The 7 Basic Rules of Quantum Mechanics

[strangerep]

You can proofread it now and post your comments here.

I'm still seeing the old version, so I'll wait for the new version to appear and then proofread it.

 

[A. Neumaier]

I'm still seeing the old version, so I'll wait for the new version to appear and then proofread it.

Strange. The new version is online for 18 hours. Maybe you got a cached version. Note that I only edited a few words in that sentence.

 

[PeterDonis]

The new version is online for 18 hours.

I'm seeing the new version.

 

[strangerep]

You can proofread it now and post your comments here.

It's still dated May 11, 2019, but I now see your modified sentence.
[ @Greg Bernhardt: is there a way for a "last-modified" date to be automatically included in these Insights, as well as the original date?]

I now replaced it by the more accurate

Even Ballentine 1998, who rejects rule (7) = his process (9.9) as fundamental, derives it at the bottom of p.243 as an effective rule.

I see no such derivation at the bottom of p243. Rather, the last paragraph on that page talks about how an imperfect apparatus could give rise to the "reduced" state eq(9.18) by environmental decoherence mechanisms. This is not a "non-destructive projective measurement" of the type addressed by Rule 7. Hence it is incorrect to link the two, as you currently do.

On p.241, Ballentine writes: ''Some evidence that the state vector retains its integrity, and is not subject
to any “reduction” process, is provided by [...]''. No state reduction is his basic credo that he wants to support here. He says on the next page that state reduction should produce a mixed state, (9.18), and on p.243 that in a spin recombination experiment, only the pure state (9.21) is compatible with the experimental results. This is his ''evidence''. Since there was no measurement at the point B/C of investigation - only unitary 2-state dynamics happens -, this is no surprise, anyone would agree. It is not a situation where state reduction should be invoked. Thus his ''evidence'' is bogus.

I think you misread Ballentine's sect 9.5. As I read it, Ballentine's point (starting at the 2nd paragraph on p242) is this: IF one supposed that all coherence were lost between the wavefunctions at points B and C, then the spin state should be (9.18), i,e., $$\rho^{inc} ~=~ \frac12 \; \Big( |+\rangle \langle +| ~+~ |-\rangle \langle -|\Big).$$ But then, the spin-recombination experiment (with sufficiently good apparatus) described on the rest of p242 and over onto the top of p243, would reveal one's error.

That's what he means by "evidence" (in my humble opinion, of course, since I'm not a mind reader, though neither is anyone else around here, afaik). In other words, IF one (mistakenly) assumed reduction at points B and C, the actual experiment furnishes evidence of one's mistake.

 

[A. Neumaier]

[ @Greg Bernhardt: is there a way for a "last-modified" date to be automatically included in these Insights, as well as the original date?]

Such an addition would be nice indeed.

 

[gill1109]

Continue reading...

I miss qBism as one of the interpretations. It is certainly is presently quite popular. It is a bit more than "shut up and calculate" because it is the claim that this is all that physics ought to do, namely tell an agent what they ought to believe given what they presently know.

I also read in the description of the Quantum Mechanics forum that there was a separate physics forum for Interpretations of Quantum Mechanics, but it seems that this never materialised.

So questions can be put about foundational issues, after all?

 

[bhobba]

So questions can be put about foundational issues, after all?

Of course, Gill. There is a very active subforum on the QM forum about foundational and interpretation issues. The only rule is our general rule against purely philosophical posts. It is recognised that it will occasionally be tough to avoid such problems, so mentors will keep an eye on it to ensure it doesn't get out of hand. I want to emphasise we have the philosophy rule, not because we are anti-philosophy on this forum. We had a sub-forum on it for many years. It just became low quality, and we do not have the mentors expert to ensure it is of the appropriate standard.

Arnold has recently posted an interesting paper on his interpretation:
https://www.physicsforums.com/threads/quantum-mechanics-via-quantum-tomography.1007993/

Thanks
Bill

 

[Demystifier]

a separate physics forum for Interpretations of Quantum Mechanics, but it seems that this never materialised.

 

[vanhees71]

WHAT? We've more postings about interpretation than about the "real" QT (pun intended)!

 

[PeterDonis]

I also read in the description of the Quantum Mechanics forum that there was a separate physics forum for Interpretations of Quantum Mechanics, but it seems that this never materialised.

Yes, it did:

https://www.physicsforums.com/forums/quantum-interpretations-and-foundations.292/

 

[Pari338]

The article is based on a first draft by @atyy and several improved versions by @tom.stoer. Other significant contributors to the discussions included @fresh_42, @kith, @stevendaryl, and @vanhees71.
I slightly expanded the final version and added headings and links to make it suitable as an insight article. Maybe the participants of the discussion 20 months ago can confirm their continued support or voice disagreements with this public version.

Nice i am new in physics its very helpful for me