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This is called a trivial bundle. Examples of non-trivial fiber bundles include the Möbius strip and Klein bottle, as well as nontrivial covering spaces. Fiber bundles, such as the tangent bundle of a manifold and other more general vector bundles, play an important role in differential geometry and differential topology, as do principal bundles.
Discovered by Heinz Hopf in 1931, it is an influential early example of a fiber bundle. Technically, Hopf found a many-to-one continuous function (or "map") from the 3 -sphere onto the 2 -sphere such that each distinct point of the 2 -sphere is mapped from a distinct great circle of the 3 -sphere ( Hopf 1931 ). [ 1 ]
Vertical and horizontal subspaces for the Möbius strip. The Möbius strip is a line bundle over the circle, and the circle can be pictured as the middle ring of the strip. . At each point on the strip, the projection map projects it towards the middle ring, and the fiber is perpendicular to the middle ri
A Lagrangian: given a fiber bundle ′, the Lagrangian is a function : ′. Suppose that the matter content is given by sections of E {\displaystyle E} with fibre V {\displaystyle V} from above. Then for example, more concretely we may consider E ′ {\displaystyle E'} to be a bundle where the fibre at p {\displaystyle p} is V ⊗ T p ∗ M ...
The Möbius strip can be constructed by a non-trivial gluing of two trivial bundles on open subsets U and V of the circle S 1. When glued trivially (with g UV =1) one obtains the trivial bundle, but with the non-trivial gluing of g UV =1 on one overlap and g UV =-1 on the second overlap, one obtains the non-trivial bundle E, the Möbius strip ...
A mapping : between total spaces of two fibrations : and : with the same base space is a fibration homomorphism if the following diagram commutes: . The mapping is a fiber homotopy equivalence if in addition a fibration homomorphism : exists, such that the mappings and are homotopic, by fibration homomorphisms, to the identities and . [2]: 405-406
This can be seen intuitively in that the Euler class is a class whose degree depends on the dimension of the bundle (or manifold, if the tangent bundle): the Euler class is an element of () where is the dimension of the bundle, while the other classes have a fixed dimension (e.g., the first Stiefel-Whitney class is an element of ()).
The Hopf fibration is an example of a non-trivial circle bundle. The unit tangent bundle of a surface is another example of a circle bundle. The unit tangent bundle of a non-orientable surface is a circle bundle that is not a principal () bundle. Only orientable surfaces have principal unit tangent bundles.