Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comment on "An Arrow of Time Operator for Standard Quantum Mechanics" -
  a sign of the time!   It is shown that the `arrow of time' operator, M_F, recently suggested by
Strauss et al., in arXiv:0802.2448v1 [quant-ph], is simply related to the sign
of the canonical `time' observable, T (apparently first introduced by Holevo).
In particular, the monotonic decrease of < M_F > corresponds to the fact that <
sgn T > increases monotonically with time. This relationship also provides a
physical interpretation of the property M_F < 1. Some further properties and
possible generalisations are pointed out, including to almost-periodic systems.

17
The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
32
The categories of this paper are: atom-ph
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
29
The categories of this paper are: funct-an
23
The categories of this paper are: solv-int
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat