Re: Questions on Russell's "Why Occam" paper

From: Hal Finney <hal.domain.name.hidden>
Date: Mon, 6 Jun 2005 13:51:36 -0700 (PDT)

I share most of Paddy Leahy's concerns and areas of confusion with
regard to the "Why Occam" discussion so far. I really don't understand
what it means to explain appearances rather than reality. It's hard to
get my mind around this kind of explanation and what to expect from it.
Also the way the Anthropic Principle applies to infinite strings seems
extremely vague until we have a clearer picture of how those strings
relate to reality.

One area I differ:

Paddy Leahy writes, quoting Russell:
> > However, as the cardinality of "my" ensemble is actually "c"
> > (cardinality of the real numbers), it is quite probably a completely
> > different beast.
>
> There you go again with your radical compression. Without the reading I've
> been doing in the last two weeks, I wouldn't have been able to decode this
> statement as meaning:
>
> 2^\aleph_0 = \aleph_1 (by definition)
>
> To assume c = \aleph_1 is the Continuum Hypothesis, which is unprovable
> (within standard arithmetic).

Actually Russell did not bring aleph_1 into the picture at all. All that
he referred to was aleph_0 and c which by definition is 2^aleph_0.
c is the cardinality of the reals and of infinite bit strings. This is
all just definitional. Whether c is the "next" infinite cardinal after
aleph_0 is the Continuum Hypothesis, but that is not relevant here.

Another area I had trouble with in Russell's answer was the concept of
a prefix map. I understand that a prefix map is defined as a mapping
whose domain is finite bit strings such that none of them are a prefix
of any other. But I'm not sure how to relate this to the infinite bit
strings that are "descriptions".

In particular, if "an observer attaches sequences of meanings to sequences
of prefixes of one of these strings", then it seems that he must have a
domain which does allow some inputs to be prefixes of others. Isn't that
what "sequences of prefixes" would mean? That is, if the infinite string
is 01011011100101110111..., then a sequence of prefixes might be 0, 01,
010, 0101, 01011, .... Does O() apply to this sequence of prefixes? If
so then I don't think it is a prefix map.

I want to make it clear by the way that my somewhat pedantic and labored
examination of this page is not an attempt to be difficult or stubborn.
Rather, I find that by the third page, I don't understand what is going
on at all! Even the very first sentence, "In the previous sections, I
demonstrate that formal mathematical systems are the most compressible,
and have highest measure amongst all members of the Schmidhuber ensemble,"
has me looking to see if I skipped a page! I don't see where this is
discussed in any way. So I hope that by pinning down and crystalizing
exactly what the first page is claiming, it will help me to see what
the more interesting third page is actually able to establish. I think
Paddy is in much the same situation.

Hal Finney
Received on Mon Jun 06 2005 - 17:41:55 PDT