Group of translations on real line with discrete topology

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Discussion Overview

The discussion revolves around the differences between the group of translations on a real line with discrete topology and the group of translations on a real line with the usual topology. Participants explore whether the discrete topology affects the properties of the translation group, including its classification as a Lie group and the nature of its generators.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions how the group of translations on a real line with discrete topology (Td) differs from that on a real line with the usual topology (Tu) and whether Td is a Lie group.
  • Another participant notes that every self-bijection is continuous in the discrete topology, suggesting that Td satisfies the group axioms and is a topological group, potentially a 0-dimensional Lie group with uncountably many disconnected components.
  • A clarification is made regarding the term "generator," with one participant expressing uncertainty about what is meant by it in the context of the real line.
  • There is a reiteration that the participant believes the groups of translations on both topologies would be the same, although this is met with a request for clarification on the definition of "translation."

Areas of Agreement / Disagreement

Participants express differing views on the implications of the discrete topology for the translation group, with some asserting similarities between Td and Tu while others seek clarification on definitions and properties. The discussion remains unresolved regarding the nature of translations and their generators in this context.

Contextual Notes

There are limitations in the definitions of "translation" and "generator," which are not clearly established in the discussion. The implications of the discrete topology on the structure and classification of the translation group are also not fully explored.

xboy
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Hi.

I wanted to know in what way the group of translations on a real line with discrete topology (let's call it Td) will be different from the group of translations on a real line with the usual topology (lets call it Tu)? Is Td a Lie Group? Will it have the same generator as Tu?
 
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Note that every self-bijection will be continuous, which is rather boring.

It will still satisfy all the group axioms- they don't depend on topology. It will be a topological group since everything will be continuous. It will be a Lie group, if you count 0-dimensional Lie groups, and it will have uncountably many disconnected components.

All of the above can be said for any group, whether or not it already has a topology. Any group G can be considered a topological group simply by giving it the discrete topology (or a Lie group, albeit a 0-dimensional one).

I don't know what you mean by "the generator of Tu". The real line doesn't have a generator, does it?
 
OK, I didn't phrase that right. What I meant was that the real line has a discrete topology. Now I take the group of translations on it. My question was whether this group would be any different from the group of translations on a (real line with usual topology) and I think that they would be the same.
 
I don't understand your question,
xboy said:
OK, I didn't phrase that right. What I meant was that the real line has a discrete topology.
Yes- everything has a discrete topology.
xboy said:
My question was whether this group would be any different from the group of translations on a (real line with usual topology) and I think that they would be the same.
What are you defining as a "translation"?
 

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