  A major goal of modern astrophysics is to understand the processes by which
the universe evolved from its initial simplicity, as seen in measurements of
the Cosmic Microwave Background, to the universe we see today, with complexity
on all scales. While the diffuse background measurements of COBE reveal the
importance of the far infrared and submillimeter in early galaxy and star
formation, the understanding of the development of complex structure requires
high resolution imaging and spectroscopy.
  We present a concept for a space mission called SPECS, the Submillimeter
Probe of the Evolution of Cosmic Structure, which provides these capabilities.
SPECS is a cold, spatial and spectral Michelson interferometer with adjustable
baselines ranging up to 1 km. It has Hubble sensitivity and angular resolution
in the far IR and submillimeter, spectral resolution up to 10,000, and a 14'
field of view. SPECS will be able to image thermal dust continuum and infrared
cooling and diagnostic line emission over a wide range of redshifts, providing
extinction-free astrophysical probes of young galaxies and early cosmic
structures, and measures of the luminosity and heavy element formation history
of the universe. SPECS would also have the potential to improve vastly our
knowledge of protostars, protoplanetary systems, Active Galactic Nuclei and
other objects in the local universe.
  We recommend that a concerted effort be made during the next decade to
develop and test certain critical technologies (photon-counting far IR
detectors, formation flying spacecraft, cold, lightweight mirrors, and active
coolers), so that SPECS can be deployed in about 2015.
