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Thread: RFC: A simple explanation for dark matter/energy

  1. #1 RFC: A simple explanation for dark matter/energy 
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    Hi!

    Regarding Dark Matter and Dark Energy, there is obviously a reason why the simple explanation that follows doesn't work. Can someone help explain it to me.

    Dark Matter:

    Hypothetical: A universe with only one galaxy. The pull of gravity is towards the center.

    A galaxy at the edge of a very large void. The pull of gravity is towards the center of the galaxy until the pull of gravity from the rest of the universe over powers this.

    Conclusion:
    Dark Matter is simply the pull of the rest of the universe over-riding the more local force(s) of gravity.

    Dark Energy:

    Hypothetical: A universe with only two galactic clusters. The pull of gravity is towards the center of gravity of the two galactic clusters.

    Two galactic clusters at the edge of large void--one closer the void, one further from the void. The pull of gravity is towards the center of gravity of the two galactic clusters until the gravity from the rest of the universe over powers it. The galaxy closer to the void will have less pull from the rest of the universe than the one closer to the rest of the universe so the two will be pulled apart from each other. The further the two are pulled apart the weaker the pull between the two and although the overall gravity of the universe will also weaken the universe is infinite and it will weaken less creating an accelerating separation between the two.

    Conclusion: The combined gravity of the universe is pulling the overall universe apart. The further the universe is pulled apart the faster the expansion.

    Thanks for your time!
    Rusty Williamson


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  3. #2  
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    Quote Originally Posted by rrw4rusty View Post
    Dark Matter:
    Hypothetical: A universe with only one galaxy. The pull of gravity is towards the center.
    A galaxy at the edge of a very large void. The pull of gravity is towards the center of the galaxy until the pull of gravity from the rest of the universe over powers this.
    If there's only one galaxy what causes the "gravity of the rest of the universe"?
    Matter is what "causes" gravity.


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  4. #3  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by rrw4rusty View Post

    Dark Matter:

    Hypothetical: A universe with only one galaxy. The pull of gravity is towards the center.

    A galaxy at the edge of a very large void. The pull of gravity is towards the center of the galaxy until the pull of gravity from the rest of the universe over powers this.

    Conclusion:
    Dark Matter is simply the pull of the rest of the universe over-riding the more local force(s) of gravity.
    The effects of dark matter are caused by extra unseen (dark) matter inside the galaxy, not outside. (As well as D's objection.)

    Dark Energy:[/B]
    Hypothetical: A universe with only two galactic clusters. The pull of gravity is towards the center of gravity of the two galactic clusters.

    Two galactic clusters at the edge of large void--one closer the void, one further from the void. The pull of gravity is towards the center of gravity of the two galactic clusters until the gravity from the rest of the universe over powers it. The galaxy closer to the void will have less pull from the rest of the universe than the one closer to the rest of the universe so the two will be pulled apart from each other. The further the two are pulled apart the weaker the pull between the two and although the overall gravity of the universe will also weaken the universe is infinite and it will weaken less creating an accelerating separation between the two.

    Conclusion: The combined gravity of the universe is pulling the overall universe apart. The further the universe is pulled apart the faster the expansion.
    I don't really understand this one. Are you suggesting that all the mass of the universe is "pulling apart" all the things inside? If so, that doesn't work. That nice Mr Newton proved a few hundred years ago that uniform distribution of mass surrounding you has no net effect.
    ei incumbit probatio qui dicit, non qui negat
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  5. #4  
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    (Weird... when I press return I do not get a line break!!) Anyway, you misunderstand, the hypothetical example has only one universe, the next statement is separate and not hypothetical and the universe does exist (how can you have a void with only one galaxy?) and the next statement also has the universe. <"The effects of dark matter are caused by extra unseen (dark) matter inside the galaxy, not outside."> This is flat out wrong. First, if it exists at all, it is outside the galaxy. Look it up. Second, my entire point is that I'm saying 'no' to 'unseen' matter (like prove its there!). <"I don't really understand this one. Are you suggesting that all the mass of the universe is "pulling apart" all the things inside? If so, that doesn't work. That nice Mr. Newton proved a few hundred years ago that uniform distribution of mass surrounding you has no net effect."> Again that's just non applicable. There is no uniform distribution of matter. If we had that we would not have stars, planets, galaxies just a bunch of evenly distributed dust.
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    Quote Originally Posted by rrw4rusty View Post
    (Weird... when I press return I do not get a line break!!) Anyway, you misunderstand, the hypothetical example has only one universe, the next statement is separate and not hypothetical and the universe does exist (how can you have a void with only one galaxy?) and the next statement also has the universe. <"The effects of dark matter are caused by extra unseen (dark) matter inside the galaxy, not outside."> This is flat out wrong. First, if it exists at all, it is outside the galaxy. Look it up. Second, my entire point is that I'm saying 'no' to 'unseen' matter (like prove its there!). <"I don't really understand this one. Are you suggesting that all the mass of the universe is "pulling apart" all the things inside? If so, that doesn't work. That nice Mr. Newton proved a few hundred years ago that uniform distribution of mass surrounding you has no net effect."> Again that's just non applicable. There is no uniform distribution of matter. If we had that we would not have stars, planets, galaxies just a bunch of evenly distributed dust.
    Your quotes are a bit mixed up, you can ask someone to show you how to fix the problem, I would but I am still not that good there are many who will help you.
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    This is flat out wrong. First, if it exists at all, it is outside the galaxy. Look it up. Second, my entire point is that I'm saying 'no' to 'unseen' matter (like prove its there!)
    This is flat out wrong. Dark matter permeates the galaxy as a sort of halo. Look it up. Second, we see the gravitational effects of dark matter in orbital speed of stars in the spiral arms.

    There is no uniform distribution of matter. If we had that we would not have stars, planets, galaxies just a bunch of evenly distributed dust.
    On the large, cosmological scale, the distribution of matter is homogeneous.
    Its the way nature is!
    If you dont like it, go somewhere else....
    To another universe, where the rules are simpler
    Philosophically more pleasing, more psychologically easy
    Prof Richard Feynman (1979) .....

    Das ist nicht nur nicht richtig, es ist nicht einmal falsch!"
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    Quote Originally Posted by rrw4rusty View Post
    (Weird... when I press return I do not get a line break!!)
    Yes, some people have that problem. Don't know why. (One poster was convinced it was part of a conspiracy to discredit him!)

    <"The effects of dark matter are caused by extra unseen (dark) matter inside the galaxy, not outside."> This is flat out wrong. First, if it exists at all, it is outside the galaxy. Look it up.
    No, dark matter has to permeate the entire galaxy as it is only mass inside a stars orbit around the galaxy that can effect it. (Again, see I. Newton, Shell Theorem.)

    Second, my entire point is that I'm saying 'no' to 'unseen' matter (like prove its there!).
    The gravitational effects of its mass on orbital velocities.
    Gravitational lensing.
    Plus multiple other lines of evidence (that I am less familiar with).

    Again that's just non applicable. There is no uniform distribution of matter. If we had that we would not have stars, planets, galaxies just a bunch of evenly distributed dust.
    On large enough scales, the universe is close to homogeneous. However, there is some serious investigation of the possibility that the recently observed acceleration could be due to large scale inhomogeneity. (If that is what you are suggesting.)

    There are very many hypotheses and possible explanations for dark energy (and dark matter) being researched.
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    Moving to New Hypothesis
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
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  10. #9  
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    Everyone...thanks for your replies!

    Hmm...perhaps I'm behind the times or just confused. I thought dark matter was first discovered because galaxies, or the stars that make them up, did not rotate in the right way because gravity from outside the galaxy was affecting them but there was nothing out there to account for the gravity (ergo dark matter). I thought that when dark matter was mapped out by looking at the ways it bent light it showed dark matter seemed like sort of a scaffolding around (outside) the galaxies which the galaxies rested in. I thought when two galaxies passed thought each other (have to look up which ones or where) and the stars keep going but the nebula (or the clouds of dust) stayed behind it was because of the dark matter outside the two galaxies held on to it.

    If dark matter permeates galaxies (is within them and outside them) then I can't see how dark matter could affect anything--same everywhere yes? If it is just within them, wow, do I have things wrong! I've never heard of stars and planets being mentioned along with dark matter. Admittedly, focusing on my first novel these last 5 or 6 years has left me out of date on these subjects but damn...???!

    Ten years ago I suggested that our observable universe was in a thinly populated area of the universe and was surrounded by areas far more dense and this was pulling matter out of our area--I was laughed out of town. What's this new theory you talk of?

    And yes, I'm sure the fact that my ENTER key does not provide a new line in this forum that, LOL, its a conspiracy to discredit me.

    Cheers from a mixed up syfy writer,
    Rusty
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  11. #10  
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    Quote Originally Posted by KALSTER View Post
    Moving to New Hypothesis
    Does this mean that I won't get any replies to my last post? Rusty
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    OK, I completely misunderstood dark matter, my apologies, I'm embarrassed and I'll be more careful in the future. I must have gotten off on the wrong foot with it long ago.

    Despite that I still do not have a good answer for why, in the case of dark matter, the overall gravity of the universe could not wash out the matter distribution differences in a spiral galaxy (as the dark matter which permeates the galaxy and its halo does). There seems to be a simple answer but I wanted check 'my' simple answer and also see if there were other reasons. I'll just say it: presumably we know the fall off of gravity, that is to say, how quickly its attraction fades with distance and, this would tell the story. As I understand it gravity's scope is infinite so...an interesting fall off.

    As for dark energy, the universe is a dynamic place. Galaxies are speeding all over the place making waves in the time space landscape. My alternative to dark energy--saying the overall gravity of the universe is causing expansion--is admit ably not well thought out. Yes the overall matter (or gravity) in the universe is going to be the same taken as a whole but as I said Galaxies are speeding all over the place so I put it out there to see what came back. Rusty
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  13. #12  
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    Quote Originally Posted by rrw4rusty View Post
    Hmm...perhaps I'm behind the times or just confused.
    I was goint to say confused, but it looks like you have figured that out for yourself. Well done.

    Ten years ago I suggested that our observable universe was in a thinly populated area of the universe and was surrounded by areas far more dense and this was pulling matter out of our area--I was laughed out of town. What's this new theory you talk of?
    I'm not sure if it is a new idea. And I'm afraid I can't provide a reference to it now (and don't really know any details). I have just seen a passing reference to some people looking at the idea that the apparent acceleration could be due to us being in/near a void.

    By they way, just in case you might be confused about this as well: dark energy is not required to explain expansion, only the recently observed (apparent) acceleration of expansion.

    [p.s. can I just say what a pleasure it is to have someone with their own idea who is willing to consider even the possibility that they might be a bit confused, not 100% correct, etc. ]
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    Quote Originally Posted by rrw4rusty View Post
    OK, I completely misunderstood dark matter, my apologies, I'm embarrassed and I'll be more careful in the future. I must have gotten off on the wrong foot with it long ago.
    I just wanted to add my appreciation to what Strange has already said. Such honest self-assessment is rare, and it will serve you well.
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    Quote Originally Posted by Strange View Post
    I'm not sure if it is a new idea. And I'm afraid I can't provide a reference to it now (and don't really know any details). I have just seen a passing reference to some people looking at the idea that the apparent acceleration could be due to us being in/near a void.
    Here is a Scientific American article about it

    http://pil.phys.uniroma1.it/~sylos/darkenergynot.pdf


    And the paper it is based on:

    [0807.1443] Living in a Void: Testing the Copernican Principle with Distant Supernovae
    "Ok, brain let's get things straight. You don't like me, and I don't like you, so let's do this so I can go back to killing you with beer." - Homer
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by Strange View Post
    I'm not sure if it is a new idea. And I'm afraid I can't provide a reference to it now (and don't really know any details). I have just seen a passing reference to some people looking at the idea that the apparent acceleration could be due to us being in/near a void.
    Here is a Scientific American article about it

    http://pil.phys.uniroma1.it/~sylos/darkenergynot.pdf


    And the paper it is based on:

    [0807.1443] Living in a Void: Testing the Copernican Principle with Distant Supernovae
    The first link (a pdf file) was invalid. Do you have a copy of the pdf file (or can you check the url)?

    thanks,
    Rusty
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    Quote Originally Posted by rrw4rusty View Post
    The first link (a pdf file) was invalid. Do you have a copy of the pdf file (or can you check the url)?
    In situations like these, I recommend doing a search for the file itself. Google "darkenergynot.pdf" and see what happens.
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    Quote Originally Posted by rrw4rusty View Post
    Quote Originally Posted by SpeedFreek View Post
    The first link (a pdf file) was invalid. Do you have a copy of the pdf file (or can you check the url)?

    thanks,
    Rusty
    I just checked the URL and it is valid, and is a direct link to the pdf file. It works fine, here.
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  19. #18  
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    Quote Originally Posted by SpeedFreek View Post
    Quote Originally Posted by rrw4rusty View Post
    Quote Originally Posted by SpeedFreek View Post
    The first link (a pdf file) was invalid. Do you have a copy of the pdf file (or can you check the url)? thanks, Rusty
    I just checked the URL and it is valid, and is a direct link to the pdf file. It works fine, here.
    Seems ok here now, too. It wasn't working when I checked previously, though; it seems that their server is a bit intermittent.
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  20. #19  
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    Sorry I didn't get back...I got to and read both articles. Thanks so much for all the help!

    Rusty
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