  At a conference devoted to ever deeper surveys hunting for ever more distant
galaxies, I posed a question for which a concensus view has been difficult to
reach: `Is there evidence for, or can we rule out, a significant population of
dust-obscured starbursts at z > 3?' If, as seems likely, submm-selected
galaxies are proto-ellipticals, one of the biggest unanswered questions is
whether a significant fraction form at very high redshift - perhaps by the
collapse of single gas clouds - or whether the entire population forms over a
range of redshifts, primarily via merging. The latter scenario is favoured
strongly by existing data for the majority of bright submm galaxies - mergers
are common; typical spectroscopic redshifts are in the range 1 to 3. However,
our reliance on radio imaging to pinpoint submm galaxies leaves open the
possibility of a significant population of very distant, massive starbursts. To
rule out such a scenario requires a completely unbiased redshift distribution
for submm-selected galaxies and this is unlikely to be forthcoming using
conventional optical/infrared spectroscopic techniques. Here, I summarise
recent attempts to close that door, or pass through to an early Universe
inhabited by a significant population of collosal, dust-obscured starbursts. I
conclude that the door is only barely ajar; however, the idea of galaxies
forming, near instantaneously, on a collosal scale is not dead: I show an SMG
imaged by MERLIN+VLA for >1Ms - the deepest high-resolution radio image so far
obtained. The data reveal a galaxy-wide starburst covering >=10kpc. Thus
interpreting SMGs in terms of compact ULIRG-like events may not always be
appropriate, as one might expect when considering the Eddington limit for
>~1000M(sun)/yr starbursts.
