- #176

- 11,056

- 3,750

I still don't understand what is yourExactly, therefore their stability upon measurement is not complete and as you say depends on energy. This is my point.

**main**point behind all your posts about stability and measurement.

- A
- Thread starter ShayanJ
- Start date

- #176

- 11,056

- 3,750

I still don't understand what is yourExactly, therefore their stability upon measurement is not complete and as you say depends on energy. This is my point.

- #177

- 588

- 43

In QT as you now seem to acknowledge(in spite of your demonstrations on the contrary in #106) measurements are not completely stable, uncertainty and coupling constants are constantly adjusted to the relevant energy because of "the fact that directly measurable quantities (like scattering cross sections) depend on energy", my main point was this and also of puzzlement that even with this lack of stability measurements are possible and consistent, and we can matematically model idealized measuring tools that are conserved(intervals, inner products, etc).I still don't understand what is yourmainpoint behind all your posts about stability and measurement.

- #178

- 11,056

- 3,750

So they are notIn QT as you now seem to acknowledge(in spite of your demonstrations on the contrary in #106) measurements are not completely stable, uncertainty and coupling constants are constantly adjusted to the relevant energy because of "the fact that directly measurable quantities (like scattering cross sections) depend on energy", my main point was this and also of puzzlement that even with this lack of stability measurements are possible and consistent, and we can matematically model idealized measuring tools that are conserved(intervals, inner products, etc).

- #179

martinbn

Science Advisor

- 1,959

- 631

I am not sure what you're asking. They would be explained the usual way, pink and green socks always match.And how would non-local correlations be explained by local hidden variables?

No, because he is considering a hypothetical scenario that we are in 1920 but have QM experimental results, there is no Bell yet.It can't be explained in this way since the Bell inequality (and related theorems) are violated by QT, and experiment shows that QT is right but not local HV theories.

- #180

- 11,056

- 3,750

But Bell theorem, that certain type of correlations cannot be explained by local hidden variables, does not depend on knowledge of quantum mechanics. A good probability theorist could have derived it in the 19th century. One of Bell's points is precisely that such correlations areI am not sure what you're asking. They would be explained the usual way, pink and green socks always match.

No, because he is considering a hypothetical scenario that we are in 1920 but have QM experimental results, there is no Bell yet.

- #181

- 588

- 43

It is, and that's why I keep asking how is the instability kept small in a random quantum context for measurement dynamics so that it is quite stable for practical purposes. You said because of interactions, and in a way I guess the couplng constants are stable enough in practice as they run very slowly for different energies, but I would like to know the mechanism as it doesn't seem to be explained by the quantum axioms and principles.So they are notcompletelystable, but they arequitestable. Isn't that enough for most practical purposes?

- #182

- 11,056

- 3,750

Exactly!and in a way I guess the couplng constants are stable enough in practice as they run very slowly for different energies

- #183

- 16,165

- 7,495

- #184

martinbn

Science Advisor

- 1,959

- 631

I see, we are in 1920, there is no QM yet, there are lucky experiments that show the unexplained QM results, and we know Bell's theorem.But Bell theorem, that certain type of correlations cannot be explained by local hidden variables, does not depend on knowledge of quantum mechanics. A good probability theorist could have derived it in the 19th century. One of Bell's points is precisely that such correlations arenotlike matching socks.

Then it will be a very big puzzle for the physicists, but in my opinion they will not find the action at a distance the most popular approach.

I am guessing that is your point, the they must conclude that there is some instantaneous action.

- #185

- 11,056

- 3,750

Yes.I am guessing that is your point, the they must conclude that there is some instantaneous action.

- #186

- 16,165

- 7,495

- #187

martinbn

Science Advisor

- 1,959

- 631

His point is that at the time relativity was relatively new and not so firm in their way of thinking so there would have been at least some who would consider the possibility of action at a distance.

- #188

- 16,165

- 7,495

- #189

- 11,056

- 3,750

That leads to another interesting counter-factual question. How would Einstein interpret QM today, after being familiar with Bell theorem and experiments that rule out local hidden variables?

- #190

- 16,165

- 7,495

(a) Einstein maybe could get more and more convinced that Q(F)T might be more complete than he thought when writing the EPR paper

(b) Einstein maybe could think that Q(F)T is even worse than he thought when writing the EPR paper and the more vigorously look for a classical unified field theory, but then knowing that he'd look for a non-local theory, which doesn't simplify the task.

That's of course speculation ;-).

- #191

- 89

- 24

Let's pick some simple example, say, measuring a normalized state a|0> + b|1> in the computational basis. There is no repetition, nor are there many identically prepared states. You make the measurement exactly once.So what can ensemble interpretation say about the measurement problem of single measurements?

What the ensemble interpretation says is that the rules of quantum mechanics describe the statistical behavior of a

What this says about a measurement problem depends on what one found problematic about measurements in the first place. In any event, it seems to me that the ensemble interpretation is not an "interpretation" in the same vein that many worlds or Bohmian mechanics are interpretations. It doesn't aim to provide a "classical" underlying model whence the laws of quantum mechanics follow. The goal is to provide a well-defined shut-up-and-calculate recipe. As such, it is compatible with a hidden variable model should one desire one, such as the Bohmian mechanics I believe you favor.

- #192

- 16,165

- 7,495

- #193

- 588

- 43

Ok, but the what is hard to understand is that the probability ineherent in nature due to QT has nothing to do with the error analysis of the measuring apparatus when one starts from the premise that measurements apparatus are part of nature and are therefore also quantum, and also when the Born rule is as much about probability as about measurements and doesn't distinguish measuring devices from other objects. , so why would one separate quantum measurements from the costruction of the measurements devices, are these devices not quantum perhaps, is there something in their construction or their functioning that scapes QT?

Last edited:

- #194

- 16,165

- 7,495

- #195

- 588

- 43

You said that defining a measurement accurately enough to be of use(measurement uncertainty) has nothing to do with the probability inherent to nature in QT, why is this if measurement devices are as quantum as anything else? Measurements are a kind of interactions, are these interactions not quantum?

- #196

- 16,165

- 7,495

- #197

- 588

- 43

I wouldn't formulate the question in such classical terms, as they can be very misleading by suggesting small balls and trajectories. I don't see any problem in principle to have a measurement apparatus that can measure a quantum field configuration that localizes its strength to an accuracy corresponding to the energy employed, much like colliders do.where is in your opinion a principle problem with being able to construct a measurement apparatus that measures, e.g., the position of an electron very accurately?

But this is not related to my question why would quantum measurement uncertainty have nothing to do with the inherent quantum uncertainty/probability.

- #198

- 16,165

- 7,495

- #199

- 588

- 43

- #200

- 588

- 43

But my quible was that no matter how small the instability or the drift is it should build up with time for the measuring tools, increasing the error instead of kipping it constant since it would be a systematic error, at least according to Schrodinger's equation. Instead of that quantum statistical mechanics mixes this uncertainty with the random error inherent to the statisitical atomic theory and cancels out the uncertainties so that they are not distinguishable from the randomization in classical statistical mechanics except for the different distributions that are obtained in the cases with spin.Exactly!

So as a matter of fact between measurements the uncertainty and the dispersion increases in a deterministic and systematic way as shown in the Schrodinger equation and its dispersion relations, and we are left with the not for well known less puzzling situation that if we don't look the uncertainty builds up regardless of the considerations of quantum statisitical mechanics but if we look(performing consecutive measurements) the uncertainty is stable and keeps a stable macroscopic picture.

- Last Post

- Replies
- 15

- Views
- 4K

- Last Post

- Replies
- 4

- Views
- 3K

- Replies
- 2

- Views
- 2K

- Last Post

- Replies
- 312

- Views
- 32K

- Replies
- 22

- Views
- 1K

- Replies
- 19

- Views
- 4K

- Replies
- 51

- Views
- 7K

- Replies
- 3

- Views
- 1K

- Last Post

- Replies
- 17

- Views
- 1K

- Replies
- 45

- Views
- 9K