Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The necessity of the second postulate in special relativity   Many authors noted that the principle of relativity together with space-time
homogeneity and isotropy restrict the form of the coordinate transformations
from one inertial frame to another to being Lorentz-like. The equations contain
a free parameter, $k$ (equal to $c^{-2}$ in special relativity), which value is
claimed to be merely an empirical matter, so that special relativity does not
need the postulate of constancy of the speed of light. I analyze this claim and
argue that the distinction between the cases $k = 0$ and $k \neq 0$ is on the
level of a postulate and that until we assume one or the other, we have an
incomplete structure that leaves many fundamental questions undecided,
including basic prerequisites of experimentation. I examine an analogous case
in which isotropy is the postulate dropped and use it to illustrate the
problem. Finally I analyze two attempts by Sfarti, and Behera and Mukhopadhyay
to derive the constancy of the speed of light from the principle of relativity.
I show that these attempts make hidden assumptions that are equivalent to the
second postulate.

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The categories of this paper are: hep-ph
31
The categories of this paper are: ao-sci
22
The categories of this paper are: chao-dyn
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
14
The categories of this paper are: math-ph
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th