I The TSVF interpretation of quantum mechanics

Spathi
Gold Member
Messages
102
Reaction score
10
TL;DR Summary
..the density matrix of two WFs (one from the past, the other from the future) becomes not only diagonal, but also with only one 1 value on the diagonal
I have found information about the interpretation based on the two-state vector formalism (TSVF). I will try to retell in my own words what I saw, but I apologize in advance for not understanding many of the said.

It is usually considered that the wave function "collapses after measurement", i.e. the collapse goes from the past to the future. However, in fact, we can just as well consider that the measurement collapses the WF from the future to the past (i.e. firstly a unitary evolution goes from the future to the past, then a jump due to measurement, etc.).

The idea of weak measurements is based on the fact that you can simultaneously use two wave functions - the one from the past to the future and the one from the future to the past. This is called TSVF.

If you take TSVF and throw out the collapse, i.e. threat it as the MWI, but with two WFs, then you get an interesting thing. From these two WFs, we can make a matrix similar to the density matrix, and this matrix will have closed dynamics and obey the von Neumann equation.
So, if the usual density matrix simply becomes diagonal as a result of decoherence, then the density matrix of two WFs becomes not only diagonal, but also with only one 1 value on the diagonal. Thus, in this interpretation, it turns out that neither the collapse of the WF nor the existence of many universes is needed.

We can interpret this as follows: if we take two MWI trees, one branching into the future, the other into the past (this depends on the initial and final conditions), superimposed them on each other, as a result, one branch is coincided and this is the actual universe.

This looks a bit like the transactional interpretation, but I believe the TSVF interpretation is better, since it has determinism, while the transactional interpretation does not.

The idea of TSVF interpretation can be formulated as follows: after preparation and before measurement of the system, there is an intermediate state, and it is determined not only by the initial controlled actions of the experimenter, but also by the final result of the measurement.

What I have written above is a retelling of posts on the Internet forums, and I must say that I myself understand little here. As far as I understand, the TSVF interpretation combines the advantages of the Copenhahen and MW interpretations: it supports the determinism, and at the same time there are no multiple universes like in the MWI. Please help me understand more on this subject, and in particular I have a question - what is the density matrix?
 
Last edited by a moderator:
Physics news on Phys.org
Spathi said:
I have found information
Where? Please give a specific reference.
 
Spathi said:
I will try to retell in my own words what I saw, but I apologize in advance for not understanding many of the said.
That's why we need a reference.
 
PeterDonis said:
That's why we need a reference.
I am sorry, but I can't provide you with a good reference. The information in the op was told to me in a private talk with one person (I gave him money for consulting me in quantum physics).

Some information is provided in the Wikipedia:

https://en.m.wikipedia.org/wiki/Two-state_vector_formalism
 
Spathi said:
Please help me understand more on this subject, and in particular I have a question - what is the density matrix?
https://en.wikipedia.org/wiki/Density_matrix
The density matrix is an important concept in normal QM. You can define various density matrices in TSVF, but I am not convinced that those without a clear correspondence to normal QM are really needed or helpful.

What else do you want to know about this subject? I also asked a question about TSVF here some time ago:
https://www.physicsforums.com/threa...ric-formulation-of-quantum-mechanics.1059038/
 
Spathi said:
The information in the op was told to me in a private talk with one person (I gave him money for consulting me in quantum physics).
If he's not willing to make the information he's giving you public (the way scientists normally do that is in a peer-reviewed paper) so that other knowledgeable people can critique it, then (a) you shouldn't be paying him, and (b) we can't discuss it here.

Thread closed.
 
I would like to know the validity of the following criticism of one of Zeilinger's latest papers https://doi.org/10.48550/arXiv.2507.07756 "violation of bell inequality with unentangled photons" The review is by Francis Villatoro, in Spanish, https://francis.naukas.com/2025/07/26/sin-entrelazamiento-no-se-pueden-incumplir-las-desigualdades-de-bell/ I will translate and summarize the criticism as follows: -It is true that a Bell inequality is violated, but not a CHSH inequality. The...
I understand that the world of interpretations of quantum mechanics is very complex, as experimental data hasn't completely falsified the main deterministic interpretations (such as Everett), vs non-deterministc ones, however, I read in online sources that Objective Collapse theories are being increasingly challenged. Does this mean that deterministic interpretations are more likely to be true? I always understood that the "collapse" or "measurement problem" was how we phrased the fact that...
This is not, strictly speaking, a discussion of interpretations per se. We often see discussions based on QM as it was understood during the early days and the famous Einstein-Bohr debates. The problem with this is that things in QM have advanced tremendously since then, and the 'weirdness' that puzzles those attempting to understand QM has changed. I recently came across a synopsis of these advances, allowing those interested in interpretational issues to understand the modern view...
Back
Top