  We consider the mechanism of photophoretic transport in protoplanetary disks
that are optically thick to radiation. Here, photophoresis is not caused by the
central star but by temperature fluctuations that subject suspended solid
particles, including chondrules, to non-isotropic thermal radiation within the
disk. These short-lived temperature fluctuations can explain time-of-flight
size sorting and general number density enhancements. The same mechanism will
also lead to velocity fluctuations of dust aggregates beyond
$100\,\mathrm{m\,s^{-1}}$ for mm-sized particles in protoplanetary disks.
Applying this in future research will change our understanding of the early
phases of collisional dust evolution and aggregate growth as particles cross
the bouncing barrier and as mass transfer rates are altered.
