The sources of gravitational waves described above are in the low-frequency end of the gravitational-wave spectrum (10 to 10 Hz). An astrophysical source at the high-frequency end of the gravitational-wave spectrum (above 10 Hz and probably 10 Hz) generates relic gravitational waves that are theorized to be faint imprints of the Big Bang like the cosmic microwave background. At these high frequencies it is potentially possible that the sources may be "man made" that is, gravitational waves generated and detected in the laboratory.