Changes

The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of [[quantum mechanics]], particularly the concept of a path of least action) the phenomenon of [[refraction]]. When a charged particle exceeds the speed of light in the medium in which it is travelling, it emits [[Cherenkov Radiation]].

The speed of light is slower in any medium which is not a vacuum, and varies from medium to medium. This variation gives rise to (as a result of [[quantum mechanics]], particularly the concept of a path of least action) the phenomenon of [[refraction]]. When a charged particle exceeds the speed of light in the medium in which it is travelling, it emits [[Cherenkov Radiation]].

Since the speed of light in a vacuum is constant, it can be used to define distances as well. The distance that light travels in one year is known as a [[light-year]], which is about 6 million million (6x10¹²) miles. For instance, the nearest large galaxy to our own [[Milky Way Galaxy]] is the [[Andromeda Galaxy]], which astronomers have measured to be about 2.5 million light years away, meaning visible light from the galaxy has taken 2.5 million years to reach Earth.

Since the speed of light in a vacuum is observed to be constant, it can be used to define distances as well. The distance that light travels in one year is known as a [[light-year]], which is about 6 million million (6x10¹²) miles.  

==StarLight Problem For the Big Bang Theory==

The [[starlight problem]] is an argument against the [[Big Bang Theory]] which theorizes a universe of billions of years old. <ref>http://www.answersingenesis.org/creation/v25/i4/lighttravel.asp</ref> The [[creation science]] organization [[Answers in Genesis]] has stated the following regarding the starlight problem for the Big Bang Theory and the work of [[Charles W. Misner]] is cited who published his work in ''[[Physical Review Letters]]'':

{{cquote|The problem is this: even assuming the big bang timescale, there has not been enough time for light to travel between widely separated regions of space. So, how can the different regions of the current [cosmic microwave background] CMB have such precisely uniform temperatures if they have never communicated with each other? This is a light-travel–time problem.<ref>http://www.answersingenesis.org/creation/v25/i4/lighttravel.asp</ref>}}

The speed of light raises several minor questions for [[Young Earth Creationism|Young Earth Creationists]] including that of the [[starlight problem]].

The speed of light raises several minor questions for [[Young Earth Creationism|Young Earth Creationists]] including that of the [[starlight problem]].