What hold galaxies together?

Discussion in 'Hydrodynamics and Aerodynamics' started by Sailor Al, Aug 3, 2022.

  1. Sailor Al
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    Sailor Al Senior Member

    Yes, angular motion is indeed a "non-relative" motion. It can be detected from any inertial frame of reference, but it's not the only one.
    Linear acceleration is also "non-relative" for the same reason.
    And that's why a gravitational field cannot be distinguished from an accelerating frame of reference.
     
  2. Paul Scott
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    Paul Scott Senior Member

    Unless you climb out of the frame of reference? like climbing from the rim to the hub of a spoked & rotating spacecraft. Same structure (frame of reference?) different sense, at least, weight. Or running inside the rim one way or the other? And then jumping? Harder to do in a gravitational field. :rolleyes: There are some proposed fluid experiments in microgravity proposed around this- do you get gravity waves outside of the earth’s gravitational field, say in a rotating rim and spoke space ship? Seems to me I came across some literature on differences of human physiology in artificial gravity vs gravitation pull on earth.

    Not perfect analogies, but the gravitational pull of the terrier is pulling me for a walk-ie!
     
  3. Sailor Al
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    Sailor Al Senior Member

    It helps if you present thoughts in structured sentences.
     
  4. Will Gilmore
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    Will Gilmore Senior Member

    That's the difference between rotational motion and an accelerating frame. If you climb out of the rotating frame, linear motion takes over. In an accelerating frame, linear motion remains the same. Acceleration in a linear frame has to have a constant force to maintain it (F=ma). I can't think of a case where energy isn't applied to create the force.

    But, in a rotating frame of reference, no force need apply. Centripetal force is energy free, even though the force is constant. It could be equally said of rotational acceleration that it is a consequence of geometry, as is said of gravity. However, centripetal force does not behave exactly like gravity. When an astronaut walks in the direction of rotation, a virtual increase in centripetal force is experienced. A ball thrown in that direction will also "fall" faster. If the astronaut turns around and walks against rotation, the virtual effects of gravity lessens. Throwing a ball in that direction can lead to the ball never landing, as one example outcome.
     
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  5. Paul Scott
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    Paul Scott Senior Member

    I’m assuming you've not lived with a 13 year old West Highland White Terrier.
     
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  6. Sailor Al
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    Sailor Al Senior Member

    Sure. No work is done in rotation because the force (centripetal) is being applied perpendicularly to the direction of motion: Work is only done, i.e. energy transferred, when the point of the force moves in the direction of the force. In linear acceleration, work is done since the point of the force is moving in the direction of the motion.
     
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  7. Alan Cattelliot
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    Alan Cattelliot Senior Member

    Thanks for sharing, Will. As the parity notion in fondamental physics is partially out of my league, I wrote this small python program, in order to find out what happens to the ratio levorotatory/dextrorotary of a random distribution of points in 3D space. Intuitively, I had the feeling that it should be 50/50, but since my statistical physics is now far far away, I can only rely on numerical experimentation. Compare with the technic described in the article, I use brute force here, so am I not able to compute the ratio for a high number of galaxies. But it can clearly be observed, when playing with this Python code, that the ratio, indeed, tends to 50/50. So I'm wondering. What exactly has been demonstrated by the work presented in the study ? Marc Kamionsky is cited "“If this result is real, someone’s going to get a Nobel Prize” . Isn't it a little too much ? With this small experiment, I would say that, having measured a little parity violation only demonstrate that the distribution of the studied galaxies is not random. Isn't it something that we already know ?

    import itertools
    # Set galaxies number
    N = 40
    foo_indexes = [n for n in range(N)]
    # Compute the permutations of 4 elements among the galaxies set
    perm = list(itertools.combinations(foo_indexes,4))
    import random
    # Create 3d coordinates of random points
    integer_list = random.sample(range(1, 1000), N)
    x_list = [x/1000 for x in integer_list]
    integer_list = random.sample(range(1, 1000), N)
    y_list = [x/1000 for x in integer_list]
    integer_list = random.sample(range(1, 1000), N)
    z_list = [x/1000 for x in integer_list]
    import numpy
    res = []
    # Iterate over the total number of tetahedra
    for i in range(len(perm)):
    # get the index of the ith tetahedra
    a = perm[0]
    b = perm[1]
    c = perm[2]
    d = perm[3]
    t = [b,c,d]
    # compute sides lenghts
    l1 = ((x_list[a]-x_list)**2+(y_list[a]-y_list)**2+(z_list[a]-z_list)**2)**0.5
    l2 = ((x_list[a]-x_list[c])**2+(y_list[a]-y_list[c])**2+(z_list[a]-z_list[c])**2)**0.5
    l3 = ((x_list[a]-x_list[d])**2+(y_list[a]-y_list[d])**2+(z_list[a]-z_list[d])**2)**0.5
    # sort sides lengths
    s = numpy.array([l1,l2,l3])
    sort_index = numpy.argsort(s)
    # compute coordinates of the base vectors
    v1 = [x_list[t[sort_index[0]]]-x_list[t[sort_index[1]]],
    y_list[t[sort_index[0]]]-y_list[t[sort_index[1]]],
    z_list[t[sort_index[0]]]-z_list[t[sort_index[1]]]]
    v2 = [x_list[t[sort_index[2]]]-x_list[t[sort_index[1]]],
    y_list[t[sort_index[2]]]-y_list[t[sort_index[1]]],
    z_list[t[sort_index[2]]]-z_list[t[sort_index[1]]]]
    # compute coordinates of the vector formed with the vertex and one of the base point, namely main vector
    v3 = [x_list[a]-x_list[t[sort_index[1]]],
    y_list[a]-y_list[t[sort_index[1]]],
    z_list[a]-z_list[t[sort_index[1]]]]
    # compute the cross product of the two vectors
    v1xv2 = numpy.cross(v1,v2)
    # compute the dot product of the cross product with the main vector
    v1xv2v3 = numpy.dot(v1xv2,v3)
    # store result
    res = res + [v1xv2v3]
    # check the signs of the dot products and count negatives and positives
    x = sum(1 for i in res if i >= 0 )
    print("Number of Combinations is :", len(perm))
    print("Number of Positive tetrahedron is:", x)
    print("Length of Negative tetrahedron is:", len(res)-x)

    Number of Combinations is : 91390
    Number of Positive tetrahedron is: 45284
    Number of Negative tetrahedron is: 46106
     
    Last edited: Mar 6, 2023
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  8. Alan Cattelliot
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    Alan Cattelliot Senior Member

    For comparison, I've done the same analysis with a evenly spaced distribution of 27 points (galaxies). Here is what I got.

    upload_2023-3-6_12-32-52.png upload_2023-3-6_12-33-43.png
    Like in a crystal lattice, the evenly spaced distribution can be the result of an underlying physical phenomenon, governing the repartition of galaxies. With this comparison, it can be checked that, using the "Tetrahedra" method, it is possible to detect the influence of a governing law. But how can we qualify and quantify this law ? What will be the result of this numerical check, applied on a numerical simulation of the galaxies formation after the Big Bang ?

    upload_2023-3-6_12-47-46.png
    The handedness of an helical cobalt complex would tend to racemic proportion with time. What could be the evolution in time of the computed ratio for galaxies?

    Bonus question : A "7-sigma" result is mentionned is the article. So, I guess that the 1 million galaxies have not been processed as a whole, but instead that computations have been done on samples. Because, given a definite number of galaxies, the ratio is not a distribution, but equals a certain value. The crystal-like distribution that I use has been obtained for points in an equilibrium condition, with no time dependency. But what would be the influence of the "age" of the galaxies, on the ratio found by the scientist ?
     
    Last edited: Mar 6, 2023
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  9. Will Gilmore
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    Will Gilmore Senior Member

    When I was a child of about ten, I took classes at the local magic shop. I remember a statement made about shuffling a deck of cards and have, as yet, not been able to fully reconcile it in my mind.

    The magician teaching the class told us, if you shuffle a brand new deck that is organized by suits and face values out of the box, the deck gets more and more randomized With each shuffle. Picture entropy. However, there is a point at which continuing to shuffle the deck will actually begin to destroy the randomness. Call the number of deck shuffles 'time'.

    It is not too difficult to picture a perfectly randomized collection or set that, when a randomizing operation is performed upon it, begins to lose its randomness just by the act of straying from the previously perfect random form.

    We weren't trying to discuss any deep philosophical questions in my magic classes, but I have revisited that statement every once in a while, on the following fifty years.

    Time may not be the issue as much as how many times the dice have been rolled. That is, if God really does play dice. As far as time itself, who knows how many beautiful ladies get to blow on the dice before they are chucked.
     
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  10. Alan Cattelliot
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    Alan Cattelliot Senior Member

    I'd rather feel the nice and warm blow of a lady in the back of my neck than the being slap in the face by the hand of God, If I were to choose...

    You've given a very nice picture of the situation. There is plenty of books on how to cheat with playing cards, enumerating the "fake" and the "pseudo" shuffle technics. While some very serious studies have been made to find the best way to shuffle, in order to achieve the best equiprobability of outcomes. The same goes with my small numerical experiment. True random numbers cannot be obtained with a classical computer, and I cannot guarantee that no biais is introduced by the random function I used, as I wouldn't use it for any encryption. My approach is very naive, and poses the question on how should we apprehend the Universe, free from any anthropocentrism. Finding the right lady and the right blow.

    "And girls of every shape and size and price,
    Each one a beauty, we so long at sea.
    And, recognising seaman on a spree,
    Smile promises of instant of paradise"

    Robert Milton, boat captain and poet.
     
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  11. Will Gilmore
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    Will Gilmore Senior Member

    I would argue that the first and the latter was the same. Except for the neck/face part.

    Randomness may just be a matter of perception. Mostly, it means, without cause. An event that can be traced back to a cause would not be a random event. In that sense, only the Big Bang, Singularity, Primal Atom, ... the beginning of everything, might be completely random. The next best concept of random is unpredictable. And that just means, without knowledge. Knowing may be the primary organizing force in the Universe.

    "The ladies go out to bring beauty to the meadow" - author unknown by me.

    -Will
     
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  12. Paul Scott
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    Paul Scott Senior Member

    Ah, the poetics of chance!

    The doctor tells you
    What you most fear-
    You’re likely to live on
    For years, and years

    -Ogden Nash

    I don’t know if his doctor was female, but it would add some complexity to the metaphor…:cool:
     
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