Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ideal clocks - a convenient fiction   We show that no device built according to the rules of quantum field theory
can measure proper time along its path. Highly accelerated quantum clocks
experience the Unruh effect, which inevitably influences their time rate. This
contradicts the concept of an ideal clock, whose rate should only depend on the
instantaneous velocity.

36
The categories of this paper are: cmp-lg
11
The categories of this paper are: hep-lat
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
23
The categories of this paper are: solv-int
12
The categories of this paper are: nucl-th
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
0
The categories of this paper are: hep-ph
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
34
The categories of this paper are: chem-ph
25
The categories of this paper are: patt-sol