The speed of light is NOT a constant! Quote from Wikipedia: The photon is currently understood to be strictly massless, but this is an experimental question. If the photon is not a strictly massless particle, it would not move at the exact speed of light in vacuum, c. Its speed would be lower and depend on its frequency. Relativity would be unaffected by this; the so-called speed of light, c, would then not be the actual speed at which light moves, but a constant of nature which is the maximum speed that any object could theoretically attain in space-time.[20] Thus, it would still be the speed of space-time ripples (gravitational waves and gravitons), but it would not be the speed of photons. Quote from Scientific American: As waves travel through a medium, they lose energy over time. This dampening effect would also happen to photons traveling through spacetime, the researchers found. Although the effect is small, high-energy photons traveling very long distances should lose a noticeable amount of energy, the researchers say. Photons can take millions of years to exit the Sun which were generated in its core . The speed of a Photon emitted by the Sun is affected by the amount of material it passes through by the time it exits the surface . The speed a Photon from the Sun is detected determines how deep within the Sun the Photon was generated Photons are affected by many factors: . Gravitational effects . Passing through dark matter . Passing through matter (glass, plastic, etc.) . Deviation from a straight line . The shortest distance between two points is a straight line, but light does not travel in a straight line . It arcs around a star or other gravitational items it passes close to (Galaxies, Dark Matter, etc.) Distance to another star may best be estimated by its relative light speed at the point of observation . The observation should be taken way away from the Earths atmosphere as the atmosphere slows light down due to its interaction with the gas molecules Photons leave and enter our Universe . Look in a dark area of our Universe to see Photons from another Universe . Our Universe glows when observed from outside our Universe I have read that scientists can stop and hold a Photon for a short amount of time Can ionized Electrons and Protons be observed traveling through space? . They can be used to detect anti-Matter from within and outside our Universe . Electrons travel at light-speed and slower . They have mass, so are many times more sensitive to the anomalies that affect Photons All of these factors affect using Photons, Electrons, Protons, Neutrons in a computer . Determine their speed in existing computers . Determine their speed in new Quantum and 'light' computers . Early CDC Computers in the 7600 Series fine tuned processing by trimming the wires connecting components to compensate for the speed of light in wires, similar to a fluidics approach. For instance, all of the inputs to an AND Gate or an OR Gate should arrive at the same time for highest efficiency Chuck Moore