Multiple Levels 'Inside' Quantum Physics?

Ian Thompson, University of Surrey

26th Sept 2000

Features of Quantum Mechanics

There are a number of `features' of QM that are apparently ad hoc and not readily understood:

1.

Does anything actually happen? Are there actual events independent of our immediate experience? (The measurement problem)

2.

Does anything exist in the physical world? (The substance problem)

3.

What do wave functions describe? (The same problem again)

4.

Are all measurements really position measurements, even though precise positions are never measured! (The preferred basis problem)

5.

Are actual and virtual events the same or different?

6.

Are all events really interactions?

New Approach

I will work towards presenting a framework of `multiple generative levels', in which I believe more sense can be made of all these disparate aspects of quantum mechanics and how they are related. I want to give a `realist' view, which describes what wave functions describe, what really goes on in nature, and how nature `works out what to do'.

First some explanation of concepts:

Multiple generative levels

are a sequence $A\rightarrow B\rightarrow C\rightarrow ..$ in which A `generates' or `produces' new forms of Busing the present form of B as a precondition. Then B generates C in the same way, and so on until the end where nothing is active.

Propensities

In order for any A to generate anything, it must be something like a `cause' or `propensity' or `potential'.
Forces are like this: they do not say what does happen: a specification of a force says what (acceleration) would be caused if a mass was acted on.
Electric fields are like this: a field strength generates a force when a charge is present.
Quantum wave functions are like this: they generate probabilities if and only if a `measurement' is made.

Multilevel Propensities

are `parallel processes' all equally real.
Level B, for example, is not just an approximate description of successive forms of other levels A or C, neither is it a microscopic constituent of either of those levels. Rather, levels A, B, C,... are to be regarded as real processes `in parallel' that interact with other by relations of `generation' and `pre-condition'.

Proposed levels

Initially, I propose three generative levels:

Here:

• an actual event is the selection of a specific `historical alternative' from among finitely many alternative configurations, the selection being generated by a `propensity to select', according to Born's probability rule.
• A `propensity to select' is the `propensity wave' (better known as the `wave function', or `wave packet' or `probability amplitude').
  `Propensity waves in configuration space' are the best way of viewing particles as quantum substances.
• A `propensity wave' at a particular time is generated from its form at a previous time by the operation of the Energy Operator (better known as the Hamiltonian) according to Schrödinger's equation

Virtual Processes

But where does the Hamiltonian come from? We cannot just invent it! We know that the potential energy part of the Hamiltonian really comes from field-theoretic virtual processes. Where are these events?

In more detail, I propose two linked sets of three generative levels each :
 

where the two sets have (broadly) corresponding processes at each level (as shown by dotted lines):

• Virtual Outcomes are the `virtual events' of quantum field theory, that generate the potential energy part of the Hamiltonian.
  They do not all `actually occur' because, for example, they may generate potentials that are never active in the selected sequence of actual outcomes.
• Propagating field quanta (virtual quantum substances) generate virtual events when interacting.
• The field-theoretic Lagrangian functional is where this generative sequence starts off, as the virtual field propagation equations are derived from it according to a Variational Principle.

I hope that this classification of several `stages' in nature, as seen in quantum mechanics, may help in a small way to understand quantum physics and what really goes on.