What Distinguishes Hilbert Spaces from Euclidean Spaces?

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Discussion Overview

The discussion centers around the distinctions between Hilbert spaces and Euclidean spaces, exploring their definitions, dimensions, and properties. Participants examine theoretical aspects, mathematical reasoning, and implications in various contexts, including quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that Hilbert spaces are infinite-dimensional, while others argue that they can also be finite-dimensional and isomorphic to Euclidean spaces.
  • One participant mentions that certain theorems valid in Euclidean space do not hold in Hilbert space due to the differences in dimensionality.
  • There is a discussion about the conditions under which a Hilbert space can be considered a Euclidean space, with some suggesting that Euclidean space is a specific case of a Hilbert space.
  • Several participants express confusion regarding the definitions and dimensionality of both spaces, particularly in the context of quantum mechanics courses that often define Hilbert spaces as infinite-dimensional.
  • One participant provides an example of a space that is a Hilbert space but not a Euclidean space, specifically mentioning the set of all continuous functions over a given interval.
  • There are references to historical perspectives on the definitions of Hilbert spaces, with some participants noting outdated terminology and the evolution of the concept.
  • Some participants express frustration over the clarity of definitions and the teaching of Hilbert spaces in academic settings.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the definitions and dimensionality of Hilbert and Euclidean spaces. Multiple competing views remain, particularly regarding the nature of Hilbert spaces and their relationship to Euclidean spaces.

Contextual Notes

The discussion reveals limitations in the clarity of definitions and the potential for confusion regarding the dimensionality of spaces. There are unresolved questions about the conditions that differentiate Hilbert spaces from Euclidean spaces.

  • #31
ajayguhan said:
So we can say that hilbert space is a a inner product vector space which can be of finite or infinite dimension.if it's finite we can call it as eucledian space...?

Another question

Every vector space where inner product is defined is a hilbert space...is it True ?

No; you need to have a specific relationship between the inner-product and the metric:

the inner-product needs to generate the norm ( and so generate the metric which is itself

generated by the norm.). The space has to be complete under this norm, altho a metric space is,

in a sense, as good as a complete metric space, since it has a completion (tho it is a nice exercise to show that the completion preserves the fact that the metric is generated by the inner-product.)

This happens iff the inner-product satisfies the parallelogram law;

out of all $$L^p$$ and $$l^p$$ spaces, only p=2 gives you a Hilbert space.

See, e.g:

http://math.stackexchange.com/questions/294544/parallelogram-law-valid-in-banach-spaces
 
Last edited:

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