Each quasar has its own characteristic redshift (the shifting of light from remote galaxies and quasars to longer wavelengths).  The redshift of quasars tells us that they are moving away from us.  We can estimate the distance to the various quasars by the known relation between redshift and distance.  Hubble's Law shows us this relation (recessional velocity = Ho x distance).  We can also determine the rate at which the entire universe is expanding by measuring these redshifts.

    Exceedingly strong gravitational fields are needed to create a large enough value of redshifts for most quasars.  The large luminosity of quasars worries some astrophysicists.  The radiation from many quasars is not steady, showing sudden and irregular fluctuations.  It would be expected that such a luminous object could not be confined to a small place and yet if the object were large and uniform then the fluctuations should not be so sudden.

    There are two explanations for the existence of a redshift.  These are the Doppler shift and the Einstein gravitational redshift.  The Doppler shift is the effect of relative motion on wavelength.  Doppler's explanation supports that quasars are rapidly moving away from us.  It could be concluded that the recession of quasars is a cosmological effect because we know that the universe is expanding and that distant galaxies are receding from us.  The second explanation for redshifts is the Einstein gravitational redshift theory.  Einstein's gravitational redshift theory states that photons that are leaving the vicinity of a quasar lose energy climbing out of the quasar's gravitational field.  They show this change by shifting to longer wavelengths.

    Because of the very high redshift found in the spectra of quasars, we know that they are receding from us at a very high percentage of the speed of light.

    Quasars have strong emission lines (bright spectral lines against a dark background).  As defined by Kirchhoff's second law, an emission line spectrum is produced by a hot, rarefied gas.  These emission lines are caused by excited gas atoms emitting radiation at specific wavelengths.  The strong emission lines of quasars tells us that something unusual is heating the gas.  Universal expansion is causing the emission lines to be redshifted.

    In the early sixties when quasars were first detected, astronomers found two quasars with strong emission lines and could not find any element which could produce such lines.  They then realized that these quasar's have  redshifted Balmer lines of Hydrogen.    These lines had been  redshifted by fifteen percent.  This is  more than any other observed object in the universe (Morrison, 574).  They were moving away from us at 45km/s which corresponds to a distance of three billion ly.  Ordinary stars produce light with strong absorption lines.  Kirchhoff's third law defines an absorption line spectrum as being produced by a cool gas in front of a continuous source of light.  This spectrum is a series of dark spectral lines among the colors of the rainbow.  The light from the star must first pass through an outer gaseous layer of the star before it reaches us.  Because quasars do not have absorption lines we can say that they do not have an outer gaseous layer.  Instead, gases are producing the light directly accounting for the strong emission lines.

    We do however observe absorption lines while observing quasars.  The most common type of absorption lines observed in quasars is the Lyman-alpha forest.  This was discovered in 1971 by Roger Lynds of Kilt Peak National observatory.  It was named this because of its appearance.  When looking at a highly redshifted quasar, the region blueward of the quasars lyman-alpha emission line is chopped us with a thicket of hundreds of absorption lines, mostly attributed to Hydrogen atoms between us and the quasar.  These lines are caused by remote clouds of gas along our line of sight to the quasar.  Hydrogen in these clouds absorbs photons from the quasar at wavelengths less redshifted than the quasars lyman-alpha line (Kaufmann)

    One of the closest quasars known to us is quasar PDS 456.  This quasar is two billion light years away from us.  We can use this information along with Hubble's law and then the Doppler shift to find the redshift value of quasar PDS 456.

        Hubble's Law-    v=Ho x r
        V=?
        Ho=75km/s/Mpc
        r=2 billion ly (convert to Mpc)
        We find v=4062 km/s Or 4.062x10*7m/s

        Using the Doppler shift we can find a redshift value.
        z= v/c = 4.6102x10*7 m/s / 3x10*8
        z=.15

    Quasars which are 10 billion plus light years away from us are z=3, corresponding to a time when the universe was one-fourth its current age.