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Thread: Cosmology

  1. #1 Cosmology 
    Join Date
    Jan 2005
    The universe is 15 billion years old. 15 billion years ago, all the stuff in the universe was concentrated in a singularity, a mathematical concept, a speck of infinite density. It exploded. This is what astronomers call the Big Bang, the point at which time began. George Gamow coined the term.

    Primordial energy and matter flew in all directions. It cooled. Gas clouds condensed into galaxies. Galaxies are aggregates of stars, the building blocks of the universe. There are 100 billion galaxies. They are distinctive. The Whirlpool and Sombrero look like works of art. Galaxies are categorized according to their structures. The Milky Way is a spiral. M87 is elliptical. The Magellanic Clouds of the Southern Hemisphere are irregular. They are satellites of the Milky Way.

    The Milky Way belongs to a Local Group of 31 galaxies. The Andromeda Galaxy M31 is part of the Local Group. M31 is a spiral similar to the Milky Way but larger. It is 2.3 million light-years from us and the fartherest visible object. It is faint.

    Numbers were assigned to fuzzy patches in the sky by Charles Messier, an 18th century comet hunter. He cataloged 103 objects so as not to mistake them for comets. Nebulas and galaxies were lumped together. The more thorough New General Catalog (NGC) dates from the 19th century.

    Galaxies are found in clusters, and these in turn comprise superclusters. The Virgo and Coma Berenices superclusters are enormous. Our Local Group is part of the Virgo supercluster. In spite of this, the universe is mostly empty.

    Proof of the Big Bang came from the work of Edwin Powell Hubble. By applying the Doppler Effect to light, Hubble found that light from galaxies shows a redshift. This suggests that galaxies are receding, travelling away from each other. This is what we mean by the Expanding Universe. If you run it backwards, there is a point at which all galaxies converge. The primeval atom! Furthermore, the farther apart galaxies get, the faster they travel. This is as Hubble's Law. The question becomes whether expansion will continue forever or whether there is enough gravity in the universe to pull it back together. This would be the Big Crunch and suggests an oscillating universe, one which alternately expands and collapses. Black holes may provide the gravity for a Big Crunch. The universe is not expanding in space. Space is being created as the universe expands. The balloon analogy is used, blowing up a balloon with dots on it to represent galaxies.

    We ask what there was before the Big Bang. The answer is nothing. There was no space, no time and no events. It was the beginning in the true sense. Penzias and Wilson provided more proof of the Big Bang when they detected its background radiation.

    E.P. Hubble was the greatest astronomy of the 20th century. Shapley was great but believed external galaxies were inside our own.

    Cosmology was a step I was trying to take since I was a teenager. Carl Sagan's Cosmos series was a breakthrough. To paraphrase Sagan, "The Cosmos is everything that has been, everything that is and everything that will be." Sagan saw man as poised on the shore of the cosmic ocean, intelligent life as a means for the cosmos to know itself. The terms "cosmos" and "universe" are interchangible.


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  3. #2 Re: Cosmology 
    Forum Masters Degree
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    Aug 2005
    Quote Originally Posted by Jim Colyer
    We ask what there was before the Big Bang. The answer is nothing. There was no space, no time and no events. It was the beginning in the true sense.
    For the most part, I basically agree with what you have to say.

    I disagree with this however. I consider it speculation on your part. The Big Bang s not necessarily the beginning of space or time; it is the beginning of space-time. The Big Bang theory does not concern itself with what went on before the Big Bang, only with what went on after. You yourself speak of the possibility of an oscillating universe. If it is indeed oscillating, then the Big Bang clearly cannot be the beginning of time or space, can it?

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  4. #3  
    Forum Isotope Zelos's Avatar
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    Jun 2006
    dont u mean 13,6 billion years according to the latest observations?
    I am zelos. Destroyer of planets, exterminator of life, conquerer of worlds. I have come to rule this uiniverse. And there is nothing u pathetic biengs can do to stop me

    On the eighth day Zelos said: 'Let there be darkness,' and the light was never again seen.

    The king of posting
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  5. #4  
    Universal Mind John Galt's Avatar
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    Jul 2005
    Jim, your short essays on various aspects of Astronomy are interesting. I understand you have set your thoughts down to help you assimilate and organise your ideas. I am sure they will also help others to new to the subject areas.
    I would find it helpful if you could preface these essays with a short comment like this:
    "Here are some notes I made on topic name. I thought they might be of interest. Please note I am fairly new to this, so some of the facts may be a little off. Please point out any errors, so that we can all learn."

    I suggest this because you have written the essays rather nicely, so that they convey authority and certainty, but there are a few points that are wrong, or misleading. Here are a couple of examples from this essay.

    Amendment 1:George Gamow very definitely did not coin the term Big Bang. He did place the hypothesis on a firm theoretical basis in two papers published in 1948, in which he developed the ideas of LeMaitre and his Primeval Atom.
    The term Big Bang was introduced by Fred Hoyle, the promoter of the rival Steady State Theory. He intended it as a sarcastic put down of Gamow's hypothesis.

    Amendment 2: Primordial energy and matter did not fly in all directions. The singularity did not explode. What is occuring is rather more subtle. Space is expanding, and so matter is moving apart, it is not the case that matter is expanding into a pre-existing space. You state this correctly further in your essay, but it is this initial statement that casual readers will tend to remember.[I am taking the conventional position here, that the Big Bang affords the best current position on the origin of the Universe. Like Hermes I am sceptical as to its validity.]

    Amendment 3:As Zelos says 13.6 billions years is thought to be a more accurate figure, currently, than 15 billion. Still, what's a billion years or two between friends?

    Amendment 4:The Andromeda galaxy is not, as you said, the farthest visible object, but is, as you meant, the farthest object visible to the naked eye.

    Amendment 5:I absolutely have to challenge the characterisation of Hubble as the greatest astronomer of the 20th Century. Great, yes. Greatest, highly questionable, and needs some form of justification.

    I hope you will take my suggestions positively and continue to contribute your well constructed overviews.
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