I have argued numerous times on this everything-list that "quantum immortality" is NOT implied by the MWI. (e.g http://www.escribe.com/science/theory/msg00287.html, http://www.escribe.com/science/theory/msg00306.html, http://www.escribe.com/science/theory/msg00313.html, http://www.escribe.com/science/theory/msg00349.html, etc.)

The basic arguments are very simple. The predictions of the MWI are very clearly no different from the predictions of a one world interpretation in an infinite universe. (Cosmological predictions are a little more interesting but I'll get to that below.) It's true that in a one world universe, the probability of me surviving to 2100 is very low. But if I find myself in that year, that's no argument for the MWI, because the fraction of observers who have lived that long is no larger in the MWI. In either case I just got 'lucky'; the effective probability distribution in the MWI is proportional to the measure distribution which is heavily weighted toward shorter lifetimes. (Note to Don: what I call measure, you called quantum measure x number of observers.)

Note also that if one believes that the MWI does imply immortality for the average observer, then it would be a disproof of the MWI, because we don't seem to be drawn from an immortal distribution of effective probability, but rather from the usual distribution of lifetimes which merely has a long time tail that decays.

Don Page I did come to essentially the same conclusion Jacques Mallah did about the evidence of living to 2100, after receiving a message from Jerry Finkelstein, even before I received Jacques' message. It is a bit paradoxical, that in the MWI one predicts the certain existence of maverick worlds, such that the beings in them (and hence not directly aware of the many more normal worlds) should conclude from their low likelihood that they are evidence against the MWI (or any other form of QM with the same basic measures), but this is presumably an inevitable consequence of a many-worlds theory. You might be interested in some comments I made in a previous version of my paper I sent to some colleagues March 19, 13 days before I put it on the LASNL eprint archive after shortening it to try to meet Phys. Rev. Lett. length requirements (which I failed to do at that time). On March 19 I was unaware of Tegmark's paper and did not remember Squires' discussion of quantum immortality, though they did not not change my opinion of it (fairly negative, as you can see from the excerpt, not at all glorious as the Christian view of heaven for believers). I'll attach this excerpt immediately below, followed by the header part of the resubmittal message, and then next (separated by #######) a message I sent to Jacques Mallah a few minutes ago.

I certainly would not advocate suicide, even if one believed in the MWI (and maybe, for a pessimist, an attempt would be even worse in the MWI because of the certainty of a world in which he had a failed attempt that left him paralyzed or in terrible pain).

Don Page James, thanks for your message. It is indeed a bit paradoxical, that the MWI predicts very-low measure worlds in which one lives very long, and yet experiencing those will not be evidence for the MWI (at least with the usual Bayesian way of evaluating evidence, when one uses the likelihood of an observation as being proportional to the quantum measure).

I could say that we will live forever in a set of worlds of measure zero, but there is not space to say it in my present paper if it is to be reprinted in Physical Review Letters. If I say who said it first, well, the first I heard it was from Edward Teller around 1983, and the earliest place in print I have seen it is pages 72-73 of Euan Squires, The Mystery of the Quantum World, 2nd edition, 1994, (I suppose the 1st edition, of 1986, also had it, but I don't have that edition.)

John Leslie I hope you have remembered my articles relevant to the points you mentioned in your message: namely, (1) "A difficulty for Everett's many-worlds thoery", International Studies in the Philosophy of Science, Vol. 10 No.3, October 1996, pages 239-246, which argues that if one gets actual multiplication of observers with the passage of time, rather than just the differentiation of a continuous infinity of observers which is given us by Deutsch's version of Everettism, then there are very strong reasons for abandoning Everett, since one would vastly expect to find oneself very near the point of death, which is where most of one's versions would find themselves (granted that the number of one's versions was exploding exponentially, in the non-Deutsch version of Everettism, right up until death arrived), and (2) "Observer-Relative Chances and the Doomsday Argument", Inquiry, Vol.40 No.4, December 1997, pages 427-436, which argues that the point considered in your email message, viz. that there may be reasons for different observers to draw different conclusions from essentially the same evidence, is a correct point [ --simple illustration: One hundred women are blindfolded and divided into a group of three and a group of ninety-seven. They are each told the name of their group, which is either A or B, but not how many are in each group. Here the women in group A have excellent grounds for thinking that A is the group of ninety-seven, while the women in group B have excellent grounds for thinking that B is the group of ninety-seven; yet the women in A, in rejecting the conclusion drawn by the women in B (viz. that B is the larger group), can be fully cognizant of all the evidence possessed by the women in B]. ...One further point. I have long argued (see, e.g., my

"Time and the Anthropic Principle", Mind, Vol.101 No.403, 1992) that if, e.g., one knew that God was to have created a trillion people if a coin fell Heads, but only five people if the coin fell Tails, and also nothing else except that one was a person created in accordance with how the coin fell, then one would NOT have any reasons for thinking that the coin fell Heads rather than Tails. However, if God were to have created a trillion people in group A AND ALSO five people in group B, and one knew only that one was in one of these groups, then one should bet heavily on being in group A (the chances of finding oneself there being a trillion to five). It seems to me that this is relevant to some attempts to see special virtues in universes (such as inflationary ones, or Everett ones) which, plausibly, give us huge numbers of observers. My conclusion is that one should indeed expect to find oneself in one such universe IF AND ONLY IF universes with few observers (e.g., ones which did not inflate, or in which there was only a small amount of inflation as suggested by George Ellis) were created AS WELL

James Higgo John, my immediate reaction to your first argument is: yes, you would expect to find yourself near death, except that you never experience death and there are always subsequent branches in which you live for an arbitrarily long time. Also, as we all know, anthropic reasoning is apt to make people in rare circumstances become very confident of something which is not true.

John Leslie 1) I was aware of the difficulty of taking account of the branches in which death is indefinitely delayed through all sorts of weirdness which quantum theory allows, and have wished for some time that I had simplified my paper by drawing attention to how, on those variants of Everett which have the exponential explosion in the number of observer-versions, one would always expect it to be really, e.g., 5th May 1999, despite apparent strong evidence that it was only 4th May, because so many more of one's versions would be observing 5th May. 2) Yes, anthropic arguments will mislead the very rare observers who are in very extraordinary circumstances. But that's true of all probabilistic arguments.

James Higgo Under exponential-Everett, as I understand it, almost everybody is 10E-43 seconds from death. It is only in very rare circumstances that we continue to exist from one Planck-time to the next. But, WAP, that is our history and we do not experience those universes in which we are dead.

Russell Standish I believe a fatal flaw in Jacques' and Don's arguments lies in

assuming that every conscious moment must be drawn from some a priori distribution of such general concious moments (Self Sampling Assumption). I think that this can only apply to the observation of one's birth order. The world that one observes must actually be conditional on the fact that you are born on your actual birthdate, and on the amount of time that has elapsed since then. Because my current age is less than the mean human lifetime, I can say that I'm currently living in a typical time. However (assuming the validity of QTI, which I do), if I find my self much much older than the mean human lifetime, then I must be living in an atypical world. This world may also be one in which homo sapiens far exceeds the usual species lifetime (assuming there is such a value). It will probably also be one in which evolution has largely stopped.

Jacques Mallah You are correct that we use the "SSA" or Copernican Anthropic Principle (CAP), but I can see no reason why you'd think it would only apply to birth order. Nor do I see any alternative to the CAP consistent with computationalism.

I've explained this stuff to you guys umpteen times. The only new thing is that perhaps Don Page's conversion will motivate you to take another look, so go back and read what I've been saying. Observations of surviving a suicide attempt are of small measure, atypical. The fraction of observers like that is small, both at a given time and over all time. This is true if there are 10^9 people and it's true if there are infinitely many worlds each with copies of the 10^9.

Russell Standish Yes, I know you have explained your position many times, and each time I've read such a post from you, I have thought that your argument is flawed. Essentially, I suspect that you do not see the difference between Bruno Marchal's first person picture, and his third person picture. It is related to (but not equivalent to) the supposed paradox of free will, which comes from a distinction between Max Tegmark's bird and frog pictures.

I somewhat despair that anything I can say could convince you, or vice versa, and that we waste a lot of time on unproductive things.

Jacques Mallah If the two 'pictures' give conflicting predictions, one of them is

wrong. In special relativity, for example, is well that many things depend on what coordinate system you use; but predictions of what a given observer will observe are invariant. If it was not so, the theory would make no sense.

Russell Standish And that is true in this case too. Each observer will see a different distribution of lifetimes for their own lifetime (the first person picture), than they will for everyone else's (the third person picture). There is no conflict here.

Jacques Mallah So according to your statement, the predictions of a theory depend on which 'picture' you use. That is nonsense.

Russell Standish It is hardly nonsense. The predictions can easily depend of the

'picture' but must be consistent with each other. Let me give a simple example:

In one picture, observer A decides to measure the spin of an electron in the x direction. In the other, observer B decides to measure the spin of the electron in the y direction. Observer A will see the spin of the electron aligned with x axis, and Observer B will see it aligned with the y axis. Both observations are correct in the first person picture of that observer. A "person" with the third person perspective, sees observers A and B as inhabiting separate `worlds' of a multiverse, each with appropriate measure that can be computed from Quantum Mechanics.

Jacques Mallah On the contrary, this is a textbook example of the way I said it works. The theory predicts some measure distribution of observers; an individual observer sees an observation drawn from that distribution. There are no different sets of predictions for different pictures, just the measure distribution and the sample from it.

Russell Standish It sounds to me like you don't think the prediction changes according to what the observer chooses to observe? An electron cannot have its spin aligned with the x axis and the y axis at the same time. Once the experimenter has chosen which direction to measure the spin, the history of that particular is observer is constrained by that fact, and the predictions of QM altered accordingly. This is true both in MWI and the Copenhagen interpretation, and is the "spooky" nature of QM.

I used to think that QM gave predictions in terms of distributions, and that because one didn't see isolated particles, rather ensembles of such particles, I didn't see a problem. The properties of an ensemble are well defined.

However, the ability of experimenters to isolate a single particle, such as a photon, or an atom, means we have to take this "spookiness" seriously.

Jacques Mallah A theory predicts some measure distribution on the space of conscious observations. From the point of view of an observer, you see one observation drawn from that measure distribution. If measure were conserved for a particular individual as a function of time, you immediately have 2 problems: How to define a particular individual? You need to, or else the measure of other people would count too, and would stay relatively constant as opposed to the rapidly diminishing measure of "you".

Russell Standish This is a furphy. I have no problem whatsoever in knowing that I am who I am. If you are unsure of your identity, then that's your problem.

Jacques Mallah The expected value of your age would be infinite, contrary to observations which indicate no unusual age on your part.

Russell Standish Again this is based on an assumption that at each time period,

consciousness must select randomly from the set of available conscious moments for that observer. (ie SSA of all conscious moments, as opposed to SSA of birthdates). As I mentioned earlier, I reject this assumption as absurd, and prefer the view that consciousness must sweep out the conscious moments in the time order they are arranged, ie I must pass through being 30 years old before I can experience being 100

or 1000 years old. Therefore being young with respect to average lifetimes is not contradictory with expecting an infinite lifetime. I would be very surprised if conciousness jumped from 30 yo, to 100yo back to 10yo etc in some unordered random fashion, but of course have no way of exactly disproving it.

Jacques Mallah The above paragraph is rather meaningless since you haven't defined 'yourself'. If 'you' are some extended implementation of a computation, you are not immortal: the number of implementations will decrease over time. I take one time step as the most logical unit but that is irrelevant to the conclusion.

Russell Standish This para still indicates that you are falling for this rather absurd sampling assumption mentioned above. Give me one good reason why you would expect consciousness to sample randomly from the set of all such "conscious points", rather than in an ordered (and potentially unbounded) sequence of self-consistent points (ie a history).

Bruno Marchal So, Jacques, you succeed in convincing Don Page against Quantum Immortality ! I would not be proud of that! It seems that you (and Don Page now) reason like that :

Maverick worlds in which I am alive in 2100 are rare, so the probability I feel alive in 2100 is low. But, at least with computationalism (or "comp" if you prefer: I mean the hypothesis that I can survive with a digital *body*), I can only compute the probability from a distribution defined on the worlds in which I survive. There is no sense in counting worlds in which I do not survive. Typicality or likelihood are relative to the observer.

Jacques Mallah What about worlds on which others survive? How do you even distinguish between "you" and others to make such a distinction? And of course time should not be a consideration: Measure is NOT conserved over time! There is NOT an equal chance of finding yourself at one age as at an older age! If there was it would disprove the MWI!

Bruno Marchal Tell me if you agree at least with the weaker proposition:

COMP + HE ====> immortality

where HE is the (extravagant) hypothesis saying that a real concrete universal dovetailer (generating and executing all programs) exists in our "universe".

Jacques Mallah Of course not. It's the same issue.

Bruno Marchal really don't understand you, Jacques. I am afraid you are inconsistent. I am referring you to the thread "valuable errors" which begins at

More precisely, in http://www.escribe.com/science/theory/index.html?mID=540,

you agree that you can survive with a digital body. And in the course of that thread you agree with what I call *mechanist or comp (first person) indeterminism* (because

you told us that "for all practical purposes, a person who is copied should expect their future selves to be effectively randomly chosen"). And you agree with the non-first-person-observability neither of any delays of "reconstitution", nor of the nature real/virtual of the reconstitutions. Etc.

But if you agree with all these points, it seems to me that "COMP + HE ====> immortality-from-a-first-person-point-of-view" follows quite easily.

Remember HE is the Extravagant Hypothesis that there IS a non stopping, and never stopping, concrete program (UD) emulating all possible programs (this makes sense with Church's Thesis) in *the* uni-multi-verse. With HE, a universal computation is

actually implemented in our (branch) universe.

Even IF, by a kind of miracle, you would NOW be a sort of concrete real "Jacques M Mallah" belonging to that concrete universe, the next instant, you should expect yourself belonging to a virtual history generate by the UD working (by HE) in that concrete universe. And this happens just because, as you say "for all practical purposes, a person who is copied should expect their future selves to be effectively randomly chosen" among the virtual (at least) reconstitutions, which are ALL implemented, one day or another (but the delays are not first person detectable), and executed in the UD. Where is the error ?

James Higgo Jacques, when did any of us propose that living to a great age would be evidence of MWI? We merely said that, as we believe in MWI, we believe we will live to a great age.

Jacques Mallah Newsflash: If a theory predicts something, and it's found to be

true, that's evidence for the theory. If it's found to be false, or that what is observed is atypical of what the theory predicts, that's evidence against the theory.

James Higgo Newsflash (2): if 2 theories predict the same thing, and it is found to be true, that is evidence for neither theory.

Jacques Mallah Are you saying that the MWI does not predict immortality, or that a single world theory does predict it? The former would make sense since immortality is observationally false, but I didn't think you'd come around so easily.

James Higgo Good grief, Jacques - for the umpteenth time: of course it does not predict immortality any more than classical physics does. But you will end up as one of those exceedingly unlikely, one in 10E500000... Jacques's that happen to survive for an aeon. Even then you will have no better proof of MWI than you do now.

Immortality is no more 'observationally false' than the statement 'you will become a petunia in six minutes'. After six minutes, you may challenge that statement (in those universes in which you are not a petunia and have not lost your power of communication in another way). And after infinity you may challenge my statement that you are immortal.

If anything, the fact that you are alive lends support to the hypothesis that you will not die. You have never been observed to die in the past.

Jacques Mallah Let me get this straight. It doesn't predict immortality, but it does; I will find myself to be old due to the MWI, but since it's not really a prediction of the MWI I won't have evidence for the MWI based on that. Your doublethink continues to amaze me.

Bruno Marchal Come on Jacques, if you have experience death, tell us ! But in that case it seems to me that you survive, isn't it ? More seriously, I guess Russell Standish is correct when he says that, you confuse first and third person point of view. QM and comp immortality are of course *immortality from a first person perspective*. You cannot expect some friend surviving a big crash thanks some QM or comp tunneling effects. But if comp (+HE) or QM is correct then, from your unique point of view, you can expect (and fear) personal surviving. In *your* crash, you will survive probably in the *most normal near world* (may be in Stalnaker or Hardegree proximity sense) from the world you crash. This also entails you can expect being seriously injured ...

Of course, with HE, the proof is rather easy (isn't it ?). For an elimination of HE see the 4th chapter in my thesis.

Jacques Mallah That's the crazy claim of you and your allies. You know full well that when I say it's observationally false, I mean the fact that you are not nearly as old as you should expect.

Bruno Marchal I will ask the allies to drop bombs on you until you stop using

so poor arguments ... (hum! ;-)). So you accept SSA in the absolute sense of Nick Bostrom. I accept SSA only in the relative and/or conditional sense. I don't think it is possible to put a measure on a set : neither of "conscious states" nor even of "observers". You can only put a conditional measure on a set of computational (including quantum one) continuations from a relative state. With relative SSA, it is not possible to be old without having been young, and this is conform to common sense.

For exemple you write also:

> Anyway, 4*10^9 years is nothing. If you were really immortal, you

>should expect to be a lot older than that.

The problem is that ANY finite number is "nothing" compared to infinity. You are saying us that immortal consciousness is in principle impossible because, whatever your age is, you should expect to be much older. I really think that this is not valid : you can easily conceive a "robot" immortal due to intensive care by its human-chain of owners. (Of course, such a robot must have an infinitely extending body to

remember an infinitely extending memory of its past, but that is not relevant for the kind of immortality (survival) we talk about).

Russell Standish I think the above few arguments are floccinauccinihilpilication. Yes, living to ages much larger than human average would be empirical support of QTI, at least for the person so involved. However, you would probably have a hard time convincing all the other individuals (who would probably be aged 0-100 years, assuming no great advances in Medicine).

Of course someone may come up with mathematical theorem limiting human lifetime - this is about the strength of what is required to disprove QTI.

James Higgo For anyone else, the sight of a billion-year-old man would not prove or disprove the Quantum Theory of Immortality. But for you, at age 1 billion, the probability that you would reach a billion, given QTI, is one. And the probability that you would reach a billion given not-QTI is very tiny. So it is not unreasonable to believe QTI. I'm not sure you can really quantify this.

On another note, the SSA is a dangerous to use when the Self is not a representative sample - the Self is immortal, whereas everyone else is not.

Russell Standish This is precisely my point. SSA can apply to birth order, but it

surely can't apply to subsequent concious moments.

George Levy I am in full agreement with this. However, left unsaid is the impact of living one billion years or one trillion years on the perception of the self . More specifically, as long as the Self views the universe RATIONALLY, there must be ANTHROPIC reasons in his perceived universe for living that long. He must perceive the universe around him to be evolving to support his own longevity. And he must also perceives himself to be evolving since he must be conscious (have memory) of living that long. Kind of "growing up." Undoubtedly, the Self resulting after one billion years of anthropically supported evolution will be very different from the common human self. Will the Self then be the "same" as the Self now? Yes in the sense of being linked to the memories of his "youth" just like an old man remembers being a child. And of course, there will be branches in the MW where Selves loses their earlier memories. But we are not concerned about these Selves since, having lost their memories, they have also lost their link to their youth, their identity. To be of interest for the perception of survival, the thread of consciousness through the MW must keep the memory intact.

Russell Standish This makes sense. Either we end up with large forgettories (which doesn't preclude retaining memories of our earliest times), or we end up being vastly evolved compared with our current existence. There is also nothing ruling out the possibility that our immortality comes through entirely mundane medical advances, rather than seeming miraculous. We could also end up living in a world with many people of similar age.

James Higgo Yes to all the above, except that it is highly unlikely we will live in a world of people of a similar age; after a few billion years, the chance that you have been wiped out by a freak accident approaches 1.

George Levy Please James, Russell, redefine the term SSA. I must have missed a critical exchange where this term was defined.

Russell Standish "Self-Sampling Assumption". It is a generalisation (or specialisation?) of the totalitarian, or Copernican principle, in that you are saying there is nothing special about you. For example, SSA is often applied to birth order - that there are as many people born before you as are born afterwards - implying some sort of population crash in the near future.

Jacques Mallah "Nature must have a mathematical criterion for [human identity], if it is going to figure in a theory of physics."

James Higgo Which implies he has a divine right to figure in a theory for physics. No, you don't, Jacques. Human identity does not figure in any physical theory; it is merely a useful social construct.