Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: In search of lost spacetime: philosophical issues arising in quantum
  gravity   This essay presents an accessible introduction to the basic motivations to
seek a quantum theory of gravity. It focuses on one approach- loop quantum
gravity - as an example of the rich philosophical issues that arise when we try
to combine spacetime and quantum physics.

33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
9
The categories of this paper are: nlin
6
The categories of this paper are: astro-ph
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex
23
The categories of this paper are: solv-int
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
13
The categories of this paper are: quant-ph
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
4
The categories of this paper are: cond-mat
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys