
Fun with the Anthropic Principle (2006) - Tomte
http://www.scottaaronson.com/democritus/lec17.html
======
rytill
I go through this chain of logic every so often:

What are the chances that anything only exists right now, and that this
experience I'm having is 'special' in some way (e.g. significantly more likely
to be occurring)? At first, it's fairly high.

Then, by thinking about all the other things in my memory, the probability of
the experience being 'special' or 'more likely to be occurring' in some way
significantly decreases. Why would my memory be complicated enough in a
'special' world to remember details about totally mundane things that seem to
have happened a long time ago?

Both before and after the chain, I'm in the real-world state of mind. But
during it, very fundamental probabilities shift. Am I being irrational here?

Tangential, but something that gives me a lot of respect for philosophers and
psychonauts is that any significant discovery you make affects your world view
irreversibly (unless you are good at selective denial). If you're happy with
your current world view, and there's a chance that you would make a discovery
that makes you unhappy, isn't it a mistake to keep going? But as a human,
maybe part of what keeps you happy is that uninhibited, unworried revealing of
new experiences.

~~~
jblow
> Am I being irrational here?

Not so much irrational as not particular enough; this line of reasoning
doesn't really work.

The thing is ... at any one instant, the amount of memory you are able to
recall / visualize / etc is very small, and if your mind is occupied by that
thought, you won't have any thoughts about the present simultaneously. It is
only the apparent continuity of time that seems to link these things.

So when you say "thinking about all the other things in my memory", well, you
can't experience all the things that are supposedly in your memory. You can
only experience one small part of that at any time. If there is only one time,
then the other stuff does not exist, you just have confidence that it exists
for some reason.

------
justinpombrio
There is a lot going on here.

1\. The part about the red-haired and green-haired people is more or less the
Sleeping Beauty problem[1]. The LessWrong community (who are Bayesians) has
concluded that this problem is under-specified and doesn't say what it's
asking, and has two different valid answers.[2]

EDIT: Actually it's a bit different. I wouldn't assume the two problems should
have the same answer.

2\. The dice room / madman experiment is ill-defined. It only works if you
have an infinite population to take people from (if there is a bound on the
number of rounds you can do, the effect vanishes), and it implicitly assumes
that every person is equally likely to be chosen. This is nonsense, because
there is no uniform distribution on the natural numbers.

Taking a closer look, put the die results in a grid, where columns are the
total length of the experiment, and there's one row for each round:

    
    
                 len=1  len=2  len=3
        round 1  snake
        round 2  normal snake
        round 3  normal normal snake
    

Here are the probabilities of these results:

    
    
                 len=1  len=2  len=3
        round 1  1/36
        round 2  35/36  1/36
        round 3  35/36  35/36  1/36
    

If you take the product of each row, that gives the probability that the
experiment ends in that particular round. If you sum up these probabilities,
you get 1, as you'd hope. (It converges slowly.)

Here are the number of people involved in each die roll, with a * if they are
killed:

    
    
                 len=1  len=2  len=3
        round 1  1*
        round 2  100    100*
        round 3  10000  10000  10000*
    

The reason this experiment is unintuitive is because you can calculate the
probability that someone will die (i) by column, assuming that the length of
the experiment is known, or (ii) by row, assuming that the round you were
selected in is known, and these give different answers. (Try it.) This is
because infinite sums are not commutative.

3\. There's no trouble with the doomsday argument, because SIA is correct :-).

[1]
[https://en.wikipedia.org/wiki/Sleeping_Beauty_problem](https://en.wikipedia.org/wiki/Sleeping_Beauty_problem)

[2]
[http://lesswrong.com/lw/32o/if_a_tree_falls_on_sleeping_beau...](http://lesswrong.com/lw/32o/if_a_tree_falls_on_sleeping_beauty/)

------
platz
It seems like it is playing a little fast and loose with the interpretation of
hypothesis, or maybe is mixing Bayesian and frequentist reasoning in the same
experiment. Either way, something seems off about the logic here (regarding
the madman thought experiment). it smells a bit like a case of equivocation,
but i can't put my finger on exactly what it is (and in shrouded in a sheath
of mathematics)

------
hyperion2010
I have come to the view that the anthropic principle is a kind of egocentric
reflection of the fact that selection doesn't just operate on systems that
reproduce in time, but also on systems that are reproduced (with lots of
variation) in space.

