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Thread: What Is The Universe?

  1. #61
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    dcl all the posts in my post below speedfreeks where aimed at him

    dcl you said... I think these values have the values that they do merely because we wouldn't be here to ask the question if they were different,,,,,

    which i translated into ... just to say well im here so that explains it...

    anyway i tend to agree with all of you great posts guys esp cougar ,,,thanks 4 the
    Alex Vilenkin mention.... i like this idea..


  2. #62
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    Quote Originally Posted by dcl View Post
    speedfreek: M-Theory proposes the possible existence of multi-dimensional membranes which interacted, causing our universe.

    dcl: Let's not lose sight of the fact that, as attractive as M-theory may be in some respects, there is absolutely no evidence for or against it. So let's remember that at best it is only a hypothesis awaiting the first evidence that it may be valid. I'm under the impression that the same must be said for loop quantum gravity.

    speedfreek: As for Loop Quantum Gravity, Abhay Ashtekar and Martin Bojowald have released papers stating that according to loop quantum gravity, the singularity of the Big Bang is avoided. What they found was a prior collapsing universe.

    dcl: I, too, think it plausible that the present expansion was preceded by a bounce from a previous contraction, but I'm not aware that there is any evidence for a bounce, so we should not seize on the idea that there was one.
    Of course, both M-Theory and Loop Quantum Gravity are hypotheses awaiting a mechanism to test them with. I agree we should not seize upon the idea that either is correct, as we have no evidence. I presented them simply as valid possibilities (ones being pursued seriously, rather than pie in the sky ideas), hence my repeated use of the term "perhaps" in my post above.


    Quote Originally Posted by dcl
    I feel that further investigation in some areas is pointless. For example, the idea that the Universe has the shape of a cube, a 3-torus, a doughnut, or a dodecahedron is pointless because the suggestion that the Universe has any of those shapes seems preposterous to me. The shape that seems plausible to me is that of an expanding four-dimensional hypersphere.
    The idea that any shape other than a four-dimensional hypersphere seems implausible to you and is therefore preposterous to you is essentially irrelevant. Cosmologists are searching for evidence of a shape, and one method is to look for matching areas in the WMAP data. Any valid shape with a non-trivial topology (and that includes a hypersphere, amongst others) might show up as repeated inhomogeneous regions in the CMBR, where these non-uniform regions were introduced during inflation. The relative positions of these regions would indicate the topology involved, but only if the fundamental domain of the universe was smaller than our observable universe.

    It may indeed seem doubtful that the fundamental domain (the whole universe) is smaller than our observable universe, but we have to do what we can to test for it and the least we can do is search our observable universe for evidence for it so that we can count it out. So far we have only counted it out across a co-moving diameter of 78 billion light years and our observable universe has a co-moving diameter of 92 billion light years so there is a little way to go yet before we can confidently state that the whole universe is larger than our observable portion of it. Until we can, there remains the possibility that we might find evidence for a non-trivial topology.

    Should we only look for evidence for the most plausible model? Is that good science?

    As you are so convinced that the hypersphere is the only plausible shape for the universe I must assume you have studied the mathematics of hyperspheres and so you should be familiar with both the Poincaré conjecture and, perhaps more pertinently, the Poincaré homology sphere, which is also known as Poincarés dodecahedral space.

  3. #63
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    Red face



    hurrah

    (does that mean edges are back in with a shot?)

  4. #64
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    Quote Originally Posted by dcl View Post
    Cougar: Here [in runningn the movie backward] your answer is incorrect. We can't get anywhere near 10-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second.

    dcl: I suggest you broaden your reading. There are any number of respected sources that give that 10-43 figure. That figure comes from the Standard Model of particle physics, not from accelerator experiments.
    Ha ha! Now that is truly funny. Would you like to peruse my Recent Reading list?

    # Chaos, Making a New Science [1987] -- James Gleick

    # Complexity, Life at the Edge of Chaos [1992] -- Roger Lewin

    # Complexification -- John Casti

    # Journey to the Great Attractor [1994]-- Alan Dressler

    # The Science of Fractal Images -- Peitgen, Saupe, eds.

    # Hyperspace, A Scientific Odyssey Through Parallel Universes, Time Warps, and the 10th Dimension [1994] -- Michio Kaku

    # The Matter Myth -- Paul Davies

    # The Cosmic Blueprint, New Discoveries in Nature's Creative Ability to Order the Universe [1988] -- Paul Davies

    # God and the New Physics -- Paul Davies

    # The Red Limit [1977]-- Timothy Ferris

    # Coming of Age in the Milky Way -- Timothy Ferris

    # The Mind's Sky, Human Intelligence in a Cosmic Context -- Timothy Ferris

    # The Key to the Universe [1977] -- Nigel Calder

    # QED, The Strange Theory of Light and Matter -- Richard Feynman

    # Surely Your Joking, Mr. Feynman! -- Richard Feynman

    # What Do You Care What Other People Think? -- Richard Feynman

    # Cosmic Catastrophes [1989] -- Clark Chapman, David Morrison

    # Searching For Certainty, What Scientists Can Know About the Future [1990] -- John L. Casti

    # Dreams of a Final Theory [1992] -- Steven Weinberg

    # The Cosmic Code [1982] -- Heinz Pagels

    # Sympathetic Vibrations, Reflections on Physics as a Way of Life [1985] -- K.C. Cole

    # The God Particle, If the Universe is the Answer, What is the Question? [1993] -- Leon Lederman with Dick Teresi

    # Genius, The Life and Science of Richard Feynman [1995] -- James Gleick

    # At Home in the Universe, The Search for the Laws of Self-Organization
    and Complexity [1995] -- Stuart Kauffman

    # The Origin of The Universe [1994] -- John D. Barrow

    # The Quark and the Jaguar, Adventures in the Simple and the Complex [1995] --
    Murray Gell-Mann

    # The Last Three Minutes, Conjectures About the Ultimate Fate of the Universe [1994] --
    Paul Davies

    # Flyby, The Interplanetary Odyssey of Voyager 2 [1987] -- Joel Davis

    # The Nemesis Affair, A Story of the Death of Dinosaurs and the Ways of Science [1986] -- David M. Raup

    # Bully for Brontosaurus -- Stephen Jay Gould

    # Eight Little Piggies, Reflections in Natural History [1993] -- Stephen Jay Gould

    # On a Piece of Chalk [1868, republished 1967] -- Thomas Henry Huxley

    # Cosmic Coincidences, Dark Matter, Mankind, and Anthropic Cosmology [1989] --
    John Gribbin and Martin Rees

    # The Collapse of Chaos, Discovering Simplicity in a Complex World [1994] --
    Jack Cohen and Ian Stewart

    # The Milky Way, Fifth Edition [1941-1981] -- Bart Bok, Priscilla Bok

    # A Hundred Billion Stars [1984] -- Mario Rigutti

    # The Lighter Side of Gravity [1982] -- Jayant V. Narlikar

    # Chaos in the Cosmos [1996] -- Barry Parker

    # A Brief History of Time -- Stephen Hawking

    # Black Holes and Baby Universes [1993] -- Stephen Hawking

    # Exploring the Galaxies [1976] -- Simon Mitton

    # The Three Big Bangs, Comet Crashes, Exploding Stars,
    and the Creation of the Universe [1996] -- Dauber and Muller

    # Mysteries of the Milky Way [1991] -- Goldsmith and Cohen

    # The Edges of Science [1990] -- Richard Morris

    # The Privilege of Being a Physicist [1989] -- Victor Weisskopf

    # Feynman's Lost Lecture [1996]

    # Cosmic Rays, Tracking Particles From Outer Space [1989] -- Michael Friedlander

    # Quarks, The Stuff of Matter [1983] -- Harald Fritzsch

    # How Nature Works, The Science of Self-Organized Criticality [1996] -- Per Bak

    # In The Beginning, After COBE and Before The Big Bang [1993] -- John Gribbin

    # The Secret Melody [1995] -- Trinh Xuan Thuan

    # Neils Bohr, A Centenary Volume [1985] -- French and Kennedy, eds.

    # The Particle Garden, Our Universe
    as Understood by Particle Physicists [1995] -- Gordon Kane

    # The Edge of the Unknown,
    101 Things You Don't Know About Science
    And No One Else Does Either [1996] -- James Trefil

    # Einstein's Legacy -- Julian Schwinger

    # The Whole Shebang,
    A State-of-the-Universe(s) Report [1997] -- Timothy Ferris

    # Creation, The Story of the Origin and Evolution of the Universe [1988] -- Barry Parker

    # In Quest of Quasars, An Introduction to Stars and Starlike Objects [1969] -- Ben Bova

    # The Twin Dimensions, Inventing Time & Space [1986] -- Geza Szamosi

    # Blind Watchers of the Sky, The People and Ideas that Shaped Our View of the Universe [1996] -- Rocky Kolb

    # Heisenberg Probably Slept Here, The Lives, Times, and Ideas of the Greatest Physicists of the 20th Century [1997] -- Richard P. Brennan

    # Beyond the Known Universe, From Dwarf Stars to Quasars [1974] -- I.M. Levitt

    # The Dark Side of the Universe [1988] -- James Trefil

    # Perfect Symmetry [1985] -- Heinz Pagels

    # The Very First Light, The True Inside Story of the Scientific Journey Back to the Dawn of the Universe [1996] -- John C. Mather and John Boslough

    # The First Three Minutes,
    A Modern View of the Origin of the Universe [1977] -- Steven Weinberg

    # Scientific Autobiography and Other Papers [1949] -- Max Planck

    # The Cosmos from Space [1987] -- David H. Clark

    # Rain of Iron and Ice, the very real threat of comet and asteroid bombardment [1996] -- John S. Lewis

    # Worlds Unnumbered, the Search for Extrasolar Planets [1997] -- Donald Goldsmith

    # Why People Believe Weird Things, pseudoscience, superstition, and other confusions of our time [1997] -- Michael Shermer

    # The Threat and the Glory [1959-90] -- Peter B. Medawar

    # Gšdel, Escher, Bach: an Eternal Golden Braid [1979] -- Douglas Hofstadter

    # The Inflationary Universe, the quest for a new theory of cosmic origins [1997] -- Alan H. Guth

    # Wrinkles in Time [1993] -- George Smoot, Keay Davidson

    # The Meaning of It All, Thoughts of a Citizen-Scientist [1998] -- Richard P. Feynman

    # The Light at the Edge of the Universe [1993] -- Michael D. Lemonick

    # Chaos and Harmony [2001] -- Trinh Xuan Thuan

    # The Fifth Miracle, The Search for the Origin of Life [1998] -- Paul Davies

    # Paradigms Regained, A Further Exploration of the Mysteries of Modern Science [2000] -- John Casti

    # The Essence of Chaos [1993] -- Edward N. Lorenz

    # Thinking in Complexity, The Complex Dynamics of Matter, Mind, and Mankind - 3rd Ed. [1997] -- Klaus Mainzer

    # Gravitation and Cosmology, Proceedings of the ICGC Conference Held at IUCAA, Pune, India, in December 1995 [1995] -- Dhurandhar and Padmanabhan (eds.)

    # The Social Meaning of Modern Biology, From Social Darwinism to Sociobiology [1986] -- Howard L. Kaye

    # Origins of Life [1985] -- Freeman Dyson

    # In Search of the Ultimate Building Blocks [1997] -- Gerard 't Hooft

    # The Large, the Small and the Human Mind [1997] -- Roger Penrose

    # The Structure of Scientific Revolutions [1962, 1970] -- Thomas S. Kuhn

    # Beyond the Black Hole, Stephen Hawking's Universe [1985] -- John Boslough

    # The Thermodynamics of Pizza, Essays on Science and Everyday Life [1991] -- Harold J. Morowitz

    # Billions and Billions, Thoughts on Life and Death at the Brink of the Millenium [1997] -- Carl Sagan

    # Beyond the Quantum Paradox [1994] -- Lazar Mayants

    # Guns, Germs, and Steel, The Fates of Human Societies [1997] -- Jared Diamond

    # Einstein, A Centenary Volume, [1979] -- A.P. French, ed.

    # Science and Beyond [1986] -- Steven Rose and Lisa Appignanesi, eds.

    # Science a la Mode, Physical Fashions and Fictions [1989] -- Tony Rothman

    # Goodbye, Descartes, The End of Logic and the Search for a New Cosmology of the Mind [1997] --Keith Devlin

    # The Runaway Universe, the Race to Find the Future of the Cosmos [2000] -- Donald Goldsmith

    # General Relativity From A to B [1978] -- Robert Geroch

    # Quantum Reality, Beyond the New Physics [1985] -- Nick Herbert

    # The Flamingo's Smile, Reflections in Natural History [1985] -- Stephen Jay Gould

    # Science, Computers, and People, From the Tree of Mathematics [1986] -- Stanislaw Ulam; Marc C. Reynolds, Gian-Carlo Rota, Eds.

    # The Flight From Science and Reason, Annals of the New York Academy of Sciences, Vol 775 [1996] -- edited by Paul R. Gross, Norman Levitt, and Martin W. Lewis

    # Doing Science, The Reality Club [1991] -- edited by John Brockman [not recommended]

    # A Tour of the Calculus [1995] -- David Berlinski

    # A Beautiful Mind, The Life of Mathematical Genius and Nobel Laureate John Nash [1998] -- Sylvia Nasar

    # Euler, The Master of Us All [1999] -- William Dunham

    # Thomas Kuhn: A Philosophical History for Our Times [2000] -- Steve Fuller

    # The Fabric of the Cosmos; Space, Time, and the Texture of Reality [2004] -- Brian Greene

    # The Life of the Cosmos [1997] -- Lee Smolin

    # The Universe at Midnight, Observations Illuminating the Cosmos [2001] -- Ken Croswell

    # Galaxies and Quasars [1979] -- William J. Kaufman

    # Conflict in the Cosmos, Fred Hoyle's Life in Science [2005] -- Simon Mitton

    # Big Bang, the origin of the universe [2004] -- by Simon Singh

    # How The Universe Got Its Spots, Diary of a finite time in a finite space [2002] -- Janna Levin

    # From Quarks to the Cosmos, Tools of Discovery [1995] -- Leon Lederman, David Schramm

    # The Big Questions, Probing the promise and limits of science [2002] -- Richard Morris

    # Alpha and Omega, The search for the beginning and end of the universe [2004] -- Charles Seife

    # Supersymmetry, Unveiling the ultimate laws of nature [2000] -- Gordon Kane

    # Black Holes and Time Warps, Einstein's Outrageous Legacy [1994] -- Kip Thorne

    # The Universe, the 11th Dimension, and Everything, What we know and how we know it [1999] -- Richard Morris

    # Faster, The Acceleration of Just about Everything [2000] -- James Gleick

    # Before the Beginning, Our Universe and Others [1997] -- Martin Rees

    # The Life of the Cosmos [1999] -- Lee Smolin

    # The Cosmic Landscape String theory and the illusion of intelligent design [2006] -- Leonard Susskind

    # Chasing Hubble's Shadows, The Search for Galaxies at the Edge of Time [2006] -- Jeff Kanipe

    # Cosmic Clouds: Birth, death, and recycling in the galaxy [1997] -- James Kaler

    # Many Worlds in One [2006] -- Alex Vilenkin

    # Endless Universe, Beyond the Big Bang [2007] -- Paul Steinhardt and Neil Turok

    # Origins: How the Planets, Stars, Galaxies, and the Universe Began [2006] -- by Stephen Eales

    # Poetry of the Universe: A Mathematical Exploration of the Cosmos [1995] -- by Robert Osserman

    # Extreme Stars, At the Edge of Creation [2001] -- by James Kaler

    Add to that The Trouble With Physics by Lee Smolin and Madmen Dream of Turing Machines by astrophysicist Janna Levin.

    I believe the misunderstanding about what we currently know when the universe was 10-43 seconds old is yours.
    Everyone is entitled to his own opinion, but not his own facts.

  5. #65
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    Quote Originally Posted by damian1727 View Post
    (does that mean edges are back in with a shot?)
    These shapes we are discussing don't have "edges" as such. You might try to visualise an expanding 4-dimensional hypersphere as having our 3D universe as its surface.

  6. #66
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    Cougar: Here [in running the movie backward] your answer is incorrect. We can't get anywhere near 10^-43 sec. From my recent reading on the subject, many major names in the field all seem to agree on how the movie would rewind back to 1 second.

    dcl: I suggest you broaden your reading. There are any number of respected sources that give that 10^-43 figure. That figure comes from the Standard Model of particle physics, not from accelerator experiments.

    Cougar: Ha ha! Now that is truly funny. Would you like to peruse my Recent Reading list? I believe the misunderstanding about what we currently know [about] when the universe was 10^-43 seconds old is yours.

    dcl: I note your long list of references, most of which appear to be either outdated or totally irrelevant to the question of how far back in time the history of the Universe has been traced via the Standard Model of particle physics. It suffices for me to cite just one reference to rebut your assertion that the movie can be rewound only to 1 second. On page 155 of James S. Trefil, "The Moment of creation", Macmillan, New York, 1983. You can find the following statement, quoted verbatim from page 155 of this book.:

    . "We will call the period from 10^-43 second to 10^-35 second after the Big Bang the GUT, or Grand Unification Theory, era."

    Trefil is a professor of physics at Stanford University. Perhaps you'd like to challenge him on that figure. His response should be even funnier than was yours to my earlier statement.
    Last edited by dcl; 2008-Jun-11 at 02:03 AM.

  7. #67
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    oooo come on guys lets not fall out over less than no time !!!

    cougar i did not realize that there were so many books....

    speed ... i am i want an edge

  8. #68
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    Quote Originally Posted by dcl View Post
    "We will call the period from 10^-43 second to 10^-35 second after the Big Bang the GUT, or Grand Unification Theory, era."
    Being able to name something doesn't mean we know much about it. Please note that the GUT era is completely inaccessible to current particle accelerators, and though several GUTs have been proposed, there is little or no data to distinguish which is supportable.

    The quote was:

    Quote Originally Posted by dcl
    ...ran the movie backward as far as knowledge would allow....
    We don't yet have "knowledge" of the state of the universe during the GUT era. Inflation (around 10-33) is looking pretty good, but even it is fairly far from a done deal.
    Everyone is entitled to his own opinion, but not his own facts.

  9. #69
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    It's deductions from the Standard Model of particle physics, not accelerator data, that tell of what we think we know about conditions in the early Universe. I am not a particle physicist, so I am not qualified to judge how valid these deductions are, but when the community of particle physicists tells us that they are confident that theory has enabled them to extrapolate physical phenomena back to 10^-43 second, I'm inclined to accept their statements at least tentatively as well-founded. These statements are not made lightly: They are not published in reputable journals until other physicists up to date on the latest findings endorse them through the peer review process. I cited only one place where the 10^-43 second figure for the beginning of the GUT era can be found. I've seen it in a number of different publications.

  10. #70
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    speedfreek: Your reference to the Poincare conjecture induced me to Google it to find out what it claims. I had of course heard of it earlier but had never managed to find out what it claimed, even after it had made a big splash in the news several years ago on finally being proven. I had supposed it to be an abstract idea in pure mathematics of no immediate interest to cosmologists.

    The same seemed to apply to the supposed relevance of the dodecahedron to cosmology. From the reference you cited, I learned that the conceivable relevance of the dodecahedron is the same as for the 3-torus when parallel faces or the former are "glued" in the topological sense. I still feel that the glued dodecahedron, like the 3-torus, is too implausible to be taken seriously as a possible model for the Universe.

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    Well sometime around 2003 we found what looked like a repeating pattern in WMAP data that indicated that the universe might be shaped like a Poincare dodecahedral space, which is why we were investigating these models. There was some observational evidence of a non-trivial topology that required further investigation and that investigation isn't finished yet.

    If you were in charge, would you have said the shape is too implausible to investigate, bearing in mind that we already had some data that seemed to indicate that shape?

  12. #72
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    Quote Originally Posted by dcl View Post
    ...when the community of particle physicists tells us that they are confident that theory has enabled them to extrapolate physical phenomena back to 10^-43 second, I'm inclined to accept their statements at least tentatively as well-founded.
    I don't believe any particle physicist has said that, certainly not confidently. 10-43 is the Planck Time. (Actually, it's 5.39 x 10-44.) It is supposedly a barrier beyond which measurement cannot go, even in principle.

    See Timeline of the Big Bang. Note the caveat at the beginning of the section on the very early universe:

    All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe.
    Everyone is entitled to his own opinion, but not his own facts.

  13. #73
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    In the following, I quote speedfreek and Cougar and comment on their comments: The first paragraph by one of us is preceded by that person's pseudonym. Succeeding paragraphs by the same person are not so labeled.

    speedfreek: Well sometime around 2003 we found what looked like a repeating pattern in WMAP data that indicated that the universe might be shaped like a Poincare dodecahedral space, which is why we were investigating these models. There was some observational evidence of a non-trivial topology that required further investigation and that investigation isn't finished yet.

    If you were in charge, would you have said the shape is too implausible to investigate, bearing in mind that we already had some data that seemed to indicate that shape?

    dcl: Without meaning to be derogatory in any way, I'm interested in knowing whether by "we" you mean a research group of which you are a member. If so, I am impressed and hope to learn from you. Can you refer me to a description of what was found in 2003 that would be accessible on the Internet? Alternatively, can you summarize briefly what was found? What group is or was doing this investigation?

    Cougar: I don't believe any particle physicist has said that, certainly not confidently. 10-43 is the Planck Time. (Actually, it's 5.39 x 10-44.) It is supposedly a barrier beyond which measurement cannot go, even in principle.

    See http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang Note the caveat at the beginning of the section on the very early universe:

    "All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe."

    dcl: I've seen the equivalent of that statement and number in a large enough number of different sources that I've assumed, possibly erroneously, that it was factual. I'd appreciate your citing statements to the contrary if you can.

    I appreciate your referring me to the Wikipedia article you cited. Incidentally, it gives 10 exp -43 second not as the Planck era but as the end of the Planck era. It gives the interval starting at 10 exp -43 second and ending at 10 exp -36 second as the Grand Unification Era.

  14. #74
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    Quote Originally Posted by dcl View Post
    dcl: Without meaning to be derogatory in any way, I'm interested in knowing whether by "we" you mean a research group of which you are a member. If so, I am impressed and hope to learn from you. Can you refer me to a description of what was found in 2003 that would be accessible on the Internet? Alternatively, can you summarize briefly what was found? What group is or was doing this investigation?
    No, I mean we as in the human race! Sorry if it misled you, I often write that way when the subject is about scientific discoveries - "We have discovered a new planet", "We think the universe is 13.7 billion years old" etc.

    This is the original story - Is the universe a dodecahedron?

    And the paper that followed the original story -
    A Hint of Poincaré Dodecahedral Topology in the WMAP First Year Sky Map

    A research group then pursued the issue but they found no evidence for any non-trivial topology across a diameter of 78 billion light years (24 Gigaparsecs) and so we can confidently state that the fundamental domain of the whole universe is at least that large. These figures are based on the WMAP data representing a sphere around us that has now grown to 46 billion light years in radius (92 billion light years diameter). They intend to continue the search until they have reached ~28 Gigaparsecs. They have discounted the dodecahedral model as the universe would have had to have had a fundamental domain only 30 billion light years across for that to work.

    This is the paper with their findings - Extending the WMAP Bound on the Size of the Universe.

    I actually agree with you about the universe probably being a hypersphere but if the fundamental domain of the universe is indeed larger than our observable portion of it, as seems likely, we will never know for sure. If the fundamental domain were smaller however (and that is a possibility), we might find evidence that allows us to determine the overall topology. (See I'm doing the we thing again - I just fall into it naturally!)

    Until they have finished the study, I wouldn't want to commit myself either way, even if I thought the most plausible shape was an S3 hypersphere. The reason is simple - if they find no evidence for a non-trivial topology at all then the whole universe must be larger than our observable portion of it. The topology will therefore always be subject to speculation.

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    Thank you, speedfreek, for your references. The article cited in the following is from one of them.

    --------

    "We use optimal filtering and the combination statistic to rule out the infamous 'soccer ball universe
    model'"

    This statement is quoted directly from the last sentence in the abstract for the article entitled "Extending the WMAP Bound on the Size of the Universe" by Joey Shapiro Key, Neil J. Cornish, David N. Spergel, and Glenn D. Starkman, submitted in Apr 2006, downloadable from http://arxiv.org/abs/astro-ph/0604616).

    Until this article is withdrawn by the authors or its substance refuted by other articles, I'd think it should stop speculation about the Universe's having the geometry of a dodecahedron with opposite faces "glued" in the topological sense, which had impressed me from the first time I heard of it as too improbable to be taken seriously. I see the possibility of Universe's having the geometry of either a 3-torus or Dr. Gay's doughnut as equally improbable. I'm not at all convinced that the Universe has the geometry of a four-dimensional hypersphere either, but I've tried unsuccessfully to find any plausible argument for rejecting it and find that it seems to readily provide plausible answers to every question I've been able to come up with..

    If anyone can provide a plausible argument against the four-dimensional hypersphere Universe, I'd like to be told of it. It envisages the Universe as having originated at a point or at least within an extremely small three-dimensional volume at the center of a four-dimensional hypersphere the three-dimensional "surface" of which is the curved and finite expanding three-dimensional Universe that we seem to find ourselves in.

    I feel that people are too quick to jump on the infinite flat Universe model that people have read into the WMAP data. As I see it, WMAP has thus far found the Universe so nearly flat as to be unable to detect any curvature, allowing people to jump to the unwarranted conclusion that the Universe is precisely flat and infinite.

    I'd like to consider any plausible models for which others would argue.

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    Yes, as I said in my above post they have discounted the "soccer ball universe" (dodecahedral space) as the fundamental domain seems too large to allow it. They have not so far been able to totally discount other non-trivial topologies.

    My original point was that it seems to me if it were up to you they shouldn't have even been following up possible evidence of the dodecahedral model as you deem that model implausible and preposterous and I am wondering if that is good science or not.

    That paper also states that they have only found space to be within 2% of being flat, so there may indeed be large scale curvature but the radius of that curvature would be larger than our observable universe.

    The paper below may interest you - it examines and eliminates some other non-trivial topologies but concludes that although we still have no evidence for a non-trivial topology, we still cannot discount it. However, the best fit to the data is the flat, simply-connected Lambda-CDM model.

    Imprints of spherical non-trivial topologies on the CMB

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    I would want to eliminate the simplest possibilities before turning to more complex ones.

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    Unfortunately, it seems that the simplest possibilities are the hardest to eliminate.

    If we never find enough evidence to confidently state the shape of the universe, but along the way we find hints for some of the less simple topologies, are you saying that we shouldn't investigate these, if not just so that we can eliminate them? This is what we (humans!) have been doing.

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    speedfreek, I think your thinking is sound, and I have no problem with it. In particular, I have no problem with people wanting to test hypothetical models for shape of the Universe that can be eliminated or confirmed as plausible only through a reasonable amount of testing. If they test those models and find persuasive evidence for their validity, the effort will have been justified. If the effort fails, the onus will be on them and the sponsors of their research to justify the cost, time, and manhours spent on the effort that might have been expended on some other research. I would not deny them the right to test their ideas, no matter how outlandish they seem to me.

    I'm saying only that all of the models of the Universe that I am aware of as having been proposed other than the four-dimensional hypersphere that I and presumably others have proposed impress me as being so improbable that I myself dismiss them out of hand, but I have no problem with others who feel differently looking for evidence to support their models.

    As for what constitutes good science, I'll leave that to others to say. If people want to invest time, effort, and money on studies that seem to others to be destined to produce negative results, I say let them go ahead if those with the money to fund the effort are willing to provide the money. If they fail, they will at least have provided an answer to a question.

    As for the glued dodecahedron model, I would have been most astonished if convincing evidence had been found for it.

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