In addition to providing a comprehensive environment for calculations and a programming language, Mathematica is also a system for representing and presenting scientific and technical knowledge. Certain packages are included with Mathematica to provide easy access to commonly used scientific data, such as the value of physical constants and conversion factors for various systems of units.
This loads the package.
Some common physical constants.
This gives the mass of a proton.
Here is the distance that light could travel in the age of the universe.
In:= SpeedOfLight AgeOfUniverse