B Is the Expansion of the Universe Uniform?

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The discussion centers on whether the universe's expansion is uniform, with participants noting that while the universe has been expanding since its inception, this expansion is not even across all regions. Gravitationally bound objects, like galaxies, do not expand, leading to variations in expansion rates. Over time, the universe's expansion rate has changed, initially slowing down and then accelerating over the last six billion years. Some participants clarify the concept of "accelerated expansion," emphasizing that it refers to the increasing speed of recession between distant objects rather than a simple acceleration of the expansion itself. Overall, the conversation highlights the complexities of cosmic expansion and its implications for understanding the universe.
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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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Hi, I’m pretty new to cosmology and I’m trying to get my head around the Big Bang and the potential infinite extent of the universe as a whole. There’s lots of misleading info out there but this forum and a few others have helped me and I just wanted to check I have the right idea. The Big Bang was the creation of space and time. At this instant t=0 space was infinite in size but the scale factor was zero. I’m picturing it (hopefully correctly) like an excel spreadsheet with infinite...
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