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Dark energy and expansion

  1. Jun 15, 2015 #1
    If we look at our own solar system, our sun is pushing gasses outwards as solar winds. Our Galaxy has what around 100 billion stars? All which most likely follow suit expelling their own atmospheres outwards as solar winds. The ratio of stars being born to stars dying is something like 350:1 that's a steady increase of gas production (recycled I mean). Thats a lot of gas, so essentially galaxies steadily increase thrust, pushing themselves away from each other by pumping gas into the "space" expanding space between them. I just don't understand the need for dark energy... the recipe for expansion seems to be clear. What am I missing?
     
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  3. Jun 15, 2015 #2

    phinds

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    The "gas" that you refer to is utterly trivial compared to the effects of what we call "dark energy", particularly given the distances between galaxies. I mean, it doesn't even cause any expansion inside galaxies so how would you expect it to affect whole galaxies that are many light years apart.
     
  4. Jun 15, 2015 #3
    Excellent point, will have to think on this for a bit, thanks for the input!
     
  5. Jun 15, 2015 #4

    Drakkith

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    Also note that thrust is the result of an object ejecting mass in one direction to create a net force that accelerates the object. Ejecting mass in all directions leads to zero net force and zero acceleration. In addition, I don't think much of this gas is ejected from the galaxy at all. Unless it acquires enough energy to escape the gravitational pull of the galaxy and not fall back into it, it does nothing in the long run.
     
    Last edited: Jun 15, 2015
  6. Jun 15, 2015 #5
    I'm sorry thrust may not have been the right word. The idea was not that the Galaxy is actually moving but that there is more matter in the form of gasses being put between the Galaxies
     
  7. Jun 15, 2015 #6

    phinds

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    Intergalactic space is basically devoid of matter (regular or dark) and putting more matter there would not cause the expansion of the universe to accelerate. Why do you think it would ? I mean, if you are NOT thinking of a "thrust" or "push", what is it that you think the gas would do to cause the expansion to accelerate?
     
  8. Jun 16, 2015 #7
    That's the real issue, there has to be mass in those "voids" we see Galaxies on the other side.
     
  9. Jun 16, 2015 #8

    Drakkith

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    No there doesn't. The voids are exactly that. Voids. The matter has been pulled from those areas of space by gravity and clumped together in other areas to form galaxies, stars, planets, etc. In the very early universe, the universe consisted of a dense plasma with small fluctuations in its density from quantum effects. These small fluctuations gave rise to the voids and matter-dense areas of the universe we see today.
     
  10. Jun 16, 2015 #9
    I understand the explanation you've given, thank you.

    However it is my understanding that a perfect vacuum has never been created. So isn't an absolute void without basis in observation? All of our observations on light take place within a massive medium of some form. Our conclusion on light should be that it does not propagate without mass, so if we see Galaxies on the other sides of voids there should be mass between object and observer.
     
  11. Jun 16, 2015 #10

    Chronos

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    You need to define, quantitatively, what you mean by 'void' then define 'nothing' within that context to properly frame your point.
     
  12. Jun 16, 2015 #11

    Drakkith

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    Voids are not absolutely void of all mass. The density of matter within the void is just much lower than outside.

    This doesn't make any sense, regardless of the fact that there is some amount of matter between galaxies.
     
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