Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Inconsistent Physics in the Presence of Time Machines   We present a scenario in $1 + 1$ and $3 + 1$ dimensional space time which is
paradoxical in the presence of a time machine. We show that the paradox cannot
be resolved and the scenario has {\em no} consistent classical solution. Since
the system is macroscopic, quantisation is unlikely to resolve the paradox.
Moreover, in the absence of a consistent classical solution to a macroscopic
system, it is not obvious how to carry out the path integral quantisation.
Ruling out, by fiat, the troublesome initial conditions will resolve the
paradox, by not giving rise to it in the first place. However this implies that
time machines have an influence on events, extending indefinitely into the
past, and also tachyonic communication between physical events in an era when
no time machine existed. If no resolution to the paradox can be found, the
logical conclusion is that time machines of a certain, probably large, class
cannot exist in $3 + 1$ and $1 + 1$ dimensional space time, maintaining the
consistency of known physical laws.

16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
31
The categories of this paper are: ao-sci
37
The categories of this paper are: supr-con
36
The categories of this paper are: cmp-lg
18
The categories of this paper are: econ
17
The categories of this paper are: q-fin
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas