I will describe cosmological simulations of Axion-like Dark Matter, motivated by string theory, providing  a well motivated cold dark matter alternative to the standard heavy particle interpretation. Standing de-Broglie scale waves and other interference effects are predicted within galaxies that we test with QSO lensing, pulsar timing and via stellar dynamics. Galaxy formation is delayed in this context relative to LCDM and examined with deep Hubble imaging of the earliest known galaxies.