Q: So what is the dimension of my Hilbert Space? A: Just enough to describe all your independent physical states, which is proportional to the number of your p

Q: So what is the dimension of my Hilbert Space? A: Just enough to describe all your independent physical states, which is proportional to the number of your particles. Q: So if some interaction creates more particles I have to increase the dimension of my Hilbert Space? A: Yes, I'm afraid so. Q: But I am used to physics providing some constant background to goings-on here and now. It was absolute Newtonian space and time, then it was warped Einsteinian spacetime, now you say it depends on how many particles I create? A: Yes. Q: But that's insane? A: Yes. A: OK, I'll allow you to create or destroy as many particles as you like, especially if you have an really big Large Hardon Collider. Q: Are you sure I can keep my Hilbert Space the same? A: Yes, aha, I have thought of a special number that does not change when you add or remove finite integers... Q: There is no such number ... oh wait, you mean infinite dimensional? A: Yes, infinite dimensional, and complex, of course. Q: Of course. Q: Does not sound in the least bit plausible. How do you add particles? A: It's called the second quantization of Quantum Field Theory using Fock Spaces. Q: Makes perfect Focking sense.