Talk:Topological defect

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This is the discussion/talk page for: Topological defect.

Contents 1 Definition issues 2 Often stable 3 Mistake? 4 Please re-review (lack of)observational evidence section

[edit] Definition issues

I think the subject is too narrowly defined. After all, topological defects arise in many other context than cosmology,

That's why I put "In cosmology," at the top, to suggest that this wasn't the only context in which topological defects were relevant. :) Unfortunately I have no knowledge of the other contexts, perhaps you could add stubs for a few? Bryan 23:38, 8 Jun 2004 (UTC)

This certainly is not the definition of topological defect which is completely independent of physical system . Loosely stated, it can expressed in terms of singularities in the mapping from some manifold to a topological space. I am not very thorough in the subject either but this article seriously needs to be rewritten. -[ 203.200.95.130, 18-Jan-2006]

[edit] Often stable

The article says a topological defect is a (often) stable configuration. Does it mean it is often used to mean a stable defect or the defects are stable most of the time? Billlion 18:08, 16 Nov 2004 (UTC)

Textures, which are often listed as being topological defects, are in fact not stable. The other types of defects listed are stable. (Of course, it's often possible to cook up exceptions, but generally the most basic strings, domain walls and monopoles are always completely classically stable.) User:mattmartin 8 Mar 2005

[edit] Mistake?

From the article:

"Typically, this occurs because the boundary on which the boundary conditions are specified has a non-trivial homotopy group which is

preserved by differential equations; the solutions to the differential equations are then topologically distinct, and are classified

by their homotopy class."

I don't think the homotopy groups of the boundary are what is relevant. It is the homotopy groups of what is called the `vacuum manifold', at least for a scalar field theory. The boundary conditions constitute a map from the boundary of your space to the vacuum manifold, and it is this map which can be homotopically non-trivial. Shambolic Entity 03:32, 2 November 2006 (UTC)

[edit] Please re-review (lack of)observational evidence section

I have clarified (I hope) that the lack of direct observational evidence for domain walls, etc., only potentially "rules out" these structures within the observable universe. I attended a lecture at Stanford last night given by Andrei Linde, who made it quite clear that he believes inflation produced a volume significantly larger (to put it mildly) than the observable universe. (If I understand him correctly, enough larger that the observable universe is such a tiny fraction of this volume that we cannot even truly claim to be able to determine whether or not two parallel lines would ultimately intersect or not). At any rate, while Linde is obviously an expert on inflation, and I believe I have understood him well enough on this point, I am, nonetheless, well outside my field here, and request review of that section. Breakpoint 02:51, 7 February 2007 (UTC)