RE: A calculus of personal identity

From: Hal Finney <>
Date: Thu, 29 Jun 2006 09:10:41 -0700 (PDT)

Stathis Papaioannou writes:
> Hal Finney writes:
> > What I argued was that it would be easier to find the trace of a person's
> > thoughts in a universe where he had a physically continuous record than
> > where there were discontinuities (easier in the sense that a smaller
> > program would suffice). In my framework, this means that the universe
> > would contribute more measure to people who had continuous lives than
> > people who teleported. Someone whose life ended at the moment of
> > teleportation would have a higher measure than someone who survived
> > the event. Therefore, I would view teleportation as reducing measure
> > similarly to doing something that had a risk of dying. I would try to
> > avoid it, unless there were compensating benefits (as indeed might be
> > the case, just as people willingly accept the risk of dying by driving
> > to work, because of the compensating benefits).
> >
> > You can say that "by definition" the person survives, but then, you
> > can say anything by definition. I guess the question is, what is the
> > reasoning behind the definition.
> OK, this is the old ASSA versus RSSA distinction. But leaving this
> argument aside, I don't see how teleportation could be analogous to a
> risky, measure reducing activity if it seemed to be a reliable process
> from a third person perspective. If someone plays Russian Roulette, we
> both agree that from a third person perspective, we are likely to observe
> a dead body eventually. But with teleportation (destructive, to one place)
> there is a 1:1 ratio between pre-experiment subjects and post-experiment
> subjects from a third person perspective. Are you suggesting that the
> predicted drop in measure will have no third person observable effect?

First, I tend to think that the phrase "third person observable" is
something of a contradiction. Observation is a first-person activity.
I would prefer to think of third person effects as simply the physical
record of events.

In this case, there will definitely be a third person effect. Having
someone teleport is a third-person difference from not having them
teleport. We are talking about two cases here that are third-person
distinguishable, with very different physical histories, hence it is
plausible that there be different subjective first-person effects.

As far as the comparison with Russian Roulette, if someone only plays it
once, there might not be a third person difference. Yet I would argue
his measure was reduced (in the multiverse).

Really, when we are talking about third person records, all we have
is the actual sequence of events that occurs. Suppose someone plays
Russian Roulette multiple times. In this universe, perhaps we see them
pull the trigger five times and survive, and on the sixth pull they die.
That subjective history, of playing RR six times, is instantiated in
this universe. This universe contributes measure to that history.

Other universes, not observable to us, may have him die after different
trials. Each of those contributes measure to subjective histories that
end at different points. The result is that the measure of his lifespan
is reduced at each trigger pull, but that in any single third-person
universe that reduction in measure is unobservable. Instead we see no
change until the final trigger pull.

Consider this example: someone commits to killing himself if you die, and
now you play Russian Roulette yourself. Each time you pull the trigger
you reduce his measure, that of the other person who will kill himself
if you die. But you will never observe him dying (in the first-person
sense). This is a case of an unobservable measure decrease which you
might nevertheless believe in.

> > As far as Lee's suggestion that people could be dying thousands of
> > times a second, my framework does not allow for arbitrary statements
> > like that. Given a physical circumstance, we can calculate what happens.
> > It's not just arbitrary what we choose to say about life and death.
> > We can calculate the measure of different subjective life experiences,
> > based on the physical record.
> >
> > If we wanted to create a physical record where this framework would
> > be compatible with saying that people die often, it would be necessary
> > to physically teleport people thousands of times a second. Or perhaps
> > the same thing could be done by freezing people for a substantial time,
> > reviving them for a thousandth of a second, then re-freezing them again
> > for a while, etc.
> >
> > If we consider the practical implications of such experiments I don't
> > think it is so implausible to view them as being worse than living a
> > single, connected, subjective life. It would be quite difficult to
> > interact in a meaningful way with the world under such circumstances.
> Assuming it could be done seamlessly, how would it make any difference? If
> you believe the important aspect of our consciousness resides in the
> activity at neural synapses, this is exactly what is happening. They
> are constantly falling apart and being repaired in an energy-requiring
> process, such that the matter comprising our synapses completely turns
> over in a matter of minutes. It's just the basic brain template that
> is maintained over time, and even that changes as we change. If you
> could somehow gold plate your neurones so that the normal turnover of
> matter due to wear and tear stops, and only the turnover due to thinking
> different thoughts occurs, do you think it would make any subjective
> difference? What if the turnover increased, or it happened all at once
> in bursts rather than gradually, all the while maintaining the same
> basic structure as occurs normally?

Yes, I think these physiological differences might make a difference in
measure, although it would probably be small. Why would you believe
otherwise? Would you suggest that no physiological change could make
a difference? The basic functionalist/computationalist paradigm?

I have argued before some problems with functionalism, and of course there
is a vast philosophical literature pro and con. The most basic problem
is that functionalism assumes that there is meaning to the question of
whether a given physical system implements a given abstract computation,
and IMO no one has ever given a satisfactory method to answer this.

In practice, as long as you stick fairly close to conventional
implementations, you're probably OK. Your gold-plated neurons are
not a big deal. People are still interacting with the real world. But
computationalism commits you to far more exotic kinds of implementations.
Uploaded brains running millions of times faster than regular ones,
for example. Or brains scattered across the universe exchanging data
at incredibly slow paces. Brains which have been suspended - are they
still alive, still "conscious", or not? The guy who gets teleported every
millisecond - what is his life like, exposed to a kaleidoscopic of images
and realities that would be impossible to meaningfully interact with?

To roughly translate my mathematical principles into words, our subjective
lives gain reality from being embedded and instantiated in real worlds.
As our connection to reality becomes fuzzier and less direct, the
degree to which we can be said to gain measure from those realities
is diminished. And likewise, as the instantiation is made simpler and
more solidly grounded to reality, measure increases. This is based
on the mathematical principle of conditional Kolmogorov complexity,
where we ask how short a program could be to output the trace of a given
subjective experience, starting from the third-person physical record.

When we come up with these exotic thought experiments that make the
concept of implementation fuzzy, it makes sense that measure would
be reduced. The more we break the connection between physical reality
and a straightforward implementation of a logical calculation, the less
measure that reality will contribute to the calculation. This is what
I see going on in some of these experiments.

Hal Finney

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Received on Thu Jun 29 2006 - 13:13:52 PDT

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