Under the Microscope:Surely one of the strangest ideas ever produced by science is the many-worlds interpretation of quantum mechanics proposed in 1957 by Princeton University graduate student Hugh Everett III. In brief, the interpretation proposes that, whenever numerous viable possibilities exist, the world splits into many worlds, one for each different possibility, and each world then develops independently, writes Dr William Reville
No communication is possible between the worlds, and people living in these worlds (and splitting along with them) have no idea this is happening. Everything that can happen, does happen, somewhere. Begob - and some of you thought I was far out when I proposed it can be reasonable to believe in God! Originally dismissed by most physicists, Everett's idea has now become respectable. The work of Hugh Everett is described by Peter Bryne in Scientific American (December 2007).
The behaviour of matter at the atomic and sub-atomic level is described by quantum mechanics. Much of this behaviour appears very strange to our expectations, conditioned by observations of the macroscopic world. In the quantum world, particles exist in a superposition of states described by a mathematical formulation called a wave function. Erwin Schrodinger (1887-1961) was the first person to write down a wave function.
The wave function lists all the possible states and assigns a probability to each - the probability that this is the state we will detect if we measure the system. In other words, when we measure the system the quantum superposition of states suddenly collapses into a single member of the superposition.
This introduces the concepts of the observer and the observed. When no one is observing, a quantum system evolves smoothly as the superposition of states described by the wave equation. Once observed, the wave function "collapses" to the single observed state, ie, the act of observing changes the system.
This is called the Copenhagen Interpretation of quantum mechanics - Copenhagen because it was energetically championed by Niels Bohr (1885-1962), the famous Danish physicist. The Copenhagen Interpretation cannot explain the observer itself, but the Many-Worlds Interpretation introduced by Everett explains the whole observer-observed system.
Physicists are conventionally taught that the equations of quantum mechanics are relevant only in the quantum world and not in the macroscopic world. Everett took a radically different view. He made the observer an integral part of the system observed and introduced a universal wave function linking object and observer as part of a single quantum system. Everything is described quantum mechanically - large objects in our macro world exist in a superposition of states also. Everett did not need collapsing wave functions and no elements of superposition ever disappear. He derived a mathematically consistent theory of a universal wave function from the equations of quantum mechanics. Multiple universes naturally emerge as a consequence of his theory.
In Everett's treatment the observer's wave function splits at each interaction of an observer with a superposed object, the universal wave function having branches for each alternative in the object's superposition. Each branch has a copy of the observer, a copy that perceived one of those alternatives as the outcome. The mathematics of wave equations dictate that the branches do not influence each other and each embarks on an independent future. In other words, there are an enormous number of versions of you who have split off in the past from the path you are now on.
Many people find the Many-Worlds Interpretation disturbing, but polls show about half of the physicists who study this area believe the Many-Worlds Interpretation describes the world as it really is. However, many of these theorists prefer not to discuss the subject outside of their own circles.
The Copenhagen Interpretation of the measurement problem where a single outcome emerges and all other possibilities disappear is an effective but inelegant device. The maths of collapse does not emerge naturally and has to be added as a postulate that seems to violate the otherwise seamless flow of the wave function equation. "The model of reality in the Copenhagen Interpretation postulates that the mechanics of reality in the quantum world reduce to and find meaning only in terms of classically observable phenomena - not the reverse," Peter Byrne writes.
Everett couldn't accept the Copenhagen Interpretation. Everett's graduate adviser John Archibald Wheeler discussed his ideas with Niels Bohr but Bohr couldn't accept them. Wheeler persuaded Everett to abridge his PhD thesis on the topic in order to make it less controversial. Everett's work was later published in full.
Disappointed that his work was poorly received, Everett stopped working in the field and took up a position as a scientific adviser at the Pentagon. He became a heavy drinker, and, sadly, had little personal relations with his children. He died in 1982 at 51 and never saw the respect paid to his ideas by physicists.
I am not nearly knowledgeable enough in this area to have a firm opinion about the reasonableness of Everett's proposal, but I was always taken by the remark of biologist JBS Haldane: "I suspect that not only is the world queerer than we suppose, but queerer than we can suppose." William Reville is associate professor of biochemistry and public awareness of science officer at UCC - http://understandingscience.ucc.ie