Evidence of Parallel Worlds

Evidence of Parallel Worlds

Despite the fact that the Everett approach is the only realist interpretation of quantum mechanics, it will not be accepted by the scientific community until it has made a novel prediction which can be verified. Quantum suicide is one way of doing this, provided that you believe you will become all of the observers present after a quantum interaction and not just one. There would be no way to convince others, however, without them playing a game of their own.

The first experimental test used to falsify the collapse approach was suggested by Deutsch in 1985 (Deutsch, 1985, pp.1-41), however it is still not practical to implement as it requires artificial intelligence (AI) and reversible nano-electronics (Deutsch, 1985, pp.1-41 and Deutsch, 1986, pp. 204-214).

In Deutsch's thought experiment, an atom, which has a determinate spin state in one axis, 'left' for example, is passed through a Stern-Gerlach apparatus which has the possibility of measuring it in another axis, as either spin 'up' or spin 'down' in this case. This means that the atom is then in a superposition of 'up' and 'down' states from the perspective of an observer who has not yet become entangled with it. This superposition travels to the AI's artificial 'sense organ'. Here it is provided with two options, it may be detected as either spin 'up' or spin 'down'. The AI's conscious mind then records the result. The collapse approach predicts that this will cause the atom to collapse into one determinate state, with either a determinate 'up' or 'down' (but not 'left' or 'right') spin. The Everett approach predicts that the mind will branch into two, one mind will record up and one down (but neither will record 'left' or 'right').

The whole process is then reversed so that the atom emerges from the entrance to the Stern-Gerlach apparatus and the mind forgets which result it recorded. This process does not erase any of the AI's other memories however, including the memory that they did record the atom to be in a definite state. If a 'left-right' detector was placed at the entrance of the Stern-Gerlach apparatus then the collapse approach predicts that it will be detected as being in either a 'left' or 'right' state with equal probability. If the Everett approach is correct then the atom will be in the same state that it was in before the measurement, it will still have a 'left' spin.

Deutsch argued that "this experiment allows the observer to 'feel' himself split into two branches: The interference phenomenon seen by our observer at the end of the experiment requires the presence of both spin values, though he accurately remembers having known at a previous time that only one of them was present. He must infer that there was more than one copy of himself (and the atom) in existence at that time, and that these copies merged to form his present self" (Deutsch, 1985, pp.1-41).

Vaidman described a similar experiment in 1998 (Vaidman, pp.254). If a photon passes through a polariser which has the possibility of sending it in two different directions, towards detectors A or B, then experiments show that it will be detected at either one detector or the other, but not both. If we remove detector A then the photon is only detected at B half of the time. Vaidman suggested that we could falsify the collapse approach by reversing the process, as Deutsch suggested, and observing how often the photon is 'recomposed'. The collapse approach predicts that a photon will only be detected at the source half the time, yet the Everett approach predicts that it will be detected every time because the photon arrives from both paths whether it was detected or not.

There are also arguments in cosmology that could falsify the collapse approach. In 1970, DeWitt argued that there would be a time before Everett's universal wavefunction had decohered and we may one day be able to test for this (DeWitt, pp.30-35). In 2000, Page suggested that the Everett approach can be empirically verified because some cosmological observations are more probable given Everett's approach (Page, pp.225-232).

These experiments will not falsify the Bohm approach because Bohm also suggested that there is no collapse of the wavefunction and so the probabilities will be the same for their approach as for Everett's.

German physicist Rainer Plaga devised an experiment to falsify the Bohm approach in 1997 (Plaga, pp.559-577). Plaga argued that it should be possible to communicate with other parallel worlds if we could repeat Deutsch's experiment and isolate part of the apparatus so that it can be changed before it has completely decohered.

Palga suggested that "a 'gateway state' between the parallel worlds" (Plaga, pp.564) could be achieved by isolating a single ion. An observer can then divide, having set the apparatus to only excite the ion if they record a certain result. If the ion is excited and they do not record that result then they can assume that the atom was excited by their parallel-self. If the Bohm approach is correct, then parallel worlds do not exist and so we cannot communicate with them. This means that the ion will never be excited unless we observe the correct result. Palga argued that "inter-world communication on a time scale of minutes should be possible with state of the art quantum-optical equipment" (Plaga, pp.573).

References

Deutsch, D., 1985, 'Quantum Theory as a Universal Physical Theory', International Journal of Theoretical Physics, Vol.24

Deutsch, D., 1986, 'Three experimental implications of the Everett interpretation', Quantum Concepts of Space and Time, Penrose R. and Isham C.J. (eds.), The Clarendon Press, Oxford

DeWitt, B. S. M., 1970, 'Quantum mechanics and Reality', Physics Today, Vol.23

Page, D., 2000, 'Can Quantum Cosmology Give Observational Consequences of Many-Worlds Quantum Theory?', American Institute of Physics Conference Proceedings, Vol.493

Plaga, R., 1997, 'Proposal for an experimental test of the many-worlds interpretation of quantum mechanics', Foundations of Physics, Vol.27

Vaidman, L., 1998, 'On Schizophrenic Experiences of the Neutron or Why We should Believe in the Many-Worlds Interpretation of Quantum Theory', International Studies in the Philosophy of Science, Vol.12, pp.245-261