- #1
ddjj77
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It's been said that the universe is flat. How can it be flat if flatness has no volume?
In summary, the concept of a "flat" universe in cosmology refers to a 3-dimensional space that is not curved. This is different from the everyday definition of "flat" which means 2-dimensional. Although diagrams may represent the universe as 2D, this is only to illustrate the concept of curved space. This distinction can be seen in Lawrence Krauss' lecture on the topic.
- #2
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ddjj77 said:
"Flat" means three-dimensional Euclidean.
http://curious.astro.cornell.edu/ab...ow-can-the-universe-be-flat-we-re-3d-beginner
- #3
ddjj77
- 64
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Maybe "flat" isn't the right term; 2-dimensional would be more accurate (see attached image). What would you call a shape with no thickness? Volumeless?
- #4
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ddjj77 said:
Those are 2D surfaces. The reason that a lot of diagrams use 2D to represent the universe is that, although you could represent the "flat" universe as a 3D box, you can't draw a curved 3D surface (you'd need 4D for that, which we don't have).
So, these diagrams lose a dimension in order to illustrate the concept of curved space.
It's interesting that you've taken the concept of "flat" so literally.
- #5
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PS Lawrence Krauss explains this right at the start of his lecture here:
- #6
ddjj77
- 64
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I thought flat was flat.
Krauss said "..it's open, closed, or flat."
Krauss said "..it's open, closed, or flat."
- #7
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ddjj77 said:
No, "flat" in cosmology means 3D but not curved. "Flat" in everyday speech means 2D.
That is an intellectual hurdle you are going to have to jump.
- #8
davenn
Science Advisor
Gold Member
2023 Award
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PeroK said:
thanks for that video
Related to Is the Universe Flat Without Volume?
1. Is the universe really flat?
This is a common question that has been asked by scientists and non-scientists alike. The answer is not a simple yes or no, as the concept of "flatness" in the universe is a complex and debated topic among researchers.
2. What does it mean for the universe to be flat?
In the context of cosmology, a flat universe means that the curvature of space-time is zero. This can be visualized as a sheet of paper, where parallel lines never meet and the angles of a triangle add up to 180 degrees.
3. How do scientists determine if the universe is flat?
There are several methods used to measure the curvature of the universe, such as studying the cosmic microwave background radiation or analyzing the distribution of galaxies. These observations can give insights into the overall shape of the universe and its curvature.
4. What are some arguments for and against a flat universe?
Some scientists argue that a flat universe is the most likely scenario based on current observations and theories, such as inflationary cosmology. However, others propose alternative theories that suggest a non-flat universe, such as a positively or negatively curved universe.
5. Why is the concept of a flat universe important in cosmology?
The flatness of the universe is a key parameter in many cosmological models and can have implications for the fate of the universe. For example, a flat or nearly flat universe supports the idea of a constant expansion rate and a potential "heat death" of the universe in the distant future.
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