Two dimensional manifold are conformally flat

In summary, the conversation discusses the concept of conformal flatness in 2D manifolds. It is mentioned that the Earth's surface, despite being curved, can be mapped conformally using lines of latitude and longitude. This is due to the fact that in 2D, the Riemann tensor only has one independent element, the Gaussian curvature, making it impossible to distinguish between Ricci curvature and sectional curvature.
  • #1
paweld
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Does anyone know why every 2D manifold is conformally flat.
 
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  • #2
If you have access to d' Inverno's textbook, have a look at excercise 6.30 .
 
  • #3
For insight, consider the example of latitude and longitude. The fact that the Earth is curved doesn't prevent you from mapping a neighborhood of the Earth's surface to Cartesian graph paper using lines of latitude and longitude. This mapping is conformal, because all the right angles remain right angles. [Oops, this isn't quite right. Only the Mercator mapping is conformal.]

Also consider that in two dimensions, the Riemann tensor only has one independent element, which is the Gaussian curvature. This means that you can't have a distinction between Ricci curvature and sectional curvature.
 
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1. What is a two dimensional manifold?

A two dimensional manifold is a mathematical space that can be described locally by two coordinates. It is a surface that can be smoothly mapped onto a plane without any creases or overlaps.

2. What does it mean for a two dimensional manifold to be conformally flat?

A two dimensional manifold is conformally flat if it can be stretched or compressed in a way that preserves angles. This means that the curvature of the manifold remains the same in all directions.

3. How is conformal flatness related to the metric tensor?

Conformal flatness is related to the metric tensor by the fact that a two dimensional manifold is conformally flat if and only if the metric tensor can be written as a scalar multiple of the standard metric tensor in Cartesian coordinates.

4. What are some examples of conformally flat two dimensional manifolds?

Some examples of conformally flat two dimensional manifolds include the surface of a sphere, a cylinder, and a torus. These surfaces can be smoothly mapped onto a plane without changing their curvature.

5. Why is the concept of conformally flat two dimensional manifolds important in physics?

In physics, conformally flat two dimensional manifolds are important because they arise in many physical theories, such as general relativity and classical mechanics. They also play a role in the study of conformal field theory, which has applications in both particle physics and string theory.

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