Physics strives for the ultimate goal of a 'theory of everything', and yet there remain several phenomena that stubbornly defy inclusion. These all relate to our conscious experience, and would include the nature thought, emotion, and perception, but they are not given to mathematical description and so physics must ignore them . Instead, they are generally relegated to a philosophical description, despite them being crucial components of our scientific studies.
Since mathematics is clearly an invaluable tool for physics and for a description of our observations then it is a crucial, but justifiable, step to assert that all of the objective reality (the world as it would be in the absence of conscious observers) must be susceptible to mathematics, and that everything else is a product of the emergent phenomenon that we call consciousness.
This results in some surprising casualties, such as motion and all dynamical change. Although mathematics can describe a rate of change, it cannot describe dynamical change as we perceive it and so it must be illusory. That perception naturally leads to notions such as chance, choice, and probability, all of which must be similarly unreal if the dynamical change of a state between two moments is a mere conscious perception.
With the loss of probability as a fundamental description of future events then we need to find a reinterpretation of the mathematics of quantum theory and the second law of thermodynamics, both of which are demonstrated.
With the loss of dynamical change then we lose our notion of causality — a phenomenon well-known to be difficult to pin down — resulting in a reinterpretation free of the constraints of 'sufficient cause', 'first cause', and mind-body problems (e.g. does your mind or your muscle move your arm?).
Another casualty is determinism as we are effectively substituting mathematical determinism in place of causal determinism, thus allowing our initial conjecture to be formalised as a determinate pattern conjecture (DPC[1]): that the objective reality exhibits a mathematically deterministic change over time.
With the recognition that mathematical determinism is the only real guiding principle for observed change then it is possible to find common ground between superdeterminism and de Broglie–Bohm theory (aka pilot wave theory), and this is important for the concept of a 'quantum block universe' (see below).
Losing causal determinism means that free will cannot be a fundamental phenomenon, and so must also be illusory. In other words, conscious entities do not have a privileged status in the universe, and are subject to the same laws as everything else. Many thinkers suspect this, and yet the debates continue unabated.
Returning full-circle, the final step explains how conscious minds (human or otherwise), within which this dynamical subjective reality is imagined, emerge from a static unchanging objective reality. If the only true dynamical change is within the mind then consciousness and subjective time (flowing and punctuated by a 'now' moment) must be bound together, and this leads to a temporal anthropic principle (TAP[2]). Our memories are therefore not transient, and constitute a static state that extends over time, and where each slice is dependent upon earlier slices and delayed inputs (event spurs) in a deterministic way. This view was accidentally captured very succinctly in the modified lyrics of a traditional song: "Yesterday holds memories in time".[3]
The repercussions of this view for fundamental physics, and for objective study in all its forms, is profound. When we ask why then it presumes causal determinism, and an answer that invokes mathematical determinism (e.g. that the slope of a parabola increases because of a relationship that we model by an equation) seems inadequate. Fundamental physics has the concept of an interaction — the state of one entity (usually a particle) directly influencing the state of another — but this does not exhibit a distinct cause or effect; it is a single event, and with no preferred direction in time.
Although cause and effect are widely held to be two separate events, this is not actually the case. It is a single event involving a causal agent, the identification of which relies on the subjective assessment of identity. As causality is a product of the mind then the selection of this causal agent is a matter of convenience for us. Whether we assert that the molecules of our hand move something, or the muscles in our arm, or some conscious decision of the mind, are all equally valid, and none contradict the laws of physics.
Let's take a specific example (one possibly requiring more detail in the book) of how a subjective notion — causality — has had a detrimental effect on fundamental physics. Einstein firmly believed in local causality, and hence thought that there was a deeper explanation of quantum mechanics that relied on 'hidden variables'. In 1932, John von Neumann proved that hidden-variable theories were incapable of reproducing the same predictions as quantum mechanics, but in 1935, a flaw was discovered in this proof by Grete Hermann that suggested non-local hidden-variable theories could be viable. It wasn't until 1964 that John Bell showed that the requirement of local causality was the separating factor, and Bell's inequality put constraints on this that have since been verified experimentally. But there are two caveats to Bell's theorem:
A non-local hidden-variable theory could explain the predictions of quantum mechanics, but what form should it take? Either there is a true instantaneous 'action at the distance' or the efficacy of some signal is faster than the speed of light. Because both of these alternatives violate special relativity then they are rarely pursued. Perhaps the most well-known example in this class was the de Broglie–Bohm theory with its causal guiding wave (aka 'pilot wave'), which has been heavily criticised despite only being a model for such a class of theories.
Superdeterminism — a concept with few advocates, but notably including Sabine Hossenfelder[4] — involves a correlation between the measurements being taken and the settings of the experiment itself. The removal of statistical independence between the experimenter and the system being measured avoids the need for super-luminal speeds and admits a different class of local hidden-variable theory. No real explanation of the nature of such correlations has emerged, only the consequences of them.
Superdeterminism is often associated with free will, or free choice, primarily because of statements made by Bell in relation to it, but free will (which the book dismisses as unreal) is not part of the mathematics describing statistical independence, and is simply an example of causal thinking. Even retrocausality (a cause affecting the past) has been invoked in a desperate attempt to explain quantum mechanics. In fact, causal thinking taints both of the above alternatives, and yet acceptance that causality is unreal can lead to a description uniting both of them as interpretations of single more-fundamental principle.
In the 'quantum block universe' (a concept introduced in §7.6), we only have mathematical determinism and not causal determinism. This removes the distinction between local and non-local because a state is determined by a mathematical relationship that works for all separations — the slope of a parabola is determined by the "pattern" described by the associated equation, and not by any neighbouring influence. The 'pilot wave' can similarly be related to mathematical determinism, with paths (both actual and potential) being the result of a wave-like mathematical relation, as originally proposed by Dirac. In essence, everything (everywhere and for all time) is correlated since a correlation is simply a connection for which there is no direct causation.
The paradoxes that we strive to explain causally are plain evidence for the objective reality being a block universe.
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[1] DPC: Determinate Pattern Conjecture: the pattern of changes over time in the block universe can be fully modelled by sets of consistent mathematical structures and axioms that are finite, deterministic, and continuous.
[2] TAP: Temporal Anthropic Principle: consciousness and subjective time cannot exist without each other; they are bound as part of the same phenomenon.
[3] Nox Arcana, "Scarborough Fair", Winter's Majesty (Monolith Graphics, 2012) , original lyrics and musical arrangements by Joseph Vargo (Nox Arcana) and vocals performed by Jeff Endemann.
[4] S. Hossenfelder, T.N. Palmer, "Rethinking Superdeterminism", arXiv.org, Cornell University eprint (https://arxiv.org/abs/1912.06462, Dec 2019). Also, Sabine Hossenfelder, "Superdeterminism: A Guide for the Perplexed" (https://arxiv.org/abs/2010.01324, Oct 2020). Also, Colm Bracken, Jonte R. Hance, Sabine Hossenfelder, "The Quantum Eraser Paradox" (https://arxiv.org/abs/2111.09347, Nov 2021).