Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the possibility of unifying the electromagnetic and the gravitational
  fields   This is the first paper by Gunnar Nordstr{\"o}m (1881--1923) on his five
dimensional theory. In his summary he states: ''It is shown, that a unifying
treatment of the electromagnetic and gravitational fields is possible, if one
considers the four dimensional spacetime world to be a surface in a five
dimensional world.'' This paper was followed by two other papers written by the
Gunnar Nordstr{\"o}m during the one year period 1914--1915, on the same
subject, which are also made available here.

36
The categories of this paper are: cmp-lg
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
18
The categories of this paper are: econ
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
17
The categories of this paper are: q-fin
4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
0
The categories of this paper are: hep-ph