Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Can we travel to the past? Irreversible physics along closed timelike
  curves   The Einstein equations allow solutions containing closed timelike curves.
These have generated much puzzlement and suspicion that they could imply
paradoxes. I show that puzzlement and paradoxes disappears if we discuss
carefully the physics of the irreversible phenomena in the context of these
solutions.

26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
11
The categories of this paper are: hep-lat
19
The categories of this paper are: eess
14
The categories of this paper are: math-ph
36
The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys