Expanding Universe (an interestin mind experiment)

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Discussion Overview

The discussion revolves around the concept of measuring the expansion of the universe through the lens of relativity, exploring how different observers might perceive expansion or contraction based on their location. Participants engage in thought experiments using analogies such as "play dough" and "raisin muffins" to illustrate their ideas about cosmic expansion and potential influences from other dimensions or universes.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant proposes a model using a giant ball of "play dough" to illustrate how observers might perceive expansion or contraction based on their location within the universe.
  • Another participant suggests that if the universe were being squeezed, it would have to be by gravity, yet observations indicate a homogeneous and isotropic universe, questioning the feasibility of such a mechanism.
  • A different perspective introduces the idea of an epicenter of compression, suggesting that expansion would occur from that point, raising questions about what an observer closer to the epicenter would perceive.
  • One participant offers an analogy of a "raisin muffin" in an oven, arguing that as the muffin expands, all raisins experience expansion relative to their positions.
  • Another participant emphasizes that in a universe with a finite speed of light, cosmological expansion should be apparent to all observers, complicating the explanation of redshifts greater than 1.66 without invoking cosmological expansion.

Areas of Agreement / Disagreement

Participants express differing views on the nature of cosmic expansion and the mechanisms behind it. There is no consensus on whether the universe could be squeezed or how observers perceive expansion, indicating an unresolved debate.

Contextual Notes

Some assumptions about the uniformity of the universe and the implications of relativistic effects are not fully explored. The discussion includes various analogies that may depend on specific interpretations of cosmic phenomena.

pfontec
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Try thinking about measuring the expansion of the universe based on relativity. That is to say that depending on where you are located in the universe you might measure expansion or you might measure contraction!
Think about this.
The observer is placed anywhere inside of a giant ball of yellow "play dough". throughout the inside of the yellow ball are many little balls of different colored "play dough" representing galaxies.
Now something starts to squeeze the yellow ball.
Now depending on where the observer is located. He will percieve the colored "play dough" (the galaxies) expanding or he we percieve the galaxies contracting.
Can it be that our universe is being sqeezed by other dimensions (other universes?

I would appreciate any comments
Thank You
Pat Fontecchio
 
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pfontec said:
Try thinking about measuring the expansion of the universe based on relativity. That is to say that depending on where you are located in the universe you might measure expansion or you might measure contraction!
Think about this.
The observer is placed anywhere inside of a giant ball of yellow "play dough". throughout the inside of the yellow ball are many little balls of different colored "play dough" representing galaxies.
Now something starts to squeeze the yellow ball.
Now depending on where the observer is located. He will percieve the colored "play dough" (the galaxies) expanding or he we percieve the galaxies contracting.
Can it be that our universe is being sqeezed by other dimensions (other universes?

I would appreciate any comments
Thank You
Pat Fontecchio
If the universe is being squeezed, then it would have to be squeezed by gravity. But observation indicate a homogenous, isotropic universe at large scales. So there does not seem to be any mechanism for squeezing.
 
Let us assume that the yellow ball is being sqeezed equally from all directions.
And let us assume that the yellow ball is compressing.
There is at the exact center of our ball a infinitesimally small point at which there can be no compression, just like the epicenter of an Earth quake.
from the exact moment that compression starts ,there is, at that exact moment, expansion away from the epicenter equal in all directions.
So if the observer were closer to the epicenter what would he observe?
 
Don´t think of it as play dough, think of it as a raisin muffin in an oven. As the muffin itself expands, the raisins expand with the muffin giving all the raisins a expansion movement from what ever raisin you are standing on.
 
But in a universe with a finite speed of light [wrt local reference frames], cosmological expansion will be apparent to all observers. It is difficult to explain redshifts > 1.66 without cosmological expansion.
 

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