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B Dark matter and energy creation

  1. Jun 6, 2017 #1
    If space is expanding and at the same time speeding up, something must be driving it. It also appears to be self perpetuating, as something cannot continue to expand, speed up and backfill at the same time? Could the driving force be dark matter/energy?
  2. jcsd
  3. Jun 6, 2017 #2


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    Staff: Mentor

    Hi John. I see you've made several threads asking questions regarding fundamental concepts of cosmology and astrophysics (which I had to remove for being too speculative, unfortunately). It's important to understand that these topics are very complex and that everything you've likely read up to now has been an extreme simplification that loses almost all real meaning. These concepts are also very counter-intuitive for most people. Therefore it is important to take things slow. Slower than you might like.

    For starters, attempting to link several different things together to develop a new explanation is a task best left to the professionals in the field. They're the ones that have the skills, time, and motivation to do things like solve the differential geometric equations required to truly understand how our current theory of gravity (General Relativity) works, let alone develop new math and physics that a new theory would require.

    Case-in-point, space does not work like you've written above. The expansion of space is better described this way: "The distance between unbound objects increases over time."

    Notice that I did not even use the word "space" there. This is because space (and by extension, spacetime) is better thought of as a framework, not as an entity or object that can move around, accelerate, and do similar things. The only truly dynamic feature of space is that the geometry of space can change over time. This change in geometry cannot be described in terms of motion, as it is not motion, but geometry.

    In real life, geometry itself is inherently bound to measurable and observable objects, as all of our measurements of space and its underlying geometry are actually measurements of objects or disturbances within space. Hence my earlier explanation that the expansion of space is better described as an increase in distance between unbound objects instead. It is these objects which are expanding away from each other, not "space itself". Though the expansion and its associated acceleration is dependent, at least in part, on the underlying geometry of space.

    I'm sure most of that makes very little sense right now, so if you have any questions please feel free to ask. In the meantime, feel free to look through the following links. I hope they prove useful:

    https://www.preposterousuniverse.com/grnotes/ (a huge amount of excellent information, but also quite advanced)
  4. Jun 6, 2017 #3
    Hi Drakkith

    Thank you for taking the time and trouble to explain, in part at least, the answer to one of my questions.
    I am an un-academic of a vintage 61 years, who just has a keen interest in Physics and reading recently has lead me to these questions.
    Just so that I am clear on what it is that you are explaining (and in layman's terms), if we imagine the universe as being a balloon filled with all of the particles that go to make a universe, the outer skin is not expanding but the contents are? Is this correct or is this another oversimplification (or could it be this simple and we are overcomplicating it?)
    I will read the content contained within your links by the way, so thank you for those as well.
  5. Jun 6, 2017 #4


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    In the balloon analogy, one imagines the universe being the skin of the balloon and its contents being specks of paint (for instance) spattered onto it. The analogy helps to understand two things:

    1. The specks of paint get farther apart with time as the balloon/universe expands. But none of the specks are "moving" with respect to the rubber. This illustrates the distinction that can be drawn between a velocity and a "separation rate".

    2. There is no center on the surface of the balloon. All specks of paint see the same situation with all the other specks moving away. All have an equally good claim to be at the "center of the universe".

    The balloon analogy is not perfect. The surface of the balloon only has two dimensions of space. The universe as we know it has three. The balloon is a closed geometrical shape -- finite, but with no edge. The universe is, as far as we know, infinite with no edge and no wrap around.

    The interior of the balloon (the air) is irrelevant to the analogy. It should be ignored. It is not part of the toy universe being modeled.

    [The raisin bread analogy does three dimensions of space and one of time]
  6. Jun 6, 2017 #5


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    No, the skin is expanding as well. But the balloon analogy is exactly that. An analogy. The balloon and its skin must expand because that's how balloons work. But space is not a balloon. The analogy helps people understand how galaxies move away from each other, but it's just an analogy and cannot describe certain things accurately.
  7. Jun 6, 2017 #6


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    @JohnM I recommend the link in my signature
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