eLISA/NGO will probe new physics and cosmology with gravitational waves, and search for unforeseen sources of gravitational waves.
eLISA/NGO is capable of detecting a stochastic background from such events from early times when typical energies were about 100 GeV to about 1000 TeV, if gravitational waves were produced with an overall efficiency of more than about 10 −7, a typical estimate from a moderately strong relativistic first-order phase transition. This corresponds to times about 3 × 10 −8 to 3 × 10 −10 seconds after the start of the Big Bang, a period not directly accessible with any other technique.
Reaching much further still beyond the range of any particle accelerator, eLISA/NGO also deeply probes possible new forms of energy such as cosmic superstrings, relics of the early Universe predicted in some versions of string theory, that are invisible in all ways except by the gravitational waves they emit. In principle, their signature could provide direct evidence for new ideas unifying all forms of mass and energy, and possibly even spacetime itself.