Open closed flat confused about what universe counts

In summary, omega is a ratio used to determine the density of the universe, and when it is equal to, less than, or greater than one, it indicates whether our universe is flat, open, or closed. However, when calculating omega, we are only considering the part of the universe that we can see, which is approximately 13 billion years old. This raises the question of whether the larger, unseen part of the universe should also be taken into account. The answer lies in the assumption that the universe is homogeneous and isotropic, meaning that the density in one part is representative of the density of the whole. Therefore, our observable part of the universe is considered the important part in determining omega's value.
  • #1
blumfeld0
148
0
hello. I know when omega is equal to, less than or greater than one our universe is either flat open or closed respectively.
omega is the ratio of the current observed density to critical denisty in the universe.
my question is that we can only see our part of the universe (that is 13 billion years old approximately) but the universe is actually much larger than that. we can't see it because light in that part hasnt reached us and some of it never will. there are particle and event horizons.
so when we calculate omega we are only looking at this part of the universe. but isn't the part greater than 13 billion years need to be taken into account to calculate observed omega. why is our part of the universe, up to our horizon, the important part to determine omegas value.
does this question make sense. i hope so
thank you

blumfeld
 
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  • #2
As you correctly stated, omega is a density ratio. If the universe at large is homogeneous and isotropic, then all we need to know is the density in one part and we know the density of the whole, is it not?
 
  • #3
yes you are right. thank you
 

1. What does "open" and "closed" mean in terms of the universe?

The terms "open" and "closed" refer to the shape of the universe. An open universe would have a saddle-like shape, while a closed universe would be curved like a sphere.

2. How is the shape of the universe determined?

The shape of the universe is determined by the amount of matter and energy present in it. If there is enough matter and energy, the universe will have a spherical shape. If there is not enough, it will have a saddle-like shape.

3. What does it mean for the universe to be "flat"?

The term "flat" refers to the amount of curvature in the universe. A flat universe would have no curvature, and would appear to be infinite in size.

4. How does the curvature of the universe affect its expansion?

The curvature of the universe does not directly affect its expansion. However, the amount of matter and energy in the universe, which determines its curvature, does play a role in the rate of expansion.

5. Why is it difficult to determine the shape and curvature of the universe?

Determining the shape and curvature of the universe is difficult because we can only observe a small portion of the universe, making it hard to get a complete picture. Additionally, the shape and curvature of the universe may change over time, making it a complex and ongoing area of research.

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