Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Emergence of time in quantum gravity: is time necessarily flowing ?   We discuss the emergence of time in quantum gravity, and ask whether time is
always "something that flows"'. We first recall that this is indeed the case in
both relativity and quantum mechanics, although in very different manners: time
flows geometrically in relativity (i.e. as a flow of proper time in the four
dimensional space-time), time flows abstractly in quantum mechanics (i.e. as a
flow in the space of observables of the system). We then ask the same question
in quantum gravity, in the light of the thermal time hypothesis of Connes and
Rovelli. The latter proposes to answer the question of time in quantum gravity
(or at least one of its many aspects), by postulating that time is a state
dependent notion. This means that one is able to make a notion of
time-as-an-abstract-flow - that we call the thermal time - emerge from the
knowledge of both: 1) the algebra of observables of the physical system under
investigation, 2) a state of thermal equilibrium of this system. Formally, this
thermal time is similar to the abstract flow of time in quantum mechanics, but
we show in various examples that it may have a concrete implementation either
as a geometrical flow, or as a geometrical flow combined with a non-geometric
action. This indicates that in quantum gravity, time may well still be
"something that flows" at some abstract algebraic level, but this does not
necessarily imply that time is always and only "something that flows" at the
geometric level.

11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
29
The categories of this paper are: funct-an
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
34
The categories of this paper are: chem-ph
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
22
The categories of this paper are: chao-dyn
24
The categories of this paper are: dg-ga