What is the Meaning of Foliate in Physics and Spacetime?

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In summary, Foliate means to turn into leaves. It comes from the root folium, which means leaf. Foliate is used to describe how a spherically symmetric spacetime can be peeled into a family of two-spheres.
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Haorong Wu
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Does "foliate" mean "consist of"?
Hi, there. I encounter the word "foliate" in GR textbooks but I have not seen it in other physics textbooks before. For example, it reads, we argue that a spherically symmetric spacetime can be foliated by two-spheres, from page 197 in spacetime and geometry by Carroll.

By this sentence, I guess maybe "foliate" means "consist of" such that the spherically symmetric spacetime can be peeled into a family of two-spheres. I am not sure if this is correct, and maybe it implies other meanings?
 
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It means to partition one manifold into a series of sub-manifolds of lower dimensions. Like an onion is a 3D ball that is foliated into 2D spheres.
 
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Wikipedia has a page on foliations.
 
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Foliate means to turn into leaves. The intended imagery is slicing 4d spacetime into a stack of 3d "leaves". For example if you take Minkowski spacetime and pick a frame then the set of surfaces of constant time in that frame are a foliation of that spacetime.
 
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Thanks, @Dale , @martinbn , @Ibix !

So "foliate" does have a meaning close to "consist of". I get the image now.
 
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Well, the root of the word is about leaves, as in “foliage”. So it is not merely “consist of” which could separate the thing into chunks rather than leaves. That is why I used the example of an onion, since the layers of an onion are formed by modified leaves.
 
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Dale said:
foliage
Ibix said:
leaves
On a tangential note, I've always thought the etymology comes more immediately from the folia of a book (i.e. sheets of paper) rather than from literal leaves at the root of the word. The imagery being that of a seemingly solid whole being separated into many stacked thin sheets.
 
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Bandersnatch said:
On a tangential note, I've always thought the etymology comes more immediately from the folia of a book (i.e. sheets of paper) rather than from literal leaves at the root of the word. The imagery being that of a seemingly solid whole being separated into many stacked thin sheets.
Indeed, but that comes from the same root folium, which means leaf in Latin, and leaf is another word for page. So it's all interconnected.
 
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I guess since I am a hobby farmer the onion comes to mind before the books. And besides, who uses actual books any more o0)
 
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Dale said:
I guess since I am a hobby farmer the onion comes to mind before the books. And besides, who uses actual books any more o0)

The Society of Book Binders is coming after you!
 
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FAQ: What is the Meaning of Foliate in Physics and Spacetime?

What is the definition of "foliate" in the context of GR?

"Foliate" refers to the presence of leaf-like structures or patterns in a geometric shape or design. In the context of GR (General Relativity), foliation is often used to describe the slicing of spacetime into distinct "leaves" or hypersurfaces.

How does foliation relate to the concept of spacetime in GR?

In GR, spacetime is often described as a four-dimensional manifold that can be "sliced" into three-dimensional hypersurfaces. These hypersurfaces represent distinct moments in time and are often referred to as "leaves" of the foliation. This allows for the visualization and study of the evolution of the universe over time.

What is the significance of foliation in GR?

Foliation plays a crucial role in understanding the dynamics of spacetime in GR. It allows for the study of how the curvature of spacetime changes over time and how this affects the behavior of matter and energy in the universe. Foliation also helps in the development of mathematical models and equations used in GR.

Are there different types of foliation in GR?

Yes, there are different types of foliation in GR, each with its own specific characteristics and applications. Some examples include spatial foliation, which divides spacetime into spatial slices, and conformal foliation, which uses a conformal transformation to map spacetime onto a flat three-dimensional manifold.

How does foliation relate to other concepts in GR, such as the Einstein field equations?

Foliation is closely related to other concepts in GR, such as the Einstein field equations, which describe the relationship between the curvature of spacetime and the distribution of matter and energy. Foliation is often used in the development and application of these equations, as it allows for the visualization and study of the dynamics of spacetime and its interactions with matter and energy.

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