Let M be a manifold and g a metric over M

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Discussion Overview

The discussion revolves around the relationship between a manifold M, a metric g defined on M, and the properties of submanifolds and subbundles. Participants explore whether submanifolds inherit the same metric as M and the implications of different types of bundles and metrics.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions if every subbundle of M must have the same metric g.
  • Another participant clarifies the distinction between "subbundle" and "submanifold," stating that a bundle is not a subset of M and cannot share the same metric.
  • A different participant notes that a manifold can possess multiple metrics, prompting a request for clarification on the specific type of subbundle being referenced.
  • There is a suggestion that the discussion may pertain to Riemannian metrics, which involve dot products on the tangent bundle and thus on subbundles.
  • The original poster confirms they meant submanifold and seeks clarification on the concept of topology being induced by a metric.
  • Another participant raises a related question about the invariant group metric of matrix groups like SU(2) and its relation to metrics induced by embeddings in Euclidean spaces.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between metrics and submanifolds versus subbundles. The discussion remains unresolved, with no consensus on the implications of metrics for submanifolds or the specifics of the original question.

Contextual Notes

There are limitations in the clarity of terms used, such as "subbundle" versus "submanifold," and the discussion includes unresolved questions about the nature of metrics and their inheritance in various contexts.

math6
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let M be a manifold and g a metric over M .
is it true that every subbundle from M must have the same metric g ?
 
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Do you mean "sub bundle" or "sub manifold"? A (vector or otherwise) bundle over a manifold M is not a subset of M and cannot have the same metric.

A submanifold, on the other hand, is a subset of M with the topology inherited from M. If the topology on M is induced by a metric, then the topology on any sub manifold is induced by the same metric. The metric is inherited from M along with the topology.
 


You can have a manifold with several different metrics on it. So, what exactly is your question? Subbundle of what? Of the frame bundle? Subbundle of the tangent bundle? Please describe, even if not quite precisely, what do you have in mind? What kind of an idea?
 


Maybe he means riemannian metric, i.e. a dot product on the tangent bundle, hence also on subbundles.
 


sorry friends but i just now i see your answers .. thnx very much .
i mean submanifold .. but sorry HallsofIvy can you explain for me what do you mean exactly when you say "If the topology on M is induced by a metric " ??
 


math6 said:
sorry friends but i just now i see your answers .. thnx very much .
i mean submanifold ..

This brings to my mind this question to which I do not remember seeing the answer: if we take a matrix group, say SU(2), is the invariant group metric the same as that induced by embedding in the the Euclidean space of 2x2 complex matrices? What about other groups like SU(1,1)?
 

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