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My understanding is that GR forms the basis of the discipline of cosmology, but your comment implies it doesn't. Could you expand on that a bit? What differenti

My understanding is that GR forms the basis of the discipline of cosmology, but your comment implies it doesn't. Could you expand on that a bit? What differentiates GR and 'mathematical GR'? Why is the formation/stability of blackholes not considered to be a part of cosmology, when the understanding of black holes is central to understanding how to universe formed? e.g. "General Relativity forms the basis for the disciplines of cosmology (the structure and origin of the Universe on the largest scales) and relativistic astrophysics (the study of galaxies, quasars, neutron stars, etc.)" from https://uwaterloo.ca/applied-mathematics/future-undergraduates/what-you-can-learn-applied-mathematics/relativity-and-cosmology https://uwaterloo.ca/applied-mathematics/future-undergraduat...

layer8 4y ago
A forming the basis of B doesn’t imply that everyone working on A will be considered a B-ologist.
- ziddoap 4y ago
  Sure, I get that, but parent said: >relatively far away from cosmology and that surprised me, because it doesn't seem that far away in my eyes. Which is why I was genuinely asking for clarification. They might not be cosmologists, but this paper seems pretty close to cosmology, not 'far away' from it. If it's not, I'm happy to be wrong, but I'd like to be corrected rather than just told I'm wrong.
codethief 4y ago
As the sibling said, even if you consider cosmology a subfield of GR (which it is only to a small degree), not all relativists will be cosmologists. But you wanted me to expand on this a bit, so here you go: Cosmology is concerned with the cosmos as whole, i.e. the largest scales of the universe. GR looks at large scales, but not necessarily the largest ones. (A typical black hole is much smaller than a galaxy.) But this is not the only difference between the fields: General Relativity is just one tool inside a cosmologist's toolbox. Most of them also need quantum field theory, statistics and image processing in their daily work. The reason is that, while Relativity by itself is usually only concerned with theory, and mathematical GR even more so, cosmologists have to match their theories to actual observations. They are interested in the history of the universe and in the large-scale (average) behavior of what you can see on the sky. Meanwhile, mathematical GR is mostly a mathematical endeavor. People in that field tend to be mathematicians, with a background either in analysis / PDE theory or in geometry or both (geometric analysis). They are interested in physics-inspired questions but not exclusively so.
curt15 4y ago
>What differentiates GR and 'mathematical GR'? Mathematical GR seeks to rigorously derive mathematical properties of the equations underlying GR, such as the existence, stability, and long-range asymptotics of their solutions. It's largely a subfield of branch of math called "nonlinear wave equations".

layer8 4y ago

A forming the basis of B doesn’t imply that everyone working on A will be considered a B-ologist.

ziddoap 4y ago
Sure, I get that, but parent said: >relatively far away from cosmology and that surprised me, because it doesn't seem that far away in my eyes. Which is why I was genuinely asking for clarification. They might not be cosmologists, but this paper seems pretty close to cosmology, not 'far away' from it. If it's not, I'm happy to be wrong, but I'd like to be corrected rather than just told I'm wrong.

codethief 4y ago

As the sibling said, even if you consider cosmology a subfield of GR (which it is only to a small degree), not all relativists will be cosmologists. But you wanted me to expand on this a bit, so here you go: Cosmology is concerned with the cosmos as whole, i.e. the largest scales of the universe. GR looks at large scales, but not necessarily the largest ones. (A typical black hole is much smaller than a galaxy.) But this is not the only difference between the fields: General Relativity is just one tool inside a cosmologist's toolbox. Most of them also need quantum field theory, statistics and image processing in their daily work. The reason is that, while Relativity by itself is usually only concerned with theory, and mathematical GR even more so, cosmologists have to match their theories to actual observations. They are interested in the history of the universe and in the large-scale (average) behavior of what you can see on the sky. Meanwhile, mathematical GR is mostly a mathematical endeavor. People in that field tend to be mathematicians, with a background either in analysis / PDE theory or in geometry or both (geometric analysis). They are interested in physics-inspired questions but not exclusively so.

curt15 4y ago

>What differentiates GR and 'mathematical GR'? Mathematical GR seeks to rigorously derive mathematical properties of the equations underlying GR, such as the existence, stability, and long-range asymptotics of their solutions. It's largely a subfield of branch of math called "nonlinear wave equations".