Insights A Poor Man's CMB Primer Part 0: Orientation - Comments

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The discussion centers on the curvature of space in relation to the model presented in "A Poor Man's CMB Primer." Participants debate whether the assumption of flat space is valid given that spacetime is known to be curved. Observations indicate that space is effectively flat on large scales, with curvature measurements being negligible. The conversation also questions the relevance of geometry to the model discussed in the post. Overall, the thread explores the implications of space curvature on cosmological models.
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A Poor Man's CMB Primer. Part 1: Orientation

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But is space is curved, wouldn't this model be incorrect? Surely on this scale any curvature would be significant
 
AgentSmith said:
But is space is curved, wouldn't this model be incorrect? Surely on this scale any curvature would be significant
The curvature has been calculated from observations. It was not measurably different from zero.
 
AgentSmith said:
space is curved

Spacetime is curved, but space, as far as we can tell, is flat, as Hornbein says (the curvature he refers to is space curvature, or more precisely the curvature of spacelike slices which are surfaces of constant time in standard cosmological coordinates).
 
AgentSmith said:
But is space is curved, wouldn't this model be incorrect? Surely on this scale any curvature would be significant
As others have commented, space has been measured to be rather flat; however, I don't see how geometry factors into anything discussed in this post. Where do you think it fits in?
 

Thread 'Matter density right after the decoupling'

https://en.wikipedia.org/wiki/Recombination_(cosmology) Was a matter density right after the decoupling low enough to consider the vacuum as the actual vacuum, and not the medium through which the light propagates with the speed lower than ##({\epsilon_0\mu_0})^{-1/2}##? I'm asking this in context of the calculation of the observable universe radius, where the time integral of the inverse of the scale factor is multiplied by the constant speed of light ##c##.
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Thread 'Hubble Constant, Dark Energy and the Expanding Universe'

Why was the Hubble constant assumed to be decreasing and slowing down (decelerating) the expansion rate of the Universe, while at the same time Dark Energy is presumably accelerating the expansion? And to thicken the plot. recent news from NASA indicates that the Hubble constant is now increasing. Can you clarify this enigma? Also., if the Hubble constant eventually decreases, why is there a lower limit to its value?
View full post »

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