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  • richardmitnick 11:02 am on December 31, 2017 Permalink | Reply
    Tags: , , , , Darki Matter, , , Mordehai Milgrom   

    From Symmetry: “Shaking the dark matter paradigm” One of the Best From 2017 

    Symmetry Mag
    Symmetry

    07/18/17
    Ali Sundermier

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    Artwork by Sandbox Studio, Chicago with Ana Kova

    A theory about gravity challenges our understanding of the universe.

    For millennia, humans held a beautiful belief. Our planet, Earth, was at the center of a vast universe, and all of the planets and stars and celestial bodies revolved around us. This geocentric model, though it had floated around since 6th century BCE, was written in its most elegant form by Claudius Ptolemy in 140 AD.

    When this model encountered problems, such as the retrograde motions of planets, scientists reworked the data to fit the model by coming up with phenomena such as epicycles, mini orbits.

    It wasn’t until 1543, 1400 years later, that Nicolaus Copernicus set in motion a paradigm shift that would give way to centuries of new discoveries. According to Copernicus’ radical theory, Earth was not the center of the universe but simply one of a long line of planets orbiting around the sun.

    But even as evidence that we lived in a heliocentric system piled up and scientists such as Galileo Galilei perfected the model, society held onto the belief that the entire universe orbited around Earth until the early 19th century.

    To Erik Verlinde, a theoretical physicist at the University of Amsterdam, the idea of dark matter is the geocentric model of the 21st century.

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    Erik Verlinde, University of Amsterdam

    https://sciencesprings.wordpress.com/2016/11/30/from-quanta-the-case-against-dark-matter/

    “What people are doing now is allowing themselves free parameters to sort of fit the data,” Verlinde says. “You end up with a theory that has so many free parameters it’s hard to disprove.”

    Dark matter, an as-yet-undetected form of matter that scientists believe makes up more than a quarter of the mass and energy of the universe, was first theorized when scientists noticed that stars at the outer edges of galaxies and galaxy clusters were moving much faster than Newton’s theory of gravity said they should. Up until this point, scientists have assumed that the best explanation for this is that there must be missing mass in the universe holding those fast-moving stars in place in the form of dark matter.

    But Verlinde has come up with a set of equations that explains these galactic rotation curves by viewing gravity as an emergent force — a result of the quantum structure of space.

    The idea is related to dark energy, which scientists think is the cause for the accelerating expansion of our universe. Verlinde thinks that what we see as dark matter is actually just interactions between galaxies and the sea of dark energy in which they’re embedded.

    “Before I started working on this I never had any doubts about dark matter,” Verlinde says. “But then I started thinking about this link with quantum information and I had the idea that dark energy is carrying more of the dynamics of reality than we realize.”

    Verlinde is not the first theorist to come up with an alternative to dark matter. Many feel that his theory echoes the sentiment of physicist Mordehai Milgrom’s equations of “modified Newtonian dynamics,” or MOND.

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    Mordehai Milgrom, at the Weizmann Institute of Science

    https://sciencesprings.wordpress.com/2017/05/18/from-nautilus-the-physicist-who-denies-dark-matter/

    Just as Einstein modified Newton’s laws of gravity to fit to the scale of planets and solar systems, MOND modifies Einstein’s laws of gravity to fit to the scale of galaxies and galaxy clusters.

    Verlinde, however, makes the distinction that he’s not deriving the equations of MOND, rather he’s deriving what he calls a “scaling relation,” or a volume effect of space-time that only becomes important at large distances.

    Stacy McGaugh, an astrophysicist at Case Western Reserve University, says that while MOND is primarily the notion that the effective force of gravity changes with acceleration, Verlinde’s ideas are more of a ground-up theoretical work.

    “He’s trying to look at the structure of space-time and see if what we call gravity is a property that emerges from that quantum structure, hence the name emergent gravity,” McGaugh says. “In principle, it’s a very different approach that doesn’t necessarily know about MOND or have anything to do with it.”

    One of the appealing things about Verlinde’s theory, McGaugh says, is that it naturally produces evidence of MOND in a way that “just happens.”

    “That’s the sort of thing that one looks for,” McGaugh says. “There needs to be some basis of why MOND happens, and this theory might provide it.”

    Verlinde’s ideas have been greeted with a fair amount of skepticism in the scientific community, in part because, according to Kathryn Zurek, a theoretical physicist at the US Department of Energy’s Lawrence Berkeley National Laboratory, his theory leaves a lot unexplained.

    “Theories of modified gravity only attempt to explain galactic rotation curves [those fast-moving planets],” Zurek says. “As evidence for dark matter, that’s only one very small part of the puzzle. Dark matter explains a whole host of observations from the time of the cosmic microwave background when the universe was just a few hundred thousand years old through structure formation all the way until today.”

    Zurek says that in order for scientists to start lending weight to his claims, Verlinde needs to build the case around his theory and show that it accommodates a wider range of observations. But, she says, this doesn’t mean that his ideas should be written off.

    “One should always poke at the paradigm,” Zurek says, “even though the cold dark matter paradigm has been hugely successful, you always want to check your assumptions and make sure that you’re not missing something that could be the tip of the iceberg.”

    McGaugh had a similar crisis of faith in dark matter when he was working on an experiment wherein MOND’s predictions were the only ones that came true in his data. He had been making observations of low-surface-brightness galaxies, wherein stars are spread more thinly than galaxies such as the Milky Way where the stars are crowded relatively close together.

    McGaugh says his results did not make sense to him in the standard dark matter context, and it turned out that the properties that were confusing to him had already been predicted by Milgrom’s MOND equations in 1983, before people had even begun to take seriously the idea of low-surface-brightness galaxies.

    Although McGaugh’s experience caused him to question the existence of dark matter and instead argue for MOND, others have not been so quick to join the cause.

    “We subscribe to a particular paradigm and most of our thinking is constrained within the boundaries of that paradigm, and so if we encounter a situation in which there is a need for a paradigm shift, it’s really hard to think outside that box,” McGaugh says. “Even though we have rules for the game as to when you’re supposed to change your mind and we all in principle try to follow that, in practice there are some changes of mind that are so big that we just can’t overcome our human nature.”

    McGaugh says that many of his colleagues believe that there’s so much evidence for dark matter that it’s a waste of time to consider any alternatives. But he believes that all of the evidence for dark matter might instead be an indication that there is something wrong with our theories of gravity.

    “I kind of worry that we are headed into another thousand years of dark epicycles,” McGaugh says.

    But according to Zurek, if MOND came up with anywhere near the evidence that has been amassed for the dark matter paradigm, people would be flocking to it. The problem, she says, is that at the moment MOND just does not come anywhere near to passing the number of tests that cold dark matter has. She adds that there are some physicists who argue that the cold dark matter paradigm can, in fact, explain those observations about low-surface-brightness galaxies.

    Recently, Case Western held a workshop wherein they gathered together representatives from different communities, including those working on dark matter models, to discuss dwarf galaxies and the external field effect, which is the notion that very low-density objects will be affected by what’s around them. MOND predicts that the dynamics of a small satellite galaxy will depend on its proximity to its giant host in a way that doesn’t happen with dark matter.

    McGaugh says that in attendance at the workshop were a group of more philosophically inclined people who use a set of rules to judge theories, which they’ve put together by looking back at how theories have developed in the past.

    “One of the interesting things that came out of that was that MOND is doing better on that score card,” he says. “It’s more progressive in the sense that it’s making successful predictions for new phenomena whereas in the case of dark matter we’ve had to repeatedly invoke ad hoc fixes to patch things up.”

    Verlinde’s ideas, however, didn’t come up much within the workshop. While McGaugh says that the two theories are closely enough related that he would hope the same people pursuing MOND would be interested in Verlinde’s theory, he added that not everyone shares that attitude. Many are waiting for more theoretical development and further observational tests.

    “The theory needs to make a clear prediction so that we can then devise a program to go out and test it,” he says. “It needs to be further worked out to get beyond where we are now.”

    Verlinde says he realizes that he still needs to develop his ideas further and extend them to explain things such as the formation of galaxies and galaxy clusters. Although he has mostly been working on this theory on his own, he recognizes the importance of building a community around his ideas.

    Over the past few months, he has been giving presentations at different universities, including Princeton, Harvard, Berkeley, Stanford, and Caltech. There is currently a large community of people working on ideas of quantum information and gravity, he says, and his main goal is to get more people, in particular string theorists, to start thinking about his ideas to help him improve them.

    “I think that when we understand gravity better and we use those equations to describe the evolution of the universe, we may be able to answer questions more precisely about how the universe started,” Verlinde says. “I really think that the current description is only part of the story and there’s a much deeper way of understanding it—maybe an even more beautiful way.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:57 am on October 18, 2017 Permalink | Reply
    Tags: , , , DAMA LIBRA Dark Matter Experiment, , , , Mordehai Milgrom, NIST PROSPECT detector, , , ,   

    From COSMOS: “Closing in on dark matter” 

    Cosmos Magazine bloc

    COSMOS Magazine

    18 October 2017
    Cathal O’Connell

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    Dark matter can’t be detected but it glues galaxies together. It outweighs ordinary matter by five to one. Maltaguy1/Getty Images

    One Saturday I hired a metal detector and drove four hours to the historic gold-rush town of Bright in Victoria, Australia, where my wedding ring lies lost, somewhere on the bed of the Ovens River. I spent the evening wading through the icy waters in gumboots, uncovering such treasures as a bottle cap, a fisher’s lead weight and a bracelet caked in rust. I did not uncover the ring. But that doesn’t mean the ring is not there.

    Like me, physicists around the world are in the midst of an important search that has so far proven fruitless. Their quarry is nothing less than most of the matter in the universe, so-called “dark matter”.

    So far their most sensitive detectors have found – to be pithy – nada. Despite the lack of results, scientists aren’t giving up. “The frequency with which articles show up in the popular press saying ‘maybe dark matter isn’t real’ massively exceeds the frequency with which physicists or astronomers find any reason to re-examine that question,” says Katie Mack, a theoretical astrophysicist at the University of Melbourne.

    In many respects, the quest for dark matter has only just begun. We can expect quite a few more null results before the real treasure turns up. So here is where we stand, and what we can expect from the next few years.

    Imagine a toddler sitting on one end of a seesaw and launching her father, at the other end, high into the air. It’s a weird and unsettling image, yet we regularly observe this kind of ‘impossible’ behaviour in the universe at large. Like the little girl on the seesaw, galaxies behave as if they have four or five times the mass we can see.

    Our first inkling of this discrepancy came in the 1930s, when the Swiss astronomer Fritz Zwicky noticed odd movements among the Coma cluster of galaxies.

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    Fritz Zwicky: The Father of Dark Matter. https://www.youtube.com/watch?v=TV0c1EFIKy4

    Zwicky’s anomaly was largely ignored until the 1970s, when astrophysicist Vera Rubin, based at the Carnegie Institute in Washington, noticed that the way galaxies spin did not tally with the laws of physics.

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    Astronomer Vera Rubin in 1974, with her “measuring engine” used to examine photographic plates. Credit: Courtesy of Carnegie Institution of Washington

    The meticulous observations by Rubin (who passed away in December 2016) convinced most of the astronomical community something was amiss. There were two possible answers to the problem: either galaxies were a lot heavier than they appeared, or our theory of gravity was kaput when it came to galaxy-scale movements.

    From the outset, astronomers preferred the first explanation. At first they thought the missing matter was probably nothing too weird – just regular astronomical objects (like planets, black holes and stars) too dim for us to see. But as we surveyed the sky with ever bigger telescopes, these so-called ‘massive compact halo objects’ (or MACHOs) never turned up in the numbers needed to explain all the extra mass.

    Other astrophysicists, such as the Mordehai Milgrom at Israel’s Weizmann Institute, explored models where gravity behaved differently at cosmic scales. [See https://sciencesprings.wordpress.com/2017/05/18/from-nautilus-the-physicist-who-denies-dark-matter/%5D

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    Mordehai Milgrom. Cosmos on Nautilus

    They were not successful.

    Slowly astronomers realised they had something radically different on their hands – a new kind of stuff they called ‘dark matter’, which must outweigh the universe’s regular matter by about five to one. “Certainly, when all the evidence is taken together,” Mack says, “there’s no competing idea right now that comes anywhere close to explaining it as well.”

    We know four main facts about dark matter. First, it has gravity. Second, it doesn’t emit, absorb or reflect light. Third, it moves slowly. Fourth, it doesn’t seem to interact with anything, even itself.

    Like detectives in a TV murder mystery, physicists have compiled a list of suspects. Topping the list are three hypothetical particles already wanted on other charges: axions, sterile neutrinos and WIMPs. Besides nailing dark matter, each would help explain a grand mystery of their own.

    The axion is a particle proposed by Roberto Peccei and Helen Quinn back in 1977 to explain a quirk of the strong force (namely, why it can’t distinguish left from right, the way the weak force does). Thirty years on, axions are still our best explanation for that puzzle.

    Axions could have any mass, but if – and it is a big ‘if’ – they have a mass about 100 billion times lighter than an electron, theorists have calculated they would have been created in the Big Bang in such vast numbers that they could account for the universe’s dark matter. Like detectives with a dragnet, physicists are searching through different possible masses in an attempt to close in from both ends and corner the axion.

    The Axion Dark Matter eXperiment (ADMX), based at the University of Washington, is dragging the lightest end of the range.

    U Washington ADMX


    U Washington ADMX Axion Dark Matter Experiment

    Since 2010 the project has been trying to catch axions by turning them into photons using strong magnetic fields. So far ADMX has ruled out the featherweight mass range between 150 to 270 billion times lighter than the electron.

    The CERN Axion Solar Telescope (CAST) is dragging the heavyweight end of the range looking for axions that are a few tens of millions to about a million times lighter than the electron.

    CERN CAST Axion Solar Telescope

    The theorised source of these hefty axions is the Sun, where they might be created by X-rays in the presence of strong electric fields. In an example of recycling at its big-science best, CAST was assembled from a piece of the Large Hadron Collider -– a giant test magnet. It aims to detect solar axions by turning them back into X-rays. It has been running since 2003. The search goes on.

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    Hypothetical particles known as axions could explain dark matter. Physicists at CERN have taken a giant magnet from the Large Hadron Collider and turned it into an axion detector, the CERN Axion Solar Telescope. Howard Cunningham/Getty Images

    Sterile neutrinos are the hypothetical heavier, lazier brothers of neutrinos – the ghostly, fast-moving particles created in nuclear reactions and in the centre of the Sun. They are called ‘sterile’ or ‘inactive’ because they only interact via gravity.

    Besides being a dark-matter candidate, sterile neutrinos would plug a number of holes in the Standard Model,

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

    which, like a subatomic version of the periodic table, has had great success in predicting the properties of the fundamental building blocks of the universe. For instance, sterile neutrinos could explain why neutrinos are so light, and why every neutrino we’ve ever seen has a ‘left-handed’ spin; sterile neutrinos would be the missing ‘right-handed’ partners.

    Physicists are trying to detect sterile neutrinos in different ways, including searching deep space for the X-rays emitted when they decay. NASA’s Chandra X-ray telescope has picked up an excess of X-rays from the Perseus cluster of galaxies, which is so far unexplained.

    NASA/Chandra Telescope

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    Perseus cluster. NASA

    Meanwhile, regular neutrino detectors based at nuclear reactors, such as Daya Bay in China, have noticed anomalies that might be explained by sterile neutrinos.

    Daya Bay, approximately 52 kilometers northeast of Hong Kong and 45 kilometers east of Shenzhen, China

    “Like Elvis, people see hints of the sterile neutrino everywhere,” quipped Francis Halzen in August 2016, when he and his colleagues at the IceCube Neutrino Observatory announced the disappointing results of their own search.


    U Wisconsin ICECUBE neutrino detector at the South Pole

    Their detector, buried up to 2.5 km deep in ice near the South Pole, found no evidence of the elusive sterile neutrino – a result that seems to rule out the Daya Bay reactor sightings. For a conclusive answer, we’ll need to wait for the next neutrino searches, such as the Precision Reactor Antineutrino Oscillation and Spectrum Measurement (PROSPECT) under construction at the US National Institute of Standards and Technology (NIST) in Maryland.

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    The PROSPECT detector will consist of an 11 x 14 array of long skinny cells filled with liquid scintillator, which is designed to sense antineutrinos emanating from the reactor core. If a sterile neutrino flavor exists, then PROSPECT will see waves of antineutrinos that appear and disappear with a period determined by their energy. Composition not drawn to scale. NIST.

    The third and most popular suspect is WIMPs – weakly interacting massive particles. The name covers a broad range of hypothetical particles that would interact via the weak force. They pop naturally out of the ideas of supersymmetry, an extension proposed to tidy up the loose ends of the Standard Model.

    Physicists calculate that the simplest possible WIMP, with a mass of about 100 billion electron volts, would have been created in the Big Bang at just the right numbers to explain dark matter: the so-called ‘WIMP miracle’.

    WIMP detectors are typically deep underground, watching for a telltale flash given out when a particle of dark matter bumps into an atomic nucleus.

    The most sensitive WIMP experiment yet is LUX, a bathtub-sized vat holding 370 kg of liquid xenon at the Sanford Underground Research Facility [SURF] in South Dakota. In 2016, the LUX team announced it had discovered no dark matter signals during its first 20-month-long search. Undeterred, the LUX team plan to upgrade to a 7,000-kg vat, LUX-ZEPLIN, by 2020.

    LBNL Lux Zeplin project at SURF

    The most intriguing dark matter result so far comes from the DAMA/LIBRA experiment in Italy. Using a detector made of highly purified sodium-iodide crystals, 1.5 km beneath Italy’s Gran Sasso mountain, scientists believe they have seen evidence of dark matter every year for the past 14 years (see Cosmos 65, p60). Their evidence comes in an annual rise and fall in background detections. Such a pattern might reflect the Earth’s relative speed through the dark-matter cloud that surrounds the Milky Way; while our planet moves around the Sun at 30 km/s, the Solar System as a whole is travelling at 230 km/s around the centre of the Milky Way.

    DAMA LIBRA Dark Matter Experiment, 1.5 km beneath Italy’s Gran Sasso mountain

    Gran Sasso LABORATORI NAZIONALI del GRAN SASSO, located in L’Aquila, Italy

    For half of the year the Earth’s orbital speed would add to the speed of the Solar System, increasing the rate of dark-matter interactions. For the other half, the speeds would subtract and the rate of interactions decrease. The problem is that lots of other things change with the seasons too, such as the thickness of the atmosphere. To rule out terrestrial effects, astronomers are setting up two identical detectors, called SABRE, in opposite hemispheres – so that one is collecting data in winter and the other in summer.

    One detector will be based at Gran Sasso, the other in Australia, in an abandoned gold mine near Stawell, Victoria. Each detector will be made of 50 kg of sodium iodide, and have noise levels 10 times lower than DAMA/LIBRA. Construction on each is under way, and could be finished this year.

    Rather than detecting dark matter, others are trying to make it. The closest we can get to the conditions of the Big Bang – where dark matter was presumably created – is in the collision chambers of the Large Hadron Collider, CERN’s 27-km long particle smasher. These chambers are ringed by sensors that can pick up the energies of millions of particles generated in each smash-up, and tally this against the known collision energy. If some energy is missing, it might indicate the creation of a particle that could not be detected by any sensors: dark matter.

    So far, notwithstanding a brief, hallucinatory blip in late 2015, the LHC has not discovered anything that might constitute a dark matter particle such as a WIMP. But the LHC has only collected about 1% of the data it is due to produce before it is retired in 2025. So it is too early to throw in the towel on producing dark matter yet. Plans are afoot for the LHC’s successor, which will be able to probe far higher energies.

    Snowmelt from the Alpine ranges had swelled the Ovens River. I had to hug the shore with my metal detector, where the water was shallow and easy to sweep. I searched those parts that I could search as thoroughly as possible. If I did not find my prize, I wanted to at least be able to point to the map and say with confidence where the ring was not.

    The map that physicists search has coordinates of energy levels and interaction strengths. Each new search sweeps out a new territory, so even a null result is valuable information. So far, in our search for the three primary candidates – axions, sterile neutrinos and WIMPs – we have only probed the most shallow, accessible waters. “There’s nothing really that says they have to be easy to detect,” Mack says. “It may just be that their interactions with our detectors are smaller than expected.”

    It took almost 50 years for the Higgs boson to be discovered. Gravitational waves took almost a century. Let’s not give up on dark matter just yet.

    I certainly won’t be giving up my own search. Next summer, when the Ovens dries, I will return to Bright and sweep the next unprobed area of the riverbed. I’d say wish me luck, but the point is to be so rigorous that luck has nothing to do with it.

    See the full article here .

    Please help promote STEM in your local schools.

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  • richardmitnick 9:41 pm on May 18, 2017 Permalink | Reply
    Tags: , , , , , , Mordehai Milgrom,   

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

    Nautilus

    Nautilus

    May 18, 2017
    Oded Carmeli

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    Mordehai Milgrom. Cosmos on Nautilus

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

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

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

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

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

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

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


    Weizmann Institute Campus

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

    1
    NASA

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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    NASA

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

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

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

    What did your colleagues at Princeton think about all this?

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

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

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

    Like Thomas Kuhn’s The Structure of Scientific Revolutions.

    10

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

    What’s it like being a science maverick?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
  • richardmitnick 10:11 am on March 1, 2017 Permalink | Reply
    Tags: , , , , , , Mordehai Milgrom, ,   

    From Nautilus: “The Physicist Who Denies that Dark Matter Exists” 

    Nautilus

    Nautilus

    3.1.17
    Oded Carmeli

    1
    Mordehai Milgrom Credit: Weizmann Institute

    Maybe Newtonian physics doesn’t need dark matter to work, but Mordehai Milgrom instead.

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

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

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

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

    This year marks Milgrom’s 50th year at the Weizmann. I visited him there to learn more about how it feels to be a science maverick, what he appreciates about Thomas Kuhn’s The Structure of Scientific Revolutions, and why he thinks dark matter and dark energy don’t exist.

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

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

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

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

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

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

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

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

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

    2
    MOND in the MakingMilgrom’s notes from 1981. On the left, each line represents the data from a separate galaxy. On the right is the MOND prediction, which is the line going through the data points.
    Mordehai Milgrom

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

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

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

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

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

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

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

    What did your colleagues at Princeton think about all this?

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

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

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

    Like Thomas Kuhn’s The Structure of Scientific Revolutions.

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

    What’s it like being a science maverick?

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

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

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

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

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

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

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

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

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

    In 2004, Bekenstein proposed his TeVeS, or Relativistic Gravitational Theory for MOND. Since then, several different relativistic MOND formulations have been put forth, including one by me, called Bimetric MOND, or BIMOND.

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

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

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

    It turned out that the expansion of the universe is accelerating, not decelerating like all of us originally thought. Any form of genuine matter, dark or not, should have slowed down acceleration. And so a whole new type of entity was invented: Dark energy. Now the accepted cosmology is that the universe is made up of 70 percent dark energy, 25 percent dark matter, and 5 percent regular matter.

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

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

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

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

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

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

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

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

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

     
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