Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Adventures in Friedmann Cosmology: An Educationally Detailed Expansion
  of the Cosmological Friedmann Equations   The general relativistic cosmological Friedmann equations which describe how
the scale factor of the universe evolves are expanded explicitly to include
energy forms not usually seen. The evolution of the universe as predicted by
the Friedmann equations when dominated by a single, isotropic, stable, static,
perfect-fluid energy form is discussed for different values of its
gravitational pressure to density ratio $w$. These energy forms include phantom
energy ($w<-1$), cosmological constant ($w=-1$), domain walls ($w = -2/3$),
cosmic strings ($w = -1/3$), normal matter ($w = 0$), radiation and
relativistic matter ($w = 1/3$), and a previously little-discussed form of
energy called "ultralight" ($w>1/3$). A brief history and possible futures of
Friedmann universes dominated by a single energy form are discussed.

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The categories of this paper are: physics
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: bayes-an
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The categories of this paper are: solv-int
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: econ
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th