Is there a scientific definition of "fairness"? The concept of fairness, in my opinion, is somehow defined by the concept of empathy through some searches by Daniel Goleman in his book Social Intelligence. 

The book deals with scientific measurement through MRI. 

Ethic and Moral are also trying to define what is fair. 

Can you give me some hint achieving a definition of what is fair? 

i.e. why killing people, slavery, exploiting are not fair stuff?
I would also urge you to think about equality vs. equity as two important facets to understanding fairness, especially in the context of heterogeneous societies. 

Simply put, Equality is the idea that all individuals are exactly equal. If X people work on a project, all of them would get remunerated exactly the same amount.

On the other hand, Equity is the idea that there exists a quid pro quo i.e. if X people work on a project individuals would get paid proportional to the amount of work they put in. 

Both could be considered "fair" depending on your perspective. In fact, it has been shown that individuals tend to switch between equity and equality when self-presentational concerns are made salient. 
(Ref: http://www.sciencedirect.com/science/article/pii/0022103176900792)

Needless to say, this "fairness" debate guides discussion on Affirmative Action in the West and social reservation policies in countries like India.  I like the following piece which sums up this discussion nicely:

http://www.ala.org/offices/oif/iftoolkits/toolkitrelatedlinks/equalityequity