  It is widely hoped that quantum gravity will shed light on the question of
the origin of time in physics. The currently dominant approaches to a candidate
quantum theory of gravity have naturally evolved from general relativity, on
the one hand, and from particle physics, on the other hand. A third important
branch of 20th century `fundamental' physics, condensed-matter physics, also
offers an interesting perspective on quantum gravity, and thereby on the
problem of time. The bottomline might sound disappointing: to understand the
origin of time, much more experimental input is needed than what is available
today. Moreover it is far from obvious that we will ever find out the true
origin of physical time, even if we become able to directly probe physics at
the Planck scale. But we might learn some interesting lessons about time and
the structure of our universe in the process. A first lesson is that there are
probably several characteristic scales associated with "quantum gravity"
effects, rather than the single Planck scale usually considered. These can
differ by several orders of magnitude, and thereby conspire to hide certain
effects expected from quantum gravity, rendering them undetectable even with
Planck-scale experiments. A more tentative conclusion is that the hierarchy
between general relativity, special relativity and Newtonian physics, usually
taken for granted, might have to be interpreted with caution.
