Sunday, 24 May 2020

special relativity - The Topology of the Lorentz group in 1+3 dimensions



This is a question of mathematical nature. Let the Lorentz group O(1,3) be defined as a matrix group.


O(1,3)={ΛM4(R)|ΛTdiag(+)Λ=diag(+)}


One defines the supremum norm on M4(R) as:


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which turns M4(R) into a topological space in the metric topology induced by the norm. Can this supremum norm be made particular for Lorentz matrices? I guess it would, right? It would immediately follow that the Lorentz group is a topological space in the subspace topology of M4(R).



Answer



Yes, O(1,3) is a topological subspace of M4(R) under this construction.


That said, there's nothing special about the topology induced by supremum norm in this regard; any subset S of a topological space X inherits a natural subspace topology from its "parent" space. You could define some weird topology on M4(R)R16 which is a product topology between n copies of R with the indiscrete topology and 16n copies of R with the discrete topology, and it would still define a topology on O(1,3).


[EDIT: my original answer discussed whether the supremum norm might imbue the resulting topological space with non-physical structure; but as Valter Moretti pointed out in a comment, all norm topologies on a finite-dimensional vector space such as R16M4(R) are equivalent, so this point is somewhat moot.]


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