A Plain-Language Primer on Determinism, Probability, and Quantum Theory

CSD Primer (Page 1 of 5)

What this is about, and why it exists

Quantum mechanics works extremely well. It predicts experimental outcomes with remarkable accuracy. Nothing in Constraint-Surface Dynamics (CSD) challenges that success.

What CSD questions is something more specific:

Why does quantum mechanics have the structure it does?

In particular:

  • Why do probabilities take the specific form they do?

  • Why are quantum states mathematical objects rather than physical ones?

  • Why does measurement produce definite outcomes if the underlying equations are smooth and reversible?

Standard quantum theory answers these questions by postulating rules. CSD asks whether those rules might instead emerge from a deeper, simpler structure.

The guiding idea

CSD is built around a simple guiding idea:

Nature may be deterministic at a deeper level, with probability appearing only because we do not have access to all the underlying information.

This is not a new philosophical claim. What is new in CSD is that this idea is implemented mathematically and operationally, without changing any of the predictions of quantum mechanics in the domain where it is known to work.

Three distinct roles, not three competing theories

One reason discussions about quantum foundations become confused is that different roles are mixed together. CSD separates them carefully.

1. What is really happening

At the deepest level, CSD assumes there is a complete physical description of a system. This description evolves smoothly and deterministically. There is no randomness here.

You do not need to know the details of this deeper description to follow the rest of the primer. What matters is only this:

  • the underlying behaviour is fully determined

  • it does not involve probabilities

2. What we can know

In practice, we never have access to that complete description. We only ever observe limited information.

Quantum states, in CSD, represent what we know, not what exists. They are bookkeeping tools that summarise large families of underlying physical situations that look the same from an experimental point of view.

This is where probability enters:

  • probability reflects limited knowledge

  • it is not a property of the underlying reality

3. What we observe

Experiments take place in spacetime. We see detectors click. We record outcomes.

In CSD, these observed events are not fundamental ingredients. They are stable, large-scale patterns that emerge from the deeper deterministic behaviour when systems interact with measuring devices.

Spacetime descriptions belong to this observed level. They are useful, accurate, and indispensable, but not fundamental.

The key separation to keep in mind

Throughout this primer, it is essential to keep these ideas separate:

  • Reality itself is deterministic.

  • Probability arises from incomplete information.

  • Spacetime events are emergent, practical descriptions of what we observe.

If these are mixed together, the framework will sound mysterious or contradictory. When they are kept separate, the structure becomes simple.

What this primer will and will not do

This primer will show, step by step, how:

  • probability can arise without randomness

  • the familiar quantum probability rule follows from symmetry

  • standard quantum dynamics can be recovered without assuming it from the start

  • measurement outcomes can be understood without adding collapse or branching rules

This primer will not:

  • propose new experimental predictions

  • modify quantum mechanics where it already works

  • claim that spacetime or quantum field theory are already solved

Those are longer-term research questions.

Why this is worth reading

Even if CSD turns out not to be the final word, it demonstrates something important:

The structure of quantum mechanics may not be fundamental. It may be the visible surface of a deeper, deterministic theory shaped by geometry and symmetry. In this programme, quantum states are treated as operational summaries of an underlying configuration, summarizing precisely the information that remains accessible once preparation, isolation, and measurement context have fixed what can be registered. This is the sense in which probabilities are epistemic: they track typical outcome frequencies relative to what is visible, not indeterminism in the underlying dynamics.

The remaining pages make that statement precise, using only the minimum machinery required.

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