10th November, 1998
Does the 'many-worlds' interpretation of quantum mechanics imply immortality?
18 Harcourt Terrace
London SW10 9JR
The Everett 'Many Worlds Interpretation' of quantum physics postulates that that all systems evolve according to the Schrödinger equation, whereas the more conventional Copenhagen Interpretation says that this is true until the moment of observation, at which point the equation 'collapses'. The proposed paper examines some philosophical questions arising from the MWI interpretation. From the Tegmark (1997) 'quantum suicide' experiment and the Stapp (1998) analysis of the quantum effects on calcium ions in neural synapses, MWI may imply a 'Quantum Theory of Immortality' (QTI).
The 'Many-Worlds' Interpretation of Quantum Physics
First, a disclaimer for those new to the subject: Niels Bohr, the founder of modern quantum theory said, "Anyone who is not shocked by quantum theory has not understood it". And he didn't know about the Many-Worlds Interpretation (MWI). The quantum mechanics (QM) presented here is quite mainstream, even though it still seems crazy to physicists, who have no choice but to accept it. The major assumption I have made is to adopt Everett's (1957) MWI, which is just one of half a dozen competing interpretations of QM. According to various polls, MWI and the original 1927 'Copenhagen Interpretation' now have a similar share of the votes among physicists, but many of the 'big names' (Hawking, Feynman, Deutsch, Weinberg) are said to (Price, 1995) have subscribed to the MWI.
The weirdness of quantum physics can be seen in the famous parallel-slit experiment. This shows that individual photons seem to split into two particles which can nevertheless interfere with each other as if they were waves. The 'Copenhagen Interpretation' of the phenomena and the equations which describe them, agreed at the 1927 Solvay conference, essentially says that the 'wave packet' somehow associated with a particle 'collapses' when it is observed - this necessitates a relationship between the observer's consciousness and the particle. The MWI, on the other hand, holds that the equations used to predict quantum mechanical events continue to hold after observation - it is just that all things happen simultaneously, but due to 'decoherence' we do not actually see, for example, a radioactive source both decay and not decay. For an explanation of how this implies parallel universes, see Vaidman (1996).
There is one way of proving that the MWI is true and the Copenhagen and other interpretations are wrong. Unfortunately, the experimenter can only prove it to himself, and never persuade anyone else of its validity.
The Tegmark 'Quantum Suicide' experiment
Tegmark (1997) describes the 'Quantum Suicide Experiment' as follows (I have simplified the text and removed the mathematical proofs):
The apparatus is a "quantum gun" which each time its trigger is pulled measures the z-spin of a particle [particles can be spin up or spin down, seemingly at random]. It is connected to a machine gun that fires a single bullet if the result is "down" and merely makes an audible click if the result is "up".... The experimenter first places a sand bag in front of the gun and tells her assistant to pull the trigger ten times. All [QM interpretations] predict that she will hear a seemingly random sequence of shots and duds such as "bang-click-bang-bang-bang-click-click-bang-click-click". She now instructs her assistant to pull the trigger ten more times and places her head in front of the barrel. This time the "shut-up-and calculate" [non-MWI interpretations of QM] have no meaning for an observer in the dead state... and the [interpretations] will differ in their predictions. In interpretations where there is an explicit non-unitary collapse, she will be either dead or alive after the first trigger event, so she should expect to perceive perhaps a click or two (if she is moderately lucky), then "game over", nothing at all. In the MWI, on the other hand, the ... prediction is that [the experimenter] will hear "click" with 100% certainty. When her assistant has completed this unenviable assignment, she will have heard ten clicks, and concluded that the collapse interpretations of quantum mechanics [all but the MWI] are ruled out to a confidence level of 1-0.5n ˜ 99.9%. If she wants to rule them out "ten sigma", she need merely increase n by continuing the experiment a while longer. Occasionally, to verify that the apparatus is working, she can move her head away from the gun and suddenly hear it going off intermittently. Note, however, that [almost all instances] will have her assistant perceiving that he has killed his boss.
What this means is that, in most universes, there is one less experimenter, but the experimenter herself does not experience death.
The QTI is formed by reformulating the 'Quantum Suicide' experiment so that the movement of a calcium ion in a brain is used as a proxy for the spin-watching 'quantum gun', following the work of Stapp.
Stapp's work on 'Quantum Theories of the Mind'
Stapp does not accept the MWI, but prefers the Copenhagen Interpretation for reasons - essentially matter of philosophical preference - given in Stapp (April, 1996) and (July 21, 1998). This does not affect the useful analysis he puts forward concerning the quantum effects inside synapses.
Stapp shows that quantum effects are indeed important in the way the brain operates. In fact, they must have a dramatic effect on the function if the brain - perhaps allowing it to function as a 'quantum computer' and take advantage of search algorithms, perhaps similar to that proposed by Grover (1997)
Stapp's (April, 1996) evidence that quantum effects must be present in the brain is as follows:
a) A calcium ion entering a bouton through a microchannel of diameter x must, by Heisenberg's indeterminacy principle, have a momentum spread of hbar/x, and hence a velocity spread of (hbar/x)/m, and hence a spatial spread in time t, if the particle were freely moving, of t(hbar/x)/m. Taking t to be 200 microseconds, the typical time for the ion to diffuse from the microchannel opening to a triggering site for the release of a vesicle of neurotransmitter, and taking x to be one nanometer, and including a factor of 10-5 for diffusion slowing, one finds the diameter of the wave function to be about 40 times 10-8 centimeters, which is comparable to the size of the calcium ion itself.
In other words, it is quite feasible that in some universes a neurotransmitter will activate its target, whereas in others it will not, simply due to the 'Heisenberg uncertainty principle'.
This is important when trying to understand how the brain can act as a 'quantum computer', and very interesting when we take these ideas in conjunction with Tegmark's experiment.
Tegmark and Stapp
Consider a calcium ion which has a 50% probability, according to Schrödinger's equations, of activating its target receptor. Imagine that that receptor will make the difference between two possible states of mind: one corresponding with a motorcyclist's decision to overtake a car on a dangerous road, and the other corresponding with the opposite decision. Assume that the overtaking manoeuvre would be fatal.
The motorcyclist is the experimenter in Tegmark's quantum suicide. According to the MWI prediction, the cyclist will perceive that he has made the decision corresponding to the staying-alive outcome with 100% certainty. Of course, onlookers in 50% of universes will see a messy accident.
The Quantum Theory of Immortality developed here avers that all life-or-death decisions correspond with the same quantum mechanical equations. In all life-or-death decisions, the 'experimenter' finds that he has chosen life.
Deutsch (1997) argues that it follows from MWI that anything possible exists - somewhere in the 'multiverse'. If this is true, we can say that there are many universes (but a very tiny proportion of the multiverse) where you, dear reader, are a billion years old.
Could it follow that you, the experimenter's consciousness, will inevitably 'end up' in one of those universes? If so, we are immortal - from our own point of view.
Problems with Quantum Theory of Immortality
The QTI rests on some contentious premises: Deutsch's development of the post-Everett 'many-worlds' hypothesis; the Tegmark 'quantum suicide' experiment, Stapp's work on quantum effects on the brain and, most tentatively, the idea that the specific case of the 'quantum gun' can be generalised into any life-or-death scenario.