Is the Geodesic Always the Shortest Path Between Two Points?

In summary, the calculus of variation states that the shortest path between two points on a surface must be geodesic. However, on a cylinder or flat torus, there may be infinitely many geodesics between points. An example on a fluted surface of negative curvature shows a geodesic that winds around the surface in a helical motion before returning to the starting point. This is similar to the helical magnetic lines of force in a tokamak.
  • #1
enricfemi
195
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it comes from the calculus of variation that the shortest path between two points on a surface must be geodesic.
then must the geodesic connected two points be the shortest path?
if not, what about the example?
Thanks for any reply!
 
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  • #2
enricfemi said:
it comes from the calculus of variation that the shortest path between two points on a surface must be geodesic.
then must the geodesic connected two points be the shortest path?
if not, what about the example?
Thanks for any reply!

check out the example in wikipedia
http://en.wikipedia.org/wiki/Geodesic
 
  • #3
enricfemi said:
it comes from the calculus of variation that the shortest path between two points on a surface must be geodesic.
then must the geodesic connected two points be the shortest path?
if not, what about the example?
Thanks for any reply!

No. On a cylinder there are infinitely many geodesics between most points. The same is true of a flat torus.
 
  • #4
wofsy said:
No. On a cylinder there are infinitely many geodesics between most points. The same is true of a flat torus.

yeah, cylinder is really a good example!
 
  • #5
There is an example of a geodesic on a fluted surface of negative curvature that winds almost all of the way down the surface circling around it in a helical motion then turns around and comes back! The shortest geodesic though between two adjacent points is a simple arc. I will try to look this up. It is pretty incredible.
 
  • #6
it reminds me the magnetic lines of force in tokamak. they are all helical.
 

FAQ: Is the Geodesic Always the Shortest Path Between Two Points?

What is a geodesic?

A geodesic is the shortest path between two points on a curved surface, such as a sphere or a curved plane. It is the equivalent of a straight line on a flat surface.

How is a geodesic calculated?

A geodesic is calculated using the principles of differential geometry. It involves finding the shortest distance between two points, taking into account the curvature of the surface and minimizing the distance traveled.

What is the significance of geodesics?

Geodesics are important in various fields such as physics, engineering, and navigation. They provide the most efficient and accurate path between two points on a curved surface and are used in the design of structures, transportation routes, and satellite orbits.

Can geodesics exist on a flat surface?

No, geodesics only exist on curved surfaces. On a flat surface, the shortest path between two points is always a straight line.

What are some real-world applications of geodesics?

Geodesics are used in the navigation of ships, planes, and satellites. They are also used in the design of bridges, roads, and other structures. In addition, geodesics are utilized in computer graphics for creating 3D models and animations.

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