Thermal noise from multilayer coatings as a limit to gravitational wave interferometer sensitivity. Thermal noise is expected to be one of the limiting sources of noise in advanced gravitational wave interferometers. The sensitivity of gravitational wave interferometers to binary neutron star inspirals in particular is very dependent on the level of thermal noise. One of the sources of thermal noise currently being studied is thermal noise from the multilayer dielectric optical coatings that must be applied to the surfaces of interferometer optics. Since thermal noise is proportional to mechanical loss, we have measured the mechanical loss of the high reflective multilayer coatings proposed for use in LIGO. The results show that thermal noise induced by these coatings is likely to be the dominant source of structural thermal noise and may be large enough to significantly reduce the overall inteferomeer sensitivity.