Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmological histories from the Friedmann equation: The universe as a
  particle   In this note, we discuss how possible expansion histories of the universe can
be inferred in a simple way, for arbitrary energy contents. No new physical
results are obtained, but the goal is rather to discuss an alternative way of
writing the Friedmann equation in order to facilitate an intuitive
understanding of the possible solutions; for students and researchers alike. As
has been noted in passing by others, this specific form of the Friedmann
equation allows us to view the universal expansion as a particle rolling along
a frictionless track. Specific examples depicted include the current
concordance cosmological model as well as a stable static universal model.

27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci