Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational waves and cosmic expansion: similarities and differences   Gravitational waves and cosmic expansion are both described in terms of
Einstein's general relativity. This article explores the similarities between
the two phenomena, as well as some differences, using the fundamental concept
of the metric of spacetime, expressed via a line element. In both contexts, the
focus is on the metric description of space, as opposed to the components of
the metric determining the properties of time. This allows for a simplified,
more accessible discussion.

1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
16
The categories of this paper are: stat
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
6
The categories of this paper are: astro-ph
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th