Tuesday, May 19, 2020

Observation, collapse and circularity

The following four premises seem to be contradictory:

  1. An observation of an event E is caused by the event E.

  2. Observation causes collapse.

  3. What is observed is the collapsed state.

  4. There is no circular causation.

Here is my first attempt to get out of this, on behalf of those attracted to the observation-causes-collapse view. For concreteness, let’s suppose that we’re observing an electron in a mixed up-down spin state, and suppose that we observe that it’s in the up state. Distinguish these two events:

  • O1: Observing whether the electron is in an up or a down state.

  • O2: Observing the electron to be in an up state.

Then I think what the defender of observation-causes-collapse can say this: O1 causes the collapsed state which in turn causes O2. But this is rather strange. For O1 and O2 actually seem to be the same coarse-grained event, which makes that coarse-grained event be its own cause! Another way to see the problem is to note that O1 is the disjunctive event of observing the electron to be in the up state or observing the electron to be in the down state. But then O2 grounds O1: disjunctions are grounded in their true disjunct(s). But then O1 is causally prior to its grounds, which seems absurd.

A second attempt: deny (3). Compare Elizabeth Anscombe’s theory that an intention to ϕ in the successful case constitutes one’s knowledge that one will ϕ or Thomas Aquinas’s theory that God’s knowledge of the world is the cause of the world’s being as it is. On these cases, the direction of fit in the knowledge is reversed. Observation of quantum phenomena could be like that.

Third attempt: cut up an act of observation into two parts. Metaphorically speaking, we could imagine the mind querying the world: “Is the electron in an up or a down state?” In response, reality collapses, and the mind observes that reality is in an up state. Thus, we have a query event Q and an observation-proper O2. It is Q that causes collapse, and P is then the observation of the collapse. This solves the circularity problem, but strictly speaking it’s incorrect to say that observation causes collapse. Rather, it is the pre-observation query event Q that causes collapse. And if simultaneous causation is possible, then Q and O2 may be simultaneous.

I think the second and third attempts are the way to go, assuming we're keeping the basic idea behind observation-causes-collapse.

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