I What makes the interpretations of Quantum Mechanics so important?

  • Thread starter timmdeeg
  • Start date

timmdeeg

Gold Member
888
56
Summary
Provided it's correct that the interpretations of Quantum Mechanics can be neither proved nor disproved why then do researchers invest so much time and talent in this field?
Last edited:

DarMM

Science Advisor
Gold Member
1,769
859
It's difficult to know exactly what Quantum Mechanics is saying about the world and in the standard formulation it doesn't directly "represent" the systems you apply it to but only the statistics of their effects on systems you control and don't model with quantum theory.

People spend a lot of time on it because many think you should have an understanding of systems in and of themselves.

The answers to your other questions are more philosophical and differ between people, but preferences ultimately motivate why people tackle the issues I mentioned above.
 
Last edited:

Vanadium 50

Staff Emeritus
Science Advisor
Education Advisor
22,975
5,239
why then do researchers invest so much time and talent in this field?
Before we can tell you why something is true, we need to know if it is true.

Judging by publications, <1% of the work discussing QM is about interpretations. Maybe even 0.1%, but I am unwilling to look at thousands of publications to count.
 
Last edited:

vanhees71

Science Advisor
Insights Author
Gold Member
12,660
4,860
The interpretation of a physical theory is just telling you how to use the formal math to derive predictions for the outcome of real-world observations and quantitative measurements. Thus, the minimal interpretation (aka shutup and calculation or orthodox interpretation), which just takes Born's rule, i.e., the probabilitist/statistical interpretation of the quantum state seriously, is all you need.

Everything else is, in my opinion, just not belonging to physics but to philosophy and thus may be interesting to think about and maybe it may help to understand QT (and particularly why the minimal interpretation is indeed all you need), but I doubt this a bit: It's rather confusing the meaning of QT as a physical theory than anything else.

For me the most relevant publications of the physical part of the "interpretation issue" are experimental quantum-optics/AMO papers, where the foundations are tested by real-world experiments, showing with overwhelming significance that the implications of minimally interpreted QT, particularly entanglement and the corresponding long-ranged correlations between far-distant parts of quantum systems, are the (so far only) correct description of how nature behaves, while deterministic local hidden-variable theories a la Bell are disproven through the violation of Bell's inequality.
 
Summary: Provided it's correct that the interpretations of Quantum Mechanics can be neither proved nor disproved why then do researchers invest so much time and talent in this field?
The founders of QM invested a lot of effort in trying to "understand" QM. With their failure to agree or reach a consensus the subject has become something of an anathema in mainstream professional literature. Which is understandable - since giants such as Einsten, Schrödinger, Heisenberg, De Broglie etc could not agree, why waste effort ourselves?

But, of course, physicists do want to understand QM, but they mostly conduct this effort in private. I know the challenge of understanding QM was the main reason I choose to study physics. In my sophomore year I settled on many worlds because, it seemed to me then (and still does), the only intepretation to yield clear, realist, unambiguous answers about reality, independent of observers. I'm sure a pilot wave advocate would say the same thing. (Not sure what a Copenhagenist would say..)

Physics is about finding a model of the world, not just a scheme that calculates the results of observations. When someone declares that all they require of physics is a calculational tool, I don't believe them, in the sense that if such an acceptable model was found, they would adopt it. The problem is that the models on offer all have some deficiencies:
1) pilot wave - pushes around the Bohm particle at FTL velocities, which many find anathema
2) many worlds - existence of parallel time lines, which many find anathema
3) copenhagen - denies reality between observations, which many find anathema.

Take your pick.
 
134
10
I think most of those, even though not all, working on the interpretations of QM hope to recover a classical world or at least a hidden variable and/or local theory which 'saves the appearances' and can be recast back into an intuitive understanding of reality that meets our human macroscopic perception and understanding. That is, an ontology that deals with by point-like particles moving in space-time along definite paths as our mind and senses are accustomed to think of, but QM seems to challenge. The De Broglie-Bohm and Many World Interpretation were quite successful in this sense. No entanglements, superpositions and strange 'spooky action at a distance' are necessary here, furnishing an ontology that dispenses with something our human understanding would like to avoid at any cost. Indeed, these show that, in principle, it is possible. If that has anything to do with reality remains to be shown. I think it hasn't and these attempts are more the sign of a psychological need than a scientific one and that reflect our human resistance to change. Such as the resistance to accept the heliocentric theory replacing the geocentric appearances.
 
That is, an ontology that deals with by point-like particles moving in space-time along definite paths as our mind and senses are accustomed to think of, but QM seems to challenge. The De Broglie-Bohm and Many World Interpretation were quite successful in this sense.
Many worlds does not have particles moving along definite trajectories. The wavefunction alone is deemed to correspond to reality, with no collapse postulate, just the unitary dynamics of time evolution. Since the time evolution equations are local and deterministic it follows that many worlds is also a local, deterministic theory.
 
Last edited:
134
10
Many worlds does not have particles moving along definite trajectories.
As far as I understand it has many definite (in the sense of deterministic) trajectories,
 
The splitting in many cases worlds is normally taken to occur at measurements or at any entropic event. If we use this criterion then the path of a particle through the double slit apparatus, for example, remains indefinite. The timeline splits when the particle is detected by a classical or macroscopic detector.
 
134
10
But, at the time of detection, doesn't it split in many timelines, for each possible projection of the state vector?
 
25,799
6,634
As far as I understand it has many definite (in the sense of deterministic) trajectories
The MWI has definite "trajectories" for the entire quantum system in its configuration space. But that is not at all the same thing as definite trajectories for each individual subsystem, or as a definite trajectory for the system in ordinary 3-space. So, for example, say we have a rock that undergoes an experiment in which quantum uncertainty is involved (for example, the radioactive decay of an atom determines whether the rock is diverted to the left or the right). Then, according to the MWI, there is a definite trajectory in the configuration space of the overall wave function of the system consisting of rock + radioactive atom, but there is no definite trajectory in ordinary 3-dimensional space for the rock itself.
 
But, at the time of detection, doesn't it split in many timelines, for each possible projection of the state vector?
No, it splits into many timelines, one for each possible state of the measuring device or some other macroscopic variable. So the double slit experiment splits according to the granularity of the photographic screen. But not according to all the possible paths (in the sum-over-histories sense) through the apparatus.
 

timmdeeg

Gold Member
888
56
Thanks for your responses.

The MW seem to require that the wave function is ontic. Would ontic versus non-ontic in principle make a tiny (not measurable) difference regarding the gravitational field of the particle before measurement?
 
9,112
2,031
No, it splits into many timelines, one for each possible state of the measuring device or some other macroscopic variable. So the double slit experiment splits according to the granularity of the photographic screen. But not according to all the possible paths (in the sum-over-histories sense) through the apparatus.
What a world is in MW's is not the same for everyone:

It does not necessarily split into many worlds, timelines etc - simply possible histories are treated on equal footing except for probabilities. This lead to the consistent/decoderent histories approach. But the point I am making is some like Gell-Mann think its basically the same as MW. Its one of the things that make QM interpretations a minefield. I may get some push-back saying this, but it's what Gell-Mann thought and probably others like Feynman and De-Witt.

Thanks
Bill
 
What a world is in MW's is not the same for everyone:
I've always found Gell-Mann annoyingly vague about the existential issues in 'his' version of MW.

But I agree, 'world' and 'split' mean what you want them to mean. The definitions I use (entropy release causes splitting) works for me because it makes world splitting an irreversible process. However they are just words; the core of Everett's conception is quite simple. The wavefunction represents reality and there is no collapse.
 

DarMM

Science Advisor
Gold Member
1,769
859
But the point I am making is some like Gell-Mann think its basically the same as MW.
I might not be understanding your meaning correctly, but he does say "only one of which occurs" when discussing entanglement. The other difference to me is that in decoherent histories the experimenter must choose the family of histories of which one element occurs.
 
9,112
2,031
I might not be understanding your meaning correctly, but he does say "only one of which occurs" when discussing entanglement. The other difference to me is that in decoherent histories the experimenter must choose the family of histories of which one element occurs.
Only one history occurs but before it occurs they all have the potential to occur - we only know the probability.

Thanks
Bill
 

DarMM

Science Advisor
Gold Member
1,769
859
Only one history occurs but before it occurs they all have the potential to occur - we only know the probability.

Thanks
Bill
Again this might be dumb, but don't we usually say that only one event or history (i.e. sequences of events) has the potential to occur prior to their occurance. What makes MWI different is precisely that they all occur. To me this seems unlike MWI.

Also would it not be more accurate to say prior to their occurance and given a complete context all the histories in that context/family have the potential to occur. Without a selected context I don't think one can discuss their potential to occur.
 
Again this might be dumb, but don't we usually say that only one event or history (i.e. sequences of events) has the potential to occur prior to their occurance. What makes MWI different is precisely that they all occur. To me this seems unlike MWI.

Also would it not be more accurate to say prior to their occurance and given a complete context all the histories in that context/family have the potential to occur. Without a selected context I don't think one can discuss their potential to occur.
Yes, in MWI all histories have occurred and all futures occur. This the essence of MWI. Gell-Mann, it seems, was never a MWorldist.
 

ftr

549
39
No entanglements, superpositions and strange 'spooky action at a distance' are necessary here, furnishing an ontology that dispenses with something our human understanding would like to avoid at any cost. Indeed, these show that, in principle, it is possible. If that has anything to do with reality remains to be shown. I think it hasn't and these attempts are more the sign of a psychological need than a scientific one and that reflect our human resistance to change. Such as the resistance to accept the heliocentric theory replacing the geocentric appearances.
I am not really quoting you to argue against it, I just want to comment differently. I think the goal of interpretation is very limited in the sense that science unlike religion (nothing against it) believes there is a natural reason for everything. Even if we assume as QM seems to say that the particles behave in a probabilistic way (no reason for its behavior) with undefined attributes before measurement, i.e. it just the way it is and don't ask why , but some don't like such stand and equate it with magic or religion faith type (that is don't ask why). OR at least if it is that way, they want to know why.
 
9,112
2,031
Again this might be dumb, but don't we usually say that only one event or history (i.e. sequences of events) has the potential to occur prior to their occurance. What makes MWI different is precisely that they all occur. To me this seems unlike MWI.
In the version of WWI most hold to, and Gell-Mann reefers to as what some very scholarly people hold to, MW is totally deterministic because its just governed by Schrodinger's Equation. All worlds occur simultaneously. But Gell-Mann does not like that, so has his variant. It's really decoherent/consistent histories but he thinks its basically the same as MW. The point is not which one is correct, I am these days heading toward the idea what interpretation you believe in etc doesn't really matter. Progress will be made and things that seem unclear now will be clearer. Just look at the difference between modern interpretations and Copenhagen. However like nowadays we have discussions about decoherence, we will have discussions about something else. As I jokingly said - turtles all the way down, I don't actually think it will be like that but what eventually comes to light who knows - to some extent at the moment we are groping in the dark. The minimum I think to make progress will be getting a better version of Quantum Gravity than the merely effective field theory one we now have. Of course, while its not generally talked about in pop-sci accounts, its likely all our theories are just effective. That needs to be rectified.

BTW I must add this is just my view - nobody really knows how things will pan out - understanding interpretations better may be the key - science is funny like that just like math is funny in the most seemingly useless looking mathematical result can turn out to be crucial in applications.

Thanks
Bill
 
9,112
2,031
It seems like that doesn't it. But as you know science is funny in that what seems useless can turn out to be critical. My views about interpretations is slowly evolving and I am coming around to the idea we need to make progress in resolving that all our theories are likely just effective eg what does EM being trivial tell us? But who really knows.

Thanks
Bill
 

Want to reply to this thread?

"What makes the interpretations of Quantum Mechanics so important?" You must log in or register to reply here.

Related Threads for: What makes the interpretations of Quantum Mechanics so important?

Replies
1
Views
3K
Replies
9
Views
3K
Replies
5
Views
912
Replies
47
Views
7K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top