Observation of Cosmological Time Dilation using Type Ia Supernovae as Clocks

This work is based on the first results from a systematic search for high redshift Type Ia supernovae. Using filters in the R-band we discovered seven such SNe, with redshift z = 0.3 - 0.5, before or at maximum light. Type Ia SNe are known to be a homogeneous group of SNe, to first order, with very similar light curves, spectra and peak luminosities. In this talk we report that the light curves we observe are all broadened (time dilated) as expected from the expanding universe hypothesis. Small variations from the expected 1+z broadening of the light curve widths can be attributed to a width-brightness correlation that has been observed for nearby SNe (z<0.1). We show in this talk the first clear observation of the cosmological time dilation for macroscopic objects.