Sources Used

http://unity3d.com/public-relations

https://www.unrealengine.com/what-is-unreal-engine-4

https://developer.valvesoftware.com/wiki/Source_Engine_Features

http://www.ibm.com/developerworks/library/os-physicsengines/

http://www.ign.com/articles/2012/10/01/the-most-impressive-physics-engine-youve-never-seen

http://www.polygon.com/2014/5/1/5671020/eve-valkyrie-unreal-engine-4-starbuck