What stage are we at in Quantum Mechanics?

[bugatti79]

I am just wondering what stage are we at in Quantum mechanics relative to Newtonian mechanics?

I think we are well sorted with the latter but is ourknowledge nowadays of QM equivalent to the egyptians thinking the sun was god thousands of years ago?

Shouldnt we start working on theories that involve consciousness?

Thanks

 

[HallsofIvy]

We are in great shape with Quantum Mechanics! Practically every electronic tool used in society today wouldn't be possible if Quantum Mechanics did not work perfectly.

Now, as to Quantum physics, i.e. the theory behind the mechanics, we are a bit confused. We have a number of basic theories and are still arguing over the precise difference between the theories.

 

[Fra]

A personal answer on this.

I am just wondering what stage are we at in Quantum mechanics relative to Newtonian mechanics?

If you compare what state are QM are at, within the inferencial framework of theories, with the state of Newtons mechanics withing realist theories then I would say that QM relates to the future like Newtons mechanics did to GR.

Even classical physics is about predictions and measurements, but the difference is that the classical picture of measuremens is that they do not affect the system, they merely serve to "verify the theory". Reality is assme to exists in an objective sense regardless of the exact measurement.

In measurement theory, the focus changes from description what really happens, to actually defining the physics as how a system responds to measurement. Here the measurement becomes an integral part of the physics, unlike realist physics.

Newtons mechanics - SR - GR.

Where Newtons mechanics has is very global static exteernal picture, which is relaxed in SR by introducing equivalence classes of inertial observers, which if further generalized by non-inertial observers in GR, where the realist of Newtons world are infact destroyed partially... SR ang GR says that the observer after all, DOES matter... but realism is still maintained as the observer invariants of equivalence classes of observers.

In measurement theory I think we have

extrinsic measurement theory(QM) - intrinsic measurement theory(??)

QM is a measurement theory, but the observer is external to the system. Just like in the old days when Gauss and Riemann seeked an intrinsic formulation of the old extrinsic euclidian geometry.

A measurement theory, where the observer is inside the system is still lacking! QM as it stands NEEDS an observer to be formulated (this is a background), moreover QM assumes that this observer is classical (an unbounded in information).

In this respect I think QM as it stands to future understanding like say
- extrinsic geometry to intrinsic geometry
- Newtons mechanics to GR

I think we have a long way left.

The fact that QM and QFT works so well still is simple! The simplification that QM needs an external classical observer DOES make sense for most situations! In any particle/accelerator experiment you have the entire laboratory frame as a gigantic classical system observing and absorbing information from experiments that are easily repeated.

The problems where this scheme unavoidable breaks down are in cosmological models (ie where the observer IS inside the system! wheter we like it or not) and also when it comes to understanding unification of forces at high energy when we reach theoretical BH formation.

But taking the parallell to egyptians is I think overstating it :)

/Fredrik

 

[bugatti79]

A measurement theory, where the observer is inside the system is still lacking!

How does one over comes this?

The fact that QM and QFT works so well still is simple! The simplification that QM needs an external classical observer DOES make sense for most situations!

How does it make sense?

The problems where this scheme unavoidable breaks down are in cosmological models (ie where the observer IS inside the system! wheter we like it or not) and also when it comes to understanding unification of forces at high energy when we reach theoretical BH formation.

Not sure I follow this. if the observer is inside the cosmological models then what is the problem?

What if consciousness is the observer? I know physicist don't want to hear that word because its a non physical entity...

Thanks
/Fredrik

I don't know how to use multi qoute!

 

[Fra]

How does one over comes this?

This is the question. There is not yet an established answer to this.

How does it make sense?

Because we study small subsystems of the universe, and although the human laboratory is of course a subsystem of the universe; relative to the small subsystem we study (say an atom!) the laboratory frame IS effectively an external observer with respect to the subsystem.

So it's clear why the special case does apply.

Not sure I follow this. if the observer is inside the cosmological models then what is the problem?

There is no external observer, where to attach the extrinsic measurment theory :)

/Fredrik

 

[Demystifier]

We are in great shape with Quantum Mechanics! Practically every electronic tool used in society today wouldn't be possible if Quantum Mechanics did not work perfectly.

Now, as to Quantum physics, i.e. the theory behind the mechanics, we are a bit confused. We have a number of basic theories and are still arguing over the precise difference between the theories.

What you call "mechanics" here, most people would call "physics". And what you call "physics" or "theories" here, most people would call "interpretations". Otherwise, you are absolutely right.

 

[jtbell]

I don't know how to use multi quote!

"Multi Quote" is actually for selecting more than one post that you want to quote from in the same post. To quote several sections from a single post, use the "Quote" button. To break up the single long quote into sections, insert, by hand, {quote} and {/quote} tags at the beginning and end of each new section. (Use square brackets instead of curly brackets.)

 

[_PJ_]

QM is a measurement theory, but the observer is external to the system.

I wouldn't say external, for any quaantum measurement, the observer is not only integral, but determines precisely what measurements are made.

 

[Fra]

What I mean by external is that the observer comes with an external context; where knowledge of the system is encoded and stored, and the resources for this are independent of the system under observation. Ie. there is no feedback from the system that deforms the memory structures, and we have fixed eternal hilbertspaces.

This is what allows for a purely descriptive view.

This does not make sense from the intrinsic perspective, because there there exists constraints of the context that forces a higher degree of incompleteness of the descriptive view, and this forces the observer to make choices and constantly change. The descriptive problem transforms into a partial description and partial decision problem.

For example; in the external view, only concern with the high energy limit is that at some point we worry about BH formation.

in the intrinsic view, the follow twist is added. This high energy limit might not even be achievable since the observer would have loose too much of it's own mass in order to perform such a measurement; meaning that each observer does come with a natural cutoff, that has a physical justification, as opposed to the technical non-physical regularisations.

Not to mention that the hilbert space would have to be SCALED, and so with it all interactions ina nontrivial way.

There are plenty of such issues that I see as clear serious problems. But it's easy to understand why there are non-issues for most particle physics since in these cases the environment is effectively the almost infinite unlimited resources that allows emergence of a puerly descriptive view (in terms of eternal and timeless laws).

/Fredrik

 

[StevieTNZ]

Are the interpretational issues that arise from QM the same with QFT and QED?

I.e. the principles of QM are required to be part of any other theory such as QFT

 

[Fra]

Are the interpretational issues that arise from QM the same with QFT and QED?

Yes, if you ask me QFT still makes use of the same "extrinsic measurement theory" as non-relativistic QM.

QFT is in a sense really just relativistic QM; but it's the "same old" framework. You naturally get "fields" from second quantization procedures. So QFT is more complex, but the basic issues above are quite similar. You still have hilbert spaces in QFT; these do belong to such extenal context.

I think it's fair to say that the issues, get WORSE in QFT, not better. But then if you see QFT as QM+SR; then QM+GR gets yet worse...

/Fredrik