Are we living in a simulation?
Yes, in a specific sense. The universe emerges from a computation running on a holographic screen, and that screen is built by observers inside the world, by us, in our subjective future. The hardware is part of the history it computes, and a designer, if the word is used at all, can only mean those builders, who also switch the screen on. Computation is the better word, because a simulation usually imitates an original kept somewhere else, and nothing in the universe stands in for one. The program is the observer consensus protocol, an ordinary computer program, and what it computes happens. Each patch proposes a local state, neighbors compare records where they overlap, mismatches are repaired, and what survives becomes public. In one run, 81,920 patches, each a bounded record-keeper, brought all 122,880 seams between them into agreement with no tick from any clock. Running the rule on a laptop makes a model of it, the way a weather program models rain.
Also in Chapter 35: What Is Anything Made Of?, Chapter 37: Why Does the Loop Have No Beginning?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read appendix a: Eighteen Questionswatch a universe make its own particles