teach you that science always goes forward: You have a body of knowledge, and then someone discovers something and expands that body of knowledge. But it doesn’t really work that way. The progress of science is never linear.

    How did you get involved with the problem of dark matter?

    Toward the end of my Ph.D., the physics department here wanted to expand. So they asked three top Ph.D. students working on particle physics to choose a new field. We chose astrophysics, and the Weizmann Institute pulled some strings with institutions abroad so they would accept us as postdocs. And so I went to Cornell to fill my gaps in astrophysics.

    After a few years in high energy astrophysics, working on the physics of X-ray radiation in space, I decided to move to yet another field: The dynamics of galaxies. It was a few years after the first detailed measurements of the speed of stars orbiting spiral galaxies came in. And, well, there was a problem with the measurements.

    To understand this problem, one needs to wrap one’s head around some celestial rotations. Our planet orbits the sun, which, in turn, orbits the center of the Milky Way galaxy. Inside solar systems, the gravitational pull from the mass of the sun and the speed of the planets are in balance. By Newton’s laws, this is why Mercury, the innermost planet in our solar system, orbits the sun at over 100,000 miles per hour, while the outermost plant, Neptune, is crawling at just over 10,000 miles per hour.

    Milky Way NASA/JPL-Caltech /ESO R. Hurt

    Now, you might assume that the same logic would apply to galaxies: The farther away the star is from the galaxy’s center, the slower it revolves around it; however, while at smaller radiuses the measurements were as predicted by Newtonian physics, farther stars proved to move much faster than predicted from the gravitational pull of the mass we see in these galaxies. The observed gap got a lot wider when, in the late 1970s, radio telescopes were able to detect and measure the cold gas clouds at the outskirts of galaxies. These clouds orbit the galactic center five times farther than the stars, and thus the anomaly grew to become a major scientific puzzle.

    One way to solve this puzzle is to simply add more matter. If there is too little visible mass at the center of galaxies to account for the speed of stars and gas, perhaps there is more matter than meets the eye, matter that we cannot see, dark matter.

    What made you first question the very existence of dark matter?

    What struck me was some regularity in the anomaly. The rotational velocities were not just larger than expected, they became constant with radius. Why? Sure, if there was dark matter, the speed of stars would be greater, but the rotation curves, meaning the rotational speed drawn as a function of the radius, could still go up and down depending on its distribution. But they didn’t. That really struck me as odd. So, in 1980, I went on my Sabbatical in the Institute for Advance Studies in Princeton with the following hunch: If the rotational speeds are constant, then perhaps we’re looking at a new law of nature. If Newtonian physics can’t predict the fixed curves, perhaps we should fix Newton, instead of making up a whole new class of matter just to fit our measurements.

    If you’re going to change the laws of nature that work so well in our own solar system, you need to find a property that differentiates solar systems from galaxies. So I made up a chart of different properties, such as size, mass, speed of rotation, etc. For each parameter, I put in the Earth, the solar system and some galaxies. For example, galaxies are bigger than solar systems, so perhaps Newton’s laws don’t work over large distances? But if this was the case, you would expect the rotation anomaly to grow bigger in bigger galaxies, while, in fact, it is not. So I crossed that one out and moved on to the next properties.

    I finally struck gold with acceleration: The pace at which the velocity of objects changes.

    3
    NASA

    We usually think of earthbound cars that accelerate in the same direction, but imagine a merry-go-round. You could be going in circles and still accelerate. Otherwise, you would simply fall off. The same goes for celestial merry-go-rounds. And it’s in acceleration that we find a big difference in scales, one that justifies modifying Newton: The normal acceleration for a star orbiting the center of a galaxy is about a hundred million times smaller than that of the Earth orbiting the sun.

    For those small accelerations, MOND introduces a new constant of nature, called a0. If you studied physics in high school, you probably remember Newton’s second law: force equals mass times acceleration, or F=ma. While this is a perfectly good tool when dealing with accelerations much greater than a0, such as those of the planets around our sun, I suggested that at significantly lower accelerations, lower even than that of our sun around the galactic center, force becomes proportional to the square of the acceleration, or F=ma2/a0.

    To put it in other words: According to Newton’s laws, the rotation speed of stars around galactic centers should decrease the farther the star is from the center of mass. If MOND is correct, it should reach a constant value, thus eliminating the need for dark matter.

    What did your colleagues at Princeton think about all this?

    I didn’t share these thoughts with my colleagues at Princeton. I was afraid to come across as, well, crazy. And then, in 1981, when I already had a clear idea of MOND, I didn’t want anyone to jump on my wagon, so to speak, which is even crazier when you think about it. Needless to say [laughs] no one jumped on my wagon, even when I desperately wanted them to.

    Well, you were 35 and you proposed to fix Newton.

    Why not? What’s the big deal? If something doesn’t work, fix it. I wasn’t trying to be bold. I was very naïve at the time. I didn’t understand that scientists are just as swayed as other people by conventions and interests.

    Like Thomas Kuhn’s The Structure of Scientific Revolutions.

    10

    I love that book. I read it several times. It showed me how my life’s story has happened to so many others scientists throughout history. Sure, it’s easy to make fun of people who once objected to what we now know is good science, but are we any different? Kuhn stresses that these objectors are usually good scientists with good reasons to object. It is just that the dissenters usually have a unique point of view of things that is not shared by most others. I laugh about it now, because MOND has made such progress, but there were times when I felt depressed and isolated.

    What’s it like being a science maverick?

    By and large, the last 35 years have been exciting and rewarding exactly because I have been advocating a maverick paradigm. I am a loner by nature, and despite the daunting and doubting times, I much prefer this to being carried with the general flow. I was quite confident in the basic validity of MOND from the very start, which helped me a lot in taking all this in stride, but there are two great advantages to the lingering opposition to MOND: Firstly, it gave me time to make more contributions to MOND than I would had the community jumped on the MOND wagon early on. Secondly, once MOND is accepted, the long and wide resistance to it will only have proven how nontrivial an idea it is.

    By the end of my sabbatical in Princeton, I had secretly written three papers introducing MOND to the world. Publishing them, however, was a whole different story. At first I sent my kernel paper to journals such as Nature and Astrophysical Journal Letters, and it got rejected almost off-hand. It took a long time until all three papers were published, side by side, in Astrophysical Journal.

    The first person to hear about MOND was my wife Yvonne. Frankly, tears come to my eyes when I say this. Yvonne is not a scientist, but she has been my greatest supporter.

    The first scientist to back MOND was another physics maverick: The late Professor Jacob Bekenstein, who was the first to suggest that black holes should have a well-defined entropy, later dubbed the Bekenstein-Hawking entropy. After I submitted the initial MOND trilogy, I sent the preprints to several astrophysicists, but Jacob was the first scientist I discussed MOND with. He was enthusiastic and encouraging from the very start.

    Slowly but surely, this tiny opposition to dark matter grew from just two physicists to several hundred proponents, or at least scientists who take MOND seriously. Dark matter is still the scientific consensus, but MOND is now a formidable opponent that proclaims the emperor has no clothes, that dark matter is our generation’s ether.

    So what happened? As far as dark matter is concerned, nothing really. A host of experiments searching for dark matter, including the Large Hadron Collider, many underground experiments and several space missions, have failed to directly observe its very existence. Meanwhile, MOND was able to accurately predict the rotation of more and more spiral galaxies—over 150 galaxies to date, to be precise.

    All of them? Some papers claim that MOND wasn’t able to predict the dynamics of certain galaxies.

    That’s true and it’s perfectly fine, because MOND’s predictions are based on measurements. Given the distribution of regular, visible matter alone, MOND can predict the dynamics of galaxies. But that prediction is based on our initial measurements. We measure the light coming in from a galaxy to calculate its mass, but we often don’t know the distance to that galaxy for sure, so we don’t know for certain just how massive that galaxy really is. And there are other variables, such as molecular gas, that we can’t observe at all. So yes, some galaxies don’t perfectly match MOND’s predictions, but all in all, it’s almost a miracle that we have enough data on galaxies to prove MOND right, over and over again.

    Your opponents say MOND’s greatest flaw is its incompatibility with relativistic physics.

    In 2004, Bekenstein proposed his TeVeS, or Relativistic Gravitational Theory for MOND.

    12
    http://astroweb.case.edu/ssm/mond/

    Since then, several different relativistic MOND formulations have been put forth, including one by me, called Bimetric MOND, or BIMOND.

    So, no, incorporating MOND into Einsteinian physics is no longer a challenge. I hear this statement still made, but only from people who parrot others, who themselves are not abreast with the developments of the last 10 years. There are several relativistic versions of MOND. What remains a challenge is demonstrating that MOND can account for the mass anomalies in cosmology.

    Another argument that cosmologists often make is that dark matter is needed not just for motion within galaxies, but on even larger scales. What does MOND have to say about that?

    According to the Big Bang theory, the universe began as a uniform singularity 13.8 billion years ago. And, just as in galaxies, observations made of the cosmic background radiation from the early universe suggest that the gravity of all the matter in the universe is simply not enough to form the different patterns we currently see, like galaxies and stars, in just 13.8 billion years. Once again, dark matter was called to the rescue: It does not emit radiation, but it does engage visible material with gravitation. And so, starting from the 1980s, the new cosmological dogma was that dark matter constituted a staggering 95 percent of all matter in the universe. That lasted, well, right until the bomb hit us in 1998.

    It turned out that the expansion of the universe is accelerating, not decelerating like all of us originally thought.

    13
    Timeline of the universe, assuming a cosmological constant. Coldcreation/wikimedia, CC BY-SA

    Any form of genuine matter, dark or not, should have slowed down acceleration. And so a whole new type of entity was invented: Dark energy. Now the accepted cosmology is that the universe is made up of 70 percent dark energy, 25 percent dark matter, and 5 percent regular matter..

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

    But dark energy is just a quick fix, the same as dark matter is. And just as in galaxies, you can either invent a whole new type of energy and then spend years trying to understand its properties, or you can try fixing your theory.

    Among other things, MOND points to a very deep connection between structure and dynamics in galaxies and cosmology. This is not expected in accepted physics. Galaxies are tiny structures within the grand scale of the universe, and those structures can behave differently without contradicting the current cosmological consensus. However, MOND creates this connection, binding the two.

    This connection is surprising: For whatever reason, the MOND constant of a0 is close to the acceleration that characterizes the universe itself. In fact, MOND’s constant equals the speed of light squared, divided by the radius of universe.

    So, indeed, to your question, the conundrum pointed to is valid at present. MOND doesn’t have a sufficient cosmology yet, but we’re working on it. And once we fully understand MOND, I believe we’ll also fully understand the expansion of the universe, and vice versa: A new cosmological theory would explain MOND. Wouldn’t that be amazing?

    What do you think about the proposed unified theories of physics, which merge MOND with quantum mechanics?

    These all hark back to my 1999 paper on MOND as a vacuum effect, where it was pointed out that the quantum vacuum in a universe such as ours may produce MOND behavior within galaxies, with the cosmological constant appearing in the guise of the MOND acceleration constant, a0. But I am greatly gratified to see these propositions put forth, especially because they are made by people outside the traditional MOND community. It is very important that researchers from other backgrounds become interested in MOND and bring new ideas to further our understanding of its origin.

    And what if you had a unified theory of physics that explains everything? What then?

    You know, I’m not a religious person, but I often think about our tiny blue dot, and the painstaking work we physicists do here. Who knows? Perhaps somewhere out there, in one of those galaxies I spent my life researching, there already is a known unified theory of physics, with a variation of MOND built into it. But then I think: So what? We still had fun doing the math. We still had the thrill of trying to wrap our heads around the universe, even if the universe never noticed it at all.

    See the full article here .

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

     
  • richardmitnick 4:44 pm on May 16, 2017 Permalink | Reply
    Tags: , Atomic Clocks, Dark Matter   

    From ars technica: “Atomic clocks and solid walls: New tools in the search for dark matter” 

    Ars Technica
    ars technica

    5/15/2017
    Jennifer Ouellette

    1
    An atomic clock based on a fountain of atoms. NSF

    Countless experiments around the world are hoping to reap scientific glory for the first detection of dark matter particles. Usually, they do this by watching for dark matter to bump into normal matter or by slamming particles into other particles and hoping for some dark stuff to pop out. But what if the dark matter behaves more like a wave?

    That’s the intriguing possibility championed by Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute in Waterloo, Ontario, Canada, where she holds the Aristarchus Chair in Theoretical Physics—the first woman to hold a research chair at the institute. Detecting these hypothetical dark matter waves requires a bit of experimental ingenuity. So she and her collaborators are adapting a broad range of radically different techniques to the search: atomic clocks and resonating bars originally designed to hunt for gravitational waves—and even lasers shined at walls in hopes that a bit of dark matter might seep through to the other side.

    “Progress in particle physics for the last 50 years has been focused on colliders, and rightfully so, because whenever we went to a new energy scale, we found something new,” says Arvanitaki. That focus is beginning to shift. To reach higher and higher energies, physicists must build ever-larger colliders—an expensive proposition when funding for science is in decline. There is now more interest in smaller, cheaper options. “These are things that usually fit in the lab, and the turnaround time for results is much shorter than that of the collider,” says Arvanitaki, admitting, “I’ve done this for a long time, and it hasn’t always been popular.”

    The end of the WIMP?

    While most dark matter physicists have focused on hunting for weakly interacting massive particles, or WIMPs, Arvanitaki is one of a growing number who are focusing on less well-known alternatives, such as axions—hypothetical ultralight particles with masses that could be as little as ten thousand trillion trillion times smaller than the mass of the electron. The masses of WIMPs, by contrast, would be larger than the mass of the proton.

    Cosmology gave us very good reason to be excited about WIMPs and focus initial searches in their mass range, according to David Kaplan, a theorist at Johns Hopkins University (and producer of the 2013 documentary Particle Fever). But the WIMP’s dominance in the field to date has also been due, in part, to excitement over the idea of supersymmetry. That model requires every known particle in the Standard Model—whether fermion or boson—to have a superpartner that is heavier and in the opposite class. So an electron, which is a fermion, would have a boson superpartner called the selectron, and so on.

    Physicists suspect one or more of those unseen superpartners might make up dark matter. Supersymmetry predicts not just the existence of dark matter, but how much of it there should be. That fits neatly within a WIMP scenario. Dark matter could be any number of things, after all, and the supersymmetry mass range seemed like a good place to start the search, given the compelling theory behind it.

    But in the ensuing decades, experiment after experiment has come up empty. With each null result, the parameter space where WIMPs might be lurking shrinks. This makes distinguishing a possible signal from background noise in the data increasingly difficult.

    “We’re about to bump up against what’s called the ‘neutrino floor,’” says Kaplan. “All the technology we use to discover WIMPs will soon be sensitive to random neutrinos flying through the Universe. Once it gets there, it becomes a much messier signal and harder to see.”

    Particles are waves

    Despite its momentous discovery of the Higgs boson in 2012, the Large Hadron Collider has yet to find any evidence of supersymmetry. So we shouldn’t wonder that physicists are turning their attention to alternative dark matter candidates outside of the mass ranges of WIMPs. “It’s now a fishing expedition,” says Kaplan. “If you’re going on a fishing expedition, you want to search as broadly as possible, and the WIMP search is narrow and deep.”

    Enter Asimina Arvanitaki—“Mina” for short. She grew up in a small Greek Village called Koklas, and, since her parents were teachers, she grew up with no shortage of books around the house. Arvanitaki excelled in math and physics—at a very young age, she calculated the time light takes to travel from the Earth to the Sun. While she briefly considered becoming a car mechanic in high school because she loved cars, she decided, “I was more interested in why things are the way they are, not in how to make them work.” So she majored in physics instead.

    Similar reasoning convinced her to switch her graduate-school focus at Stanford from experimental condensed matter physics to theory: she found her quantum field theory course more scintillating than any experimental results she produced in the laboratory.

    Central to Arvanitaki’s approach is a theoretical reimagining of dark matter as more than just a simple particle. A peculiar quirk of quantum mechanics is that particles exhibit both particle- and wave-like behavior, so we’re really talking about something more akin to a wavepacket, according to Arvanitaki. The size of those wave packets is inversely proportional to their mass. “So the elementary particles in our theory don’t have to be tiny,” she says. “They can be super light, which means they can be as big as the room or as big as the entire Universe.”

    Axions fit the bill as a dark matter candidate, but they interact so weakly with regular matter that they cannot be produced in colliders. Arvanitaki has proposed several smaller experiments that might succeed in detecting them in ways that colliders cannot.

    Walls, clocks, and bars

    One of her experiments relies on atomic clocks—the most accurate timekeeping devices we have, in which the natural frequency oscillations of atoms serve the same purpose as the pendulum in a grandfather clock. An average wristwatch loses roughly one second every year; atomic clocks are so precise that the best would only lose one second every age of the Universe.

    Within her theoretical framework, dark matter particles (including axions) would behave like waves and oscillate at specific frequencies determined by the mass of the particles. Dark matter waves would cause the atoms in an atomic clock to oscillate as well. The effect is very tiny, but it should be possible to see such oscillations in the data. A trial search of existing data from atomic clocks came up empty, but Arvanitaki suspects that a more dedicated analysis would prove more fruitful.

    Then there are so-called “Weber bars,” which are solid aluminum cylinders that Arvanitaki says should ring like a tuning fork should a dark matter wavelet hit them at just the right frequency. The bars get their name from physicist Joseph Weber, who used them in the 1960s to search for gravitational waves. He claimed to have detected those waves, but nobody could replicate his findings, and his scientific reputation never quite recovered from the controversy.

    Weber died in 2000, but chances are he’d be pleased that his bars have found a new use. Since we don’t know the precise frequency of the dark matter particles we’re hunting, Arvanitaki suggests building a kind of xylophone out of Weber bars. Each bar would be tuned to a different frequency to scan for many different frequencies at once.

    Walking through walls

    Yet another inventive approach involves sending axions through walls. Photons (light) can’t pass through walls—shine a flashlight onto a wall, and someone on the other side won’t be able to see that light. But axions are so weakly interacting that they can pass through a solid wall. Arvanitaki’s experiment exploits the fact that it should be possible to turn photons into axions and then reverse the process to restore the photons. Place a strong magnetic field in front of that wall and then shine a laser onto it. Some of the photons will become axions and pass through the wall. A second magnetic field on the other side of the wall then converts those axions back into photons, which should be easily detected.

    This is a new kind of dark matter detection relying on small, lab-based experiments that are easier to perform (and hence easier to replicate). They’re also much cheaper than setting up detectors deep underground or trying to produce dark matter particles at the LHC—the biggest, most complicated scientific machine ever built, and the most expensive.

    “I think this is the future of dark matter detection,” says Kaplan, although both he and Arvanitaki are adamant that this should complement, not replace, the many ongoing efforts to hunt for WIMPs, whether deep underground or at the LHC.

    “You have to look everywhere, because there are no guarantees. This is what research is all about,” says Arvanitaki. “What we think is correct, and what Nature does, may be two different things.”

    See the full article here .

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    Ars Technica was founded in 1998 when Founder & Editor-in-Chief Ken Fisher announced his plans for starting a publication devoted to technology that would cater to what he called “alpha geeks”: technologists and IT professionals. Ken’s vision was to build a publication with a simple editorial mission: be “technically savvy, up-to-date, and more fun” than what was currently popular in the space. In the ensuing years, with formidable contributions by a unique editorial staff, Ars Technica became a trusted source for technology news, tech policy analysis, breakdowns of the latest scientific advancements, gadget reviews, software, hardware, and nearly everything else found in between layers of silicon.

    Ars Technica innovates by listening to its core readership. Readers have come to demand devotedness to accuracy and integrity, flanked by a willingness to leave each day’s meaningless, click-bait fodder by the wayside. The result is something unique: the unparalleled marriage of breadth and depth in technology journalism. By 2001, Ars Technica was regularly producing news reports, op-eds, and the like, but the company stood out from the competition by regularly providing long thought-pieces and in-depth explainers.

    And thanks to its readership, Ars Technica also accomplished a number of industry leading moves. In 2001, Ars launched a digital subscription service when such things were non-existent for digital media. Ars was also the first IT publication to begin covering the resurgence of Apple, and the first to draw analytical and cultural ties between the world of high technology and gaming. Ars was also first to begin selling its long form content in digitally distributable forms, such as PDFs and eventually eBooks (again, starting in 2001).

     
  • richardmitnick 1:52 pm on May 9, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter,   

    From Physics: “Synopsis: Antiprotons May Hold Dark Matter Signal” 

    Physics LogoAbout Physics

    Physics Logo 2

    Physics

    May 9, 2017
    Michael Schirber

    Recently released data on cosmic-ray antiprotons may contain hints of dark matter, as revealed by two new analyses.

    1
    NASA

    One promising way to detect dark matter is to search for “excess” cosmic rays that presumably originate from dark matter (DM) particles annihilating each other in collisions. Two teams have separately analyzed recent data on cosmic-ray antiprotons obtained by the Alpha Magnetic Spectrometer (AMS) experiment. Both groups find indications of an excess of antiprotons that may correspond to a DM particle with a mass of several tens of GeV∕c2.

    Cosmic rays contain a small sprinkling of antimatter particles, such as positrons and antiprotons. Most of these antiparticles are created in “astrophysical” collisions between a high-energy cosmic ray and interstellar gas. However, a small portion could come from DM annihilations or decays. The challenge in identifying such a DM signature is to accurately model the much larger astrophysical background in which the signal is hidden.

    In their study, Alessandro Cuoco and collaborators from RWTH Aachen University, Germany, assumed two scenarios—one with and one without DM. They ran simulations for both cases, adjusting different parameters to achieve the best fit to antiproton, proton, and helium cosmic-ray data from AMS and other experiments. They found that a model with a DM particle—in this case one with a mass of 80 GeV∕c2

    —provided a better match to the antiproton observations than a model with no DM.

    Meanwhile, Ming-Yang Cui from the Chinese Academy of Sciences and colleagues performed an independent analysis based on a slightly different set of assumptions. Their strategy relied on cosmic-ray observations of the boron-to-carbon ratio, which gives an indication of how far cosmic rays travel to reach us. They found that a model with a DM particle of mass between 40 and 60 GeV∕c2

    gave the best fit to the antiproton data. Both these and Cuoco and colleagues’ results are in broad agreement with the dark matter explanation for an observed excess of gamma rays from the center of our Galaxy.

    This research is published in Physical Review Letters.

    Synopsis on:
    Alessandro Cuoco, Michael Krämer, and Michael Korsmeier
    Phys. Rev. Lett. 118, 191102 (2017)

    Ming-Yang Cui, Qiang Yuan, Yue-Lin Sming Tsai, and Yi-Zhong Fan
    Phys. Rev. Lett. 118, 191101 (2017)

    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 12:44 pm on May 9, 2017 Permalink | Reply
    Tags: , , , , , Dark Matter, Detecting infrared light, ESA/Euclid, ,   

    From JPL-Caltech: “NASA Delivers Detectors for ESA’s Euclid Spacecraft” 

    NASA JPL Banner

    JPL-Caltech

    May 9, 2017
    Elizabeth Landau
    Jet Propulsion Laboratory, Pasadena, Calif.
    818-354-6425
    elizabeth.landau@jpl.nasa.gov

    Giuseppe Racca
    Euclid Project Manager
    Directorate of Science
    European Space Agency
    giuseppe.racca@esa.int

    René Laureijs
    Euclid Project Scientist
    Directorate of Science
    European Space Agency
    Rene.Laureijs@esa.int

    ESA/Euclid spacecraft

    Three detector systems for the Euclid mission, led by ESA (European Space Agency), have been delivered to Europe for the spacecraft’s near-infrared instrument. The detector systems are key components of NASA’s contribution to this upcoming mission to study some of the biggest questions about the universe, including those related to the properties and effects of dark matter and dark energy — two critical, but invisible phenomena that scientists think make up the vast majority of our universe.

    “The delivery of these detector systems is a milestone for what we hope will be an extremely exciting mission, the first space mission dedicated to going after the mysterious dark energy,” said Michael Seiffert, the NASA Euclid project scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, California, which manages the development and implementation of the detector systems.

    Euclid will carry two instruments: a visible-light imager (VIS) and a near-infrared spectrometer and photometer (NISP). A special light-splitting plate on the Euclid telescope enables incoming light to be shared by both instruments, so they can carry out observations simultaneously.

    The spacecraft, scheduled for launch in 2020, will observe billions of faint galaxies and investigate why the universe is expanding at an accelerating pace. Astrophysicists think dark energy is responsible for this effect, and Euclid will explore this hypothesis and help constrain dark energy models. This census of distant galaxies will also reveal how galaxies are distributed in our universe, which will help astrophysicists understand how the delicate interplay of the gravity of dark matter, luminous matter and dark energy forms large-scale structures in the universe.

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

    Additionally, the location of galaxies in relation to each other tells scientists how they are clustered. Dark matter, an invisible substance accounting for over 80 percent of matter in our universe, can cause subtle distortions in the apparent shapes of galaxies. That is because its gravity bends light that travels from a distant galaxy toward an observer, which changes the appearance of the galaxy when it is viewed from a telescope.

    Gravitational Lensing NASA/ESA

    Euclid’s combination of visible and infrared instruments will examine this distortion effect and allow astronomers to probe dark matter and the effects of dark energy.

    Detecting infrared light, which is invisible to the human eye, is especially important for studying the universe’s distant galaxies. Much like the Doppler effect for sound, where a siren’s pitch seems higher as it approaches and lower as it moves away, the frequency of light from an astronomical object gets shifted with motion. Light from objects that are traveling away from us appears redder, and light from those approaching us appears bluer. Because the universe is expanding, distant galaxies are moving away from us, so their light gets stretched out to longer wavelengths. Between 6 and 10 billion light-years away, galaxies are brightest in infrared light.

    JPL procured the NISP detector systems, which were manufactured by Teledyne Imaging Sensors of Camarillo, California. They were tested at JPL and at NASA’s Goddard Space Flight Center, Greenbelt, Maryland, before being shipped to France and the NISP team.

    Each detector system consists of a detector, a cable and a “readout electronics chip” that converts infrared light to data signals read by an onboard computer and transmitted to Earth for analysis. Sixteen detectors will fly on Euclid, each composed of 2040 by 2040 pixels. They will cover a field of view slightly larger than twice the area covered by a full moon. The detectors are made of a mercury-cadmium-telluride mixture and are designed to operate at extremely cold temperatures.

    “The U.S. Euclid team has overcome many technical hurdles along the way, and we are delivering superb detectors that will enable the collection of unprecedented data during the mission,” said Ulf Israelsson, the NASA Euclid project manager, based at JPL.

    Delivery to ESA of the next set of detectors for NISP is planned in early June. The Centre de Physique de Particules de Marseille, France, will provide further characterization of the detector systems. The final detector focal plane will then be assembled at the Laboratoire d’Astrophysique de Marseille, and integrated with the rest of NISP for instrument tests.

    For more information about Euclid, visit:

    http://sci.esa.int/Euclid

    See the full article here .

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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge [1], on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

    Caltech Logo

    NASA image

     
  • richardmitnick 12:31 pm on May 9, 2017 Permalink | Reply
    Tags: , , , Book "We Have No Idea", , Dark Matter, , , , Understanding the unknown universe   

    From Symmetry: “Understanding the unknown universe” 

    Symmetry Mag

    Symmetry

    05/09/17
    Diana Kwon

    The authors of We Have No Idea remind us that there are still many unsolved mysteries in science.

    1
    http://www.sciencefocus.com/feature/black-holes/unknown-universe-%E2%80%93-10-questions-still-confounding-cosmologists

    What is dark energy? Why aren’t we made of antimatter? How many dimensions are there?

    These are a few of the many unanswered questions that Jorge Cham, creator of the online comic Piled Higher and Deeper, and Daniel Whiteson, an experimental particle physicist at the University of California, Irvine, explain in their new book, We Have No Idea. In the process, they remind readers of one key point: When it comes to our universe, there’s a lot we still don’t know.

    The duo started working together in 2008 after Whiteson reached out to Cham, asking if he’d be willing to help create physics cartoons. “I always thought physics was well connected to the way comics work,” Whiteson says. “Because, what’s a Feynman diagram but a little cartoon of particles hitting each other?” (Feynman diagrams are pictures commonly used in particle physics papers that represent the interactions of subatomic particles.)

    2
    A Feynman Diagram such as the one shown above is a succinct way of summarising a mathematical calculation. However, even though it looks like a ‘cartoon’ representation of the physics, it does not describe the physical process. https://protonsforbreakfast.wordpress.com/2014/04/13/feynman-diagrams-are-maths-not-physics/

    Before working on this book, the pair made a handful of popular YouTube videos on topics like dark matter, extra dimensions and the Higgs boson. Many of these subjects are also covered in We Have No Idea.

    One of the main motivators of this latest project was to address a “certain apathy toward science,” Cham says. “I think we both came into it having this feeling that the general public either thinks scientists have everything figured out, or they don’t really understand what scientists are doing.” [the main reason for this blog is that the press does not write about science.]

    To get at this issue, the pair focused on topics that even someone without a science background could find compelling. “You don’t need 10 years of physics background to know [that] questions about how the universe started or what it’s made of are interesting,” Whiteson says. “We tried to find questions that were gut-level approachable.”

    CMB per ESA/Planck

    ESA/Planck

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

    Another key theme of the book, the authors say, is the line between what science can and cannot tell us. While some of the possible solutions to the universe’s mysteries have testable predictions, others (such as string theory) currently do not. “We wanted questions that were accessible yet answerable,” says Whiteson. “We wanted to show people that there were deep, basic, simple questions that we all had, but that the answers were out there.”

    Many scientists are hard at work trying to fill the gaping holes in our knowledge about the universe. Particle physicists, for example, are exploring a number of these questions, such as those about the nature of antimatter and mass.

    3
    Artwork by Jorge Cham

    Some lines of inquiry have brought different research communities together. Dark matter searches, for example, were primarily the realm of cosmologists, who probe large-scale structures of the universe. However, as the focus shifted to finding out what particle—or particles—dark matter was made of, this area of study started to attract astrophysicists as well.

    Why are people trying to answer these questions? “I think science is an expression of humanity and our curiosity to know the answers to basic questions we ask ourselves: Who are we? Why are we here? How does the world work?” Whiteson says. “On the other hand, questions like these lead to understanding, and understanding leads to being able to have greater power over the environment to solve our problems.

    In the very last chapter of the book, the authors explain the idea of a “testable universe,” or the parts of the universe that fall within the bounds of science. In the Stone Ages, when humans had very few tools at their disposal, the testable universe was very small. But it increased as people built telescopes, satellites and particle colliders, and it continues to expand with ongoing advances in science and technology. “That’s the exciting thing,” Cham says. “Our ability to answer these questions is growing.”

    Some mysteries of the universe still live in the realm of philosophy. But tomorrow, next year or a thousand years from now, a scientist may come along and devise an experiment that will be able to find the answers.

    “We’re in a special place in history when most of the world seems explained,” Whiteson says. Thousands of years ago, basic questions, such as why fire burns or where rain comes from, were still largely a mystery. “These days, all those mysteries seem answered, but the truth is, there’s a lot of mysteries left. [If] you want to make a massive imprint on human intellectual history, there’s plenty of room for that.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 10:10 am on May 8, 2017 Permalink | Reply
    Tags: Dark Matter, , , Hubble Views The Final Frontier For Dark Matter,   

    From Ethan Siegel: “Hubble Views The Final Frontier For Dark Matter” 

    Ethan Siegel
    May 8, 2017

    1
    The streaks and arcs present in Abell 370, a distant galaxy cluster some 5-6 billion light years away, are some of the strongest evidence for gravitational lensing and dark matter that we have. NASA, ESA/Hubble, HST Frontier Fields

    When you look out into the distant Universe, in most locations, you’ll find a field of faint, distant galaxies: beautiful, but nothing special.

    2
    The ‘parallel field’ of Abell 370 showcases a deep view of a region of space with no particularly massive or significant structure inside. This is what most of the Universe looks like, when imaged deeply enough. NASA, ESA/Hubble, HST Frontier Fields

    Six billion light years away, Abell 370 is one of the most massive, dense ones discovered so far, but one galaxy, noticed early on, provided a hint of something more.

    4
    The distorted galaxy shown here is actually two images of a single galaxy located twice as far away as the rest of the galaxy; it is the effects of gravitational lensing that cause the odd appearance and multiple images. NASA, ESA/Hubble, HST Frontier Fields

    The “stretched-out” galaxy you see here isn’t a distorted cluster member, but is instead two images of a single galaxy, twice as far away as the cluster itself.

    5
    An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, such as a foreground galaxy cluster. NASA/ESA

    This phenomenon of gravitational lensing stretches galaxies into streaks and arcs, magnifying them, and creating multiple images.

    6
    The streaks of galaxies shown here are not representative of the actual shapes of the galaxies themselves, but rather the galaxies subject to the effects of the gravitational lens they pass through. Undistorted galaxies, like the one at the top left, are most likely in the foreground of the lens. NASA, ESA/Hubble, HST Frontier Fields

    It also enables us to reconstruct the mass distribution of the cluster, revealing that it’s mostly due to dark matter.

    7
    The mass distribution of cluster Abell 370. reconstructed through gravitational lensing, shows two large, diffuse halos of mass, consistent with dark matter with two merging clusters to create what we see here. NASA, ESA, D. Harvey (École Polytechnique Fédérale de Lausanne, Switzerland), R. Massey (Durham University, UK), the Hubble SM4 ERO Team and ST-ECF

    There are two separate clumps present, showing that this is likely two clusters merging together.

    8
    Despite the presence of large, elliptical galaxies, the location where the mass density is greatest, indicated by the dotted circle, corresponds to no known massive galaxy or other structure based in normal matter. The only explanation for this is the presence of an invisible source of mass: dark matter. NASA, ESA/Hubble, HST Frontier Fields / E. Siegel (annotation)

    Most importantly, dark matter must be present — and present outside of the individual galaxies themselves — to explain these gravitational effects.

    9
    A 2009 image, based on only a fraction of the Hubble data available today, revealed some of the incredible structure in Abell 370. The current data, benefitting from 8 extra years, showcases even more information about the distant, massive Universe. NASA/ESA Hubble

    Additional observations from 2009-2017 reveal unprecedented details about the massive, distant 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 4:02 pm on May 5, 2017 Permalink | Reply
    Tags: , Astrophysicists Turn GPS Satellite Constellation into Giant Dark Matter Detector, , , , Dark Matter,   

    From MIT Tech Review: “Astrophysicists Turn GPS Satellite Constellation into Giant Dark Matter Detector” 

    MIT Technology Review
    M.I.T. Technology Review

    May 4, 2017
    Emerging Technology from the arXiv
    If Earth is sweeping through an ocean of dark matter, the effects should be visible in clock data from GPS satellites.

    1

    The Global Positioning System consists of 31 Earth-orbiting satellites, each carrying an atomic clock that sends a highly accurate timing signal to the ground. Anybody with an appropriate receiver can work out their position to within a few meters by comparing the arrival time of signals from three or more satellites.

    And this system can easily be improved. The accuracy of GPS signals can be made much higher by combining the signals with ones produced on the ground. Geophysicists, for example, use this technique to determine the position of ground stations to within a few millimeters. In this way, they can measure the tiny movements of entire continents.

    This is an impressive endeavor. Geophysicists routinely measure the difference between GPS signals and clocks on the ground with an accuracy of less than 0.1 nanoseconds. They also archive this data providing a detailed record of how GPS signals have changed over time. This archival storage opens the possibility of using the data for other exotic studies.

    Today Benjamin Roberts at the University of Nevada and a few pals say they have used this data to find out whether GPS satellites may have been influenced by dark matter, the mysterious invisible stuff that astrophysicists think fills our galaxy. In effect, these guys have turned the Global Positioning System into an astrophysical observatory of truly planetary proportion.

    The theory behind dark matter is based in observations of the way galaxies rotate. This spinning motion is so fast that it should send stars flying off into extra-galactic space.

    But this doesn’t happen. Instead, a mysterious force must somehow hold the stars in place. The theory is that this force is gravity generated by invisible stuff that doesn’t show up in astronomical observations. In other words, dark matter.

    If this theory is correct, dark matter should fill our galaxy, too, and as the sun makes its stately orbit round the galactic center, Earth should plough through a great ocean of dark matter.

    There’s no obvious sign of this stuff, which makes physicists think it must interact very weakly with ordinary visible matter. But they hypothesize that if dark matter exists in small atomic-sized lumps, it might occasionally hit atomic nuclei head on, thereby transferring their energy to visible matter.

    That’s why astrophysicists have built giant observatories in underground mines to look for the tell-tale energy released in these collisions. So far, they’ve seen nothing. Or at least, there is no consensus that anybody has seen evidence of dark matter. So other ways to look for dark matter are desperately needed.

    Enter Roberts and co. They start with a different vision of what dark matter may consist of. Instead of small particles, another option is that dark matter may take the form of topological defects in space-time left over from the Big Bang. These would be glitches in the fabric of the universe, like domain walls, that bend space-time in their vicinity.

    Should the Earth pass through such a defect, it would change the local gravitational field just slightly over a period of an hour or so.

    But how to detect such a change in the local field? To Roberts and co, the answer is clear. According to relativity, any change in gravity also changes the rate at which a clock ticks. That’s why orbiting clocks run a little bit slower than those on the surface.

    If the Earth has passed through any topological defects in the recent past, the clock data from GPS satellites would have recorded this event. So by searching through geophysicists’ archived records of GPS clock timings, it ought to be possible to see such events.

    That’s the theory. In practice, this work is a little more complicated because GPS timing signals are also influenced by other factors such as atmospheric conditions, random variations, and other things. All these need to be taken into account.

    But a key signature of a topological defect is that its influence should sweep through the fleet of satellites as the Earth passes through it. So any other kinds of local timing fluctuation can be ruled out.

    Roberts and co study the data over the last 16 years, and their results make for interesting reading. These guys say they have found no sign that Earth has passed through a topological defect in that time. “We find no evidence for dark matter clumps in the form of domain walls,” they say.

    Of course, that doesn’t rule out the existence of dark matter or even that dark matter exists in this form. But it does place strong limits on how common topological defects can be and how strong their influence is.

    Until now, the limits have been set using observations of the cosmic microwave background radiation, which should reveal topological defects, albeit at low resolution. The work of Roberts and co improves these limits by five orders of magnitude.

    And better data should be available soon. The best clocks in Earth laboratories are orders of magnitude more accurate than the atomic clocks on board GPS satellites. So a network of clocks on Earth should act as an even more sensitive observatory for topological defects. These clocks are only just becoming linked together in networks, so the data from them should be available in the coming years.

    This greater sensitivity should allow physicists to look for other types of dark matter, which may take the form of solitons or Q-balls, for example.

    All this is part of a fascinating process of evolution. The technology behind the GPS system can be traced directly back to the first attempts to track the Sputnik spacecraft after the Soviets launched it in 1957. Physicists soon realized they could determine its location by measuring the radio signals it generated at different places.

    It wasn’t long before they turned this idea on its head. Given the known location of a satellite, is it possible to determine your location on Earth using the signals it broadcasts? The GPS constellation is a direct descendant of that train of thought.

    Those physicists would surely be amazed to know that the technology they developed is also now being used as a planetary-sized astrophysical observatory.

    Ref: arxiv.org/abs/1704.06844: GPS as a Dark-Matter Detector: Orders-of-Magnitude Improvement on Couplings of Clumpy Dark Matter to Atomic Clocks

    See the full article here .

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