Does partial tracing make us see things that do not occur?

In summary, Partial tracing is a technique used to map large Hilbert spaces to smaller ones, particularly when dealing with unobservable degrees of freedom or a limited view of the environment. It is similar to the concept of Flatland, where inhabitants can only see two dimensions and may perceive non-existent intersection points. In quantum mechanics, measurable quantities can be calculated using partial tracing, such as entropy. However, there are open problems such as the measurement and ontology problems.
  • #1
Heidi
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Hi Pfs
Partial tracing maps what occurs in a big Hilbert space toward a smaller one. We have to use it when degrees of freedom are physically unobservable or when we have only a coarse grained view of the environment. it is like in Flatland , where the two dimensional inhabitants has no access to the third dimension. non they only see the shadows of what is above. for them non parallel lines always have an intersection point even if this point does not exist above them. They see this point !
Are there also for us things that we see and measure which are like these intersection points ( due to partial tracing)?
 
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  • #2
we know that particles do not follow trajectories but we see the pictures of charged particles in a magnetic field. Is it not the same for the notion of event? is the emition of a photon an event like those in our life?
 
  • #3
I guess you mean the tracks charged particles make in a cathode ray tube showing "classical trajectories" under the influence of electric and/or magnetic fields and which were used in the early 1900ds to check Einstein's special theory of relativity (e.g., by Kaufmann) vs. other electron-theoretical models (most famously Abraham's).

This is of course no contradiction to quantum theory and well understood since 1929:

N. Mott, The Wave Mechanics of alpha-Ray Tracks,
Proceedings of the Royal Society of London. Series A 126, 79
(1929), https://doi.org/10.1098/rspa.1929.0205
 
  • #4
Heidi said:
non they only see the shadows of what is above. for them non parallel lines always have an intersection point even if this point does not exist above them. They see this point !
I don't think that it's a good metaphor for partial tracing. Partial tracing is just a quantum analog of marginal probability computation.
https://en.wikipedia.org/wiki/Marginal_distribution
 
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  • #5
Heidi said:
Are there also for us things that we see and measure which are like these intersection points ( due to partial tracing)?
An example of measurable quantity calculated with the help of partial tracing is entropy.
 
  • #6
Heidi said:
Does partial tracing make us see things that do not occur?
It's actually the opposite, often partial tracing makes us not see things that occur.
 
  • #7
Yes partial tracing can give the entropy. It shows that at the beginning the entropy of the universe was very very low. it is what we calculate and "see". but is it an objective thing?
Rovelli has doubts. maybe it looks like that because WE are now in a peculiar region or we are peculiar observers. this low entropy correspond to our coarse grained point of view.

what are for you the open problems in QM?
 
  • #8
Heidi said:
Yes partial tracing can give the entropy. It shows that at the beginning the entropy of the universe was very very low. it is what we calculate and "see". but is it an objective thing?
Rovelli has doubts. maybe it looks like that because WE are now in a peculiar region or we are peculiar observers. this low entropy correspond to our coarse grained point of view.
Yes entropy is objective, and yes entropy depends on our coarse graining. I don't see a contradiction.

Heidi said:
what are for you the open problems in QM?
The measurement problem and (closely related) the ontology problem.
 
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FAQ: Does partial tracing make us see things that do not occur?

What is partial tracing?

Partial tracing is a technique used in quantum mechanics to calculate the state of a subsystem of a larger quantum system. It involves tracing over the degrees of freedom of the subsystem that are not of interest, in order to obtain information about the remaining degrees of freedom.

How does partial tracing affect our perception of reality?

Partial tracing does not directly affect our perception of reality. It is a mathematical tool used to analyze and understand quantum systems. It does not change the physical reality of the system, but rather helps us to better understand and describe it.

Can partial tracing make us see things that do not actually occur?

No, partial tracing does not create or fabricate any new information about a quantum system. It simply helps us to extract relevant information from a larger system. The results obtained through partial tracing are based on the physical reality of the system.

Are there any limitations to using partial tracing?

Yes, partial tracing is only applicable to quantum systems. It cannot be used to analyze classical systems. Additionally, it may not be suitable for all types of quantum systems and may not provide accurate results in certain cases.

How is partial tracing used in scientific research?

Partial tracing is used in various fields of research, such as quantum computing, quantum information theory, and quantum optics. It is a valuable tool for analyzing complex quantum systems and understanding their behavior. It is also used in experimental studies to interpret and analyze data obtained from quantum systems.

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