# Wave function of an observer, 'always collapsed'?

• dmtr
In summary, the observer can always be completely described by a bit string, while everything else only by a qbit string.
dmtr
Would it be correct to say, that the observer's wave function is 'always collapsed'? I.e. that the observer can always be completely described by a bit string, while everything else only by a 'qbit string'.

For practical reasons, yes

If you are asking on the fundamental level, then it is interpretation dependent.

In collapse theories, like CI, answer is "YES", but nobody could ever explain why some configurations of atoms are "observers" while others are not.

In non-collapse theories, the answer is N/A :)

dmtr said:
Would it be correct to say, that the observer's wave function is 'always collapsed'? I.e. that the observer can always be completely described by a bit string, while everything else only by a 'qbit string'.

First I would like to ask what you mean by "the observers wave function".

1) if you are considering a second observer then the original observer is just a sub-system just like any other system, and can generally be in superposition with respect to the third observer. The practical exceptions to this are IMO special cases, where the first observer has enough confidence in his state to be questioned by the second observer without beeing destabilized and eventually reach a steady state where the original observers is in equilibrium with it's closest environment (but then you are ignoring the equilibration process, which may be acceptable for practical purposes in cases where it's almsot instant)

2) OTOH, if you are considering something like the observers description of himeself, I don't think that doesn't make much sense since from the inside view, all there is IMO is a view of the outside. Ie. all that is one the inside, is an image of the outside. So the image of the outside, "IS" more or less the identity of the observer if you see in the sense of Zureks (what the obsever is, is indistinguishable from what the observer knows)

3) if you are considering some kind of birds view of the observer, then I really don't know what you mean as I see no realizable physical setup that corresponds to that situation except for special cases. In a sense the human laboratory is almost like a birds view of what is going on inside an accelerator. But again this is a special (limiting case).

dmtr said:
the observer can always be completely described by a bit string

Assuming (1) above, I would choose to say no. The yes case, is IMO a special case, not a general rule.

/Fredrik

Dmitry67 said:
For practical reasons, yes

If you are asking on the fundamental level, then it is interpretation dependent.

In collapse theories, like CI, answer is "YES", but nobody could ever explain why some configurations of atoms are "observers" while others are not.

In non-collapse theories, the answer is N/A :)

Why N/A? It seems to me, that the observer can be completely described either by a bit string or a qbit string. There are simply no other choices. And it should not be interpretation dependent. If the answer is "YES" in the CI it should be "YES" in the MWI as well (of course that would be different string in each 'branch').

There is a reason why it is interesting. If a bit string or a qbit string is associated with an observer, the statistical mechanics can be applied to it, thus defining entropy, temperature, etc.

To Fredrik: A second observer view (1) is not really interesting (for the reasons you've mentioned). So I'm considering (2), the observers description of himself, identity.

N/A because:
1. In non-collapse, there is no difference between the observers and any other systems. And clearly, you see that not all systems are always 'collapsed'
2. If there is no collapse, how you can ask if wavefunction is 'collapsed'?
3. I am not sure that observer can observe itself *to the full extent* - https://www.physicsforums.com/showthread.php?t=337197

Dmitry67 said:
N/A because:
1. In non-collapse, there is no difference between the observers and any other systems. And clearly, you see that not all systems are always 'collapsed'
2. If there is no collapse, how you can ask if wavefunction is 'collapsed'?
3. I am not sure that observer can observe itself *to the full extent* - https://www.physicsforums.com/showthread.php?t=337197

I guess it should read 'always collapsed from the point of view of the observer'. But you are right this 'wavefunction collapse' talk IS interpretation depended, so it is best to avoid it.

On the other hand it seems to me, that the requirement to use bits or qbits in the description of the observer should not depend on the interpretation.

dmtr said:
To Fredrik: A second observer view (1) is not really interesting (for the reasons you've mentioned). So I'm considering (2), the observers description of himself, identity.

dmtr said:
There is a reason why it is interesting. If a bit string or a qbit string is associated with an observer, the statistical mechanics can be applied to it, thus defining entropy, temperature, etc.

It sound like if you have an idea looking for some way of the observer to do instrinsic "statistics" and thus define a subjective entropy etc, making them subjective quantities, and thus make statistical inferences?

I support that quest, but IMO there is no answer to it(assuming I read you right) within the standard framework, making the discussion unsuitable for this thread I suppose?

Also I agree with Dmitry that self-observation might need clarification. I'm not sure what you mean. In one sense, querying yourself as a whole doesn't make sense, unless you consider partial observations in the sense of internal processes. But I think the general case is much more complex than eithre a bitstrong only or a qubit string only.

But for the simplest possible intrinsic starting point, which I like to think of as distinguishability, a classical bit seems more fundamental since it contains much less information that a qubit they way I see this.

/Fredirk

## 1. What is the wave function of an observer?

The wave function of an observer refers to the mathematical representation of the state of a system in quantum mechanics. It describes the probability of finding a particle or a system in a particular state at a given time.

## 2. What does it mean for the wave function to be "always collapsed"?

When we say the wave function is "always collapsed," it means that the observer's interaction with the system causes the wave function to collapse into a single state or outcome. This is known as the collapse of the wave function and is a fundamental concept in quantum mechanics.

## 3. How does the wave function of an observer differ from the wave function of a system?

The wave function of an observer is different from the wave function of a system because it takes into account the observer's role in measuring the system. The wave function of a system only describes the state of the system itself, whereas the wave function of an observer includes the observer's perspective and interaction with the system.

## 4. Can the wave function of an observer be measured or observed?

No, the wave function of an observer cannot be directly measured or observed. The wave function is a mathematical concept used to understand and predict the behavior of quantum systems, and it does not have a physical manifestation that can be observed.

## 5. Are there any theories that explain the collapse of the wave function?

There are various interpretations and theories that attempt to explain the collapse of the wave function, such as the Copenhagen interpretation and the many-worlds interpretation. However, there is currently no widely accepted explanation for the collapse of the wave function.

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