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Q&A

Comments on Are there other topologies on $\mathbb R$ that make it a topological field?

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Are there other topologies on $\mathbb R$ that make it a topological field?

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As is well known, $\mathbb R$ with the standard topology is a topological field. It is also not hard to check that the discrete and the indiscrete topology on $\mathbb R$ result in a topological field, simply from the fact that all functions from a discrete topology are continuous, as are all functions to an indiscrete topology.

However I wonder if there are other topologies that make $\mathbb R$ into a topological field, in particular other topologies that can be easily written down.

Here's one idea: Let's define a set as open if its intersection with the rational numbers agrees with the intersection of an open set of the standard topology with the rational numbers. This is easily seen to be a topology, however I'm not sure if it makes all operations continuous.

History

2 comment threads

On continuity of the last-mentioned topology in the OP (1 comment)
Different approaches, what would be intersting for you? (2 comments)
Different approaches, what would be intersting for you?
watchmaker‭ wrote 10 months ago

I can see two ways to approach it.

One is to look at $\mathbb R$ as a vector space over $\mathbb Q$ looking at it as a product of topological spaces and giving each one of the obvious topologies. Doesn't realy look like the answer you are looking for.

Second way is to describe all the topologies for which the field-operations are continuous. I've tried my mind on that but got stuck on if the prerequisites realy give interesting topologies or if they simply collapse into the already known trivial ones.

Which way shall we proceed, what would you like to see?

celtschk‭ wrote 10 months ago · edited 10 months ago

By definition, a topological field is a field with a topology such that all field operations are continuous. So the second way it is. Edit: I only now notice that unlike in the question title, in the actual question body I wrote "topological vector space" - what I wrote in the title is actually what I meant.I'll edit.