evidence for my beliefs in ten thousand different places....And to me it's just totally overwhelming.
It's like there's an animal I want to find. I've found his footprints. I've found his droppings. I’ve found
the half-chewed food. I find pieces of his fur, and so on. In every case it fits one kind of animal, and
it's not like any animal anyone's ever seen. People say, Where is this animal? I say, Well, he was
here, he's about this big, this that, and the other. And I know a thousand things about him. I don't
have in hand, but I know he's there....What I see is so compelling that it can't be a creature of my
imagination.
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In commenting on Fredkin's theory of digital physics, Wright writes,
Fredkin ... is talking about an interesting characteristic of some computer programs,
including many
cellular automata: there is no shortcut to finding out what they will lead to. This, indeed, is a basic
difference between the "analytical" approach associated with traditional mathematics, including
differential equations, and the "computational" approach associated with algorithms. You can
predict a future state of a system susceptible to the analytic approach without figuring out what
states it will occupy between now and then, but in the case of many cellular automata, you must go
through all the intermediate states to find out what the end will be like: there is no way to know the
future except to watch it unfold....Fredkin explains: "There is no way to know the answer to some
question any faster than what's going on. "... Fredkin believes that the universe is very literally a
computer and that it is being used by someone, or something, to solve a problem. It sounds like a
good-news/bad-news joke: the good news is that
our lives have purpose; the bas news is that their
purpose is to help some remote hacker estimate pi to nine jillion decimal places.
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Fredkin went on to show that although energy is needed for information storage and retrieval, we can
arbitrarily reduce the energy required to perform any particular example of information processing. and that
this operation has no lower limit.
64
That implies that information rather than matter and energy may be
regarded as the more fundamental reality.
65
I will return to Fredkin's insight regarding the extreme lower limit
of energy required for computation and communication in chapter 3, since it pertains to the ultimate power of
intelligence in the universe.
Wolfram builds his theory primarily on a single, unified insight. The discovery that has so excited
Wolfram is a simple rule he calls cellular automata rules 110 and its behavior. (There are some other
interesting automata rules, but rule 110 makes the point well enough.) Most of Wolfram's analyses deal with
the simplest possible cellular automata, specifically those that involve just a one-dimensional line of cells,
two possible colors (black and white), and rules based only on the two immediately adjacent cells. For each
transformation, the color of a cell depends only on its own previous color and that of the cell on the left and
the cell on the right. Thus, there are eight possible input situations (that is, three combinations of two colors).
Each rules maps all combinations of these eight input situations to an output (black or white). So there are
2
8
(256) possible
rules for such a one-dimension, two-color, adjacent-cell automaton. Half the 256 possible
rules map onto the other half because of left-right-symmetry. We can map half of them again because of
black-white equivalence, so we are left with 64 rule types. Wolfram illustrates the action of these automata
with two-dimensional patterns in which each line (along the
y
-axis) represents a subsequent generation of
applying the rule to each cell in that line.
Most of the rules are degenerate, meaning they create repetitive patterns of no interest, such as cells of
a single color, or a checkerboard pattern. Wolfram calls these rules class 1 automata. Some rules produce
arbitrarily spaced streaks that remain stable, and Wolfram classifies these as belonging to class 2. Class 3
rules are a bit more interesting, in that recognizable features (such as triangles) appear in the resulting
pattern in a essentially random order.
However, it was class 4 automata that gave rise to the "aha" experience that resulted in Wolfram's
devoting a decade to the topic. The class 4 automata, of which rule 110 is the quintessential example,
produce surprisingly complex patterns that do not repeat themselves. We see in them artifacts such as lines
at
various angles, aggregations of triangles, and other interesting configurations. The resulting pattern,
however, is neither regular nor completely random; it appears to have some order but is never predictable.
Why is this important or interesting? Keep in mind that we began with the simplest possible starting
point: a single black cell. The process involves repetitive application of a very simple rule.
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From such a
repetitive and deterministic process, one would expect repetitive and predictable behavior. There are two
surprising results here. One is that the results produce apparent randomness. However, the results are more
interesting than pure randomness, which itself would become boring very quickly. There are discernible and
interesting features in the designs produced, so that the pattern has some order and apparent intelligence.
Wolfram include a number of example of these images, many of which are rather lovely to look at.
Wolfram makes the following point repeatedly: "Whenever a phenomenon is encountered that seems
complex it is taken almost for granted that the phenomenon must be the result of some underlying
mechanism that is itself complex. But my discovery that simple programs can produce
great complexity
makes it clear that this is not in fact correct."
67
I do find the behavior of rule 110 rather delightful. Furthermore, the idea that a completely deterministic
process can produce results that are completely unpredictable is of great importance, as it provides an
explanation for how the world can be inherently unpredictable while still based on fully deterministic rules.
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However, I am not entirely surprised by the idea that simple mechanisms can produce results more
complicated than their starting conditions. We've seen this phenomenon in fractals, chaos and complexity
theory, and self-organizing systems (such as neural nets and Markov models), which start with simple
networks but organize themselves to produce apparently intelligent behavior.
At a different level, we see it in the human brain itself, which starts with only about thirty to one hundred
million bytes of specification in the compressed genome yet ends up with a complexity that is about a billion
times greater.
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It is also not surprising that a deterministic process can produce apparently random results. We have
has random-number generators (for example, the "randomize" function in Wolfram's program Mathematics)
that use deterministic processes to produce sequences that pass statistical tests for randomness. These
programs date back to the earliest days of computer software, such as the first version of Fortran. However,
Wolfram does provide a thorough theoretical foundation for this observation.
Wolfram goes on to describe how simple computational mechanisms can exist in nature at different
levels, and he shows that these simple and deterministic mechanisms can produce all
of the complexity that
we see and experience. He provides myriad examples, such as the pleasing designs of pigmentation on
animals, the shape and markings on shells, and patterns of turbulence (such as the behavior of smoke in the
air). He makes the point that computation is essentially simple and ubiquitous. The repetitive application of
simple computational transformations, according to Wolfram, is the true source of complexity in the world.
My own view is that this is only party correct. I agree with Wolfram that computation is all around us,
and that some of the patterns we see are created by the equivalent of cellular automata. But a key issue to
ask is this:
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