Is the Expansion of the Universe Uniform?

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Discussion Overview

The discussion revolves around whether the expansion of the universe is uniform, exploring the nature of cosmic expansion over time and the implications of gravitational effects on different cosmic structures. Participants examine the concept of expansion in relation to both theoretical and observational perspectives.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant suggests that the universe has always expanded, questioning whether this expansion has been uniform, using an analogy of dice in water to illustrate uneven growth.
  • Another participant notes that the rate of expansion has varied over time, initially slowing down and then accelerating in the last 6 billion years, while emphasizing that gravitationally bound objects like galaxies do not expand.
  • A different viewpoint claims that the rate of expansion has consistently decreased over time, with objects accelerating away from one another, and clarifies the distinction between constant expansion and accelerated expansion.
  • Several participants express confusion regarding a statement about variables increasing and decreasing over time, indicating a lack of clarity in that part of the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the universe's expansion, with some asserting that it has varied over time while others contest this by stating it has consistently decreased. There is no consensus on the uniformity of expansion or the implications of gravitational effects.

Contextual Notes

Participants reference varying rates of expansion and gravitational influences, but the discussion lacks clarity on specific definitions and assumptions regarding expansion and acceleration.

hsdrop
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I know that the universe is expanding since the beginning of time or at least the beginning of the universe it self. So I was wondering if the universe has always expanded evenly (some parts getting bigger while other grow not as fast) and if it doing so now??
The example in my head is like dropping die in water. The die on the outer edge will dissipate faster than the die in the middle of the drops. Or even some other kind of form of the idea.
 
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Overall, the rate of expansion appears to have varied over time,
at first slowing down then, since the last 6bn years, speeding up again.
However the expansion is not even since gravitationaly bound objects, like galaxies, don't expand at all.
Most of the Universe though is (almost) empty, no significant amount of matter and therefore gravity exists.
That is what is expanding, and at a given point in time the rate of expansion is the same everywhere,
 
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rootone said:
Overall, the rate of expansion appears to have varied over time,
at first slowing down then, since the last 6bn years, speeding up again.
Not quite. From what we can tell, the rate of expansion has done nothing but decrease. Early-on it decreased very rapidly, and less so more recently. The rate has been slowing down slowly enough over the last few billion years that objects have started accelerating away from one another.

If this is confusing, notice that constant expansion means a constant recession speed per distance, so as things get further, they move faster relative to one another.

This is why I refer to it as an "accelerated expansion" rather than "the expansion is accelerating".
 
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It suggests that as time goes forward, one variable increases while another decreases.
There is a moment when they have the same value, but there is no significance in that value.
 
rootone said:
It suggests that as time goes forward, one variable increases while another decreases.
There is a moment when they have the same value, but there is no significance in that value.
What are you talking about?
 
rootone said:
It suggests that as time goes forward, one variable increases while another decreases.
There is a moment when they have the same value, but there is no significance in that value.
Yep, you lost me on that one as well.
 

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