Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Why Does Quantum Field Theory In Curved Spacetime Make Sense? And What
  Happens To The Algebra of Observables In The Thermodynamic Limit?   This article aims to explain some of the basic facts about the questions
raised in the title, without the technical details that are available in the
literature. We provide a gentle introduction to some rather classical results
about quantum field theory in curved spacetime and about the thermodynamic
limit of quantum statistical mechanics. We also briefly explain that these
results have an analog in the large N limit of gauge theory.

20
The categories of this paper are: acc-phys
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
12
The categories of this paper are: nucl-th
26
The categories of this paper are: bayes-an
23
The categories of this paper are: solv-int
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
3
The categories of this paper are: physics
18
The categories of this paper are: econ