Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Paradoxes of time travel   Paradoxes that can supposedly occur if a time machine is created are
discussed. It is shown that the existence of trajectories of ``multiplicity
zero'' (i.e. trajectories that describe a ball hitting its younger self so that
the latter cannot fall into the time machine) is not paradoxical by itself.
This {\em apparent paradox} can be resolved (at least sometimes) without any
harm to local physics or to the time machine. Also a simple model is adduced
for which the absence of {\em true} paradoxes caused by self-interaction is
proved.

19
The categories of this paper are: eess
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
3
The categories of this paper are: physics
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat