Why is predicting products of chemical reactions difficult? [closed]








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I was going to ask whether there are software that could be used to predict the products of any given chemical reaction. However, I then noticed these two earlier questions


* [Chemical software for solving reactions](https://chemistry.stackexchange.com/questions/2808/chemical-software-for-solving-reactions?rq=1)
* [Software for predicting chemical reactions](https://chemistry.stackexchange.com/questions/8351/software-for-predicting-chemical-reactions?rq=1)


where it is said such predictions are too difficult to make. What makes the prediction difficult? 




Because you need would need to solve the [Dirac equation](http://en.wikipedia.org/wiki/Dirac_equation) (relativistic Schrodinger equation) for all the particles in the system to get a completely accurate result. 


Even solving the time independent non-relativistic Schrodinger equation for $\ce{H2+}$ in isolation, where there is only one electron and two protons involves approximating the protons as fixed relative to each other. 


Now imagine trying solving a system of $10^{23}$ molecules each having multiple nuclei, and dozens or even hundreds of electrons, and including time dependence!


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