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  • richardmitnick 10:52 am on June 21, 2021 Permalink | Reply
    Tags: "Klarman postdoc seeks ‘theory of everything’ by approximation", Attempting to unify gravity with other fundamental forces of physics., , , , , Quantum Gravity, ,   

    From Cornell Chronicle (US) : “Klarman postdoc seeks ‘theory of everything’ by approximation” 

    From Cornell Chronicle (US)

    June 21, 2021
    Kate Blackwood
    cunews@cornell.edu

    1
    Francesco Sgarlata.

    Two pillar theories in physics – general relativity and quantum mechanics – stand up well on their own, but are incompatible with each other.

    “These two theories describe two different regimes of phenomena,” said Francesco Sgarlata, a Klarman Postdoctoral Fellow in physics in the College of Arts and Sciences (A&S).

    2

    Quantum mechanics, he said, describes physical phenomena at atomic or sub-atomic scales; general relativity describes very large phenomena.

    “The two theories are both correct in that they both predict very well, and we don’t have any violation of these theories. However, the two theories are inconsistent with each other,” Sgarlata said, adding that the inconsistencies show up in processes at extremely small scales.

    A member of the first cohort of six Klarman Fellows, Sgarlata is using his three-year fellowship to join theoretical physicists at Cornell and around the world in trying to solve this inconsistency.

    Physicists have long sought a “theory of everything,” or theory of quantum gravity, that would unify quantum mechanics and general relativity. In recent decades, researchers have tried a top-down approach, trying to come up with a unifying theory, such as string theory.

    Sgarlata, in contrast, is taking a bottom-up approach to finding a theory of quantum gravity, which attempts to unify gravity with other fundamental forces of physics.

    “We seek an approximation,” he said. “We don’t know what this theory of everything is. [Instead,] we are trying to write down some theory which can be seen as an approximation of quantum gravity, and we study what conditions this theory will have in order to be a good approximation of quantum gravity.”

    Sgarlata is working with Cornell’s theoretical physics community, including his faculty host, Csaba Csaki, professor of physics (A&S), and Thomas Hartman, associate professor of physics (A&S), to “identify some hidden properties of quantum gravity,” one at a time – and then build from there.

    “Francesco’s research is on the fundamental properties of particles and forces,” Hartman said. “His goal is to understand what particles are consistent with basic principles of relativity and quantum mechanics, and how these particles can interact.”

    Sgarlata’s background is in particle physics, Hartman said, while his own background is in black hole physics and string theory.

    “There is a lot of overlap, but these are two different perspectives,” Hartman said, “so this is a great opportunity for us to collaborate on new ideas. We are working on joining forces and combining our approaches.”

    To find conditions necessary to support a theory of quantum gravity, Sgarlata and collaborators focus on “first principles” – those we experience in everyday life but are difficult to prove mathematically. One example is causality – the link between cause and effect.

    “If I punch you, you will start feeling pain after I punch you, not before,” Sgarlata said. “We assume that this theory of everything respects causality.”

    Other first principles the researchers consider are unitarity (probabilities must add up to 1); and locality (particles only interact with neighboring particles.)

    From a “swampland” of possible theories arise islands of probable theories, Sgarlata said, narrowing the scope. “We get some constraints on the parameters of the theory,” he said.

    Hartman said that Sgarlata uses methods from particle physics to develop and interpret theories of physics at high energies.

    “In some cases, his methods can even be used to understand some corners of the more mysterious theory of quantum gravity at ultrashort distances,” Hartman said. “Over the next couple years, I think Francesco’s research at Cornell will lead to better insight into fundamental particles and new connections between particles, gravity and black holes.”

    The Klarman Fellowship, Sgarlata said, offers independence to pursue research collaborations toward solving the biggest problems in physics.

    “We have the tools to understand features of quantum gravity,” he said. “Today we are reinterpreting these concepts in a more modern way, and we are discovering new concepts of physics just by our interpretations.”

    See the full article here .


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    Once called “the first American university” by educational historian Frederick Rudolph, Cornell University represents a distinctive mix of eminent scholarship and democratic ideals. Adding practical subjects to the classics and admitting qualified students regardless of nationality, race, social circumstance, gender, or religion was quite a departure when Cornell was founded in 1865.

    Today’s Cornell reflects this heritage of egalitarian excellence. It is home to the nation’s first colleges devoted to hotel administration, industrial and labor relations, and veterinary medicine. Both a private university and the land-grant institution of New York State, Cornell University is the most educationally diverse member of the Ivy League.

    On the Ithaca campus alone nearly 20,000 students representing every state and 120 countries choose from among 4,000 courses in 11 undergraduate, graduate, and professional schools. Many undergraduates participate in a wide range of interdisciplinary programs, play meaningful roles in original research, and study in Cornell programs in Washington, New York City, and the world over.

    Cornell University (US) is a private, statutory, Ivy League and land-grant research university in Ithaca, New York. Founded in 1865 by Ezra Cornell and Andrew Dickson White, the university was intended to teach and make contributions in all fields of knowledge—from the classics to the sciences, and from the theoretical to the applied. These ideals, unconventional for the time, are captured in Cornell’s founding principle, a popular 1868 quotation from founder Ezra Cornell: “I would found an institution where any person can find instruction in any study.”

    The university is broadly organized into seven undergraduate colleges and seven graduate divisions at its main Ithaca campus, with each college and division defining its specific admission standards and academic programs in near autonomy. The university also administers two satellite medical campuses, one in New York City and one in Education City, Qatar, and Jacobs Technion-Cornell Institute(US) in New York City, a graduate program that incorporates technology, business, and creative thinking. The program moved from Google’s Chelsea Building in New York City to its permanent campus on Roosevelt Island in September 2017.

    Cornell is one of the few private land grant universities in the United States. Of its seven undergraduate colleges, three are state-supported statutory or contract colleges through the SUNY – The State University of New York (US) system, including its Agricultural and Human Ecology colleges as well as its Industrial Labor Relations school. Of Cornell’s graduate schools, only the veterinary college is state-supported. As a land grant college, Cornell operates a cooperative extension outreach program in every county of New York and receives annual funding from the State of New York for certain educational missions. The Cornell University Ithaca Campus comprises 745 acres, but is much larger when the Cornell Botanic Gardens (more than 4,300 acres) and the numerous university-owned lands in New York City are considered.

    Alumni and affiliates of Cornell have reached many notable and influential positions in politics, media, and science. As of January 2021, 61 Nobel laureates, four Turing Award winners and one Fields Medalist have been affiliated with Cornell. Cornell counts more than 250,000 living alumni, and its former and present faculty and alumni include 34 Marshall Scholars, 33 Rhodes Scholars, 29 Truman Scholars, 7 Gates Scholars, 55 Olympic Medalists, 10 current Fortune 500 CEOs, and 35 billionaire alumni. Since its founding, Cornell has been a co-educational, non-sectarian institution where admission has not been restricted by religion or race. The student body consists of more than 15,000 undergraduate and 9,000 graduate students from all 50 American states and 119 countries.

    History

    Cornell University was founded on April 27, 1865; the New York State (NYS) Senate authorized the university as the state’s land grant institution. Senator Ezra Cornell offered his farm in Ithaca, New York, as a site and $500,000 of his personal fortune as an initial endowment. Fellow senator and educator Andrew Dickson White agreed to be the first president. During the next three years, White oversaw the construction of the first two buildings and traveled to attract students and faculty. The university was inaugurated on October 7, 1868, and 412 men were enrolled the next day.

    Cornell developed as a technologically innovative institution, applying its research to its own campus and to outreach efforts. For example, in 1883 it was one of the first university campuses to use electricity from a water-powered dynamo to light the grounds. Since 1894, Cornell has included colleges that are state funded and fulfill statutory requirements; it has also administered research and extension activities that have been jointly funded by state and federal matching programs.

    Cornell has had active alumni since its earliest classes. It was one of the first universities to include alumni-elected representatives on its Board of Trustees. Cornell was also among the Ivies that had heightened student activism during the 1960s related to cultural issues; civil rights; and opposition to the Vietnam War, with protests and occupations resulting in the resignation of Cornell’s president and the restructuring of university governance. Today the university has more than 4,000 courses. Cornell is also known for the Residential Club Fire of 1967, a fire in the Residential Club building that killed eight students and one professor.

    Since 2000, Cornell has been expanding its international programs. In 2004, the university opened the Weill Cornell Medical College in Qatar. It has partnerships with institutions in India, Singapore, and the People’s Republic of China. Former president Jeffrey S. Lehman described the university, with its high international profile, a “transnational university”. On March 9, 2004, Cornell and Stanford University(US) laid the cornerstone for a new ‘Bridging the Rift Center’ to be built and jointly operated for education on the Israel–Jordan border.

    Research

    Cornell, a research university, is ranked fourth in the world in producing the largest number of graduates who go on to pursue PhDs in engineering or the natural sciences at American institutions, and fifth in the world in producing graduates who pursue PhDs at American institutions in any field. Research is a central element of the university’s mission; in 2009 Cornell spent $671 million on science and engineering research and development, the 16th highest in the United States. Cornell is classified among “R1: Doctoral Universities – Very high research activity”.

    For the 2016–17 fiscal year, the university spent $984.5 million on research. Federal sources constitute the largest source of research funding, with total federal investment of $438.2 million. The agencies contributing the largest share of that investment are the Department of Health and Human Services and the National Science Foundation(US), accounting for 49.6% and 24.4% of all federal investment, respectively. Cornell was on the top-ten list of U.S. universities receiving the most patents in 2003, and was one of the nation’s top five institutions in forming start-up companies. In 2004–05, Cornell received 200 invention disclosures; filed 203 U.S. patent applications; completed 77 commercial license agreements; and distributed royalties of more than $4.1 million to Cornell units and inventors.

    Since 1962, Cornell has been involved in unmanned missions to Mars. In the 21st century, Cornell had a hand in the Mars Exploration Rover Mission. Cornell’s Steve Squyres, Principal Investigator for the Athena Science Payload, led the selection of the landing zones and requested data collection features for the Spirit and Opportunity rovers. NASA-JPL/Caltech(US) engineers took those requests and designed the rovers to meet them. The rovers, both of which have operated long past their original life expectancies, are responsible for the discoveries that were awarded 2004 Breakthrough of the Year honors by Science. Control of the Mars rovers has shifted between National Aeronautics and Space Administration(US)’s JPL-Caltech (US) and Cornell’s Space Sciences Building.

    Further, Cornell researchers discovered the rings around the planet Uranus, and Cornell built and operated the telescope at Arecibo Observatory located in Arecibo, Puerto Rico(US) until 2011, when they transferred the operations to SRI International, the Universities Space Research Association (US) and the Metropolitan University of Puerto Rico [Universidad Metropolitana de Puerto Rico](US).

    The Automotive Crash Injury Research Project was begun in 1952. It pioneered the use of crash testing, originally using corpses rather than dummies. The project discovered that improved door locks; energy-absorbing steering wheels; padded dashboards; and seat belts could prevent an extraordinary percentage of injuries.

    In the early 1980s, Cornell deployed the first IBM 3090-400VF and coupled two IBM 3090-600E systems to investigate coarse-grained parallel computing. In 1984, the National Science Foundation began work on establishing five new supercomputer centers, including the Cornell Center for Advanced Computing, to provide high-speed computing resources for research within the United States. As an National Science Foundation (US) center, Cornell deployed the first IBM Scalable Parallel supercomputer.

    In the 1990s, Cornell developed scheduling software and deployed the first supercomputer built by Dell. Most recently, Cornell deployed Red Cloud, one of the first cloud computing services designed specifically for research. Today, the center is a partner on the National Science Foundation XSEDE-Extreme Science Engineering Discovery Environment supercomputing program, providing coordination for XSEDE architecture and design, systems reliability testing, and online training using the Cornell Virtual Workshop learning platform.

    Cornell scientists have researched the fundamental particles of nature for more than 70 years. Cornell physicists, such as Hans Bethe, contributed not only to the foundations of nuclear physics but also participated in the Manhattan Project. In the 1930s, Cornell built the second cyclotron in the United States. In the 1950s, Cornell physicists became the first to study synchrotron radiation.

    During the 1990s, the Cornell Electron Storage Ring, located beneath Alumni Field, was the world’s highest-luminosity electron-positron collider. After building the synchrotron at Cornell, Robert R. Wilson took a leave of absence to become the founding director of DOE’s Fermi National Accelerator Laboratory(US), which involved designing and building the largest accelerator in the United States.

    Cornell’s accelerator and high-energy physics groups are involved in the design of the proposed ILC-International Linear Collider(JP) and plan to participate in its construction and operation. The International Linear Collider(JP), to be completed in the late 2010s, will complement the CERN Large Hadron Collider(CH) and shed light on questions such as the identity of dark matter and the existence of extra dimensions.

    As part of its research work, Cornell has established several research collaborations with universities around the globe. For example, a partnership with the University of Sussex(UK) (including the Institute of Development Studies at Sussex) allows research and teaching collaboration between the two institutions.

     
  • richardmitnick 9:20 am on June 18, 2021 Permalink | Reply
    Tags: "Physicists Nearly Reach Elusive Quantum Ground State on The Largest 'Object' Yet", Achieving the quantum ground state of a cloud of atoms isn't easy. You need to cool the atom by applying just the right amount of force to stop its vibrations., , , , , , , , Quantum Gravity, , , The work represents a new way to probe the quantum realm.   

    From Massachusetts Institute of Technology (US) via Science Alert (AU) : “Physicists Nearly Reach Elusive Quantum Ground State on The Largest ‘Object’ Yet” 

    MIT News

    From Massachusetts Institute of Technology (US)

    via

    http://www.sciencealert.com/”> Science Alert (AU)

    17 JUNE 2021
    MICHELLE STARR

    1
    One of LIGO’s mirrors. Credit: Caltech/ MIT Advanced aLIGO (US).

    Very rarely is anything completely still. All normal matter in the Universe is made of humming particles, minding their own business and vibrating at their own frequencies.

    If we can get them to slow down as much as possible, the material enters what is known as the motional ground state. In this state, physicists can perform tests of quantum mechanics and quantum gravity, probing the boundary with classical physics to search for a way to unify the two.

    Previously, this has been performed in the nanoscale; but now, for the first time, it’s been done on a massive ‘object’ – the collective motions of the four mirrors of the LIGO gravitational wave interferometer, known as an optomechanical oscillator, with an effective mass of 10 kilograms (22 pounds).

    Caltech /MIT Advanced aLigo .

    The work represents a new way to probe the quantum realm.

    “Nobody has ever observed how gravity acts on massive quantum states,” said mechanical engineer Vivishek Sudhir of MIT.

    “We’ve demonstrated how to prepare kilogram-scale objects in quantum states. This finally opens the door to an experimental study of how gravity might affect large quantum objects, something hitherto only dreamed of.”

    Achieving the quantum ground state of a cloud of atoms isn’t easy. You need to cool the atom by applying just the right amount of force to stop its vibrations. If you don’t cool it enough, it merely slows; so you need to know the exact energy level and direction of the atom’s vibrations in order to apply the appropriate force to stop it.

    This is called ‘feedback cooling’, and on the nanoscale it’s simpler to do, because it’s easier to isolate the smaller groups of atoms and minimize interference. The larger you go, though, the harder it becomes to handle that interference.

    LIGO is one of the most precise instruments for measuring fine motion. It’s designed to detect tiny ripples in space-time generated by collisions between massive objects up to billions of light-years away.

    It consists of an L-shaped vacuum chamber, with laser lights beamed along its two 4-kilometer (2.5-mile) tunnels, and sent to a beam splitter to four mirrors, one at each end of each tunnel. When space-time ripples, the mirrors distort the light, producing an interference pattern that scientists can decode to determine the cause. And it’s so sensitive that it can detect a change just one ten-thousandth the width of a proton, or 10-19 meters.

    Each of LIGO’s four 40-kilogram mirrors is suspended, and it’s their collective motion that makes up the oscillator. The balance of the mirrors effectively reduces 160 kilograms of total weight to a single object of just 10 kilograms.

    “LIGO is designed to measure the joint motion of the four 40-kilogram mirrors,” Sudhir said. “It turns out you can map the joint motion of these masses mathematically, and think of them as the motion of a single 10-kilogram object.”

    By precisely measuring the motion of this oscillator, the team hoped to work out exactly the rate of feedback cooling required to induce the motional ground state… and then, obviously, apply it.

    Unfortunately the very act of measuring throws a degree of randomness into the equation, making it difficult to predict the kinds of nudges needed to sap the energy out of the mirror’s atoms.

    To correct for this, the team cleverly studied each photon to estimate the activity of previous collisions, continuously building a more accurate map of how to apply the correct forces and achieve cooling.

    Then, they applied the calculated force using electromagnets attached to the backs of the mirrors.

    It worked. The oscillator stopped moving, almost completely. Its remaining energy was equivalent to a temperature of 77 nanokelvin (-273.15 degrees Celsius, or -459.67 degrees Fahrenheit).

    Its motional ground state, 10 nanokelvin, is extremely close, especially considering the room temperature starting point. And 77 nanokelvin is also very close to the temperatures used in motional ground state studies on the nanoscale.

    Moreover, it opens the door to some exciting possibilities. Macro-scale demonstrations and measurements of quantum phenomena – and maybe even applications for the same.

    But quantum gravity is the big kicker. Kilogram-mass objects are more susceptible to gravity; the team’s work raises hope to use this mass regime to study the quantum realm.

    “Preparing something in the ground state is often the first step to putting it into exciting or exotic quantum states,” said physicist Chris Whittle of MIT and the LIGO collaboration.

    “So this work is exciting because it might let us study some of these other states, on a mass scale that’s never been done before.”

    The research has been published in Science.

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    MIT Seal

    USPS “Forever” postage stamps celebrating Innovation at MIT.

    MIT Campus

    Massachusetts Institute of Technology (US) is a private land-grant research university in Cambridge, Massachusetts. The institute has an urban campus that extends more than a mile (1.6 km) alongside the Charles River. The institute also encompasses a number of major off-campus facilities such as the MIT Lincoln Laboratory, the Bates Center, and the Haystack Observatory, as well as affiliated laboratories such as the Broad and Whitehead Institutes.

    Founded in 1861 in response to the increasing industrialization of the United States, Massachusetts Institute of Technology (US) adopted a European polytechnic university model and stressed laboratory instruction in applied science and engineering. It has since played a key role in the development of many aspects of modern science, engineering, mathematics, and technology, and is widely known for its innovation and academic strength. It is frequently regarded as one of the most prestigious universities in the world.

    As of December 2020, 97 Nobel laureates, 26 Turing Award winners, and 8 Fields Medalists have been affiliated with MIT as alumni, faculty members, or researchers. In addition, 58 National Medal of Science recipients, 29 National Medals of Technology and Innovation recipients, 50 MacArthur Fellows, 80 Marshall Scholars, 3 Mitchell Scholars, 22 Schwarzman Scholars, 41 astronauts, and 16 Chief Scientists of the U.S. Air Force have been affiliated with Massachusetts Institute of Technology (US) . The university also has a strong entrepreneurial culture and MIT alumni have founded or co-founded many notable companies. Massachusetts Institute of Technology (US) is a member of the Association of American Universities (AAU).

    Foundation and vision

    In 1859, a proposal was submitted to the Massachusetts General Court to use newly filled lands in Back Bay, Boston for a “Conservatory of Art and Science”, but the proposal failed. A charter for the incorporation of the Massachusetts Institute of Technology, proposed by William Barton Rogers, was signed by John Albion Andrew, the governor of Massachusetts, on April 10, 1861.

    Rogers, a professor from the University of Virginia (US), wanted to establish an institution to address rapid scientific and technological advances. He did not wish to found a professional school, but a combination with elements of both professional and liberal education, proposing that:

    “The true and only practicable object of a polytechnic school is, as I conceive, the teaching, not of the minute details and manipulations of the arts, which can be done only in the workshop, but the inculcation of those scientific principles which form the basis and explanation of them, and along with this, a full and methodical review of all their leading processes and operations in connection with physical laws.”

    The Rogers Plan reflected the German research university model, emphasizing an independent faculty engaged in research, as well as instruction oriented around seminars and laboratories.

    Early developments

    Two days after Massachusetts Institute of Technology (US) was chartered, the first battle of the Civil War broke out. After a long delay through the war years, MIT’s first classes were held in the Mercantile Building in Boston in 1865. The new institute was founded as part of the Morrill Land-Grant Colleges Act to fund institutions “to promote the liberal and practical education of the industrial classes” and was a land-grant school. In 1863 under the same act, the Commonwealth of Massachusetts founded the Massachusetts Agricultural College, which developed as the University of Massachusetts Amherst (US)). In 1866, the proceeds from land sales went toward new buildings in the Back Bay.

    Massachusetts Institute of Technology (US) was informally called “Boston Tech”. The institute adopted the European polytechnic university model and emphasized laboratory instruction from an early date. Despite chronic financial problems, the institute saw growth in the last two decades of the 19th century under President Francis Amasa Walker. Programs in electrical, chemical, marine, and sanitary engineering were introduced, new buildings were built, and the size of the student body increased to more than one thousand.

    The curriculum drifted to a vocational emphasis, with less focus on theoretical science. The fledgling school still suffered from chronic financial shortages which diverted the attention of the MIT leadership. During these “Boston Tech” years, Massachusetts Institute of Technology (US) faculty and alumni rebuffed Harvard University (US) president (and former MIT faculty) Charles W. Eliot’s repeated attempts to merge MIT with Harvard College’s Lawrence Scientific School. There would be at least six attempts to absorb MIT into Harvard. In its cramped Back Bay location, MIT could not afford to expand its overcrowded facilities, driving a desperate search for a new campus and funding. Eventually, the MIT Corporation approved a formal agreement to merge with Harvard, over the vehement objections of MIT faculty, students, and alumni. However, a 1917 decision by the Massachusetts Supreme Judicial Court effectively put an end to the merger scheme.

    In 1916, the Massachusetts Institute of Technology (US) administration and the MIT charter crossed the Charles River on the ceremonial barge Bucentaur built for the occasion, to signify MIT’s move to a spacious new campus largely consisting of filled land on a one-mile-long (1.6 km) tract along the Cambridge side of the Charles River. The neoclassical “New Technology” campus was designed by William W. Bosworth and had been funded largely by anonymous donations from a mysterious “Mr. Smith”, starting in 1912. In January 1920, the donor was revealed to be the industrialist George Eastman of Rochester, New York, who had invented methods of film production and processing, and founded Eastman Kodak. Between 1912 and 1920, Eastman donated $20 million ($236.6 million in 2015 dollars) in cash and Kodak stock to MIT.

    Curricular reforms

    In the 1930s, President Karl Taylor Compton and Vice-President (effectively Provost) Vannevar Bush emphasized the importance of pure sciences like physics and chemistry and reduced the vocational practice required in shops and drafting studios. The Compton reforms “renewed confidence in the ability of the Institute to develop leadership in science as well as in engineering”. Unlike Ivy League schools, Massachusetts Institute of Technology (US) catered more to middle-class families, and depended more on tuition than on endowments or grants for its funding. The school was elected to the Association of American Universities (US)in 1934.

    Still, as late as 1949, the Lewis Committee lamented in its report on the state of education at Massachusetts Institute of Technology (US) that “the Institute is widely conceived as basically a vocational school”, a “partly unjustified” perception the committee sought to change. The report comprehensively reviewed the undergraduate curriculum, recommended offering a broader education, and warned against letting engineering and government-sponsored research detract from the sciences and humanities. The School of Humanities, Arts, and Social Sciences and the MIT Sloan School of Management were formed in 1950 to compete with the powerful Schools of Science and Engineering. Previously marginalized faculties in the areas of economics, management, political science, and linguistics emerged into cohesive and assertive departments by attracting respected professors and launching competitive graduate programs. The School of Humanities, Arts, and Social Sciences continued to develop under the successive terms of the more humanistically oriented presidents Howard W. Johnson and Jerome Wiesner between 1966 and 1980.

    Massachusetts Institute of Technology (US) ‘s involvement in military science surged during World War II. In 1941, Vannevar Bush was appointed head of the federal Office of Scientific Research and Development and directed funding to only a select group of universities, including MIT. Engineers and scientists from across the country gathered at Massachusetts Institute of Technology (US) ‘s Radiation Laboratory, established in 1940 to assist the British military in developing microwave radar. The work done there significantly affected both the war and subsequent research in the area. Other defense projects included gyroscope-based and other complex control systems for gunsight, bombsight, and inertial navigation under Charles Stark Draper’s Instrumentation Laboratory; the development of a digital computer for flight simulations under Project Whirlwind; and high-speed and high-altitude photography under Harold Edgerton. By the end of the war, Massachusetts Institute of Technology (US) became the nation’s largest wartime R&D contractor (attracting some criticism of Bush), employing nearly 4000 in the Radiation Laboratory alone and receiving in excess of $100 million ($1.2 billion in 2015 dollars) before 1946. Work on defense projects continued even after then. Post-war government-sponsored research at MIT included SAGE and guidance systems for ballistic missiles and Project Apollo.

    These activities affected Massachusetts Institute of Technology (US) profoundly. A 1949 report noted the lack of “any great slackening in the pace of life at the Institute” to match the return to peacetime, remembering the “academic tranquility of the prewar years”, though acknowledging the significant contributions of military research to the increased emphasis on graduate education and rapid growth of personnel and facilities. The faculty doubled and the graduate student body quintupled during the terms of Karl Taylor Compton, president of Massachusetts Institute of Technology (US) between 1930 and 1948; James Rhyne Killian, president from 1948 to 1957; and Julius Adams Stratton, chancellor from 1952 to 1957, whose institution-building strategies shaped the expanding university. By the 1950s, Massachusetts Institute of Technology (US) no longer simply benefited the industries with which it had worked for three decades, and it had developed closer working relationships with new patrons, philanthropic foundations and the federal government.

    In late 1960s and early 1970s, student and faculty activists protested against the Vietnam War and Massachusetts Institute of Technology (US) ‘s defense research. In this period Massachusetts Institute of Technology (US) ‘s various departments were researching helicopters, smart bombs and counterinsurgency techniques for the war in Vietnam as well as guidance systems for nuclear missiles. The Union of Concerned Scientists was founded on March 4, 1969 during a meeting of faculty members and students seeking to shift the emphasis on military research toward environmental and social problems. Massachusetts Institute of Technology (US) ultimately divested itself from the Instrumentation Laboratory and moved all classified research off-campus to the MIT (US) Lincoln Laboratoryfacility in 1973 in response to the protests. The student body, faculty, and administration remained comparatively unpolarized during what was a tumultuous time for many other universities. Johnson was seen to be highly successful in leading his institution to “greater strength and unity” after these times of turmoil. However six Massachusetts Institute of Technology (US) students were sentenced to prison terms at this time and some former student leaders, such as Michael Albert and George Katsiaficas, are still indignant about MIT’s role in military research and its suppression of these protests. (Richard Leacock’s film, November Actions, records some of these tumultuous events.)

    In the 1980s, there was more controversy at Massachusetts Institute of Technology (US) over its involvement in SDI (space weaponry) and CBW (chemical and biological warfare) research. More recently, Massachusetts Institute of Technology (US) ‘s research for the military has included work on robots, drones and ‘battle suits’.

    Recent history

    Massachusetts Institute of Technology (US) has kept pace with and helped to advance the digital age. In addition to developing the predecessors to modern computing and networking technologies, students, staff, and faculty members at Project MAC, the Artificial Intelligence Laboratory, and the Tech Model Railroad Club wrote some of the earliest interactive computer video games like Spacewar! and created much of modern hacker slang and culture. Several major computer-related organizations have originated at MIT since the 1980s: Richard Stallman’s GNU Project and the subsequent Free Software Foundation were founded in the mid-1980s at the AI Lab; the MIT Media Lab was founded in 1985 by Nicholas Negroponte and Jerome Wiesner to promote research into novel uses of computer technology; the World Wide Web Consortium standards organization was founded at the Laboratory for Computer Science in 1994 by Tim Berners-Lee; the MIT OpenCourseWare project has made course materials for over 2,000 Massachusetts Institute of Technology (US) classes available online free of charge since 2002; and the One Laptop per Child initiative to expand computer education and connectivity to children worldwide was launched in 2005.

    Massachusetts Institute of Technology (US) was named a sea-grant college in 1976 to support its programs in oceanography and marine sciences and was named a space-grant college in 1989 to support its aeronautics and astronautics programs. Despite diminishing government financial support over the past quarter century, MIT launched several successful development campaigns to significantly expand the campus: new dormitories and athletics buildings on west campus; the Tang Center for Management Education; several buildings in the northeast corner of campus supporting research into biology, brain and cognitive sciences, genomics, biotechnology, and cancer research; and a number of new “backlot” buildings on Vassar Street including the Stata Center. Construction on campus in the 2000s included expansions of the Media Lab, the Sloan School’s eastern campus, and graduate residences in the northwest. In 2006, President Hockfield launched the MIT Energy Research Council to investigate the interdisciplinary challenges posed by increasing global energy consumption.

    In 2001, inspired by the open source and open access movements, Massachusetts Institute of Technology (US) launched OpenCourseWare to make the lecture notes, problem sets, syllabi, exams, and lectures from the great majority of its courses available online for no charge, though without any formal accreditation for coursework completed. While the cost of supporting and hosting the project is high, OCW expanded in 2005 to include other universities as a part of the OpenCourseWare Consortium, which currently includes more than 250 academic institutions with content available in at least six languages. In 2011, Massachusetts Institute of Technology (US) announced it would offer formal certification (but not credits or degrees) to online participants completing coursework in its “MITx” program, for a modest fee. The “edX” online platform supporting MITx was initially developed in partnership with Harvard and its analogous “Harvardx” initiative. The courseware platform is open source, and other universities have already joined and added their own course content. In March 2009 the Massachusetts Institute of Technology (US) faculty adopted an open-access policy to make its scholarship publicly accessible online.

    Massachusetts Institute of Technology (US) has its own police force. Three days after the Boston Marathon bombing of April 2013, MIT Police patrol officer Sean Collier was fatally shot by the suspects Dzhokhar and Tamerlan Tsarnaev, setting off a violent manhunt that shut down the campus and much of the Boston metropolitan area for a day. One week later, Collier’s memorial service was attended by more than 10,000 people, in a ceremony hosted by the Massachusetts Institute of Technology (US) community with thousands of police officers from the New England region and Canada. On November 25, 2013, Massachusetts Institute of Technology (US) announced the creation of the Collier Medal, to be awarded annually to “an individual or group that embodies the character and qualities that Officer Collier exhibited as a member of the Massachusetts Institute of Technology (US) community and in all aspects of his life”. The announcement further stated that “Future recipients of the award will include those whose contributions exceed the boundaries of their profession, those who have contributed to building bridges across the community, and those who consistently and selflessly perform acts of kindness”.

    In September 2017, the school announced the creation of an artificial intelligence research lab called the MIT-IBM Watson AI Lab. IBM will spend $240 million over the next decade, and the lab will be staffed by MIT and IBM scientists. In October 2018 MIT announced that it would open a new Schwarzman College of Computing dedicated to the study of artificial intelligence, named after lead donor and The Blackstone Group CEO Stephen Schwarzman. The focus of the new college is to study not just AI, but interdisciplinary AI education, and how AI can be used in fields as diverse as history and biology. The cost of buildings and new faculty for the new college is expected to be $1 billion upon completion.

    The Caltech/MIT Advanced aLIGO (US) was designed and constructed by a team of scientists from California Institute of Technology (US), Massachusetts Institute of Technology (US) , and industrial contractors, and funded by the National Science Foundation (US) .

    MIT/Caltech Advanced aLigo .

    It was designed to open the field of gravitational-wave astronomy through the detection of gravitational waves predicted by general relativity. Gravitational waves were detected for the first time by the LIGO detector in 2015. For contributions to the LIGO detector and the observation of gravitational waves, two Caltech physicists, Kip Thorne and Barry Barish, and Massachusetts Institute of Technology (US) physicist Rainer Weiss won the Nobel Prize in physics in 2017. Weiss, who is also an Massachusetts Institute of Technology (US) graduate, designed the laser interferometric technique, which served as the essential blueprint for the LIGO.

    The mission of Massachusetts Institute of Technology (US) is to advance knowledge and educate students in science, technology, and other areas of scholarship that will best serve the nation and the world in the twenty-first century. We seek to develop in each member of the Massachusetts Institute of Technology (US) community the ability and passion to work wisely, creatively, and effectively for the betterment of humankind.

     
  • richardmitnick 10:28 am on February 11, 2021 Permalink | Reply
    Tags: "Researchers gather numerical evidence of quantum chaos in the Sachdev-Ye-Kitaev model", , , , , Chaos in quantum systems composed of strongly interacting particles also known as “many-body chaos”, , , , Quantum Gravity,   

    From UC Berkeley via phys.org: “Researchers gather numerical evidence of quantum chaos in the Sachdev-Ye-Kitaev model” 

    From UC Berkeley

    via


    phys.org

    February 11, 2021
    Ingrid Fadelli , Phys.org

    1
    A schematic phase diagram showing the behavior of the Sachdev-Ye-Kitaev model for different regimes of temperature and system size. From high to low temperature, the model transitions from behaving like interacting particles, to a semiclassical black hole, to a highly quantum black hole. Credit: Kobrin et al.

    Over the past few years, many physicists worldwide have conducted research investigating chaos in quantum systems composed of strongly interacting particles, also known as “many-body chaos”. The study of many-body chaos has broadened the current understanding of quantum thermalization (i.e., the process through which quantum particles reach thermal equilibrium by interacting with one another) and revealed surprising connections between microscopic physics and the dynamics of black holes.

    Researchers at University of California, Berkeley have recently carried out a study [Physical Review Letters] examining many-body chaos in the context of a renowned physical construct called the Sachdev-Ye-Kitaev (SYK) model. The SYK model describes a cluster of randomly interacting particles and was the first microscopic quantum system predicted to exhibit many-body chaos.

    “Our work is motivated by the fundamental question of how quickly information can spread in strongly-interacting quantum systems,” Bryce Kobrin, one of the researchers who carried out the study, told Phys.org. “A few years ago, a beautiful theoretical prediction emerged which suggested that in certain high-dimensional systems, information spreads exponentially fast, analogous to the butterfly effect in classical chaos.”

    In addition to hypothesizing this rapid spread of information in certain high-dimensional systems, previous studies proved that there is a universal speed limit on the rate at which this ‘chaos’ can develop. Interestingly, the only known or hypothesized systems that reach this limit are closely related to black holes, or more specifically, quantum theories that describe black holes. A major surprise was when researchers predicted that the SYK model also saturates the universal bound on chaos. This insight led to further analyses indicating that the low-temperature properties of the SYK model are, in effect, equivalent to that of a charged black hole.

    Although these ideas have been supported by theoretical calculations, verifying their validity and observing quantum chaos in numerical simulations has so far proved to be an enduring challenge. Kobrin and his colleagues set out to investigate the chaotic nature of the SYK model. They did this by simulating the dynamics of exceptionally large systems using cutting-edge numerical techniques they developed. Subsequently, they analyzed the data they collected using a method based on calculations from quantum gravity.

    “As a function of temperature, we observed the system change from behaving like ordinary interacting particles to agreeing precisely with the predicted behavior of a quantum black hole,” Kobrin said. “By developing new procedures to analyze our results, we determined the rate of chaos and explicitly showed that, at low temperatures, it approached the theoretical upper bound.”

    Kobrin and his colleagues gathered direct numerical evidence of a new dynamical phenomenon, namely many-body chaos, which translates chaos from classical mechanics to strongly interacting quantum systems. Their findings also highlight the valuable interplay between quantum simulations and quantum gravity theories.

    While in their recent study the researchers used the numerical tools that they created to examine many-body chaos in the SYK model in the future the same techniques could be applied to other models that are difficult to examine using common analysis frameworks. Ultimately, this could aid the ongoing search for quantum systems that exhibit the same behavior as black holes. Finally, the methods employed by this team of researchers could also inspire the development of experimental techniques to simulate quantum dynamics on controllable quantum hardware, for instance using arrays of cold atoms or trapped ions.

    “I am excited to investigate other phenomena at the intersection between quantum information and quantum gravity,” Kobrin said. “For example, it is predicted that by coupling together two copies of the SYK model, one can form a so-called traversable wormhole through which information can be communicated. This is a highly counterintuitive result which demonstrates that quantum chaos can, in fact, help move information from one place to another.”

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

    UC Berkeley Seal

     
  • richardmitnick 4:25 pm on January 27, 2021 Permalink | Reply
    Tags: "How heavy is Dark Matter? Scientists radically narrow the potential mass range for the first time", , , Dark Matter cannot be either ‘ultra-light’ or ‘super-heavy’., Gravity acts on Dark Matter just as it acts on the visible universe., If it turns out that the mass of Dark Matter is outside of the range predicted by the Sussex team then it will also prove that an additional force acts on Dark Matter., , , Quantum Gravity, U Sussex (UK)   

    From U Sussex (UK): “How heavy is Dark Matter? Scientists radically narrow the potential mass range for the first time” 

    From U Sussex (UK)

    27 January 2021
    Anna Ford

    1
    Credit: Greg Rakozy on Unsplash.

    Scientists have calculated the mass range for Dark Matter – and it’s tighter than the science world thought.

    Their findings – due to be published in Physical Letters B in March – radically narrow the range of potential masses for Dark Matter particles, and help to focus the search for future Dark Matter-hunters. The University of Sussex researchers used the established fact that gravity acts on Dark Matter just as it acts on the visible universe to work out the lower and upper limits of Dark Matter’s mass.

    The results show that Dark Matter cannot be either ‘ultra-light’ or ‘super-heavy’, as some have theorised, unless an as-yet undiscovered force also acts upon it.

    The team used the assumption that the only force acting on Dark Matter is gravity, and calculated that Dark Matter particles must have a mass between 10-3 eV and 107 eV. That’s a much tighter range than the 10-24 eV – 1019 GeV spectrum which is generally theorised.

    What makes the discovery even more significant is that if it turns out that the mass of Dark Matter is outside of the range predicted by the Sussex team, then it will also prove that an additional force – as well as gravity – acts on Dark Matter.

    Professor Xavier Calmet from the School of Mathematical and Physical Sciences at the University of Sussex, said:

    “This is the first time that anyone has thought to use what we know about quantum gravity as a way to calculate the mass range for Dark Matter. We were surprised when we realised no-one had done it before – as were the fellow scientists reviewing our paper.

    “What we’ve done shows that Dark Matter cannot be either ‘ultra-light’ or ‘super-heavy’ as some theorise – unless there is an as-yet unknown additional force acting on it. This piece of research helps physicists in two ways: it focuses the search area for Dark Matter, and it will potentially also help reveal whether or not there is a mysterious unknown additional force in the universe.”

    Folkert Kuipers, a PhD student working with Professor Calmet, at the University of Sussex, said:

    “As a PhD student, it’s great to be able to work on research as exciting and impactful as this. Our findings are very good news for experimentalists as it will help them to get closer to discovering the true nature of Dark Matter.”

    The visible universe – such as ourselves, the planets and stars – accounts for 25 per cent of all mass in the universe. The remaining 75 per cent is comprised of Dark Matter.

    It is known that gravity acts on Dark Matter because that’s what accounts for the shape of galaxies.

    Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM denied the Nobel, some 30 years later, did most of the work on Dark Matter.

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


    Coma cluster via NASA/ESA Hubble.


    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.
    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.
    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.

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


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


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

    See the full article here.

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Sussex (UK) is a leading research-intensive university near Brighton. We have both an international and local outlook, with staff and students from more than 100 countries and frequent engagement in community activities and services.

     
  • richardmitnick 12:37 pm on December 8, 2020 Permalink | Reply
    Tags: , Entangled quantum systems, , , , Quantum Gravity, , , Three of the four fundamental forces in physics can be described in terms of quantum theory. This is not the case for the fourth force (gravity).,   

    From University of Gronigen [Rijksuniversiteit Groningen] (NL) via phys.org: “Experiment to test quantum gravity just got a bit less complicated” 

    From University of Gronigen [Rijksuniversiteit Groningen] (NL)

    via


    phys.org

    December 8, 2020

    1
    In the proposed experiment, two diamonds are each placed in superposition and studied in freefall. Apart from gravity, the Casimir effect also draws them together, causing noise in the experiment. A thin copper plate can shield this effect, reducing the noise and making the experiment more manageable. Credit: A. Mazumdar, University of Groningen.

    Is gravity a quantum phenomenon? That has been one of the big outstanding questions in physics for decades. Together with colleagues from the UK, Anupam Mazumdar, a physicist from the University of Groningen, proposed an experiment that could settle the issue. However, it requires studying two very large entangled quantum systems in freefall. In a new paper
    [Physical Review A], which has a third-year Bachelor’s student as the first author, Mazumdar presents a way to reduce background noise to make this experiment more manageable.

    Three of the four fundamental forces in physics can be described in terms of quantum theory. This is not the case for the fourth force (gravity), which is described by Einstein’s theory of general relativity. The experiment that Mazumdar and his colleagues previously designed could prove or disprove the quantum nature of gravity.

    Superposition

    A well-known consequence of the quantum theory is the phenomenon called quantum superposition: in certain situations, quantum states can have two different values at the same time. Take an electron that is irradiated with laser light. Quantum theory says that it can either absorb or not absorb the photon energy from the light. Absorbing the energy would alter the electron’s spin, a magnetic moment that can be either up or down. The result of quantum superposition is that the spin is both up and down.

    These quantum effects take place in tiny objects, such as electrons. By targeting an electron in a specially constructed miniature diamond, it is possible to create superposition in a much larger object. The diamond is small enough to sustain this superposition, but also large enough to feel the pull of gravity. This characteristic is what the experiment exploits: placing two of these diamonds next to each other in freefall and, therefore, canceling out external gravity. This means that they only interact through the gravity between them.

    Challenging

    And that is where another quantum phenomenon comes in. Quantum entanglement means that when two or more particles are generated in close proximity, their quantum states are linked. In the case of the diamonds, if one is spin up, the other, entangled diamond should be spin down. So, the experiment is designed to determine whether quantum entanglement occurs in the pair during freefall, when the force of the gravity between the diamonds is the only way that they interact.

    “However, this experiment is very challenging,” explains Mazumdar. When two objects are very close together, another possible mechanism for interaction is present, the Casimir effect. In a vacuum, two objects can attract each other through this effect. “The size of the effect is relatively large and to overcome the noise it creates, we would have to use relatively large diamonds.” It was clear from the outset that this noise should be reduced to make the experiment more manageable. Therefore, Mazumdar wanted to know if shielding for the Casimir effect was possible.

    Lockdown

    He handed the problem to Thomas van de Kamp, a third-year Bachelor’s student of Physics. “He came to me because he was interested in quantum gravity and wanted to do a research project for his Bachelor’s thesis,” says Mazumdar. During the spring lockdown, when most normal classes were suspended, Van de Kamp started working on the problem. “Within a remarkably short time, he presented his solution, which is described in our paper.”

    This solution is based on placing a conducting plate of copper, around one millimeter thick, between the two diamonds. The plate shields the Casimir potential between them. Without the plate, this potential would draw the diamonds closer to each other. But with the plate, the diamonds are no longer attracted to each other, but to the plate between them. Mazumdar: “This removes the interaction between the diamonds through the Casimir effect, and therefore removes a lot of noise from the experiment.”

    Remarkable

    The calculations performed by Van de Kamp show that the masses of the two diamonds can be reduced by two orders of magnitude. “It may seem like a small step, but it does make the experiment less demanding.” Furthermore, other parameters such as the level of vacuum needed during the experiment also become less demanding due to the shielding of the Casimir effect. Mazumdar says that a further update on the experiment, which also includes a contribution from Bachelor’s student Thomas van de Kamp, will probably appear in the near future. “So, his six-month project has brought him co-authorship on two papers, quite a remarkable feat.”

    See the full article here.

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    The University of Gronigen [Rijksuniversiteit Groningen] (NL) is a public research university in the city of Groningen in the Netherlands. The university was founded in 1614 and is the second-oldest university in the Netherlands. In 2014, the university celebrated its 400th anniversary. Currently, RUG is placed in the top 100 universities worldwide according to three international ranking tables.

    The university was ranked 65th in the world, according to Academic Ranking of World Universities (ARWU) in 2019. In April 2013, according to the results of the International Student Barometer, the University of Groningen, for the third time in a row, was voted the best university of the Netherlands.

    The University of Groningen has eleven faculties, nine graduate schools, 27 research centres and institutes, and more than 175-degree programmes. The university’s alumni and faculty include Johann Bernoulli, Aletta Jacobs, four Nobel Prize winners, nine Spinoza Prize winners, one Stevin Prize winner, royalty, multiple mayors, the first president of the European Central Bank, and a secretary general of NATO.

     
  • richardmitnick 2:47 pm on September 29, 2020 Permalink | Reply
    Tags: "How big can a fundamental particle be?", , , , Quantum Gravity, , ,   

    From Symmetry: “How big can a fundamental particle be?” 

    Symmetry Mag
    From Symmetry<

    09/29/20
    Sarah Charley

    Extremely massive fundamental particles could exist, but they would seriously mess with our understanding of quantum mechanics.

    1
    Illustration by Sandbox Studio, Chicago with Steve Shanabruch.

    Fundamental particles are objects that are so small, they have no deeper internal structure.

    There are about a dozen “matter” particles that scientists think are fundamental, and they come in a variety of sizes. For instance, the difference between the masses of the top quark and the electron is equivalent to the difference between the masses of an adult elephant and a mosquito.

    Still, all of these masses are extremely tiny compared to what’s physically possible. The known laws of physics allow for fundamental particles with masses approaching the “Planck mass”: a whopping 22 micrograms, or about the mass of a human eyelash. To go back to our comparisons with currently known particles, if the top quark had the same mass as an elephant, then a fundamental particle at the Planck mass would weigh as much as the moon.

    Could such a particle exist? According to CERN Theory Fellow Dorota Grabowska, scientists aren’t completely sure.

    “Particles with a mass below the Planck scale can be elementary,” Grabowska says. “Above that scale, maybe not. But we don’t know.”

    Scientists at particle accelerators such as the Large Hadron Collider at CERN are always on the look-out for undiscovered massive particles that could fill in the gaps of their models. Finding new particles is so important that the global physics community is discussing building larger colliders that could produce even more massive particles. US involvement in the LHC is supported by the US Department of Energy’s Office of Science and the National Science Foundation.

    CERN FCC Future Circular Collider map.

    ILC schematic, being planned for the Kitakami highland, in the Iwate prefecture of northern Japan.

    China Circular Electron Positron Collider (CEPC) map. It would be housed in a hundred-kilometer- (62-mile-) round tunnel at one of three potential sites. The documents work under the assumption that the collider will be located near Qinhuangdao City around 200 miles east of Beijing.

    If scientists found a fundamental particle with a mass above the Planck scale, they would need to revisit how they think about particle sizes. For the kind of research performed at the LHC, fundamental particles are all considered to be the same size—no size at all.

    “When we think about the pure mathematics, elementary particles are, by definition, point-like,” Grabowska says. “They don’t have a size.”

    Treating fundamental particles as points works well in particle physics because their masses are so small that gravity, which would have an effect on more massive objects, is not really a factor. It’s kind of like how truck drivers planning a trip don’t need to consider the effects of special relativity and time dilation. These effects are there, at some level, but they don’t have a noticeable impact on drive time.

    But a fundamental particle above the Planck scale would sit at the threshold between two divergent mathematical models. Quantum mechanics describes objects that are very tiny, and general relativity describes objects that are very massive. But to describe a particle that is both very tiny and very massive, scientists need a new theory called quantum gravity.

    Mathematically, physicists could no longer consider such a massive particle as a volume-less point. Instead, they would need to think about it behaving more like a wave.

    The particle-wave duality concept was born about 100 years ago and states that subatomic particles have both particle-like and wave-like properties. When scientists think about an electron as a particle, they consider that it has no physical volume. But when they think about it as a wave, it extends throughout all the space it’s granted, such as the orbit around the nucleus of an atom. Both interpretations are correct, and scientists typically use the one that best suits their area of research.

    The mass-to-radius ratio of these waves is important because it determines how they feel the effects of gravity. A super massive particle with tons of room to roam would barely feel the force of gravity. But if that same particle were confined to an extremely small space, it could collapse into a miniature black hole. Scientists at the LHC have searched for such tiny black holes—which would evaporate almost immediately—but so far have come up empty-handed.

    According to Grabowska, quantum gravity is tricky because there is no way to experimentally test it with today’s existing technology. “We would need a collider 14 orders of magnitude more energetic than the LHC,” she says.

    But thinking about the implications of finding such a particle helps theorists push the known laws of physics.

    “Our model of particle physics breaks down when pushed to certain scales,” says Netta Engelhardt, a quantum gravity theorist at the Massachusetts Institute of Technology. “But that doesn’t mean that our universe doesn’t feature these regimes. If we want to understand massive objects at tiny scales, we need a model of quantum gravity.”

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:33 am on April 25, 2019 Permalink | Reply
    Tags: "Could An Incompleteness In Quantum Mechanics Lead To Our Next Scientific Revolution?", , , , Quantum Gravity   

    From Ethan Siegel: “Could An Incompleteness In Quantum Mechanics Lead To Our Next Scientific Revolution?” 

    From Ethan Siegel
    Apr 24, 2019

    1
    The proton’s structure, modeled along with its attendant fields, show how even though it’s made out of point-like quarks and gluons, it has a finite, substantial size which arises from the interplay of the quantum forces and fields inside it. The proton, itself, is a composite, not fundamental, quantum particle. (BROOKHAVEN NATIONAL LABORATORY)

    A single thought experiment reveals a paradox. Could quantum gravity be the solution?

    Sometimes, if you want to understand how nature truly works, you need to break things down to the simplest levels imaginable. The macroscopic world is composed of particles that are — if you divide them until they can be divided no more — fundamental. They experience forces that are determined by the exchange of additional particles (or the curvature of spacetime, for gravity), and react to the presence of objects around them.

    At least, that’s how it seems. The closer two objects are, the greater the forces they exert on one another. If they’re too far away, the forces drop off to zero, just like your intuition tells you they should. This is called the principle of locality, and it holds true in almost every instance. But in quantum mechanics, it’s violated all the time. Locality may be nothing but a persistent illusion, and seeing through that facade may be just what physics needs.

    2
    Quantum gravity tries to combine Einstein’s general theory of relativity with quantum mechanics. Quantum corrections to classical gravity are visualized as loop diagrams, as the one shown here in white. We typically view objects that are close to one another as capable of exerting forces on one another, but that might be an illusion, too. (SLAC NATIONAL ACCELERATOR LAB)

    Imagine that you had two objects located in close proximity to one another. They would attract or repel one another based on their charges and the distance between them. You might visualize this as one object generating a field that affects the other, or as two objects exchanging particles that impart either a push or a pull to one or both of them.

    You’d expect, of course, that there would be a speed limit to this interaction: the speed of light. Relativity gives you no other way out, since the speed at which the particles responsible for forces propagate is limited by the speed they can travel, which can never exceed the speed of light for any particle in the Universe. It seems so straightforward, and yet the Universe is full of surprises.

    3
    An example of a light cone, the three-dimensional surface of all possible light rays arriving at and departing from a point in spacetime. The more you move through space, the less you move through time, and vice versa. Only things contained within your past light-cone can affect you today; only things contained within your future light-cone can be perceived by you in the future. (WIKIMEDIA COMMONS USER MISSMJ)

    We have this notion of cause-and-effect that’s been hard-wired into us by our experience with reality. Physicists call this causality, and it’s one of the rare physics ideas that actually conforms to our intuition. Every observer in the Universe, from its own perspective, has a set of events that exist in its past and in its future.

    In relativity, these are events contained within either your past light-cone (for events that can causally affect you) or your future light-cone (for events that you can causally effect). Events that can be seen, perceived, or can otherwise have an effect on an observer are known as causally-connected. Signals and physical effects, both from the past and into the future, can propagate at the speed of light, but no faster. At least, that’s what your intuitive notions about reality tell you.

    4
    Schrödinger’s cat. Inside the box, the cat will be either alive or dead, depending on whether a radioactive particle decayed or not. If the cat were a true quantum system, the cat would be neither alive nor dead, but in a superposition of both states until observed. (WIKIMEDIA COMMONS USER DHATFIELD)

    But in the quantum Universe, this notion of relativistic causality isn’t as straightforward or universal as it would seem. There are many properties that a particle can have — such as its spin or polarization — that are fundamentally indeterminate until you make a measurement. Prior to observing the particle, or interacting with it in such a way that it’s forced to be in either one state or the other, it’s actually in a superposition of all possible outcomes.

    Well, you can also take two quantum particles and entangle them, so that these very same quantum properties are linked between the two entangled particles. Whenever you interact with one member of the entangled pair, you not only gain information about which particular state it’s in, but also information about its entangled partner.

    5
    By creating two entangled photons from a pre-existing system and separating them by great distances, we can ‘teleport’ information about the state of one by measuring the state of the other, even from extraordinarily different locations. (MELISSA MEISTER, OF LASER PHOTONS THROUGH A BEAM SPLITTER)

    This wouldn’t be so bad, except for the fact that you can set up an experiment as follows.

    You can create your pair of entangled particles at a particular location in space and time.
    You can transport them an arbitrarily large distance apart from one another, all while maintaining that quantum entanglement.
    Finally, you can make those measurements (or force those interactions) as close to simultaneously as possible.

    In every instance where you do this, you’ll find the member you measure in a particular state, and instantly “know” some information about the other entangled member.

    6
    A photon can have two types of circular polarizations, arbitrarily defined so that one is + and one is -. By devising an experiment to test correlations between the directional polarization of entangled particles, one can attempt to distinguish between certain formulations of quantum mechanics that lead to different experimental results.(DAVE3457 / WIKIMEDIA COMMONS)

    What’s puzzling is that you cannot check whether this information is true or not until much later, because it takes a finite amount of time for a light signal to arrive from the other member. When the signal does arrive, it always confirms what you’d known just by measuring your member of the entangled pair: your expectation for the state of the distant particle agreed 100% with what its measurement indicated.

    Only, there seems to be a problem. You “knew” information about a measurement that was taking place non-locally, which is to say that the measurement that occurred is outside of your light cone. Yet somehow, you weren’t entirely ignorant about what was going on over there. Even though no information was transmitted faster than the speed of light, this measurement describes a troubling truth about quantum physics: it is fundamentally a non-local theory.

    7
    Schematic of the third Aspect experiment testing quantum non-locality. Entangled photons from the source are sent to two fast switches that direct them to polarizing detectors. The switches change settings very rapidly, effectively changing the detector settings for the experiment while the photons are in flight. (CHAD ORZEL)

    There are limits to this, of course.

    It isn’t as clean as you want: measuring the state of your particle doesn’t tell us the exact state of its entangled pair, just probabilistic information about its partner.

    There is still no way to send a signal faster than light; you can only use this non-locality to predict a statistical average of entangled particle properties.

    And even though it has been the dream of many, from Einstein to Schrödinger to de Broglie, no one has ever come up with an improved version of quantum mechanics that tells you anything more than its original formulation.

    But there are many who still dream that dream.

    8
    If two particles are entangled, they have complementary wavefunction properties, and measuring one places meaningful constraints on the properties of the other. (WIKIMEDIA COMMONS USER DAVID KORYAGIN)

    One of them is Lee Smolin, who cowrote a paper [Physical Review D] way back in 2003 that showed an intriguing link between general ideas in quantum gravity and the fundamental non-locality of quantum physics. Although we don’t have a successful quantum theory of gravity, we have established a number of important properties concerning how a quantum theory of gravity will behave and still be consistent with the known Universe.

    9
    A variety of quantum interpretations and their differing assignments of a variety of properties. Despite their differences, there are no experiments known that can tell these various interpretations apart from one another, although certain interpretations, like those with local, real, deterministic hidden variables, can be ruled out. (ENGLISH WIKIPEDIA PAGE ON INTERPRETATIONS OF QUANTUM MECHANICS)

    There are many reasons to be skeptical that this conjecture will hold up to further scrutiny. For one, we don’t truly understand quantum gravity at all, and anything we can say about it is extraordinarily provisional. For another, replacing the non-local behavior of quantum mechanics with the non-local behavior of quantum gravity is arguably making the problem worse, not better. And, as a third reason, there is nothing thought to be observable or testable about these non-local variables that Markopoulou and Smolin claim could explain this bizarre property of the quantum Universe.

    Fortunately, we’ll have the opportunity to hear the story direct from Smolin himself and evaluate it on our own. You see, at 7 PM ET (4 PM PT) on April 17, Lee Smolin is giving a public lecture on exactly this topic at Perimeter Institute, and you can watch it right here.


    1:18:47

    I’ll be watching along with you, curious about what Smolin is calling Einstein’s Unfinished Revolution, which is the ultimate quest to supersede our two current (but mutually incompatible) descriptions of reality: General Relativity and quantum mechanics.

    10

    Best of all, I’ll be giving you my thoughts and commentary below in the form of a live-blog, beginning 10 minutes before the start of the talk. [See the full article.]

    Find out where we are in the quest for quantum gravity, and what promises it may (or may not) have for revolutionizing one of the greatest counterintuitive mysteries about the quantum nature of reality!

    Thanks for joining me for an interesting lecture and discussions on science, and just maybe, someday, we’ll have some interesting progress to report on this topic. Until then, you don’t have to shut up, but you still do have to calculate!

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “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 1:10 pm on July 27, 2018 Permalink | Reply
    Tags: , , , , , Quantum Gravity, This Simple Thought Experiment Shows Why We Need Quantum Gravity   

    From Ethan Siegel: “This Simple Thought Experiment Shows Why We Need Quantum Gravity” 

    From Ethan Siegel
    Jul 27, 2018

    1
    Quantum gravity tries to combine Einstein’s general theory of relativity with quantum mechanics. Quantum corrections to classical gravity are visualized as loop diagrams, as the one shown here in white. Whether space (or time) itself is discrete or continuous is not yet decided, as is the question of whether gravity is quantized at all. (SLAC NATIONAL ACCELERATOR LAB)

    If our current laws of physics can’t predict what will happen, even probabilistically, we need something new.

    There are two theories we have that explain all the particles and their interactions in the known Universe: General Relativity and the Standard Model of particle physics. General Relativity describes gravity perfectly everywhere we’ve ever looked. From the smallest-scale attractions we’ve ever measured in a laboratory to the expansion and curvature of space due to Earth, the Sun, black holes, galaxies, or the entire Universe, our observations and measurements have never deviated from what we’ve observed. The Standard Model is equally successful for the other three forces: electromagnetism and the strong and weak nuclear forces. Every experiment, measurement, and observation has agreed perfectly with these two theories.

    It sounds great, until you try to combine the two. If we do that, it all falls apart. The solution? We need a quantum theory of gravity. Here’s why.

    2
    The spacetime curvature around any massive object is determined by the combination of mass and distance from the center-of-mass. Other concerns, like velocity, acceleration, and other sources of energy, must be factored in. (T. PYLE/CALTECH/MIT/LIGO LAB)

    From Einstein’s theory of gravity, we can compute what the curvature of space is at any location in the Universe, from here on planet Earth to the largest scales in the cosmos. We’ve performed experiments that have tested the gravitational force law down to micron-sized scales, and on astrophysical scales in extreme environments, such as the galactic center, merging neutron stars, and at the edges of black holes. Even esoteric predictions, such as the production of gravitational waves, the effect of frame-dragging, or the precession of planetary orbits, are completely in line with every measurement we’ve ever taken. In every case, Einstein’s theory perfectly describes reality.

    3
    The Standard Model of particle physics accounts for three of the four forces (excepting gravity), the full suite of discovered particles, and all of their interactions. Quarks and leptons are fermions, which have a host of unique properties that the other (bosons) particles do not possess. (CONTEMPORARY PHYSICS EDUCATION PROJECT / DOE / NSF / LBNL)

    From the Standard Model, we know how electricity, magnetism, radioactive decays and nuclear forces work. Take any particle and let it interact (or not) with anything else in the Universe, and we’ll know the probability distribution of all possible outcomes. Even though the quantum world isn’t entirely deterministic, we can still successfully describe the expected set of outcomes in a mathematically precise fashion. If we perform the same experiment thousands upon thousands of times, we’ll see the results match our best quantum predictions, even for bizarre and unintuitive setups.

    But if we take a look at one such setup in particular — the famed double-slit experiment — we can see immediately why a quantum theory of gravity is absolutely necessary.

    4
    The wave-like properties of light became even better understood thanks to Thomas Young’s two-slit experiments, where constructive and destructive interference showed themselves dramatically. These experiments were known for classical waves since the 17th century; around 1800, Young showed they applied to light as well. (THOMAS YOUNG, 1801)

    Imagine you’ve got a set of quantum particles: they could be photons, neutrinos, electrons, or anything else. Imagine that you’ve set them up so they’ll bombard a tiny area of a barrier, with two slits cut into the barrier extremely close together, to allow these quantum particles to pass through. Behind the barrier, you’ll set up a screen, so you can detect where the particles wind up. This is the classic setup of the double slit experiment.

    If you send through a bunch of particles at once, they act just like a wave. The particles might go through one slit or the other, but they interfere. At the end of the day, you wind up with a clearly identifiable interference pattern on the screen, the same way you would for a water wave passing through a similar set of slits.

    5
    Double slit experiments performed with light produce interference patterns, as they do for any wave. The properties of different light colors is due to their differing wavelengths. (TECHNICAL SERVICES GROUP (TSG) AT MIT’S DEPARTMENT OF PHYSICS)

    Well, you can’t have your particles interfering with one another, so you decide to send them through one-at-a-time. You measure where it hits the screen and record it, and then you fire the next particle. It doesn’t matter which particle you choose; if we can detect it on the screen, we see the same behavior. The interference pattern builds up one-particle-at-a-time, but clearly emerges. Somehow, these quantum particles are passing through both slits simultaneously, and are interfering with themselves.

    6
    The wave pattern for electrons passing through a double slit, one-at-a-time. If you measure “which slit” the electron goes through, you destroy the quantum interference pattern shown here. Note that more than one electron is required to reveal the interference pattern. (DR. TONOMURA AND BELSAZAR OF WIKIMEDIA COMMONS)

    Perhaps you decide you’re not a fan of this quantum weirdness, so you decide to measure which slit each particle goes through. You set up a photodetector around each slit, and measure when a particle passes through it. The first particle goes through, and you detect its passage through slit #2. The second one arrives, and also goes through slit #2. The third one goes through slit #1, then the fourth through #2, and then the fifth through #1 again. You repeat this, over and over, for thousands of particles. And when you look at the resulting pattern on the screen, you find something extremely troublesome: the interference pattern is gone. Instead, all you see is a pile of particles that passed through slit #1, along with another pile that passed through slit #2. They did not interfere.

    7
    If you measure which slit an electron goes through, you don’t get an interference pattern on the screen behind it. Instead, the electrons behave not as waves, but as classical particles. (WIKIMEDIA COMMONS USER INDUCTIVELOAD)

    This is weird! This unintuitive weirdness is at the heart of what makes quantum physics, and the Standard Model in general, such a powerful tool. At a fundamental, quantum level, we can accurately predict when you have this quantum behavior and when you won’t, and what that behavior will look like when it appears.

    For the electromagnetic, strong nuclear, and weak nuclear forces, this works exquisitely well. It works so well that, as bizarre as they may be, no repeatable experiment has ever disagreed with any significance from the Standard Model’s predictions. And yet, if we were to ask the following simple question, we don’t have any way to arrive at an answer:

    What happens to the gravitational field of an electron when it passes through a double slit?

    8
    The gravitational field of the electron, as it passes through a double slit, would behave differently if gravity is fundamentally quantum (bottom) or non-quantum (top). (Sabine Hossenfelder)

    The reason we can’t answer it is we don’t know a huge number of properties about gravity on the quantum scale. We don’t know whether gravity is quantized or not. The particles must be quantized, but gravity might not be, and if it isn’t, the double slit experiment would give different results than if it is.

    We don’t know whether space is fundamentally discrete (with a minimum length scale) or continuous. If there were a minimum length, there would be a fundamental resolution limit to our experiments, one we might someday encounter at high enough energies. There are questions we cannot answer about how gravity behaves under certain experimental conditions.

    9
    Even two merging black holes, one of the strongest sources of a gravitational signal in the Universe, doesn’t leave an observable signature that could probe quantum gravity. For that, we’ll have to create experiments that probe either the strong-field regime of relativity, i.e., near the singularity, or that take advantage of clever laboratory setups. (SXS, THE SIMULATING EXTREME SPACETIMES (SXS) PROJECT (BLACK-HOLES.ORG))

    We know, in principle, that the gravitational field should remain localized around the electron’s position, just as it would for any mass. But what does this mean when the electron’s position is inherently uncertain? Does the gravitational field always go primarily through one slit or the other? And does the act of observing (or not observing) change the gravitational field? And if so, how?

    The gravitational field of the electron is weak; we cannot observe it in practice. Equations developed by Wheeler, Feynman, and DeWitt in the 1960s describe the expected behavior of a particle in the weak-field limit of quantum gravity, but those equations have never been experimentally tested. To do so is presently beyond the realm of what we’re capable of, but there is hope.

    10
    The experimental setup that’s enabled the measurement of gravitational fields and effects down to milligram-scale masses, From “A micromechanical proof-of-principle experiment for measuring the gravitational force of milligram masses.”

    There are proposed experimental setups that would allow us to measure the gravitational field more precisely than ever before: down to milligram masses. On the other hand, we’ve managed to bring relatively large objects (compared to fundamental particles) into quantum superpositions of states: up to nanogram-scale masses. The exact energy levels of these states depend on the total gravitational self-energy of the system, making this a realistic, plausible test to determine whether gravity is quantized or not. When technology and experimental techniques advance far enough, these two scales will intersect. When that moment comes, we’ll be able to probe the quantum gravitational regime.

    11
    The energy levels of a nanogram-scale disk of osmium, and how the effect of self-gravitation will (right) or won’t (left) affect the specific values of those energy levels. The disk’s wavefunction, and how it’s affected by gravitation, may lead to the first experimental test of whether gravity is truly a quantum force. (ANDRÉ GROSSARDT ET AL. (2015); ARXIV:1510.0169)

    The description that General Relativity puts forth — that of matter telling space how to curve, and curved space telling matter how to move — needs to be augmented to include an uncertain position that has a probability distribution to it. Whether gravity is quantized or not is still an unknown, and has everything to do with the outcome of such a hypothetical experiment. How an uncertain position translates into a gravitational field, exactly, remains an unsolved problem on the road to a full quantum theory of gravity. The principles that underlie quantum mechanics must be universal, but how those principles apply to gravity, and in particular to a particle passing through a double slit, is a great unknown of our time.

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “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 9:28 pm on November 24, 2017 Permalink | Reply
    Tags: , , Free-fall experiment could test if gravity is a quantum force, , , Quantum Gravity, ,   

    From New Scientist: “Free-fall experiment could test if gravity is a quantum force” 

    NewScientist

    New Scientist

    22 November 2017
    Anil Ananthaswamy

    1
    Free-falling. Manuela Schewe-Behnisch/EyeEm/Getty

    Despite decades of effort, a theory of quantum gravity is still out of grasp. Now a group of physicists have proposed an experimental test of whether gravity is quantum or not, to settle questions about the force’s true nature.

    The search for quantum gravity is an effort to reconcile Einstein’s general relativity with quantum mechanics, which is a theory of all the fundamental particles and the forces that act on them – except gravity. Both are needed to explain what happens inside black holes and what happened at the big bang. But the two theories are incompatible, leading to apparent paradoxes and things like singularities, where the theories break down.

    If gravity is a quantum mechanical force, adjacent free-falling masses, each of which is in a superposition of being in two places at once, could get entangled by gravity such that measuring the properties of one mass could instantly influence the other. To test this, Sougato Bose of University College London and his colleagues have proposed an experiment.

    Branching paths

    It starts with a neutrally charged mass weighing about 10^-14 kilograms. Embedded within the mass is some material with a property called spin, which can be up or down. This mass falls through a continuously varying magnetic field, which changes the path of the mass depending on its spin. It is like the mass encounters a fork in the road and takes one path if its spin is up, and another if its spin is down.

    As it falls, the mass is in a superposition of being on both paths. Next, a series of microwave pulses manipulate the spin at various stages of descent and thus the paths the mass takes. At the bottom, the paths then come together again and the mass is brought to its original state.

    To use this set-up to test the quantum nature of gravity, two such masses would be dropped through the magnetic field. Each mass has two possible paths. This results in four possible states for the two masses combined. One of these states represents paths in which the masses come closest together.

    This distance should be no less than 200 micrometres to avoid other interactions that can dominate gravity. Once the masses are back to their original state, a test to see if their spin components are entangled should tell us if gravity is indeed a quantum force. The assumption, of course, is that the experiment ensures there are no other ways in which the masses can get entangled – such as via electromagnetic interactions or the Casimir force.

    Bose points out, however, that a null result – in which no entanglement is observed – wouldn’t constitute proof that gravity is classical, unless the experiment can definitively rule out all other interactions with the environment that can destroy entanglement, such as collisions with stray photons or molecules.

    Quantum roots?

    Antoine Tilloy at the Max Planck Institute of Quantum Optics in Germany is impressed. But he points out that a positive result will falsify only some classes of theories of classical gravity. “That said, the class is sufficiently large that I think the result would still be amazing,” he says.

    Even a verifiable null result would be exciting because it would mean gravity doesn’t have quantum roots, says Maaneli Derakhshani of Utrecht University in the Netherlands. “This would then raise tough but interesting questions about how and when exactly gravity ‘turns on’ in the quantum-classical transition for ordinary matter,” says Derakhshani. “A null result would be the most surprising and interesting outcome.”

    The biggest hurdle to carrying out the experiment for real would be putting such relatively large masses in a superposition. The most massive objects that have been observed to be in two places at once are still orders of magnitude smaller than what is required here. But efforts to go higher are ongoing.

    This work is soon to be published in Physical Review Letters.

    Reference: arxiv.org/abs/1707.06050

    See the full article here .

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  • richardmitnick 2:21 pm on September 21, 2017 Permalink | Reply
    Tags: But quantum mechanics doesn’t really define what a measurement is, , Gravity at its most fundamental comes in indivisible parcels called quanta, GRW model-Ghirardi–Rimini–Weber theory, In quantum theory the state of a particle is described by its wave function, Much like the electromagnetic force comes in quanta called photons, , Quantum Gravity,   

    From New Scientist: “Gravity may be created by strange flashes in the quantum realm” 

    NewScientist

    New Scientist

    20 September 2017
    Anil Ananthaswamy

    1
    Gravity comes about in a flash. Emma Johnson/Getty

    HOW do you reconcile the two pillars of modern physics: quantum theory and gravity? One or both will have to give way. A new approach says gravity could emerge from random fluctuations at the quantum level, making quantum mechanics the more fundamental of the two theories.

    Of our two main explanations of reality, quantum theory governs the interactions between the smallest bits of matter. And general relativity deals with gravity and the largest structures in the universe. Ever since Einstein, physicists have been trying to bridge the gap between the two, with little success.

    Part of the problem is knowing which strands of each theory are fundamental to our understanding of reality.

    One approach towards reconciling gravity with quantum mechanics has been to show that gravity at its most fundamental comes in indivisible parcels called quanta, much like the electromagnetic force comes in quanta called photons. But this road to a theory of quantum gravity has so far proved impassable.

    Now Antoine Tilloy at the Max Planck Institute of Quantum Optics in Garching, Germany, has attempted to get at gravity by tweaking standard quantum mechanics.

    In quantum theory, the state of a particle is described by its wave function. The wave function lets you calculate, for example, the probability of finding the particle in one place or another on measurement. Before the measurement, it is unclear whether the particle exists and if so, where. Reality, it seems, is created by the act of measurement, which “collapses” the wave function.

    But quantum mechanics doesn’t really define what a measurement is. For instance, does it need a conscious human? The measurement problem leads to paradoxes like Schrödinger’s cat, in which a cat can be simultaneously dead and alive inside a box, until someone opens the box to look.

    One solution to such paradoxes is a so-called GRW model that was developed in the late 1980s. It incorporates “flashes”, which are spontaneous random collapses of the wave function of quantum systems. The outcome is exactly as if there were measurements being made, but without explicit observers.

    Tilloy has modified this model to show how it can lead to a theory of gravity. In his model, when a flash collapses a wave function and causes a particle to be in one place, it creates a gravitational field at that instant in space-time. A massive quantum system with a large number of particles is subject to numerous flashes, and the result is a fluctuating gravitational field.

    It turns out that the average of these fluctuations is a gravitational field that one expects from Newton’s theory of gravity (arxiv.org/abs/1709.03809). This approach to unifying gravity with quantum mechanics is called semiclassical: gravity arises from quantum processes but remains a classical force. “There is no real reason to ignore this semiclassical approach, to having gravity being classical at the fundamental level,” says Tilloy.

    “I like this idea in principle,” says Klaus Hornberger at the University of Duisburg-Essen in Germany. But he points out that other problems need to be tackled before this approach can be a serious contender for unifying all the fundamental forces underpinning the laws of physics on scales large and small. For example, Tilloy’s model can be used to get gravity as described by Newton’s theory, but the maths still has to be worked out to see if it is effective in describing gravity as governed by Einstein’s general relativity.

    Tilloy agrees. “This is very hard to generalise to relativistic settings,” he says. He also cautions that no one knows which of the many tweaks to quantum mechanics is the correct one.

    Nonetheless, his model makes predictions that can be tested. For example, it predicts that gravity will behave differently at the scale of atoms from how it does on larger scales. Should those tests find that Tilloy’s model reflects reality and gravity does indeed originate from collapsing quantum fluctuations, it would be a big clue that the path to a theory of everything would involve semiclassical gravity.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

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