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

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

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    From CNN

    August 17, 2018
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    FNAL’s Don Lincoln

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

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

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

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

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

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

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

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

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

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

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

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

    So, what conclusion can we draw?

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

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

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

    See the full article here .

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  • richardmitnick 4:33 pm on August 20, 2018 Permalink | Reply
    Tags: , Anomalies, Bosons and fermions, Branes, , , , , Murray Gell-Mann, Parity violation, , , , , Superstring theory, , The second superstring revolution, Theorist John Schwarz   

    From Caltech: “Long and Winding Road: A Conversation with String Theory Pioneer” John Schwarz 

    Caltech Logo

    From Caltech

    08/20/2018

    Whitney Clavin
    (626) 395-1856
    wclavin@caltech.edu

    John Schwarz discusses the history and evolution of superstring theory.

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    John Schwarz. Credit: Seth Hansen for Caltech

    The decades-long quest for a theory that would unify all the known forces—from the microscopic quantum realm to the macroscopic world where gravity dominates—has had many twists and turns. The current leading theory, known as superstring theory and more informally as string theory, grew out of an approach to theoretical particle physics, called S-matrix theory, which was popular in the 1960s. Caltech’s John H. Schwarz, the Harold Brown Professor of Theoretical Physics, Emeritus, began working on the problem in 1971, while a junior faculty member at Princeton University. He moved to Caltech in 1972, where he continued his research with various collaborators from other universities. Their studies in the 1970s and 1980s would dramatically shift the evolution of the theory and, in 1984, usher in what’s known as the first superstring revolution.

    Essentially, string theory postulates that our universe is made up, at its most fundamental level, of infinitesimal tiny vibrating strings and contains 10 dimensions—three for space, one for time, and six other spatial dimensions curled up in such a way that we don’t perceive them in everyday life or even with the most sensitive experimental searches to date. One of the many states of a string is thought to correspond to the particle that carries the gravitational force, the graviton, thereby linking the two pillars of fundamental physics—quantum mechanics and the general theory of relativity, which includes gravity.

    We sat down with Schwarz to discuss the history and evolution of string theory and how the theory itself might have moved past strings.

    What are the earliest origins of string theory?

    The first study often regarded as the beginning of string theory came from an Italian physicist named Gabriele Veneziano in 1968. He discovered a mathematical formula that had many of the properties that people were trying to incorporate in a fundamental theory of the strong nuclear force [a fundamental force that holds nuclei together]. This formula was kind of pulled out of the blue, and ultimately Veneziano and others realized, within a couple years, that it was actually describing a quantum theory of a string—a one-dimensional extended object.

    How did the field grow after this paper?

    In the early ’70s, there were several hundred people worldwide working on string theory. But then everything changed when quantum chromodynamics, or QCD—which was developed by Caltech’s Murray Gell-Mann [Nobel Laureate, 1969] and others—became the favored theory of the strong nuclear force. Almost everyone was convinced QCD was the right way to go and stopped working on string theory. The field shrank down to just a handful of people in the course of a year or two. I was one of the ones who remained.

    How did Gell-Mann become interested in your work?

    Gell-Mann is the one who brought me to Caltech and was very supportive of my work. He took an interest in studies I had done with a French physicist, André Neveu, when we were at Princeton. Neveu and I introduced a second string theory. The initial Veneziano version had many problems. There are two kinds of fundamental particles called bosons and fermions, and the Veneziano theory only described bosons. The one I developed with Neveu included fermions. And not only did it include fermions but it led to the discovery of a new kind of symmetry that relates bosons and fermions, which is called supersymmetry. Because of that discovery, this version of string theory is called superstring theory.

    When did the field take off again?

    A pivotal change happened after work I did with another French physicist, Joël Scherk, whom Gell-Mann and I had brought to Caltech as a visitor in 1974. During that period, we realized that many of the problems we were having with string theory could be turned into advantages if we changed the purpose. Instead of insisting on constructing a theory of the strong nuclear force, we took this beautiful theory and asked what it was good for. And it turned out it was good for gravity. Neither of us had worked on gravity. It wasn’t something we were especially interested in but we realized that this theory, which was having trouble describing the strong nuclear force, gives rise to gravity. Once we realized this, I knew what I would be doing for the rest of my career. And I believe Joël felt the same way. Unfortunately, he died six years later. He made several important discoveries during those six years, including a supergravity theory in 11 dimensions.

    Surprisingly, the community didn’t respond very much to our papers and lectures. We were generally respected and never had a problem getting our papers published, but there wasn’t much interest in the idea. We were proposing a quantum theory of gravity, but in that era physicists who worked on quantum theory weren’t interested in gravity, and physicists who worked on gravity weren’t interested in quantum theory.

    That changed after I met Michael Green [a theoretical physicist then at the University of London and now at the University of Cambridge], at the CERN cafeteria in Switzerland in the summer of 1979. Our collaboration was very successful, and Michael visited Caltech for several extended visits over the next few years. We published a number of papers during that period, which are much cited, but our most famous work was something we did in 1984, which had to do with a problem known as anomalies.

    What are anomalies in string theory?

    One of the facts of nature is that there is what’s called parity violation, which means that the fundamental laws are not invariant under mirror reflection. For example, a neutrino always spins clockwise and not counterclockwise, so it would look wrong viewed in a mirror. When you try to write down a fundamental theory with parity violation, mathematical inconsistencies often arise when you take account of quantum effects. This is referred to as the anomaly problem. It appeared that one couldn’t make a theory based on strings without encountering these anomalies, which, if that were the case, would mean strings couldn’t give a realistic theory. Green and I discovered that these anomalies cancel one another in very special situations.

    When we released our results in 1984, the field exploded. That’s when Edward Witten [a theoretical physicist at the Institute for Advanced Study in Princeton], probably the most influential theoretical physicist in the world, got interested. Witten and three collaborators wrote a paper early in 1985 making a particular proposal for what to do with the six extra dimensions, the ones other than the four for space and time. That proposal looked, at the time, as if it could give a theory that is quite realistic. These developments, together with the discovery of another version of superstring theory, constituted the first superstring revolution.

    Richard Feynman was here at Caltech during that time, before he passed away in 1988. What did he think about string theory?

    After the 1984 to 1985 breakthroughs in our understanding of superstring theory, the subject no longer could be ignored. At that time it acquired some prominent critics, including Richard Feynman and Stephen Hawking. Feynman’s skepticism of superstring theory was based mostly on the concern that it could not be tested experimentally. This was a valid concern, which my collaborators and I shared. However, Feynman did want to learn more, so I spent several hours explaining the essential ideas to him. Thirty years later, it is still true that there is no smoking-gun experimental confirmation of superstring theory, though it has proved its value in other ways. The most likely possibility for experimental support in the foreseeable future would be the discovery of supersymmetry particles. So far, they have not shown up.

    What was the second superstring revolution about?

    The second superstring revolution occurred 10 years later in the mid ’90s. What happened then is that string theorists discovered what happens when particle interactions become strong. Before, we had been studying weakly interacting systems. But as you crank up the strength of the interaction, a 10th dimension of space can emerge. New objects called branes also emerge. Strings are one dimensional; branes have all sorts of dimensions ranging from zero to nine. An important class of these branes, called D-branes, was discovered by the late Joseph Polchinski [BS ’75]. Strings do have a special role, but when the system is strongly interacting, then the strings become less fundamental. It’s possible that in the future the subject will get a new name but until we understand better what the theory is, which we’re still struggling with, it’s premature to invent a new name.

    What can we say now about the future of string theory?

    It’s now over 30 years since a large community of scientists began pooling their talents, and there’s been enormous progress in those 30 years. But the more big problems we solve, the more new questions arise. So, you don’t even know the right questions to ask until you solve the previous questions. Interestingly, some of the biggest spin-offs of our efforts to find the most fundamental theory of nature are in pure mathematics.

    Do you think string theory will ultimately unify the forces of nature?

    Yes, but I don’t think we’ll have a final answer in my lifetime. The journey has been worth it, even if it did take some unusual twists and turns. I’m convinced that, in other intelligent civilizations throughout the galaxy, similar discoveries will occur, or already have occurred, in a different sequence than ours. We’ll find the same result and reach the same conclusions as other civilizations, but we’ll get there by a very different route.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

    Caltech campus

     
  • richardmitnick 8:27 am on September 14, 2017 Permalink | Reply
    Tags: , Brian Greene, Cosmology- origins of the universe, , , , , , Superstring theory, Unified theory of physics,   

    From Harvard Gazette: “A master of explaining the universe” 

    Harvard University
    Harvard University

    September 13, 2017
    Colleen Walsh

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    Brian Greene ’84, a Columbia University theoretical physicist and mathematician, has made it his mission to illuminate the wonders of the universe for non-scientists. Photo by Greg Kessler/World Science Festival

    Harvard Overseer and Columbia physicist Brian Greene seeks wider audience for the wonders of science.

    He is the founder of the World Science Festival, the author of numerous best-selling books, including the Pulitzer Prize finalist “The Elegant Universe,” and an expert at explaining knotty concepts. Now he’s back at Harvard. On Sept. 19, Brian Greene ’84, Harvard Overseer and Columbia University theoretical physicist and mathematician, will explore shifting ideas of space, time, and reality in a talk at the Radcliffe Institute for Advanced Study. The Gazette caught up with Greene to ask him about his years at Harvard, his passion for science, and how he defines superstring theory in a tweet.

    GAZETTE: Where did your initial interest in math and physics come from?

    GREENE: When I was a kid growing up in Manhattan I was deeply fascinated with mathematics, and at a young age my dad taught me the basics of arithmetic. I was captivated from then on by the ability to use a few simple rules to undertake calculations that no one had ever done before. Now, most of these calculations weren’t ever done because they weren’t interesting, but for a kid to be able to do something new is deeply thrilling. Later on, when I learned in high school and most forcefully when I got to college at Harvard that math isn’t merely a game but it’s something that can help you understand what happens out there in the real universe, then I was kind of hooked for life.

    GAZETTE: Were there any classes or professors that had a big impact on you at Harvard?

    GREENE: Oh, huge. Howard Georgi was my freshman physics professor, and he had a deep impact on my love of the subject. There’s now a mathematician who wasn’t at Harvard when I was an undergrad but whom I worked with extensively as a graduate student and then he moved to Harvard, Shing-Tung Yau in the Mathematics Department. He had a deep impact on me. The Harvard faculty had quite a formative impact on me across the years.

    GAZETTE: I know you are famous for being able to explain awesome scientific concepts. In the age of social media, can you define superstring theory in a tweet?

    GREENE: Superstring theory is our best attempt to realize Einstein’s dream of the unified theory. #unification.

    GAZETTE: So break that down for me, and this doesn’t have to be in a tweet format. What is the unified theory of physics and why is it so important?

    GREENE: Einstein envisioned that there might be a master law of physics, perhaps captured by a single mathematical equation that would be so powerful that in principle it could describe every physical process in the universe — the big stuff, the small stuff, and everything in between. And he believed it so deeply that he pursued it relentlessly for the last 30 years of his life. On various occasions Einstein announced that he had the unified theory, always, however, to have to retract that sometime later when he realized that his latest proposal didn’t quite work. In the end it was a very frustrating experience for him. And when he died, that dream of unification died with him. But about 10 or 15 years later some scientist stumbled upon a new approach — this approach called superstring theory — and over the course of decades realized that this may in fact be the unified theory that Einstein was looking for. And that’s what we have been developing ever since.

    GAZETTE: What has been the main focus of your work for the last several years?

    GREENE: I have been working on issues of cosmology, origins of the universe. I’ve been working on the possibility of a multiverse — that we might live in a reality that comprises more than one universe. I’ve been working on some strange features of quantum mechanics called quantum entanglement, where distant objects can somehow act as though they are sitting right next to each other. Again this is a discovery that sort of goes back to Einstein himself, so things in that domain have been my main focus of late.

    GAZETTE: Tell me more about multiple universes.

    GREENE: Well, it’s a curious idea because for most people the word universe means everything: all that there is. But developments over the past couple of decades have convinced many of us that there is at least a possibility that what we have long thought to be everything is actually perhaps just a small part of a much bigger reality. And that bigger reality might have other realms that would rightly be called universes of their own, and if that’s the case then the grand picture of reality involves a whole collection of universes, and that’s why we no longer use the word universe to describe all there is … we speak of “multi” — there are multiverses because of this multiplicity of universes.

    GAZETTE: Is there current or future research that you could see really changing the nature of how we see the universe?

    GREENE: My own feeling, and it’s shared by colleagues, is that the next breakthrough will come when we deeply understand the fundamental ingredients of space and time themselves. And this is an open question. Just like matter is made up of atoms and molecules, could it be that space and time are themselves made up of more fundamental constituents? In fact, this is what I will be talking about at Radcliffe, recent work that at least hints at an answer to what the ingredients of space and time might actually be.

    GAZETTE: What has inspired you to work to make science understandable?

    GREENE: My view of science is not that it’s merely an effort to unearth the basic laws of physics, but I view it more as a very human undertaking to see how we fit into the grand scheme of things and to answer the questions that have been asked since the time we could ask questions: Where did we come from? What are we made of? How did the universe come to be? What is time? What will happen in the distant future? All these questions I think speak deeply to who we are as a species, and for the vast majority of people to be cut off from the most up-to-date thinking on these deep questions because they don’t speak mathematics, they don’t have a graduate degree in physics, I think that’s tragic. So for decades now I’ve felt that part of my charge is to bring these ideas to a wider audience, to make them available to anyone who has a curiosity and a little bit of stick-to-itiveness to push through some deep, difficult, but ultimately gratifying ideas.

    GAZETTE: If you weren’t a physicist what would you be?

    GREENE: Well, if I was starting out today I think I would probably go into neuroscience. I like to think of the big questions. Where did the universe come from? Where did life come from? And where does mind come from? And for those I think the time is really ripe to understand the nature of intelligence and thought. I think there are going to be great, great breakthroughs in that area in the next couple of decades.

    GAZETTE: Favorite physicist?

    GREENE: There’s nobody who compares with Isaac Newton in terms of the leap that he pushed humanity through from the way we understood the world before he began to think about it until after he existed.

    GAZETTE: What is your take on Voyager?

    GREENE: The “Star Trek” version or the real version?

    GAZETTE: The real version.

    GREENE: I think it’s a great symbol of who we are as a species. We are explorers. We are deeply committed to understanding the universe, and to envision these little spacecraft that have left the solar system and they are floating out there in the great unknown as harbingers, if you will, of human life back on the planet is a deeply moving picture and one that really captures who we are.

    See the full article here .

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    Stem Education Coalition

    Harvard University campus
    Harvard is the oldest institution of higher education in the United States, established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. It was named after the College’s first benefactor, the young minister John Harvard of Charlestown, who upon his death in 1638 left his library and half his estate to the institution. A statue of John Harvard stands today in front of University Hall in Harvard Yard, and is perhaps the University’s best known landmark.

    Harvard University has 12 degree-granting Schools in addition to the Radcliffe Institute for Advanced Study. The University has grown from nine students with a single master to an enrollment of more than 20,000 degree candidates including undergraduate, graduate, and professional students. There are more than 360,000 living alumni in the U.S. and over 190 other countries.

     
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