Does retrocausality follow from logic?

  • #1
entropy1
Gold Member
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Main Question or Discussion Point

I can't remember where this subject came forward in my topics, so I created a new topic.

Suppose that:
  1. If X happens, we observe A, and:
  2. If Y happens, we observe B.
Could we then say:
  1. If we observe A, Y did not happen, and:
  2. If we observe B, X did not happen,
if we apply this to quantummechanical events {X,Y} and observations {A,B} thereof?

{X,Y} are exclusive, {A,B} are exclusive.
In case of binary events: X=¬Y and A=¬B.

And if we could manipulate the observation, would it then (logically) be possible to manipulate which event happened by doing so?

A way to manipulate the observation could perhaps be choice of measurement basis.

This is mainly logic applied to quantum mechanics.
 

Answers and Replies

  • #2
12,633
9,148
I can't remember where this subject came forward in my topics, so I created a new topic.

Suppose that:
  1. If X happens, we observe A, and:
  2. If Y happens, we observe B.
Could we then say:
  1. If we observe A, Y did not happen, and:
  2. If we observe B, X did not happen,
No, we can not. O.k. we can, but it is wrong. You imply a dependence and continue to argue based on this false assumption, hence everything below is wrong.
... if we apply this to quantummechanical events {X,Y} and observations {A,B} thereof?

{X,Y} are exclusive, {A,B} are exclusive.
In case of binary events: X=¬Y and A=¬B.

And if we could manipulate the observation, would it then (logically) be possible to manipulate which event happened by doing so?

A way to manipulate the observation could perhaps be choice of measurement basis.

This is mainly logic applied to quantum mechanics.
 
  • #3
entropy1
Gold Member
916
53
In my view, there is an issue with retrocausality:

Suppose A excerts a retrocausal influence on history H. Then, if this influence is excerted by free will in the present, then H will change, and history is subjective (because it adapts to the free will of A).

If H is objective it is as it is, and if A has excerted influence on it, A would have no free will, for H is objective and will not change.

If H is objective and A has free will, then there cannot be retrocausal influence.

So we have three properties that cannot hold all three: objectivity, free will and retrocausality.
 
Last edited:
  • #4
DrChinese
Science Advisor
Gold Member
7,242
1,053
Suppose A excerts a retrocausal influence on history H. Then, if this influence is excerted by free will in the present, then H will change, and history is subjective (because it adapts to the free will of A).
Retrocausal interpretations need not look like what you describe. The quantum future can be a monogamous participant in measurement context (one which consists of a component in the present, and one or more components in the future). That way, there are no paradoxes to consider (like killing your father - you cannot change the macroscopic past).

An example is entanglement swapping. You can entangle pairs of particles before or after they are detected. Because the results are quantum random, there is nothing that changes (to the eye anyway) which you switch from entangling before detection vs. after detection (maintaining what you call objectivity). You have full free will (as far as anyone knows).
 

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