So much rubbish has been written about consciousness and quantum physics that I hesitate to wade into the morass. I nevertheless believe that something interesting and substantive may be gained by conducting thought experiments with respect to the relation of quantum physics and consciousness if we use the many-worlds interpretation (MWI) of quantum phenomena, as well as the experience of dreaming as the stand-in for consciousness.
Given that this is a thought experiment, I also consider it worthwhile bringing in some of the “possible worlds” philosophy developed by many modern philosophers to solve puzzles in modal logic, most especially the version developed by David Lewis.
But first MWI: According to the Everett version of MWI, every time a quantum experiment with different possible outcomes is performed (this arguably obtains for all phenomena exhibiting chaotic dynamics), all outcomes are obtained, but we see only one outcome; the one measured/observed in this world. The other outcomes actually occur but each in a different world!
These other unseen worlds are considered absolutely real. They obey the laws of physics just as our world does. When the experiment is performed and a measurement occurs, the current world is split off, or branches off into a new history. The new world is a duplicate of the parent world up to the last atom but it will have a new history, slightly different from and counterfactual to the parent world and beginning from the branching event itself.
For a branching event to occur, there must be suppression of coherence of the superposition of two localized wave-particle packets (decoherence) with respect to a quantum system’s evolving interaction with its internal and external environments. Once decoherence occurs, a branching event occurs and a new world is born.
A very big question is, can any of these worlds (whether in MWI or in Lewisian framework) interact with one another? Can signals be exchanged between worlds?
In the possible worlds framework developed by David Lewis and other philosophers, worlds cannot interact. Nor is it clear if MWI allows interaction between worlds. Some Everettian theorists seem to argue that the alternate worlds are so far away from Earth that information signals cannot be exchanged between the two worlds.
If no interaction is possible, then individuals are world-bound, and even though we have copies of ourselves in other worlds, they are mere counterparts of the individuals in the parent world. I have a counterpart in every daughter world I initiate — but even though my counterpart is identical to me in every respect, these counterparts are not "me," but mere counterparts.
There are some reasons to believe, however, that worlds can interact. As has been pointed out by others, if a counterpart has a brain identical to mine (and identical memories, etc.) then by the law of the identity of indiscernibles, the counterpart is me. As the counterpart develops a history that diverges from the parent world, anything is possible. Yet at the moment of inception, he must be me.
If he is me, then interaction must be possible as I can infallibly know what the other is thinking (at least at the inception of the branching event) and that is a genuine piece of knowledge about the other world.
Another reason to believe that signal exchange between worlds might be possible is the following: According to the possible worlds framework, to say that things could be otherwise for me is to say that there is literally a world where they are in fact different in a relevant way for me. But if no interaction with that other world is possible for me, then the fact that the alternative world actually exists in a relevant way is not available to me, and for all intents and purposes, freedom is an illusion and I live in a world of metaphysical necessity.
But my experience directly contradicts this supposition. I can form counterfactuals concerning my experience and do so every day (regardless of whether freedom is an illusion). It really does seem to be the case that things could have gone differently for me in myriad ways at virtually every instant of my life. Thus, if I accept my experience of free action and contingency in my life as real and if the many-worlds idea is correct, then some interaction between worlds must be permitted.
Now, suppose world-boundedness is incorrect — or at least can be relaxed as a constraint for both MWI and the possible worlds framework. What follows for the nature and functions of dreaming?
First, note that dreaming largely consists of counterfactual simulations of what might have been and what might be for the dreamer. A first default and easy hypothesis would be then that dreaming actually really depicts events occurring in a real alternate world unfolding from the initial branching event. Given that counterfactual simulations are constructions of alternate histories and futures for the dreamer, we ask: Where do these alternate histories occur? The most reasonable answer is, of course, they occur in the mind of the dreamer.
But this is a thought experiment, so we can ask: If the many-worlds framework is correct and dreaming consists of counterfactual simulations of what might have been and what might be for the dreamer in a world that branches off of the dreamer’s parent world, then is it possible that dreams actually depict what is going on in the life of my counterpart in the alternate world he lives in? If that is the case, then my dreams are portals into the life of one of these branching worlds predicted by the MWI.
If so, then we can further ask: What does the dreamer’s counterpart in the daughter world dream of? If you have a counterpart in an alternate world, he has dreams. What does he dream of? He is presumably dreaming of you (his counterpart) and your life’s events.
Is, therefore, your counterpart’s counterfactual simulations real accurate depictions of your actual life? In this case, we now have an answer to all those many philosophers who have asked, "is life but a dream?" The answer is literally yes; the dream of a counterpart to you who lives in a branching universe that is a daughter world to your world.
Under this scenario, the content of dreams would be simple perceptions of the lives of your counterparts who live in daughter worlds to your world, and the interpretation of dreams would be a simple matter of checking in with what is occurring in the lives of your counterparts as they are created each time a branching event occurs. Lucid dreams would be attempts to alter the histories of an alternate world, and so on.
Does this simple thought experiment teach us anything interesting about dreams? Yes, if the thought experiment has any veracity at all, it suggests that dreaming is a perceptual process more than it is a memory process.
Even if MWI and possible worlds are not realities and have no relevance for dreams, the thought experiment suggests that the extent to which counterfactual simulations occur in dreams suggests that we live as much in the imaginative, counterfactual realm of dreams as we do in the actual world. That is because our sense that our lives could have gone differently depends substantially on counterfactual simulations that occur every night in our dreams. But the thought experiment is built on so many tentative steps that it can only be considered at this point mere speculation, if not complete rubbish.