The consequence of time dilation in photon emission is that the wavelength of a photon is lengthened, or redshifted, by an amount that depends on the strength of the gravitational field. This effect, known as gravitational redshift , has practical astronomical interest because it occurs when a photon of light escapes from a star. If the star's gravitational field is sufficiently intense, we can measure the change in wavelength. The measured redshifts agree satisfactorily with those predicted by Einstein's theory. Finally, the gravitational redshift has been verified with even greater accuracy in a laboratory experiment.
Gravity waves are ripples in the overall geometry of space and time.
For example, two stars in a binary system continually alter the geometry of space and time in their vicinity because of their orbital motion. These adjustments appear as tiny ripples that propagate out through all of space and time like ripples on the surface of a pond. Gravity waves might be detectable with a very sensitive apparatus for large astronomical objects undergoing violent activity, such as supernova outbursts or the nucleus of an active galaxy, but unfortunately not for small events like ordinary binary stars. The detecting apparatus works on the principle that any gravitational wave passing through the detector momentarily deforms space and causes the detector to vibrate slightly. At first it seemed that they had succeeded in detecting gravity waves coming from the Galaxy's center.