Journal Club #7

"So, if we watch a recording of a soccer match played a long time ago, the outcome is undetermined, not just if we are watching the match for the first time and never read about the outcome, but perhaps also if we've seen the match before and forgot about the outcome." - S. Mitra, from arxiv version of an essay called Changing the Past by Forgetting submitted to FQXi The Nature of Time essay contest.

Alas, not the winning entry, or I would have been kicking myself... But Mitra did win the February arxiv.org quant-ph article-for-discussion contest that goes on in my head. (Congratulations.)

It was tough decision this month. Diosi's paper, titled Does wave function collapse cause gravity?, was a strong second, and lost out only due to the gaping coffee and math deficits in my tiny sector of the multiverse. (Sorry.) Inhabitants of other sectors of the multiverse are highly encouraged to read this paper, as wave function collapse (which establishes the definite state of an object - one might even say it is the state that corresponds to an object bearing a distinct identity) is linked to gravity, which I have previously speculated might have something to do with the neurophysics of economically seaming the represenations of distinct objects together.

But back to Mitra's essay...

You got me with the first line - "As pointed out by David Deutsch, it is possible to experimentally disprove all collapse interpretations of quantum mechanics if one could make measurements in a reversible way." An idea previously discussed by this author as well. But not something about which you can simply declare "Oh, I did that" and expect to be believed. ;)

What gets me about this paper is that the erasure of memory is discussed as a 'unitary operator that disentangles the observer from the spin.' Come again? Are we talking about a complete, or a partial, disentanglement? Heck, why are we jumping straight to entanglement/disentanglement analogies for memory/forgetting in the first place? I've been really careful to avoid leaping to entanglement as an explanation for anything other than observable entanglement behavior between two particles.

The author's use of a 'machine observer' provides an opening to discuss ideal memory erasure, which is presumably not a condition that can be easily found in human observers. My predisposition is to map 'forgetting' from our existing understanding of neurochemical and/or neuroelectrical dynamics in the human observer, and see how that maps onto reports of a changed past. That work could be extended into blocking memory encoding to prevent a permanent 'entanglement' with a particular outcome state. But I digress...

If I'm reading the paper correctly, the author suggests the use of memory resetting to a backup (prior) state as an escape from a forthcoming disaster. "The observer facing disaster can thus be almost sure to escape the disaster by doing a memory resetting." Interesting... I've escaped the 'disaster' of not finding the items I was looking for while shopping by 'forgetting' that I had just witnessed the absence of the desired item. Although I've never really thought of it as 'forgetting', but rather as a 'shifting of attention' until that observation was no longer in short-term memory.

It also follows then that we would want to be careful about what type of observations we make, as they may prove to be 'unforgettable', thereby "trapp[ing] us in the wrong sector of the multiverse." Sometimes a lack of information is a good thing - think of it as 'degrees of freedom' in your ability to select an outcome state. ;)

One final note - all of the essays on The Nature of Time can be viewed here, along with the number of popular votes they received. I'd like to meet the person who actually read all of those essays before voting. I'm just saying - that's a lot of essays...