Admiral

Re: Anthropic double slit
YellowSubmarine wrote:
On a more general note, any metaphysical notion, be it an interpretation of quantum mechanics, a general concept about other universes, is in its nature unscientific, can't be proven by science and probably can't be proven at all. Quantum mechanics does one thing – describes how our universe works within its own space and time. It can't be used to extrapolate what happens outside the universe, before the universe or after you die from your own perspective, because those "places" haven't been observed, can't possibly be observed and are very likely to differ so significantly in nature that anything you know is inapplicable to them at all.
Two examples:
1. Assume multiworld interpretation of quantum mechanics leads to quantum immortality for all individuals. For our universe to exist, let alone support life, the quantum fluctuations, their randomness and indeterminism in quantum processes need to be within precise constraints as defined by the laws of physics we know (or think we know). Any change in quantum fluctuations could destroy the universe, and if randomness stopped being random, I am not sure what will happen. And that's exactly what will be going on in your immortalverse. Of course, you could just be struck with an enormous streak luck winning the intergalactic lottery every Planck time turning into an eternal anomaly that lives against all odds and against the laws of physics, but this is profoundly more unlikely than finding yourself in a universe where your luck matches the local laws of physics. Living for a second that way has a probability that makes the Ackermann function sweat.
2. Existence itself is undefined for these metaphysical realms. Existence is the things that we can observe directly or indirectly. Nobody will observe your afterlife, nor will you observe anyone else's, so it doesn't even exist, how can we be talking about the more welldefined physical concepts? Worse, existence here is tied to probability – if six people saw a goose, there is probably a goose, because the likelihood of light shaped like a goose just randomly popping into six people's eyes is just incredible. Well, if the whole of your personal existence is more unlikely than that, how can anything exist in your realm?
I do believe in immortality of sorts that arises from much simpler things that have nothing to do with quantum mechanics or complex physics though:
 I think that we overestimate our personal importance, and that a person carrying out your legacy or mentally arriving at the same place as you accidentally is more than enough, and your personal uniqueness doesn't add much to that if at all, and you can share and immortalise your memories if you think they are this important.
 If you were immortal in the traditional sense, your life would start repeating itself. When it does, you're as good as dead, you'd be living the same finite thing over and over again.
 Living your life over and over is the same as living it once. Time is the natural progression from cause to effect that we observe, implying there's more to it is giving it metaphysical properties we have not observed. If the effect takes you back to the cause, that does nothing for the posterity of anything inbetween, outside of our perception of time, which in the grand scheme of things is irrelevant. Been there, done that.

Your points, firstly of the nonobservability of a "quantumly immortal" being by the rest of us mere mortals, and secondly of the problem of a "quantumly immortal" being's experience being dominated by improbable events, are both well taken, assuming I understood what you were getting at.
I do have problems with some of your other contentions, though. Two are worth elaborating on:
It can't be used to extrapolate what happens outside the universe, before the universe or after you die from your own perspective, because those "places" haven't been observed, can't possibly be observed and are very likely to differ so significantly in nature that anything you know is inapplicable to them at all.

I think that this view is too simplistic. Science, even quantum physics, exists only because of collaboration. There is, in any collaboration, routinely the acceptance by each party of contributions from other parties. To demand that quantum physics can only concern itself with what each individual could verify on his own, would be to strip it of the overwhelming majority of its content and to transform it into a discipline in which no progress could be made. Verification does not depend on everything being verified by each individual. Therefore, statements that apply to reality before or after a person's lifespan are not necessarily utterly meaningless to that person. Rather, they can be coordinated into the individual's personal experience, not at all dissimilarly to the way accounts of events to which the individual is not party to generally are.
If you were immortal in the traditional sense, your life would start repeating itself.

Your claim here really demands proof. Here are two reasons why your claim is not at all obvious.  Almost all real numbers are irrational. The decimal expansions of rational numbers eventually repeat, but those of irrational numbers do not.
 Almost all real differentiable functions are aperiodic.
Let f(x) be a nonconstant real differentiable periodic function that is normalized so that max{abs(f(x))}=1. Then, for any positive real number c, g(x) defined by g(x)=c*x*f(x) is differentiable but aperiodic. The derivative of g(x) clearly exists, and it is given by g'(x)=c*f(x)+c*x*f'(x). Real differentiable functions are continuous, and therefore, real differentiable periodic functions must be bounded (therefore, any real differentiable periodic function can be normalized). Because f(x) is nonconstant, it cannot vanish identically. Therefore, c*x*f(x) is not bounded, and so g(x) cannot be periodic.
So, for every such periodic function f(x), there are as many such aperiodic functions g(x) as there are elements of the continuum.
Moreover, since we assumed that c>0 and that f(x) is normalized, for each such g(x), the inverse value f(x) is uniquely determined. Note that g(x)/x must have a removable singularity at x=0, by the assumption that it was determined by a periodic function in the first place. In other words, lim(g(x)/x,x=0)=c*f(0).
Since there is thus no overlap among these aperiodic functions, the totality of such aperiodic examples therefore utterly dwarfs the set of all normalized periodic functions.
This latter objection perhaps carries more weight than the former (which is why I even bothered to formulate a readily understandable partial proof sketch), if we assume that scientifically derived models of reality are the solutions to systems of differential equations.
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“A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP” — Leonard Nimoy (19312015)
