The gravitational contraction of gas, stirring by galactic and stellar feedback, and the push of galaxies ploughing through space create density inhomogeneities and motions in the intergalactic medium. This density and velocity structure can be probed in a one-dimensional way along the line of sight to individual background QSOs. The missing spatial information in the plane of the sky can be probed, in a tomographic approach, by observing closely spaced multiple lines-of-sight. Occasionally distant QSOs are gravitationally lensed by foreground galaxies and the lensing effect produces multiple images, which are sometimes separated by several arseconds on the sky. Taking spectra of these slightly displaced images enables us to probe the intervening intergalactic and interstellar matter at high redshift on very small (parsec to kiloparsec) scales . With Wal Sargent and Tom Barlow (Caltech) I have thus attempted to measure the texture and the turbulence of a variety of gaseous environments at high redshift. It appears that most of the IGM (by volume) has little velocity or spatial structure on scales smaller than a kiloparsec. In contrast the ubiquitous, somewhat denser, high ionization gas producing the CIV absorption systems in QSO spectra does show some residual turbulence on similar scales. We interpret this tentatively as evidence for galactic winds or gas stirred by ram pressure from moving galaxies. Going to even denser, low ionization gas (commonly seen in absorption by singly ionized magnesium, "MgII") the gas becomes much more turbulent. For MgII systems, unlikely the other two classes of absorbers we have not found yet a minimum size below the clouds may be featureless and the clouds show structure down to at least 100-200 pc. In one case of a very low ionization system at redshift 3.5 we observe column density differences by an order of magnitude over a distance of only 26 parsecs. The object is consistent with an individual old supernova remnant (but other interpretations may be possible). Thus, with the highest density, lowest ionization absorbers we seem to probe conditions directly in the interstellar medium of high redshift galaxies.
