Decoherence and the Dust Particle

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Discussion Overview

The discussion revolves around the concept of environmental decoherence, particularly in relation to the localization of a cosmic dust particle through interactions with photons. Participants explore the implications of decoherence on quantum states, the time frames involved, and the nature of measurement in quantum mechanics. The conversation touches on theoretical, conceptual, and mathematical aspects of decoherence.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about the purpose of decoherence, questioning what it resolves regarding macroscopic superpositions.
  • Another participant suggests that decoherence can occur within a time frame on the order of ##10^{-6}## seconds, particularly in interstellar space, but notes that in denser environments, such as room-temperature air, decoherence happens much more rapidly.
  • A different viewpoint posits that a single photon can induce decoherence, implying that the timeframe is dependent on the density of photons rather than a specific duration for interactions.
  • Concerns are raised about whether the time between interactions matters if multiple photons are required for localization, with a participant noting that a single interaction is not irreversible.
  • Discussion includes the idea that many particles in the dust may contribute to decoherence if the interaction with light is incoherent.
  • Another participant questions whether the excitation of a single photon affects the degree of irreversibility in localization, suggesting that it may only impact a small portion of the dust particle's mass.
  • Some participants express unease with the framing of decoherence as it relates to single particles versus ensembles, questioning the clarity of the problem statement.
  • One participant proposes that the theory of decoherence may reflect logical limitations rather than serving as a mechanism for state reduction, emphasizing the role of photon paths in localization.
  • Another participant highlights the relationship between quantum mechanics and logic, suggesting a deeper connection that is complex and challenging to articulate.

Areas of Agreement / Disagreement

Participants exhibit a range of views on the nature and implications of decoherence, with no clear consensus reached. Some agree on the potential for single photon interactions to induce decoherence, while others emphasize the necessity of multiple interactions and the irreversibility associated with them. The discussion remains unresolved regarding the fundamental nature of decoherence and its implications for quantum state localization.

Contextual Notes

Participants note limitations in understanding the role of decoherence in single versus multiple particle scenarios, as well as the dependence on specific conditions such as photon density and interaction coherence. There is also mention of unresolved mathematical aspects related to the Hamiltonian in quantum mechanics.

  • #61
bhobba said:
Basically - yes.

OK. Thanks Bill. I think I can make peace in my head with this general idea. If I'm understanding what you're saying, I should be able to envision decoherence as setting the allowed logical limits for parameters of state reduction, but I don't have to accept it as the "causative process" for that state reduction. I get the feeling that pursuing the point beyond that generality takes us into interpretational concepts that are not directly related to the formalism of theory, so I won't torture you with that discussion... today[emoji16].

Just an aside thought however... When I recognize that the state of the entire expanded system is reduced correspondingly as the dust particle becomes localized, it seems as though the logical ramifications could (should?) expand exponentially throughout large swaths of the universe. Yes?
 
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  • #62
Feeble Wonk said:
When I recognize that the state of the entire expanded system is reduced correspondingly as the dust particle becomes localized, it seems as though the logical ramifications could (should?) expand exponentially throughout large swaths of the universe. Yes?

No.

Thanks
Bill
 
  • #63
bhobba said:
No.

Thanks
Bill
Is this because the information regarding the photon emission is so minimal (and potentially reversible) relative to the localization of the dust particle?
 
  • #64
bhobba said:
No.

Thanks
Bill
...and yes I'm only asking in general terms. I strongly suspect that this is another one of those things that I'm not going to properly understand without the necessary command of the mathematics. I simply mean, is the reason that the state reduction not more expansive because the photon emission event is reversible in terms of the decoherence, or is it just because so little information is exchanged?
 
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  • #65
Feeble Wonk said:
...and yes I'm only asking in general terms. I strongly suspect that this is another one of those things that I'm not going to properly understand without the necessary command of the mathematics. I simply mean, is the reason that the state reduction not more expansive because the photon emission event is reversible in terms of the decoherence, or is it just because so little information is exchanged?

I gave the correct explanation. It mentions none of the things you mention. They have nothing to do with anything.

You are trying to reason linguistically and getting yourself very confused.

Please stop that because I will not respond any more.

Thanks
Bill
 
  • #66
Fair enough.
 
  • #67
Feeble Wonk said:
Fair enough.

Please note that Hobba and Neumaier are Ph.D. in mathematics so they don't have patience in dealing those below undergraduate in mathematics or physics. Advisers who are most patient are the rest like atyy or mfb. I guess the quantum physics forums have to be divided into two.. for undergraduates and for advanced laymen. We are advanced laymen who struggled for years reading many books. And because our professions are not mathematicians.. we want to ask direct question. In your case you asked: "When I recognize that the state of the entire expanded system is reduced correspondingly as the dust particle becomes localized, it seems as though the logical ramifications could (should?) expand exponentially throughout large swaths of the universe. Yes?". Only other advisers who are not Ph.D mathematicians can answer it. Also note Hobba and Neumaier hate the idea of wave functions as representing the objects in actual. They tend to think of the math only and really admit "They don't know" it's connection to reality.. hence both are Ensemblers.

Anyway. I'd like to know the answer to your questions too. So let's hope others ask it too. You are asking "is the reason that the state reduction not more expansive because the photon emission event is reversible in terms of the decoherence, or is it just because so little information is exchanged?" I think you are talking about the entanglement so complex that irreversibility is the norm.. but if wave function has ontology.. then indeed everything is reversible. In pure maths.. since you can't know or describe the environment because it's too complex.. then it's reversible. I think jilang has grasped this question and can comment. (I think it is a good idea that Hobba and Neumaier only deal with threads with Intermediate and Advanced and leave the B to the other Science Advisors with more patience. Thanks.
 
  • #68
cube137 said:
Please note that Hobba and Neumaier are Ph.D. in mathematics

I don't have a Phd in math - I have the equivalent of an Honours degree in applied math and computer science. I have partially completed a masters but had to give it away for various reasons. I am self taught in physics so know exactly what is required to understand this stuff. A few weeks of an hour or so study each night is all that's required to learn enough to understand the technical explanation I gave.

If you don't want to do that you will be in a constant state of confusion going around in circles trying to understand what can't be understood without it. I gave the correct explanation - all that is needed is to understand it.

You may think its a mater of patience. IMHO it isn't. It's that this stuff can't be understood on the terms you want to understand it - it can't be done - wishful thinking that someone with more patience will do it simply will not work. This is not just my view eg have a look at the likes MFB gave my posts.

cube137 said:
Also note Hobba and Neumaier hate the idea of wave functions as representing the objects in actual.

That's incorrect. But fits in with my observation you will not understand what's really being said if you don't know at least a smattering of the technicalities.

My ignorance ensemble interpretation is agnostic to such things.

Thanks
Bill
 
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  • #69
bhobba said:
I don't have a Phd in math - I have the equivalent of an Honours degree in applied math and computer science. I have partially completed a masters but had to give it away for various reasons. I am self taught in physics so know exactly what is required to understand this stuff. A few weeks of an hour or so study each night is all that's required to learn enough to understand the technical explanation I gave.

If you don't want to do that you will be in a constant state of confusion going around in circles trying to understand what can't be understood without it. I gave the correct explanation - all that is needed is to understand it.

You may think its a mater of patience. IMHO it isn't. It's that this stuff can't be understood on the terms you want to understand it - it can't be done - wishful thinking that someone with more patience will do it simply will not work. This is not just my view eg have a look at the likes MFB gave my posts.
That's incorrect. But fits in with my observation you will not understand what's really being said if you don't know at least a smattering of the technicalities.

My ignorance ensemble interpretation is anostic to such things.

Thanks
Bill

What is funny is you don't understand Feeble question when he asked:

"When I recognize that the state of the entire expanded system is reduced correspondingly as the dust particle becomes localized, it seems as though the logical ramifications could (should?) expand exponentially throughout large swaths of the universe. Yes?"

Yet you answered "no". Later you mentioned the question kinda doesn't make even sense. So you should have answered "Feeble what you said doesn't make sense".

Anyway. I have read your every thread in this forums for more than a day and already get the gist of it. I know what you meant when you stated that

"You have |a> representing the state of the photons, |b> the state of the dust particle. The combined state is u = |a>|b>. Due to interactions between the two described by a Hamiltonian and Schroedinger's equation that state changes. The equation is i∂u/∂t = Hu where H is the Hamiltonian. You solve it to get the state at any time t. Now what we find is this new state is no longer factorisable into the state of the photons and the state of the dust particle. They are entangled. However if we just observe the dust particle we find its in a mixed state of position ie |b> = Σpi |bi><bi| where each |bi><bi| is an eigenstate of position. This means it can be interpreted as having a definite position with probability pi. Note I have used the notation for a state |a> and |a><a| interchangeably. What a state is and what it means is explained in the references - that's one of the things you need to understand. You can't understand this without it."

I understood it. Now I saw Feeble Wonk has been participating for more than 3 years in this thread. So I think he understood it too. Therefore I'd like him to ask the question using the above language.

Feeble. When you asked "When I recognize that the state of the entire expanded system is reduced correspondingly as the dust particle becomes localized, it seems as though the logical ramifications could (should?) expand exponentially throughout large swaths of the universe. Yes?" Can you rephrase it using Hobba language. I'll tried. Is it like asking:

"When you only have a few |a> representing the state of the photons, and |b> the state of the dust particle. And the simple combined state is u = |a>|b>. Due to interactions between the two described by a Hamiltonian and Schroedinger's equation that state changes. Does the state expand exponentially throughout large swaths of the universe?"

Feeble. I'm confused by your question. What do you mean "Does the state expand exponentially throughout large swaths of the universe?". Please use more accurate questions.

I'm interested in your interests in decoherence and have the same questions as you do.
 
  • #70
cube137 said:
What is funny is you don't understand Feeble question when he asked:

Have you stopped to consider it actually doesn't make sense? Which it doesn't BTW eg exponential - where exactly that comes from beats me - actually it doesn't beat me - its a symptom of what I have been saying. This is my last comment in this thread - its serving no useful purpose and needs to be closed IMHO.

Thanks
Bill
 
  • #71
bhobba said:
Have you stopped to consider it actually doesn't make sense? Which it doesn't BTW eg exponential - where exactly that comes from beats me - actually it doesn't beat me - its a symptom of what I have been saying.
I think we should just drop it. It seems to be getting personal, and I certainly had no intention of that. By "exponential", I simply meant expanding rapidly. As I've confessed previously, my mathematical terminology is sadly lacking. For that matter, the entire reference to expansion is likely a misconception as well. Your point is taken.
 
  • #72
cube137 said:
Please note that Hobba and Neumaier are Ph.D. in mathematics so they don't have patience in dealing those below undergraduate in mathematics or physics. Advisers who are most patient are the rest like atyy or mfb. I guess the quantum physics forums have to be divided into two.. for undergraduates and for advanced laymen. We are advanced laymen who struggled for years reading many books.
Well, then some tip: If you invest such a long time in reading "many books", why then don't you read the right books? It's fun to read one or two popular-science books. The problem is that most of them are very bad. It's very difficult to write a good popular-science book also for experts in the field (and you should sort out any popular-science book not written by an expert in the field, i.e., a scientist working in it). So if you are willing to spend several years in reading books, read good textbooks. You'll need to study a lot of math first, then classical mechanics and some classical electrodynamics to get used to the mathematical tools, but that's fun too!
 
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  • #73
May I ask one basic question? Does a photon being emitted by a particle constitute a physical interaction (in terms of decoherence) in anyway comparable to a photon being absorbed by a particle?
 
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  • #74
Never mind. I think it might be best to start a different thread with a different mind set, and let this one die a merciful death.
 
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