Are Cellular Automata always computers? I was reading on Complex Systems journal and found a paper where the author states that a cellular automaton can be viewed as a computer.
In the introduction part:

Cellular automata can be viewed as either computers or logical universes where computers may be embbed.


What i am trying to understand is, is it always a given Cellular Automaton  is a computer ?
like Elementary Cellular Automata {ECA} rule 110 and rule 90, i know that rule 110 is universal which makes it a computer but what about rule 90 ... what about other ECA rules are they also computers ?

Suppose we have a cellular automaton (x), how do we know that it is a logical universe (as stated by the author), how can we know if it is a logical universe where computers can be embedd in or not and how can we know if it is just a computer ?

I know that logical universes are Cellular Automata, but what dimensions these universes should be to implement a computer easily, 1D like ECA or 2D like Conway's Game of Life ?
"... is it always a given Cellular Automaton is a computer?"...


I interpret "is a computer" as "being capable of universal computation" or in other words "being capable of simulating an arbitrary Turing machine".

The answer is clearly NO; a trivial example is a CA that doesn't modify the input:

0[0]0 -&gt; 0
0[0]1 -&gt; 0
0[1]0 -&gt; 1
0[1]1 -&gt; 1
1[0]0 -&gt; 0
1[0]1 -&gt; 0
1[1]0 -&gt; 1
1[1]1 -&gt; 1


(rule 204)

According to Wolfram's (qualitative) classification, only type-4 CAs exhibit a behaviour that can potentially be "universal". But it is an informal statement (like many others in Wolfram's NKS) ... in order to say that a particular CA is/is not Universal you must prove it formally.

For a more rigorous introduction to the argument I suggest you to read some research articles on the subject, for example: Kristian Lindgren, Mats G. Nordhal. Universal Computation in Simple One-Dimensional Cellular Automata. Complex Systems 4 (1990) 299-318

Or - for a good, more general, introduction to computational universality - read Chapter 7: The Grand Unified Theory of Computation of the (IMO excellent) book:  Cristopher Moore, Stephan Mertens. The Nature Of Computation (2011)