Does the Expansion of Space Mean Everything is Growing?

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Discussion Overview

The discussion revolves around the concept of the expansion of space and its implications for the growth of objects within the universe. Participants explore the analogy of a balloon to illustrate this expansion, questioning how it affects the perception of distances and the nature of objects in space. The conversation touches on theoretical implications and gravitational influences, with a focus on both conceptual and technical aspects.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant expresses skepticism about the balloon analogy, suggesting that if everything expands proportionally, one would not perceive the expansion without an external reference.
  • Another participant notes that local gravitational fields, such as those of the Earth and Sun, counteract the expansion of space, implying that these bodies do not expand with the universe.
  • A different perspective is offered, suggesting that the dots on the balloon analogy should be viewed as ink droplets on the surface, which would not be pulled apart due to surface tension during inflation.
  • Another participant argues that in a three-dimensional universe, the concept of "dots" is misleading, as they would represent accumulations of particles, raising questions about the forces that keep these particles together against the backdrop of cosmic expansion.
  • A reference to the Theory of Relativity is made, highlighting how massive objects deform the fabric of space-time, which may relate to the discussion of expansion.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as there are multiple competing views regarding the implications of space expansion on objects and the nature of gravitational forces. The discussion remains unresolved with differing interpretations of the balloon analogy and the effects of local gravitational fields.

Contextual Notes

Limitations include the assumptions made about the nature of expansion and the gravitational influences at play, as well as the dependence on analogies that may not fully capture the complexities of the universe's expansion.

Saoist
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while i have no problem with the whole universe expanding thing, i have qualms with the balloon idea.

you take an uninflated balloon, draw a dot on it, and blow it up. as well as the balloon increasing in size, the dot does also.

if (ignoring the X^2/3 law :P) the human body was expanding gradually so proportions stayed the same, you wouldn't perceive your feet getting further from you, because they're getting larger as well. assuming no external reference, you'd never realize the expansion was occurring.

i guess what I'm tryna ask is: if space is expanding surely everything, objects etc, must be expanding as a consequence, so how can it be stated that "galaxies are moving away as a result of *the expansion*," because we'd never perceive it.

hope this makes sense
 
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This question has been asked many times before in these Forums it is; "If space is expanding then what expands with it?"

As I said before:

It is generally accepted that gravitational attraction of the local gravitational fields, of the Earth, Sun, Milky Way galaxy, and possibly the Local Group, overwhelm the cosmological expansion and these bodies do not expand with the universe.

Einstein himself wrote a paper in the 1940's to prove that the solar system was not co-expanding with the universe. He did so by cutting out a spherical volume from the cosmological model and replacing it with a void with a spherical mass inserted in the middle; thus embedding a Schwarzschild solution inside a cosmological one. The question is how do you take the limit of the Schwarzschild metric as [itex]r \rightarrow \infty[/itex]

Garth
 
Hi Saoist! It would be better to picture the dots as ink droplets resting on the balloon surface, not embedded. Surface tension will prevent the droplets from being pulled apart as the balloon inflates.
 
Plus, there are no "dots" in our 3-d spatial Universe, except for maybe particles by their lonesome. So, what you envision as a "dot" would really be an accumulation of particles. It then should be a question of whether the other forces overwhelm/keep those particles together over what is causing the Universe to expand.
 
If you have heard of Theory of Relativity, it points out a star as a massive object deforming the "fabric of space-time".
 

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