As human beings, we can't calculate as fast as a computer. In fact, there are many things which human beings can't do as fast as a computer, including numerical calculations. Hence, for a match to be considered 'fair', human beings should be given adequate time for thinking. This would assist them in faring better against the computer. Today, machines appear to have surpassed humans and the match where Deep Blue defeated Kasparov created history of a kind. For humans, apart from calculation, intuition, instinct, and experience also matter.
However, I don't think we should be dissapointed with the fact that machines can defeat grandmasters. The reason they are able to do so is because apart from calculation, they are also fed with opening book data and various other data and strategies which grandmasters have learnt only by experience. This knowledge which is fed into the engine is knowledge which human beings have acquired over hundreds of years so ultimately, the credit for their success also goes to the human beings who have accumulated this wealth of knowledge over the years.
Mathematically speaking, for eg. if you consider the starting position, there are 20 possible moves. After 1) e4 .. e4, this increases the no. of possible moves to 28.
Mathematically speaking, the algorithms used by computers are of exponential complexity - meaning that if you consider a number,for eg., 28 as the average no. of possible moves per person - so if a computer needs to calculate to a depth of n, it would have to consider 28^n possibilities. Such exponential complexity algorithms are amongst the most difficult algorithms for a computer to handle. To get an idea of this, 28^5 = 17 million(eight digits), 28^10 = a 15 digit number. By contrast, 8^5 = 32,000, and 8^10 = 1 billion(10 digits). If there are lesser pieces on the board, the computer has fewer moves to calculate. However, fewer pawns would mean more openness which means more moves to calculate. So if you want to beat the computer, you need to keep as many pieces on the board as possible(avoid exchanges) - go for a slow game with no exchanges near the beginning, where the computer still has a lot of moves to calculate even after it goes out of the opening book.