Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spacetime as a deformable solid   In this letter we discuss the possibility of treating the spacetime by itself
as a kind of deformable body for which we can define an fundamental lattice,
just like atoms in crystal lattices. We show three signs pointing in that
direction. We simulate the spacetime manifold by a very specific congruence of
curves and use the Landau-Raychadhuri equation to study the behavior of such a
congruence. The lattice appears because we are forced to associate to each
curve of the congruence a sort of fundamental "particle". The world-lines of
these particles should be identified with the congruence fulfilling the
spacetime manifold. The conclusion is that when describing the deformations of
the spacetime the Einstein equations emerge and the spacetime metric should be
treated as a secondary (not fundamental) object of the theory.

16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph
6
The categories of this paper are: astro-ph
0
The categories of this paper are: hep-ph
23
The categories of this paper are: solv-int
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
3
The categories of this paper are: physics