In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.
Their average web application development cost is around $500K and their staff or contractors' salary is in the six figure plus range. Their proposals are usually based on a lot of fluff with the development rate ranging from $400 - $800 per hour. These types of companies focus on custom development.
All of these factors play a role in determining how much money can be made working as a web developer. My informed estimate is that as a freelance web developer you can earn a minimum of around $32,000 per year before taxes (working full time with very little experience).