The High-Redshift Supernova Search -- Evidence for a Positive Cosmological Constant

A new component of the Universe which leads to an accelerated cosmic expansion is found from the measurements of distances to high-redshift type Ia supernovae. We describe the method and the results obtained from the observations of distant supernovae. The dependence on the understanding of the local type Ia supernovae is stressed. The lack of a good understanding of the stellar evolution leading to the explosion of the white dwarf, the exact explosion physics and the current difficulties in calculating the emission from the ejecta limit the theoretical support. Despite the current ignorance of some of the basic physics of the explosions, the cosmological result is robust. The empirical relations seem to hold for the distant supernovae the same way as for the local ones and the spectral appearance is identical. The distances to the high-redshift supernovae are larger than expected in a freely coasting, i.e. empty, Universe. A positive cosmological constant is inferred from these measurements.