Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Now, and the Flow of Time   The progression of time can be understood by assuming that the Hubble
expansion takes place in 4 dimensions rather than in 3. The flow of time
consists of the continuous creation of new moments, new nows, that accompany
the creation of new space. This model suggests a modification to the metric
tensor of the vacuum that leads to testable consequences. Two cosmological
tests are proposed, but they present both experimental and theoretical
problems. A more practical and immediate test is based on a predicted lag in
the emergence of gravitational radiation when two black holes merge. In such
mergers (as recently observed by the LIGO team), a macroscopic volume (millions
of cubic kilometers) of space is created in the region in which the
gravitational wave is generated; this one-time creation of new space should be
accompanied by the creation of detectable level of new time, resulting in a
time delay that could be observed as a growing lag in the emission of the wave
as the merger takes place

28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
6
The categories of this paper are: astro-ph
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
8
The categories of this paper are: hep-ex
13
The categories of this paper are: quant-ph
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph