I needed something to purge all the coverage of prostitutes, political sniping, and chaos from my mind and hence thought I’d write about a problem in quantum physics.
Although quantum physics has enjoyed numerous successes as a theory, one major remaining problem is determining how the world we experience is connected to the quantum states alleged by the theory.
In more detail, here is the problem: in quantum theory the states of particles are expressed mathematically as wave functions. One common example is that of location. Intuitively, a particle can only have one location at a single time. But, just as an ocean wave can combine with another wave, a wave function can be added to another wave function and this creates a state known as superposition. In the case of location, this can be expressed in terms of probabilities. For example, a particle might have a 25% chance of being at location A and a 75% chance of being at location B.
In the world of experience, when someone goes to determine the location of a particle, it will be found to have a definite location (in the example, A or B). The challenge is explaining the metaphysics behind this. In philosophical terms, the problem is how to explain the foundation of probability and chance.
The standard answer in physics is the Copenhagen Interpretation proposed by Niels Bohrs and some other thinkers. The explanation is that people and our scientific particle location devices exist in the classical realm (in the Newtonian and not the Coke or Macintosh sense of “classic”).
On this view, when you or I set out to determine the location of a particle, the observation causes (somehow) the wave function to be resolved. Crudely put, the dice are rolled and the particle is “placed” at location A or B.
Exactly how this works is obviously quite a mystery. In fact, this sort of thing was originally intended to show that Quantum physics is absurd (the famous Schroedinger’s Cat thought experiment was created for this purpose).
Hugh Everett called this “solution” to the problem “a philosophic monstrosity.” That seems reasonable-it certainly seems to fail to provide an adequate account. Further, it creates a dual reality account that seems to be rather inelegant and probably has interaction problems on par with the classic mind-body problem.
Everett proposed a rather science fiction type solution. Rather than have a dualistic reality (quantum and classic) he proposed a single type of reality-everything is quantum in nature. This entails, on his view, that for each supposition there is a world for each possibility. In the particle example mentioned above, there would be two worlds: one, let us call it World One, in which the particle is located at A and one, let us call it World Two, in which the particle is located at B. Naturally, each world contains an observer who sees the particle as it is in his/her world. The observers, obviously enough, do not see the other world. From the perspective of the person in world One, the particle had a chance of being at A or B but was, in fact, at A. From the perspective of the person in World Two, the particle could have been at A or B but was, in fact, at B.
While this view is interesting, it does have many problems.
First, there is what David Lewis dubbed as the “incredulous stare” response to his own proposal about multiple worlds. It just seems intuitively odd to accept that each possible quantum state has its own world-for all the untold (possibly infinite) possibilities. That seems, as one might say, insane.
Second, and more seriously, there is the obvious metaphysical problem: from what do these worlds arise? Accepting their existence would seem to involve accepting ex-nihilo creation (getting something from nothing). That is, to say the least, problematic.
Third, this view has implications for such matters as free will and ethics. This model seems to indicate that each possible state is real and hence everything that could have happened did happen (sometimes in other worlds, sometimes in this one). As such, I do not chose, I simply branch. Since each possibility has to occur, then I cannot be blamed (or praised) for any action I take (or fail to take). If I could chose, then (in theory) some possible states would not be real states in some other world. But, by hypothesis, to be a possible state is to be a real state in this world or another. Since, as Kant argued, ethics requires free will, then ethics would be right out. This obviously does not prove the theory is false-it might be true.
Fourth, this theory has profound implications for personal identity. If every observation causes me (and the world) to branch, then which one is the real me? By hypothesis I am unaware of the other Mike’s in the multitude of branches. As such, on many theories of personal identity, they would not be me and I would not be them. Also, intuitively, they are not me and I am not them. It could be argued that we (me?) form some sort of trans-world person. This is odd, but not the oddest theory I’ve considered.
Tying this back to ethics, this also raises the problem of responsibility. Consider a case in which a person does an immoral action but could have decided not to do it. In the usual view of responsibility, the person would be held responsible because he did the action. This can apply to the many worlds view in a way-in this world, he took the action and is hence responsible. But, as argued above, he could not have done otherwise-this is the world where he does it. In some other world or worlds, he (or the branch of him) did not do it and hence is not responsible. But, unless he gets to chose the world he is in which he cannot, for the reason give above) he cannot really be held accountable-he did not chose to do it. He had to do it because of the nature of reality. It could be said that he could have done otherwise-but on this view that just means that a branch did not do it. That hardly seems to count as choice. That would be like ascribing choice to dice.
One final point is that this view has interesting implications for religions with an afterlife. When a person dies, what happens? Which branch would be rewarded for which good deeds and which punished for which bad deeds? Or perhaps they would all get gathered up into one entity and all the sins and good deeds would be tallied and weighed. Would each branch person get a distinct reward and punishment? Well, it would certainly take an omniscient being to sort all this out.
For more about the Many Worlds view, I’d suggest “The Many Worlds of Hugh Everett” by Peter Byrne in Scientific American, December 2007 pages 98-105. The article does an excellent job of presenting the theory as well as telling the somewhat sad story of the man behind the theory.
Perhaps the best account of possible worlds in philosophy is On the Plurality of Worlds by David Lewis.