Time Dilation in the Light Curve of the Distant Type Ia Supernovae SN 1995K

The light curve of a distant Type Ia supernova acts like a clock that can be used to test the expansion of the Universe. SN~1995K, at a spectroscopic redshift of $z=0.479$, provides one of the first meaningful data sets for this test. We find that all aspects of SN~1995K resemble local supernova Ia events when the light curve is dilated by $(1+z)$, as prescribed by cosmological expansion. In a static, non-expanding universe SN~1995K would represent a unique object with a spectrum identifying it as a regular Type Ia supernova but a light curve shape and luminosity which do not follow the well-established relations for local events. We conclude that SN~1995K provides strong evidence for an interpretation of cosmological redshifts as due to universal expansion. Theories in which photons dissipate their energy during travel are excluded as are age-redshift dependencies.