Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Structure of the Cosmos

  1. Mar 1, 2009 #1
    I was watching a video about the structure of the universe and they had some neat graphics showing a map of the universe and it's relation to this dark matter. Since most of the Cosmos is really far away causing our view of it to be old also, do they take this into account and correct for this when making a map of the universe? or does it not matter? Because a map of what the Universe looks like from our point of view is not what it truely looks like. a Galaxay 300,000,000ly away has traveled quite a distance and is no longer in the place where we see it. They said that when they made the map of the Cosmos they were showing that they did enter the information they knew about the galaxies shown. Such as redshift. It seems like it wouldn't take much to make a "current" picture of the Cosmos. Just have a program where you input all the known galaxies, thier velocity, direction of motion and distance from earth. Then you could have the program correct thier position for thier distance from earth(how long the light has been traveling to get here). Actually most of the information for a program like that sounds like it has allready been entered into that map that was shown on the video I saw.

    P.S. All the maps I have seen of the Cosmos though have looked almost exactly like pictures of neuron's and neural clusters I have also seen. the visual corelation between the 2 reminds me of mandelbrot sets or fractal paterns. Is the visual similarity between the large scale structure of the universe and the small scale structure of the brain simple coincidence? Or is there some deeper meaning? Something to do with the formation of the universe and galaxies following the same mathmatical formulas that control the growth of brain structure? Hmmmm........ Wish I was smart enough to research and write a paper on hat.
    Last edited: Mar 1, 2009
  2. jcsd
  3. Mar 2, 2009 #2


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    The calculator I normally recommend to newcomers automatically calculates the today distance when you put in the redshift.

    Google "wright calculator". I've probably recommended it to you already. Playing around with it is a good way to get used to the standard cosmo model.

    The today distance is also called the "comoving" distance (for historical reasons going back to Hubble in the 1930s, no longer important). The socalled "comoving" coordinates, based on the distance to the object today, are normally used to locate stuff.

    It would be normal for any astronomer to construct a map of today's universe using comoving coordinates. That is, today's distance. I can't think of how else you would map the universe as it is today and I don't think anyone has ever done it any other way.

    You can be fairly confident they were using today distance.

    Good observation. Universe structure is visually similar to some other natural things including what you mention---I see what you point out.
    I also see cobwebs.

    Computer simulations can get such results just using simple gravity rules. You start with an 3D space filled with a kind of dust cloud, almost but not quite perfectly uniform. space uniformly filled with stuff that is not moving. but not quite uniform, some random wavy unevenness

    And it begins to fall slowly together. And at first it forms strands, and where the strands nearly cross it forms blobs. and the blobs eventually turn into clusters of galaxies.

    Somebody did some especially nice computer simulations of structure formation. Maybe a link will show up.
    Last edited: Mar 2, 2009
  4. Mar 2, 2009 #3
    Thank you
  5. Mar 2, 2009 #4


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    You are very welcome! To get some of those good visuals, google "Smoot TED".

    Smoot is a nobel laureate and TED is an organization that gets creative people to put on slideshows and records them and has them online.
    Tech, Entertainment, Design.

    When Smoot gave his TED talk he used short animations of early universe structure formation, and somewhere it gives the guy's name who made them, and you can find more at the guy's website.
    They are cool. They show how the cobwebs or the neural networks can come into being out of nearly uniform soup, just by the operation of simple gravity attraction.
  6. Mar 2, 2009 #5


    User Avatar
    Science Advisor

    Yes. Typically we use what are called co-moving coordinates where the expansion of the universe is divided out. What this means is that two far-away objects will typically remain about the same distance apart in these coordinates as the universe expands.

    Just bear in mind that any very large distance measure (beyond a billion light years or so) becomes highly arbitrary. It turns out that there are many different ways of talking about the distance between us and a faraway galaxy, and no one way is preferred. I believe the measure that is usually called just the "distance" is what is known as the comoving distance. Basically this can be understood as the inferred distance that that object would be from us "now" from the expansion that has occurred since the light was emitted.

    (I put now in quotes because "now" is just as arbitrary as distance...yes, curved space-time does make things a bit confusing, but physicists have developed a very explicit formalism for describing all of these things. It's not a problem in the field, it's just a problem in intuitive interpretations and communicating it to the public.)

    It has to do with the non-linear nature of gravity at short ranges.
  7. Mar 2, 2009 #6
    I'm not sure that the [large-scale structure ~ neuronal morphology] analogy will survive a detailed examination, but if you want to see an infinite discrete fractal model of the cosmos wherein there are meaningful analogies between the microcosm and the macrocosm, see the following website: http://www3.amherst.edu/~rloldershaw/menu.html .

    Yours in science,
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook