Computer simulation and modeling are amazing disciplines. They are used all over the place. Examples include predicting weather (weather models & earth simulations), testing engineering designs (simulating the design and operations), simulating physical phenomena (testing physical, chemical, and biological models before running experiments), and simulating networks to test things such as computer networks or even human networks to study the spread of  diseases (e.g. how will a new flu outbreak spread through the world). In short, simulation is awesome.

So here is the thing, I argue that if you build a big enough model, a big enough computer, and a good enough simulator, you can probably simulate the universe in its entirety. I think this is possible because I currently think that there is no fundamental random process in the universe (i.e. if you can account for everything, you can predict anything). Actually, there is still argument amongst physicists of whether properties in quantum mechanics appear random because of unknown hidden variables (i.e. randomness does not exist) or because there exists something that is fundamentally random in the universe. .. but let’s skip this for now.

Anyway, let’s get to the cool part.

Imagine that we can build a *huge* simulator that can account for everything and predict (read: compute) anything.  This simulator would be able to replay everything from the moment of the big bang, to the formation of Earth, to the rise of human beings, to the conversations you have with your friends, to me typing this post now. Surely this is an amazing simulator.

Now imagine that you have access to this simulator. Not only that, but being the curious person you are, you use it to fast-forward and play events in the future. So the simulator will tell you what events will happen in the future. So you look at the simulator and it will tell you what I will eat tomorrow, what will life look like in the future, where will your children, .. everything. It will tell you everything. Again, this is an awesome possum simulator.

Now the mind-bending part.

If you look at that simulator to see you future, will your future moves happen because you want to do them or because the simulator told you to do them? For example, if the simulator told me to eat pizza tomorrow, will I eat pizza tomorrow because I want to, or because the simulator told me to? Remember, I can’t trick that program because it would have already accounted for me trying to trick it. So the minute you look at your future you don’t know whether you would have acted that way because you wanted to or because the program told you to.

For example, assume you have been a good person all your life, but the simulator told you that you will become a thief. Would that happen because you would have “naturally” became a thief, or because the simulator told you so?

Luckily (and unfortunately) it currently doesn’t look like we can ever build such a simulator because it has to also account for itself as part of the universe, so it has to be as big as itself plus the universe in which it resides (you see the problem).

For the computer scientists in the crowd, would such a simulator be able to solve the halting problem?