What is the role of dark energy in the expansion of the universe?

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Discussion Overview

The discussion centers on the role of dark energy in the expansion of the universe, exploring various perspectives on the mechanisms behind cosmic expansion, the nature of voids in space, and the implications of mass and gas distribution in intergalactic regions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant suggests that the gas produced by stars and galaxies contributes to the expansion of the universe, questioning the necessity of dark energy.
  • Another participant counters that the amount of gas ejected by stars is negligible compared to the effects of dark energy, particularly over vast distances between galaxies.
  • Concerns are raised about the concept of thrust, with a participant explaining that ejecting mass in all directions results in zero net force, thus questioning the role of gas in cosmic expansion.
  • Some participants argue that intergalactic space is largely devoid of matter, suggesting that adding more gas would not accelerate the expansion of the universe.
  • There is a discussion about the nature of voids in space, with one participant asserting that voids are areas where matter has been pulled away by gravity, while another questions the existence of absolute voids based on observational limitations.
  • One participant emphasizes the need to define what is meant by 'void' and 'nothing' to clarify the discussion.
  • Another participant argues that while voids are not completely devoid of mass, their density is significantly lower than in other regions, challenging the notion that light cannot propagate through them.

Areas of Agreement / Disagreement

Participants express differing views on the significance of gas in the expansion of the universe and the nature of voids, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

The discussion reveals limitations in definitions and assumptions regarding voids and the role of mass in cosmic expansion, with some participants calling for clearer quantitative definitions.

FallingSky
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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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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.
 
Excellent point, will have to think on this for a bit, thanks for the input!
 
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.
 
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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
 
FallingSky said:
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
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?
 
That's the real issue, there has to be mass in those "voids" we see Galaxies on the other side.
 
FallingSky said:
That's the real issue, there has to be mass in those "voids" we see Galaxies on the other side.

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.
 
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.
 
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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.
 
  • #11
FallingSky said:
. So isn't an absolute void without basis in observation?

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

FallingSky said:
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.

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

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