Light does NOT travel at a "universal speed of light."

There's "an elephant in the room" that no one seems to want to talk about because it just generates arguments: Light does NOT travel at a "universal speed of light."  The "speed of light is different in water, in air, in glass, and in a vacuum.  So, there can be no "universal speed of light."  It is not even constant in a vacuum.

Einstein's relativity theory was presented as a PRINCIPLED, rather than a CONSTRUCTIVE, theory. A principled theory is one that begins with scientific principles and then uses those principles to explain the phenomena; a constructive theory starts with actual observations and culminates in theories that explain and reconcile those observations.

Einstein's "principled theory" is interpreted to say that the speed of light is "constant" throughout the universe and therefore light must cause Time to slow down or DILATE when the object emitting light is in motion or near a gravitational mass.

A CONSTRUCTIVE theory based upon observations, however, shows the reverse. The speed of light changes depending upon the "time" occurring at the source of the light.

Thus, due to gravitational time dilation, light coming from the Sun is traveling slower than the speed of light as we measure it here on Earth in a laboratory. And light coming from distant stars is coming at various speeds due to gravitational and velocity time dilation at the sources.

Any calculations which assume that the speed of light is fixed throughout the universe, such as the calculations involved in Dark Energy, will be incorrect.

A new scientific paper "Time Dilated Light (A Constructive Relativity Theory)" has been published to explain everything. It is available at this link: http://vixra.org/pdf/1607.0289v3.pdf