It's possible the entire universe is "running" as a black hole hole computer, here's why: If something with the same mass as the universe was a Black Hole, the event horizon would have a radius of 14 billion light years - which we observe about our own universe. Black Holes are also the most computationally dense possible objects, because they represent the limit on how much information you can pack into a finite volume. This is known as the Bekenstein Bound, which is actually a statement about maximum possible entropy, but, it turns out the thermodynamic entropy of a physical system is the same as the Shannon entropy of the information required to describe that system. Okay, so it just so happens that Black Holes are the best possible computers and our universe has the right mass and size to be a Black Hole. How do the computations get done? First, I/O for black hole computers: When you drop something into a black hole, as it falls towards the event horizon the strength of gravity dilates time such that all quantum mechanical phenomenon become frozen to an outside observer, and the complete quantum mechanical description of the object, I.e. it's information content, becomes imprinted on the event horizon. Thats your input. At the same time, the black hole is slowly evaporating via Hawking radiation - there is a constant background fluctuation in the energy content of space you can think of as a "quantum foam", or as pairs of matter and antimatter particles popping into existence and annihilating each other. At the sharp boundary of the event horizon, one member of the particle-antiparticle pair is captured and falls into the black hole, and the other radiates away to space. That's your output. These two phenomena are connected by how the gravitational influence of matter falling into the black hole subtly warps the local shape of the event horizon boundary, which affects how the Hawking radiation is emitted. Okay, so you can interface with a BH CPU by dropping things in and looking at the radiation emitted. What's going on inside? There's two things to consider: The first is that via the Holographic Principle, it is in fact possible to perfectly reconstruct a complex three dimensional configuration of atoms, molecules, and energy by information encoded on a bounding volume. The second is that you don't necessarily get a "point" of infinite density inside a black hole - in the Einstein–Cartan–Sciama–Kibble theory of gravity, which relaxes a constraint on a feature of spacetime which accounts for the quantum mechanical property of intrinsic spin. As the matter compresses more and more, a spin-spin repulsion force grows to counter gravitational collapse and the matter reaches a finite critical density at which point it rebounds, and expands, forming the far-side of an Einstein-Rosen bridge wormhole to an expanding universe. Okay, so you get an expanding universe like the one we live inside of, where the 3D physical processes inside can be represented by information encoded on the enclosing surface, such that the edge of our Hubble Volume is the Event Horizon of the Black Hole. Sounds good so far. What does the computing? It turns out, "computing" is what is happening when physical systems "do their thing" - when two atoms bond together, when molecules react, when a cellular organelle churns out a protein, when an animal develops immunity to a disease - all these physical processes are of the nature of transforming information, I.e. the physical configuration of things, according to some state machine or transformation matrix or Hamiltonian operator - some set of rules determine what happens with the next clock cycle. And there likely are clock cycles and indivisible bits - an implication of the Holographic Principle is that the interior spacetime is not infinitely divisible, otherwise it would take an unlimited amount of information to describe. And indeed there is a "smallest" duration and length