# Quantum Mechanics Interpretations?

1. Jul 9, 2013

### Patriciamsv

When an object's state is determined and ultimately decided as one, what happens to the wave functions as the property of the object is determined?

The Copenhagen interpretation suggest that the wave function "collapses" into one.

The many-worlds interpretation suggests that each possible wave function branches off into a new universe.

What other interpretations are there to explain decoherence of quantum objects?

2. Jul 9, 2013

### hilbert2

In the "Bohmian interpretation", quantum mechanics is completely deterministic, and the apparent indeterminacy of the result of a single measurement is explained with hidden variables (unknown mechanical degrees of freedom). Bohmian mechanics is, however, more complicated than is necessary to explain experimental data related to QM, and the argument of Occam's razor can be used against it. It has never been a popular interpretation.

3. Jul 9, 2013

### Staff: Mentor

Some other interpretations do not assign any physical reality to the wave function - if it is just a mathematical tool, it is not problematic if it vanishes. This still leaves the question when and in which way it should vanish and what we have afterwards (a new wave function?).

4. Jul 10, 2013

### Demystifier

Decoherence can be explained without using any specific interpretation. Interpretations are needed to explain the existence of single measurement outcomes (which is not the same as decoherence). There are actually many interpretations, such as
http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics

To see which ones are the most popular ones, see e.g.
In particular, posts #80 and #85 give the top-3 lists according to some small-sample polls.

5. Jul 10, 2013

### bhobba

They are many and varied. But check em out if you like:
http://en.wikipedia.org/wiki/Interpretations_of_quantum_mechanics

I hold to the Ensemble interpretation, which is the one Einstein held to:
http://en.wikipedia.org/wiki/Ensemble_interpretation

In that interpretation, similar to the concept of probability which is simply a device to help calculate the outcomes of certain situations it doesn't exist out there in a real sense and when say you roll a dice and get a number it doesn't mean anything (in the sense of something real suddenly changing) that the state has changed from one where an outcome occurs with a certain probability to one where it is known for sure. Technically you go from a mixed state to a pure state. Exactly the same thing happens with QM - its twist though is its not just mixed states that have unknown outcomes - pure states do as well.

Thanks
Bill

Last edited: Jul 10, 2013
6. Jul 10, 2013

### Quantumental

Bhobba can you *please* stop saying that Einstein adhered to the Ensemble Interpretation? He did not.
He believed QM was deterministic, Ensemble Interpretation isn't.
Infact the Ensemble Interpretation isn't a interpretation at all, it doesn't say *anything* about what really occurs.

7. Jul 10, 2013

### bhobba

That is simply untrue as standard textbooks such as Ballentine - Quantum Mechanics - A Modern Development make clear - as well as many articles such as Wikipedia:
http://en.wikipedia.org/wiki/Ensemble_interpretation
'Probably the most notable supporter of such an interpretation was Albert Einstein:
The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems.'

And that the Ensemble Interpretation is not an interpretation would have to one of the silliest statements I have ever heard. If you are going to continue to promulgate such claims you are going to have to back them up.

Indeed if you make statements like 'what really occurs' you are going to have to precisely define what reality is in order to determine if anything is really occurring in the first place - and have that definition generally accepted.

Thanks
Bill

8. Jul 10, 2013

### ZapperZ

Staff Emeritus
Before this gets any uglier (and thread such as this has the tendency to do just that), please do not degenerate this into a MY-INTERPRETATION-IS-BETTER-THAN-YOUR-INTERPRETATION-type of an argument. This is NOT what the OP asked for.

So set aside arguing about your favorite color, and just tell the OP what are the different colors that are available. That is what that has been asked for!

Zz.

9. Jul 10, 2013

### kith

Einstein believed that QM was incomplete, not deterministic. It is not a contradiction to have an interpretation about an effective theory and at the same time to believe in a fundamental theory from which the effective one can be derived. What's wrong with the statement "QM gives the real behaviour of ensembles but not of individual systems"?

Just like thermodynamics gives the real beahaviour of ensembles but not of individual particles. The interpretation that thermodynamics is about ensembles of particles and can be deduced from their known interactions had certainly been around at the time where stat mech hadn't fully accomplished this.

10. Jul 10, 2013

### kith

Personally, I think time symmetric interpretations are quite interesting. Loosely speaking, the idea is that measurement outcomes depend not only on past preparation of the system but also on the future.

However -as Demystifier noted-, we don't need an interpretation to "explain" decoherence. Decoherence is derived from the formalism and is itself used in explaining the measurement problem in various interpretations.

11. Jul 11, 2013

### audioloop

Well said.
categorical sentences and definitive truths.
like I am owner of the truth......

12. Jul 11, 2013

### Staff: Mentor

13. Jul 16, 2015

### shaun_o_kane

Re: please do not degenerate into a my interpretation is prettier than yours. That's what Science is about. Interpretations have flaws, but interpretations also have value. There is a good chance that the correct interpretation will help to drive Physics forward. A honest beauty contest is important and it is what Bohr and Einstein spent a lot of time on.

For example, the many-worlds interpretation has the following problem: Many worlds says that the Universe continual splits into multiple copies of itself whenever a measurement is made. Each measurement outcome has an associated Universe where the outcome has occurred. The Universe is divided into two; before the measurement and afterwards. But Relativity tells us that different observers have different ideas of simultaneity. A distant event may or may not be included in the new universes. That's not really pretty at all.

And I fail to see why the original question needs to completely determine what can follow. If we are only here to answer the question, then we should point him at a webpage. I have to say that closing down discussions on interpretation to listing them, or perhaps even explaining them, seems despicable. It reminds me of the Top Gear show where the US Department of State insisted that Top Gear make a factual show and not an entertaining one. Bonkers.

You sound like you do not value interpretations and think nothing can come of them. I think you are very wrong.

14. Jul 16, 2015

### bhobba

That's incorrect. The universe actually splitting is a crude way of viewing what's going on in MW.

Its simply an interpretive assumption about the outcome of decoherence. Each part of the mixed state is interpreted as a world.

Thanks
Bill

15. Jul 17, 2015

### haushofer

How, exactly? As I understand it, Bohmian mechanics tries to provide a clear ontology for QM. The Copenhagen interpretation suffers from the measurement problem. How then can we use this "Ockham's razor" to choose between the Copenhagen and Bohmian interpretation? Aren't we allowed to introduce extra structure for solving a problem?

I often see people claim what you say, but I never really understand it. Just because the Bohmian interpretation has an equation more? To me that sounds kind of simplistic, to be honest.

16. Jul 17, 2015

### Staff: Mentor

This thread is closed pending moderation.

Edit: this thread will remain closed. I encourage all participants to review the forum rules on philosophy and speculation.

Last edited: Jul 20, 2015