## 4 Complete ToEs (CToEs)  
A ToE by definition is a perfect model of the universe. It should allow to predict all phenomena. Most ToEs require a specification of some initial conditions, e.g. the state at the big bang, and how the state evolves in time (the equations of motion). In general, a ToE is a program that in principle can \"simulate\"the whole universe. An All-a-Carte universe perfectly satisfies this condition but apparently is rather a theory of nothing than a theory of everything. So meeting the simulation condition is not sufficient for qualifying as a Complete ToE. We have seen that (objective) ToEs can be completed by specifying the location of the observer. This allows us to make useful predictions from our (subjective) viewpoint. We call a ToE plus observer localization a subjective or complete ToE. If we allow for stochastic (quantum) universes we also need to include the noise. If we consider (human) observers with limited perception ability we need to take that into account too. So  
**A complete ToE needs specification of**  
1. initial conditions
2. state evolution
3. localization of observer
4. random noise
5. perception ability of observer  
We will ignore noise and perception ability in the following and resume to these issues in Sections 7 and 5, respectively. Next we need a way to compare ToEs. **Epistemology. ** I assume that the observers' experience of the world consists of a single temporal binary sequence which gets longer with time. This is definitely true if the observer is a robot equipped with sensors like a video camera whose signal is converted to a digital data stream, fed into a digital computer and stored in a binary file of increasing length. In humans, the signal transmitted by the optic and other sensory nerves could play the role of the digital data stream. Of course (most) human observers do not possess photographic memory. We can deal with this limitation in various ways: digitally record and make accessible upon request the nerve signals from birth till now, or allow for uncertain or partially remembered observations. Classical philosophical theories of knowledge [19] (e.g., as justified true belief) operate on a much higher conceptual level and therefore require stronger (and hence more disputable) philosophical presuppositions. In my minimalist \"spartan\" information-theoretic epistemology, a bit-string is the only observation, and all higher ontologies are constructed from it and are pure \"imagination\". **Predictive power and elegance. ** Whatever the intermediary guiding principles for designing theories/models (elegance, symmetries, tractability, consistency), the ultimate judge is predictive success. Unfortunately we can never be sure whether a given ToE makes correct predictions in the future. After all we cannot rule out that the world suddenly changes tomorrow in a totally unexpected way (cf. the quote at beginning of this article). We have to compare theories based on their predictive success in the past. It is also clear that the latter is not enough: For every model we can construct an alternative model that behaves identically in the past but makes different predictions from, say, year 2020 on. [PERSON]'s falsifiability dogma is little helpful. Beyond postdictive success, the guiding principle in designing and selecting theories, especially in physics, is elegance and mathematical consistency. The predictive power of the first heliocentric model was not superior to the geocentric one, but it was much simpler. In more profane terms, it has significantly less parameters that need to be specified. **Ockham's razor** suitably interpreted tells us to choose the simpler among two or more otherwise equally good theories. For justifications of Ockham's razor, see [6] and Section 8. Some even argue that by definition, science is about applying Ockham's razor, see [20]. For a discussion in the context of theories in physics, see [21]. It is beyond the scope of this paper to repeat these considerations.