A critical note on time in the multiverse
  In recent analyses of standard, single-universe, cosmology, it was pointed
out that specific assumptions regarding the distribution and motion of matter
must be made in order to set up the cosmological standard model with a global
time parameter. Relying on these results, we critically examine the notion of
time in the multiverse, and in particular the idea that some parts of the
multiverse are older than others. By focusing on the most elaborated multiverse
proposal in cosmology, the inflationary multiverse, we identify three problems
for establishing a physically well-defined notion of global time; a quantum
problem, a collision problem and a fractal problem. The quantum problem, and
the closely related "cosmic measurement problem", may even undermine the idea
that parts of the multiverse causally and temporally precede our universe.
