Gravitational waves and phase transitions in the early Universe

Future gravitational wave detectors, such as the LISA (Laser Interferometer Space Antenna) satellite mission, will give us a unique window to the very early Universe. As opposed to electromagnetic radiation, the Universe was transparent to gravitational waves from the beginning, and with sufficiently sensitive instruments it may be possible to observe the relic gravitational wave signal from processess which produced gravitational waves. These processes include first order phase transitions. While the Standard Model of particle physics does not have first order phase transitions, these exist in many beyond-the-standard-model extensions. Thus, observation of primordial gravitational waves from phase transitions would be a direct signal of beyond-the-standard-model physics, possibly at energy scales beyond the reach of planned particle accelerators. In this talk I review the gravitational wave generation in phase transitions and how computer simulations are used to accurately calculate the resulting gravitational wave spectrum.