The problem there is that if you want to compute the behaviour of say 2 electrons, you need a huge computer with avagadro number of particles. Now imagine the number of particles you need to simulate the numbers of particles in the universe we observe. That number is mind bogglingly big. If we had the that much stuff lying around, it would interact with things and we could observe the consequences of these interactions.
The problem there is that if you want to compute the behaviour of say 2 electrons, you need a huge computer with avagadro number of particles. Now imagine the number of particles you need to simulate the numbers of particles in the universe we observe. That number is mind bogglingly big. If we had the that much stuff lying around, it would interact with things and we could observe the consequences of these interactions.