## 2 Theories of Something, Everything & Nothing
** Pure gravitational and pure quantum phenomena are perfectly predictable by general relativity and the standard model, respectively. Phenomena involving both, like the big bang, require a proper final unification. String theory is _the_ candidate for a final unification of the standard model with the gravitational force. As such it describes the universe at its largest and smallest scale, and all scales in-between. String theory is essentially parameter-free, but is immensely difficult to evaluate and it seems to allow for many solutions (spatial compactifications). For these and other reasons, there is currently no uniquely accepted cosmological model. **(C) Cosmological models. ** Our concept of what the universe is, seems to ever expand. In ancient times there was Earth, Sun, Moon, and a few planets, surrounded by a sphere of shiny points (fixed stars). The current textbook universe started in a big bang and consists of billions of galaxy clusters each containing billions of stars, probably many with a planetary system. But this is just the visible universe. According to inflation models, which are needed to explain the homogeneity of our universe, the \"total\" universe is vastly larger than the visible part. **(M) Multiverse theories. ** Many theories (can be argued to) imply a multitude of essentially disconnected universes (in the conventional sense), often each with their own (quite different) characteristics [14]. In [PERSON]'s oscillating universe a new big bang follows the assumed big crunch, and this repeats indefinitely. [PERSON] proposed that every black hole recursively produces new universes on the \"other side\" with quite different properties. [PERSON]'s many-worlds interpretation of quantum mechanics postulates that the wave function doesn't collapse but the universe splits (decoheres) into different branches, one for each possible outcome of a measurement. Some string theorists have suggested that possibly all compactifications in their theory are realized, each resulting in a different universe. **(U) Universal ToE. ** The last two multiverse suggestions contain the seed of a general idea. If theory X contains some unexplained elements Y (quantum or compactification or other indeterminism), one postulates that every realization of Y results in its own universe, and we just happen to live in one of them. Often the anthropic principle is used in some hand-waving way to argue why we are in this and not that universe [8]. Taking this to the extreme, [PERSON] [9, 15] postulates a multiverse (which I call universal universe) that consists of every computable universe (note there are \"just\" countably many computer programs). Clearly, if our universe is computable, then it is contained in the universal universe, so we have a ToE already in our hands. Similar in spirit but neither constructive nor formally well-defined is [PERSON]'s mathematical multiverse [16]. **(R) Random universe. ** Actually there is a much simpler way of obtaining a ToE. Consider an infinite sequence of random bits (fair coin tosses). It is easy to see that any finite pattern, _i.e._, any finite binary sequence, occurs (actually infinitely often) in this string. Now consider our observable universe quantized at e.g. Planck level, and code the whole space-time universe into a huge bit string. If the universe ends in a big crunch, this string is finite. (Think of a digital high resolution 3D movie of the universe from the big bang to the big crunch). This big string also appears somewhere in our random string, hence our random string is a perfect ToE. This is reminiscent of the [PERSON] brain idea that in a sufficiently large random universe, there exist low entropy regions that resemble our own universe and/or brain (observer) [17, Sec.3.8]. **(A) All-a-Carte models. ** The existence of true randomness is controversial and complicates many considerations. So ToE (R) may be rejected on this ground, but there is a simple deterministic computable variant.