Why the quantum suicide experiment must fail

Max Tegmark writes in arXiv:quant-ph/9709032v1:

Many physicists would undoubtedly rejoice if an omniscient genie appeared at their death bed, and as a reward for life-long curiosity granted them the answer to a physics question of their choice. But would they be as happy if the genie forbade them from telling anybody else? Perhaps the greatest irony of quantum mechanics is that if the MWI is correct, then the situation is quite analogous if once you feel ready to die, you repeatedly attempt quantum suicide: you will experimentally convince yourself that the MWI is correct, but you can never convince anyone else!

Could you convince other people? Suppose you set up the quantum suicide experiment. You might do it in a public place, before a large crowd, and do everything possible to convince people that it is correctly configured (i.e. not faked in any possible way.) Assuming MWI is true, then in the vast majority of universes, they would see you die. But in a very small minority of universes, they would see you miraculously not die. What should those in the minority who see you live think of you? That you were some kind of divine being, invincible against even the most stupendous odds? Of course, your invincibility would be a one time affair, for if you were to repeat the experiment, in the vast majority of universes in which the you lived the first time you would die the second; still, there would always be that, ever smaller minority, of universes, which continue to be wowed by your divine invincibility, every single time. And, if such a divine being were to open its lips and speak to us, ought we not believe its wisdom?

No. Surely, even if we observed such a feat, the logical conclusion would be that in some way, unknown to us, you have faked the experiment. Assuming MWI, universes in which you lived by faking the experiment would be more likely than those in which you lived by carrying out the experiment correctly. Assuming the negation of MWI, the epistemic probability of undetectable fakery will be greater than the probability of miraculous survival. So, it seems, whether MWI is true or not, no one would ever be justified in believing MWI based on a third person observation of the quantum suicide experiment, even if they were in one of the vast minority of universes in which the experimental subject lives.

Indeed, even in the first person case: suppose there is conspiracy with arbitrary resources, whose mission, deriving from some peculiar sense of mischievousness, is to deceive you into believing that you have successfully carried out the quantum suicide experiment, thus causing you to believe that you have thereby proven to yourself the truth of MWI. Now, conspiracy theories inherently have a very remote probability of being true. And yet, how does that probability compare to the probability of survival in a quantum suicide experiment? Now, an interesting observation: the probability of the conspiracy existing and being successful, however small it is, is largely constant in terms of experimental duration. If your resources are sufficient to successfully deceive me for five minutes, surely they are also sufficient to deceive me for ten or fifteen minutes; thus the probability of a fifteen minute deception is not substantially less than the probability of a five minute deception. Whereas, the probability of a survival universe exponentially decays in terms of experimental duration. So, however small the probability of the conspiracy theory, we can easily make the experiment long enough that its probability will be greater than the probability of survival. So, it would seem, even if you carried out quantum suicide and lived, you would not be justified in believing the truth of MWI; the more reasonable conclusion is the existence of a conspiracy to make you believe in the truth of MWI.

So, it would seem, that the quantum suicide experiment can never justify us in believing in the truth of MWI, irrespective of the outcome of the experiment.

Now, I’ve attempted to show that quantum suicide cannot even convince us first person of the truth of MWI, contra Tegmark. But, let us suppose that Tegmark’s original point is in fact correct – that quantum suicide can be convincing first person but not third person. The question is — is an experiment whose very nature means that no one who successfully performs it could ever convince anyone else thereby a valid experiment? From a philosophy of science perspective, science is inherently a social activity, and thus it seems that such an inherently anti-social experiment could never be a scientific experiment, and, whatever knowledge about the world it might give us, such knowledge would not belong to science.

A religious believer is discussing the afterlife with a positivist. The positivist says:

If the existence of an afterlife would lead to paranormal activity, such as communication with ghosts or memories of past lives, as some have claimed, then it is a theory unsupported by the evidence. But, the idea as espoused by more sober religionists such as yourself, with no necessary paranormal implications, is not even a theory, because it does not even make unsupported predictions, it makes no predictions at all.

The religious believer (well, in this case a believer in one particular religion) replies:

On the contrary, my theory does make experimental predictions. I predict that after you die, you will reawaken before the judgement seat, as per Romans 14:10-12.

Now, both the MWI theorist’s quantum suicide experiment, and the Christian’s death experiment, are actually quite similar. They are both experiments that involve the death of the experimenter. Now, one has to ask, is it really valid to call an experiment that requires the death of the experimenter an “experiment”? Again, science is a social reality, and death is a separation from that reality. So an experiment which requires the investigator’s death (as opposed to the death of a mere subject) seems not to be an experiment. I suppose, the positivist needs to ask, whether their devotion to experimentalism is to a specifically scientific experimentalism, or a more broadly construed, even extra-scientific, experimentalism?

The Christian has one advantage which the MWI theorist does not; religious accounts of the afterlife, whatever their specific detail, tend to be inevitably social. If you wake up after death in some shape or form of afterlife, you may be unable to inform the living of your momentous discovery, but at least you will be able to share your Eureka moment with your fellow dead. So, the Christian’s experiment, is more scientific than the MWI theorist’s — it shares science’s inherent sociability, albeit in the context of a different society.