hal@rain.org wrote:
> Light, in their model, is a disturbance propagating at the maximum
> speed of one cell per tick in the CA. And in fact CA workers often
> do refer to one cell per tick as "the speed of light" by analogy to
> relativity theory. In section 9.3 the authors attempt to show that
> all uniformly moving observers will measure the speed of light to be
> the same in all directions. But again I didn't find the argument clear
> or persuasive. For one thing, it would seem that the geometry of the
> CA array should be relevant. In a three dimensional cubic geometry CA
> (which they choose without discussing other polyhedral geometries),
> disturbances can propagate faster in the diagonal direction than along
> the axes. Living in such a CA would seem to give a set of preferred
> directions. They don't seem to discuss this effect. They don't have
> a clear definition of how clocks and rulers would be expected to work,
> making it hard to interpret their explanations of what people would see.
>
> Overall I can't help feeling that they have jumped past the hard parts
> with some handwaving and vague arguments. If the universe is a CA, it
> would seem that there ought to be some constraints on the properties it
> would have. Their arguments would apply to virtually any CA, and that
> can't be right.
>
Mike Lorrey