Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vacuum Friction   We know that in empty space there is no preferred state of rest. This is true
both in special relativity but also in Newtonian mechanics with its associated
Galilean relativity. It comes as something of a surprise, therefore, to
discover the existence a friction force associated with spontaneous emission.
he resolution of this paradox relies on a central idea from special relativity
even though our derivation of it is non-relativistic. We examine the
possibility that the physics underlying this effect might be explored in an ion
trap, via the observation of a superposition of different mass states.

2
The categories of this paper are: math
23
The categories of this paper are: solv-int
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
35
The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
16
The categories of this paper are: stat
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
21
The categories of this paper are: adap-org
27
The categories of this paper are: comp-gas