Transcript Light and Gravity

Gravitational Red Shift
Gravitational Red Shift - The reddening of light from a very massive
object caused by photons escaping and traveling away from the object's
strong gravitational field. An example of gravitational redshift is light
escaping from the surface of a neutron star.
Gravitational Red Shift
Gravitational redshift -- that is, the redshifting of photons that climb out of a
gravity well -- occurs for fundamentally the same reason that projectiles
slow down when rising -- because they have to transfer kinetic energy
(their speed) into potential energy (their height). Projectiles, such as a
cannon ball, do this by slowing down.
Gravitational Red Shift
Photons, however, cannot slow down -- they are constrained to always
travel at exactly c, the speed of light, and no faster. So how does a photon
shed this required kinetic energy? By lowering in energy and thus
frequency. Since a lower frequency means a longer, or "redder,"
wavelength, this process is called gravitational redshifting. (A similar
process occurs when a photon is falling into a gravitational well; it trades
potential energy for kinetic energy and gains in frequency, and thus gets a
shorter, "bluer," wavelength; this is called a blueshift.)
Gravitational Red Shift
Illustration of the gravitational red-shift predicted by the General Theory of
Relativity. A heavy object is denoted by a deformation of space
represented by the funnel. As light leaves the vicinity of this object it is
shifted towards the red: for a sufficiently compact and massive object a
blue laser on the surface will be seen as red in outer space.