Quantum Interpretation Poll (2011)

Fyzix

I think it's time for the annual quantum interpretation poll.

Vote for which interpretation you currently think represents reality.

A. Neumaier

Since this seems to be an annual poll, could you please link to the poll's result of the last few years?

Consistent histories interpretations are missing.
Also, there is no way to specify the details for ''other'' (last button).

Fyzix

Just search of quantum interpretations, there seems to have been like 20 of them, but I decided to call this annual so it can be the offical one of 2011 and not be moved to the philosophy section.

Yeah I forgot consistent histories, but isn't it just copenhagen really?
There is collapse and it's indeterministic.

Specify details for other here in the thread.

A. Neumaier

Could you please list the few most recent of these?

It is not Copenhagen, else it would not have its own name.

I have my own interpretation.
I call it the the thermal interpretation since it agrees with how one does measurements in thermodynamics (the macroscopic part of QM (derived via statistical mechanics), and therefore explains naturally the classical properties of our quantum world. It is outlined in my slides at http://www.mat.univie.ac.at/~neum/ms/optslides.pdf and the entry ''Foundations independent of measurements'' of Chapter A4 of my theoretical physics FAQ at http://www.mat.univie.ac.at/~neum/ph...aq.html#found0 . It is described in detail in Chapter 7 of my book ''Classical and Quantum Mechanics via Lie algebras'' at http://lanl.arxiv.org/abs/0810.1019 . See also the following PF posts:
http://www.physicsforums.com/showthr...al#post3187039
http://www.physicsforums.com/showthr...al#post3193747


The thermal interpretation
It is superior to any I found in the literature, since it
-- acknowledges that there is only one world,
-- is observer-independent and hence free from subjective elements,
-- satisfies the principles of locality and Poincare invariance, as defined in relativistic quantum field theory,
-- is by design compatible with the classical ontology of ordinary thermodynamics
-- has no split between classical and quantum mechanics,
-- applies both to single quantum objects (like a quantum dot, the sun or the universe) and to statistical ensembles,
-- allows to derive Born's rule in the limit of a perfect von-Neumann measurement (the only case where Born's rule has empirical content),
-- has no collapse (except approximately in non-isolated subsystems).
-- uses no concepts beyond what is taught in every quantum mechanics course,
No other interpretation combines these merits.

The thermal interpretation leads to a gain in clarity of thought, which results in saving a lot of time otherwise spent in the contemplation of meaningless or irrelevant aspects arising in poor interpretations.


The thermal interpretation is based on the observation that quantum mechanics does much more than predict probabilities for the possible results of experiments done by Alice and Bob. In particular, it quantitatively predicts the whole of classical thermodynamics.

For example, it is used to predict the color of molecules, their response to external electromagnetic fields, the behavior of material made of these molecules under changes of pressure or temperature, the production of energy from nuclear reactions, the behavior of transistors in the chips on which your computer runs, and a lot more.

The thermal interpretation therefore takes as its ontological basis the states occurring in the statistical mechanics for describing thermodynamics (Gibbs states) rather than the pure states figuring in a quantum mechanics built on top of the concept of a wave function. This has the advantage that the complete state of a system completely and deterministically determines the complete state of every subsystem - a basic requirement that a sound, observer-independent interpretation of quantum mechanics should satisfy.

The axioms for the formal core of quantum mechanics are those specified in the entry ''Postulates for the formal core of quantum mechanics'' of Chapter A4 of my theoretical physics FAQ at http://www.mat.univie.ac.at/~neum/ph...tml#postulates . There only the minimal statistical interpretation agreed by everyone is discussed. The thermal interpretation goes far beyond that, assigning states and an interpretation for them to individual quantum systems, in a way that large quantum systems are naturally described by essentially classical observables (without the need to invoke decoherence or collapse). The new approach is consistent with assigning a well-defined (though largely unknown) state to the whole universe, whose properties account for everythng observable within this universe.

The fundamental mathematical description of reality is taken to be standard quantum field theory. It doesn't matter for the thermal interpretation whether or not there is a deeper underlying deterministic level.


In my thermal interpretation of quantum physics, the directly observable (and hence obviously ''real'') features of a macroscopic system are the expectation values of the most important fields Phi(x,t) at position x and time t, as they are described by statistical thermodynamics. If it were not so, thermodynamics would not provide the good macroscopic description it does.

However, the expectation values have only a limited accuracy; as discovered by Heisenberg, quantum mechanics predicts its own uncertainty. This means that <Phi(x)> is objectively real only to an accuracy of order 1/sqrt(V) where V is the volume occupied by the mesoscopic cell containing x, assumed to be homogeneous and in local equilibrium. This is the standard assumption for deriving from first principles hydrodynamical equations and the like. It means that the interpretation of a field gets more fuzzy as one decreases the size of the coarse graining - until at some point the local equilibrium hypothesis is no longer valid.

This defines the surface ontology of the thermal interpretation. There is also a deeper ontology concerning the reality of inferred entities - the thermal interpretation declares as real but not directly observable any expectation <A(x,t)> of operators with a space-time dependence that satisfy Poincare invariance and causal commutation relations.
These are distributions that produce measurable numbers when integrated over sufficiently smooth localized test functions.


Deterministic chaos is an emergent feature of the thermal interpretation of quantum mechanics, obtained in a suitable approximation. Approximating a multiparticle system in a semiclassical way (mean field theory or a little beyond) gives an approximate deterministic system governing the dynamics of these expectations. This system is highly chaotic at high resolution. This chaoticity seems enough to enforce the probabilistic nature of the measurement apparatus. Neither an underlying exact deterministic dynamics nor an explicit dynamical collapse needs to be postulated.

The same system can be studied at different levels of resolution. When we model a dynamical system classically at high enough resolution, it must be modeled stochastically since the quantum uncertainties must be taken into account. But at a lower resolution, one can often neglect the stochastic part and the system becomes deterministic. If it were not so, we could not use any deterministic model at all in physics but we often do, with excellent success.

This also holds when the resulting deterministic system is chaotic. Indeed, all deterministic chaotic systems studied in practice are approximate only, because of quantum mechanics. If it were not so, we could not use any chaotic model at all in physics but we often do, with excellent success.

tom.stoer

I don't really understand the difference between "Many Worlds (With splitting of worlds)" and "Everettian MWI (Decoherence)".

In case we have two classical scenarios (e.g. Schrödinger's cat, coin tossing, ...) decoherence explains why we always observe one of these two classical scenarios instead of a quantum superposition. But decoherence does NOT explain why we observe exactly THIS scenario. It explains why the cat is either dead or alive. But if there IS a dead cat it does NOT explain why the cat dead, not alive.

There is another ingredient required, e.g. MWI with random splitting of worlds.

Am I wrong?

unusualname

That "thermal interpretation" sounds cool ;-)

just a quick (maybe annoying) question, is QM linear in the thermal interpretation?

A. Neumaier

Of course. Everything valid in standard quantum mechanics and quantum field theory remains valid in the thermal interpretation. In particular, the Schroedinger equation holds without any modification.

A. Neumaier

Both items look strange.

Many worlds makes no sense without splitting of worlds.

Decoherence has _nothing_ to do with the much older Everett interpretation, though it can be combined with it. But it is no independent interpretation since it needs either the statistical interpretation or some form of MWI to get off ground.

Also ''Copenhagen'' comprises very different interpretations depending on who defines it.

And De Broglie--Bohm is today usually called Bohmian mechanics.



To be meaningful, each selectable item should be accompanied by a paragraph explaining what is meant by it, with a positive list and a negative list of features.

Maybe it would be better to collect a list of features of which the various interpretations combine some of these, and ask to indicate which of these features are present or absent in each participant's own view.

unusualname

i assume you mean the Schrödinger Evolution eqn, which is a postulate of QM (maybe unfairly named), not the non-relativistic Schrödinger eqn, which has limited applicability.

Hmm, I like the overall philosophy, might be worth studying the book in more detail

@OP, people are not really that into thinking along the lines of "interpretations" any more, there are fundamental issues like discreteness of space-time to consider before you can commit to any of the old-fashioned interpretations. I agree with A.Neumaier that consistent histories, or any model that includes decoherence is considered most plausible, but as I say there are fundamental issues which require resolution before a commitment to a QM "interpretation" can be made.

A. Neumaier

The Schroedinger equation i hbar psidot = H psi is valid universally in (conservative) quantum mechanics. This includes the relativistic case and quantum field theory, where H is the generator of time translations of the Poincare group.
You are welcome!

unusualname

Yes, some people don't realise that the Schrödinger Evolution equation is valid universally even in qft, this is due to undergraduate introductions to QM where everyone learns the non-relativistic equation with Schrödinger's name, the evolution law should perhaps be called the Heisenberg-Schrödinger eqn.

A. Neumaier

I think it is due do the fact that (because of renormalization issues) books on relativistic QFT don't talk about time evolution but only about the S-matrix. The whole formalism looks so different from QM that it seems to be a completely different subject.

See http://www.physicsforums.com/showthread.php?t=476412 for a discussion of this.

Fyzix

Well the difference is that MWI with splitting, means literally physical copies of the universe at each measurement...

To check out the difference: http://plato.stanford.edu/entries/qm-everett/

unusualname

Yeah, that thread reminds me of why I don't think you've quite got it right. But as i say I like the overall philosophy but can't partake in an exchange of exactly why i think you're wrong since:

1 it would make the thread go against the founding rules of the forum
2 I can't be arsed since I haven't quite established my own thinking yet, and until then I would not be able to reply to your sophisticated mathematical arguments with due clarity.

yoda jedi

lack;
Consistent Histories, Modal Approach, Two-State Vector Formalism, Relational Interpretation.

Dmitry67

2 for Copenhagen???
Who???

A. Neumaier

ND Mermin
Copenhagen computation: How I learned to stop worrying and love Bohr
http://arxiv.org/pdf/quant-ph/0305088