For the orthogonal group is the group of isometries of a real -dimensional Hilbert space. This is naturally a Lie group
This is canonically isomorphic to the group of orthogonal matrices.
The analog for complex Hilbert spaces is the unitary group.
The Whitehead tower of the orthogonal group plays an important role in applications related to quantum physics.
The first steps are
Fivebrane group to String group to Spin group to special orthogonal group to orthogonal group.
Given a manifold , lifts of the structure map of the -principal bundle to which the tangent bundle is associated through this tower define, respectively
on .
fivebrane group string group spin group special orthogonal group orthogonal group