# Importance of differential geometry in physics?

1. Jan 16, 2013

### cytochrome

How important is differential geometry in physics? Can someone give me some applicable fields?

2. Jan 17, 2013

### DiracPool

General relativity and finding the shortest distance to Grandma's house over the hills and far away.

3. Jan 17, 2013

### kweba

Hahaha this is funny, I like your humor. Like! (sorry, there's no like button, but you get the gist.)

Are you referring to Geodesics (shortest path between two points)?

4. Jan 17, 2013

### DiracPool

Yes, that's why Reimann developed his models originally, it was for land survey work. Little did he know what would become of it.

5. Jan 17, 2013

### kweba

Like DiracPool said, Differential Geometry is the key mathematics in Einstein's General theory of Relativity.

It is used to derive Einstein's field equations to describe the curvature of Spacetime in the presence of a body of mass and energy. This curvature of Spacetime results to the phenomenon we know as gravity, including how the planets move in orbit around the Sun, among others. The mathematics (Differental Geometry) used in Einstein's field equations also predicted the existence of black holes, including concepts of the Event Horizon and Singularity as key and important regions in black holes. (I think it was the Schwarzschild solution to Einstein's equations who pioneered this prediction/discovery, being the first pioneering solution to Einstein's field equations.)

To learn and read more about the mathematics of General Relativity, and how Differential Geometry is extensively used in the theory and other areas of physics, here's some links:

http://en.wikipedia.org/wiki/Mathematics_of_general_relativity[/PLAIN] [Broken]
(Granting the wikipedia article shows and discusses high level mathematics, so it might be hard to really get a grasp on them. I myself tried to read it, but lacking knowledge of tensors and differential geometry in general, makes it very difficult to understand)

http://en.wikipedia.org/wiki/Differential_geometry#Applications

To quote the Wiki, under the Applications section:

Last edited by a moderator: May 6, 2017
6. Jan 17, 2013

### kweba

Ohh really? I didn't know that. I thought Riemann developed his models just for pure mathematical pursuits? Was it for real-world applications? And his works were primarily based from the earlier works of Gauss, right? (Wikipedia says that Riemann studied under Gauss, with Gauss being his doctoral advisor.) It was said that Gauss discovered/developed non-Euclidean Geometries but did not publish it.

By land survey, you mean: http://en.wikipedia.org/wiki/Surveying ? I must admit, it's the first time I heard about such a thing, atleast as a scientific field kind of sense. What is it about?

7. Jan 17, 2013

### Andy Resnick

Other than GR, it's essential in continuum mechanics (stress-strain), both in the bulk and at deformable interfaces.

8. Jan 17, 2013

### WannabeNewton

Hate to be technical but they aren't necessarily the shortest paths. They extremize but don't necessarily minimize. Other than what has already been mentioned, differential geometry is very important in more advanced formulations of classical mechanics.

9. Jan 17, 2013

### DiracPool

10. Jan 19, 2013

### kweba

0Hate to be technical but they aren't necessarily the shortest paths. They extremize but don't necessarily minimize.[/QUOTE]

Oh thank you for correcting me, and clearing it out!

Which are Lagrangian mechanics and Hamiltonian mechanics, right? Oh cool it says that in Wikipedia:

To quote the Wiki page of Differential Geometry, under the Applications section, the third item under Physics:
I did not know this. I thought since Lagrangian mechanics and Hamiltonian mechanics are still considered to be "classical" in Physics, I thought the mathematics utilized in these formulations are limited to Calculus/Analysis. I considered Differential Geometry to be relatively modern and advanced, so yeah. But then again, I still haven't studied even an undergraduate physics/mathematics course (Still not yet in University/College), so obviously I'm wrong to assume. :)

Last edited: Jan 19, 2013
11. Jan 19, 2013

### Timo

To answer the first question: It's pretty unimportant compared to e.g. differentiation and integration in R^n, linear algebra or differential equations.

12. Jan 20, 2013

### kloptok

Differential geometry is also needed if one wants to understand the geometric setting of gauge theories which are formulated using a mathematical object called fiber bundles. In short, it is good to study differential geometry if you want to be a theoretical physicist.

13. Jan 22, 2013

### kweba

Apparently:
http://en.wikipedia.org/wiki/Carl_Friedrich_Gauss#Middle_years_.281799.E2.80.931830.29

Riemann, in turn, pioneered and develop his own branch of differential geometry, Riemannian Geometry, which is the key specific mathematics from Differential Geometry used in GR.

To quote http://en.wikipedia.org/wiki/Riemannian_geometry:
This is a cool video, thanks!

Last edited by a moderator: May 6, 2017
14. Jan 25, 2013

### Sankaku

[citation needed]

There is no way this is believable without some kind of reference.