DP and Me:
Comment and Response
The following comments were received from pre-publication reviewers of "DP and Me."
Reviewer #1 (Computer Scientist)
I found the article interesting and stimulating in its description of Digital Physics, a field that was
outside of my awareness before, though the basic concepts are familiar.
The transition in the final two paragraphs, however, puzzles me. It would seem to me that this idea
of God as programmer and the universe as his program leads me to a conclusion that is in
opposition to that of the author. I, and all other people, as a part of that created universe, are
merely subroutines of the master program. Where does free will come in?
- The author responds: Both reviewers take from my essay that DP leads to the
conclusion that "I, and all other people, [are] part of that created universe . . . merely
subroutines of the master program." In the original draft, I incorrectly stated that I imagine
myself as a "character" in God's virtual reality "game," and I can see that this does indeed
imply that I see myself as part of the programming. Although this is one possible
conjecture (and it is the metaphysical position implicit in the motion picture The Thirteenth
Floor), it is not a necessary conclusion flowing from DP and it is not my view.
- Using the metaphor of the computer simulation, I see myself as the user -- the person playing the
game and interacting with, but not part of, the programming. In my judgment, the most
persuasive interpretation of QM (referred to below) supports the conjecture that conscious
beings (humans) are not part of the created universe -- at least, not in the same way as the
sun, moon and stars. Accordingly, I have modified my essay to read, "I can look around
and imagine myself as an interactive participant in the virtual reality simulation programmed
by God," and I have added a paragraph which attempts to make explicit the correspondences of the metaphor. I see myself as the user, not the programming and not
the machine, and I regret the confusion.
- The scientific question is whether quantum mechanical systems are "collapsed" into
a definite state by intrinsic qualities of the system itself; or whether the appearance of
definiteness requires the intervention of something outside of the system. The speculations
fall roughly into two categories: first, that some as-yet-undetected physical mechanism
operates on the elements of our universe when the physical system reaches some undefined
level of complexity. This supposes that the quantum effects we note on the sub-sub
microscopic scale disappear at the macroscopic scale because of some unknown type of
self-measurement going on within the system. The second category of speculation is that
something outside of QM itself operates on the system to produce a result. It is the je ne
sais quoi that turns mathematics into material upon measurement or observation, and it can
be termed "consciousness" or "mind" or perhaps "soul".
- The latter approach, which I favor, has been urged by Eugene Wigner and John
Wheeler, who argue the experimental results and logic to conclude essentially that a
QM "measurement" is not complete until it has been received by a conscious entity such as
a human being. Others are decidedly skeptical, insisting that scale and complexity alone, or
hidden variables within the system, or some other intrinsic mechanism, must suffice to
produce the experimental results. John Polkinghorne is an example of one who is skeptical
that humanness has any special place in the greater scheme of things.
- The scientific debate is unresolved, but the author is convinced by Wigner and
Wheeler (and by proclivity) that QM is the program and consciousness is an attribute of the
user. This conclusion is bolstered in the context of DP by Roger Penrose's argument that true consciousness cannot be achieved by a computational system. This implies that
human consciousness is not a part of the program, not generated as subroutines: we are
"other". We exist independently of the program, probably in the same realm as the
computer itself, perhaps in the realm of the programmer. In the same way that a video
game player "measures" the space and landscapes and characters inhabiting a particular
room by manipulating the joystick to bring it on screen -- thereby making that room appear
as dots on the computer monitor (while all other rooms remain inchoate as programming on
the CD-ROM which is not needed at the moment) -- so our consciousness "measures" the
states of QM quantities which affect us and leaves undisturbed those which do not. By this
interpretation, we humans are "players" and not "scenery" (and not scripted "characters").
- The question of free will is answered in this analogy. Just as a game player/user
has free will to turn left or turn right, to rescue or destroy an opponent, to act and seize the
prize or hesitate and be destroyed, so the human has free will to operate within the universe
created by God. Exercise of this free will must affect the outcome of the simulation for the
individual player (for the individual human) and for those with whom the user comes into
contact (think of networked, interactive, multi-user games). However, it cannot affect the
game itself any more than the user can change the digits burned into the CD-ROM placed
into the computer's drive. Nor can it impinge upon the prerogative of the programmer to
dictate an ultimate conclusion by literal deus ex machina, nor even to substitute an
improved game, version 2.01, as a new heaven and a new earth (Isa 65:17 and 66:22; 2Pet
3:13; Rev. 21:1).
Also, computer science has some interesting results regarding the limitations of computation, in
particular, that there are well-defined problems for which there is provably no possible computer
program for solving them. Doesn't this place a limit on God?
- The author responds: While I am aware of some of the limits of computation, I
do not agree that these might limit the programmer in any sense which affects the subjects
of the simulation. Alan Turing initially defined certain problems that were not computable.
The halting problem comes to mind. Also, there is Goedel's Incompleteness Theorem
which appears to show that no computational system -- no formal system of propositions
which is what a computer program is -- can be complete unto itself. (These are arguments
used by Penrose to show that computers are incapable of innate consciousness.) However,
Fredkin actually makes use of the halting problem to argue that DP can emulate quantum
randomness (see comments to reviewer #2). Nor do I expect this material world to be
perfect or complete in the way that God is perfect and complete.
- If I am making music, I may be "limited" by the tools I choose. If I choose an
oboe, there are certain sounds I will never produce; if I choose a piano, my range is
extended but still limited; if I choose a computerized digital synthesizer, my range is
extended further but still finite. However, I do not feel that these limitations of my
choosing -- or even in what is at hand for me to choose -- define me as a musician.
Similarly, I do not have any sense that God is a limited God because he chose to create a
digital universe for his children, any more than if he had built them a tree fort.
- I have not included any specific response to this concern in my revision, as it seems
to call for a more detailed discussion than the short essay will bear and I do not feel I have
any ready answer apart from the above. However, I have qualified the assertion that
"nothing is impossible with God" by continuing, "just as nothing is impossible with the
programmer who created and controls all things with respect to the subjects of the
And the computer program metaphor seems to argue against divine intervention rather than support
- The author responds: The cellular automata computer architecture posited by
DP indeed argues for the evolution of complexity in the material world by unattended
operation of the rules, and against micro-management interventions at the level of
commands for causing a mulberry tree to uproot itself and be planted in the sea (Lk 17:6).
For this reason, I tend to side with the evolutionists and against Creationists on the
question of whether God decided what he wanted humans to look like and then molded
them since, in my view, the shape of the earthen vessel is completely beside the point. On
the other hand, the large if not infinite possibilities of the digital computer itself supply
endless varieties of programming techniques of which strict CA is only one -- a facility
which makes the Fredkin Hypothesis "too easy" in the words of one reviewer. My own
feeling is that there are other programming features at work not yet incorporated in state-of
the-art cellular automata. However, I recognize that this is something of a punt on the
- I have attempted to address this concern in my discussion of the Newtonian
clockwork model, added toward the end of the essay.
So, though I think there is some value in thinking of God as a computer programmer, and this
article sets the table for this, the last two paragraphs yank away the table cloth and bring the dishes
crashing to the floor.
- The author responds: I think that is a bit strong. I have revised these paragraphs
somewhat, and I have included other qualifications throughout acknowledging that different views
are possible within the basic DP hypothesis. However, the conclusion of the essay doesn't really
purport to be anything but a personal credo, and I do not see that it is contradicted by anything that
precedes it. If the basic problem stems from the regrettable reference to myself as "character" and
the attendant misunderstanding about my views on free will, then perhaps the reviewer will be
content to indulge me. Otherwise, I can only hope that the disagreement will provoke further
comment such as the reviewers have provided.
Reviewer #2 (Physicist)
In this article, Ross Rhodes presents a thesis that the universe is basically a large computer
program being run by God. While I am not opposed to the journal publishing such a view, I feel
that this is really a very old concept hidden in the language of technology. Following Newton and
the beginning of the scientific process of modeling the universe via differential equations the
clockwork model of the universe was discussed and accepted by many. The idea was that the
universe was created and then set in motion to run itself out like a predictable clockwork
mechanism. Elaborate and complex mechanical models of the solar system, which would run to
demonstrate eclipses and other phenomena were constructed. The view of the author is essentially
this model with the twist that we have a "computer program" rather than a mechanical mechanism.
The author has a slight variation in that it seems that God has more freedom to reprogram the
system and provides a more active sustaining role for God than in the traditional clockwork model.
- The author responds: This is a most difficult comment, and I must leave it to more
general philosophers to exegete the nuances among world views. However, it seems to me
that such distinctions as "a 'computer program' rather than a mechanical mechanism," and
"God has [complete] freedom to reprogram the system" and "a more active sustaining role
for God than in the traditional clockwork model" are by no means trivial. One might as
well opine that Einstein's view of the universe was only a slight variation on the Newtonian
model, incorporating Lorentz transformations of coordinate spaces and throwing in a few
extra terms to account for the constancy of light speed. (I seem to recall reading comments
along this line by quantum physicists arguing that their science is more revolutionary than
general relativity.) For myself, imagining myself as a participant in God's computer
simulation has an entirely different quality from imagining myself caught up in God's
- There are, as well, many more antecedents to the computer model. The dichotomy
between the user and the programming recalls Bishop George Berkeley's 18th century
reaction against the Newtonian clockwork model through a strict idealist vision of matter
which exists only as a perception of mind -- a view which echoes in Christian Science
doctrine. Note however that the computer simulation model does not insist that the
programming is dependent on the mind for its existence, but only for its manifestation.
- The DP hypothesis is consonant, in part, with many such world views, ancient and
modern. It is an encompassing metaphor for the universe -- something that Schrödinger
thought to be quite beyond reach -- and a satisfying explanation for why the universe
appears to be fundamentally tied to mathematics in the same way that a computer program
is tied to its algorithms. I do not see it as criticism that DP leads to a world view which
recalls elements of earlier philosophical speculations, from Plato through the Principia and
beyond. How could it do otherwise?
- The best I can manage in my revision is to suggest some promising comparisons,
including a very brief reference to the clockwork model and to Berkeley's idealism, which I
have done in the new paragraphs of the essay.
To me the answer is too easy. For example, in what manner does human free will enter into this
model? If we are all just part of God's virtual reality program, then it seems that the program
determines my behavior rather than my faith and life choices. This is not the first model of the
universe that has faced this aspect with difficulty.
- The author responds: On the question of free will and the unwarranted implications
of my original draft, see my remarks to reviewer #1.
- With respect to the ease, I, too, find the model easier than any other proposed
conception of quantum reality -- by several orders of magnitude. Having delved into the
many worlds thesis, the mechanics of Bohm's hidden variables, and others, I find them not
so much impossible as hideously contrived. The computer model, by contrast, is
wonderfully simple and accessible. And although some approaches to programming an
emulation of the universe might be as complex and contrived as any of the above, the CA
model again brings us to simplicity itself. But simplicity and ease are not bad qualities for
an answer. William of Occam first took his "razor" to the multiplication of souls proposed
by Aquinas, and since that time the most elegant answer has generally been reckoned the
I do have some difficulties with some of the discussions of quantum mechanics. These difficulties
do not affect the author's main premise but do detract from enthusiasm for the author's main
thesis. Early in the paper the author implies that computers can reproduce the "position" of
electrons. What can be modeled is the probabilistic nature of the electron, or other quantum
system, but to imply that this really models the system is an overstatement because computers are
pseudo-random devices at best. If I know the starting random number, I can, in fact, predict all
following computations. The computer results "look" right but are still essentially different form
an unpredictable individual measurement.
- The author responds: In his seminal papers, Fredkin acknowledges that true
randomness is impossible in a digital universe. To obtain a suitably isomorphic model of
QM, Fredkin proposes an alternative involving "unknowable determinism." In brief,
Fredkin describes the operations of a cellular automaton in which there is no slack in the
computations. "Every part of space [every cell] is computing its future as fast [as]
possible, while information pours in from every direction." The consequence is that there is
no shortcut to obtaining the eventual result. Even in principle, and following a
deterministic set of rules, a programmer would have no choice but to simulate the
operations of the particular cellular automaton, input the initial conditions (which would be
the "state" of every cell in the universe of the cellular automaton), and run the program to
find out what happens. The result, according to Fredkin, is that randomness emerges as an
apparently intrinsic quality of the system as far as any observer can discern. This may be
seen as a computer science analog to a "hidden variables" approach to QM, incorporating
the flavor of chaos theory to explain how deterministic rules can result in something that
cannot be determined in advance, even in principle.
- Other solutions have been discussed in the digital physics community and there
is not as yet any widespread consensus. This week's Science notes that a good form of
randomness can be achieved by obtaining input from outside of the computer's
programming, rather than from an algorithm. So far as my original draft may have
implied that computer science has already achieved a true emulation of QM, randomness
and all, I have clarified the point in revision by substituting "simulate" for "reproduce" in
the third paragraph, and "mimic" for "model" in the fourth paragraph. I have also added a
brief reference to Fredkin's efforts to deal with the acknowledged limitations of digital
computing, which were necessary before he could propose DP in the first instance.
The suggestion that automata are the answer to modeling physical reality is a wonderful approach
for some systems but totally inappropriate for a great number of other systems. This approach
does deal with many interacting systems but generally only classical systems rather than quantum
I would also take issue with the notion that there is no underlying reality. That reality may not be
particulate in nature, but surely if there is no "reality" there is no certainty. Even if the reality is the
wave function, which is hard to envision but still real, it may be uncomfortable but still not the
vague nothing implied by the author.
- The author responds: This comment ("a great number of other systems") suggests
that there is a problem with CA of which I am not aware, and which I have not been able to
discover. There are indeed many mathematical problems which can be more easily solved
by other algorithms, but you can't create a universe by hard-wiring the solution to a
quadratic equation. In general, CA seems well-suited to applications in quantum field
theory. "In terms of structure as well as applications, [cellular automata] are the computer
scientist's counterpart to the physicist's concept of a 'field' governed by 'field
equations'." CA also offers a potential model for the sum over histories approach of
QED because information affecting all neighboring cells literally takes all paths to all
destinations. Similarly, it offers a good conceptual basis for the thorny problem of QM's
ubiquitous waves propagating without any medium.
- Apart from the question of randomness (referred to above and inherent in any
computer architecture including CA), the principal objection that I have found to CA as a
quantum modeling tool seems to be that it does not easily lend itself to non-local effects.
That is, if we accept the EPR paradox, Bell's Theorem, and the associated (and ongoing)
experimental verifications of these, then we may have to accept some form of non-local
interactions in our world. CA, on the other hand, is based fundamentally on local
interactions -- the interplay of each cell with its immediate neighbors according to their
programmed rules. As one person familiar with CA puts it, "The concept of a cell for each
point in space interacting only with its neighbors pretty much precludes you from building
a non-local model."
- Fredkin did not address non-locality in his exposition of a CA universe, and there
does not appear to be a consensus about it in the DP community. Following on Fredkin's
solution to the randomness problem, it may be that non-locality is an "emergent"
characteristic, i.e., necessarily appearing to the user but actually incident to some other
computational process. Analytically, the problems of randomness and non-locality have
- In any event, considering the fits that non-locality gives to every other variety of
theoretical physicist, it seems unfair to hold this against DP's reliance on cellular automata.
Generally speaking, the computer is a particularly good metaphor for the concept of non
locality because, for example, two apparently independent and unrelated pixels at opposite
sides of the monitor may be intricately connected in the programming. Bear in mind that
CA is not really a collection of independent computers, but a single computer running a
collection of identical subroutines. Since the "cells" are never truly independent (or, at
least, are never more independent than the programmer wishes to make them), it would be
possible in principle to allow for interactions with whatever other cells are called for,
regardless of whether they are defined for purposes of the simulation as "neighbors." This
would seem to mar the beautiful simplicity of the CA model which is its most appealing
quality, but it is not forbidden.
- I have not addressed these concerns in my revision, first, because I am not entirely
sure that I understand the comment, and second, because the discussion seems a bit more
technical than I had intended for the essay.
- The author responds: The predominant attitude I have come across with respect to
the wavefunction is that it is a mere calculational tool, and not an independent reality.
- Be that as it may, the question of reality becomes somewhat confused in the
digital physics model and metaphor, because one must refer to perhaps six realms
of experience, each with distinct attributes. These are 1) the physical world, which
corresponds to the images projected on a computer screen; 2) the process that
defines the physical world (the "wavefunction"), which corresponds to the
underlying programming code; 3) the process of measurement governing the
interpretation and projection of the data, which corresponds roughly to the user
interface; 4) the non-corporeal existence of the conscious being (me), which
corresponds to the realm of existence of the user when not engaged in the
simulation (i.e., that which we would experience if the simulation terminated and
we walked out of the arcade); 5) the realm of the universe-generating mechanism
itself, which corresponds to the room and machinery of the ultimate computer
(which may or may not be the same as the realm of the user); and 6) the realm of
God, which corresponds to the existence of the programmer (and which, again,
may or may not be the same as the realm of the user and/or the machinery).
- In asking whether the subject under contemplation is "real," I tend to use a
Cartesian touchstone: "Does it have separate and independent existence in the same way
that I think and, therefore, am?" Employing this criterion, realms 1, 2, and 3 appear
artificial and, to my way of thinking, do not constitute "reality"; realms 4, 5, and 6 have at
least the same level of existence as my consciousness and, accordingly, I think of them as
"real." This is not to say that the universe, with its underlying programming and processes,
has no existence. The wavefunction certainly exists independently of me -- I cannot change
it -- just as my computer's operating system and applications exist; however, it is plainly a
different order of existence from that of the user. Perhaps it would be best to discard the
distinction between real and unreal, and simply stick with the metaphor as parable.
- In revision, I have qualified my thumbnail of the Copenhagen Interpretation to state
that "there is no underlying physical existence associated with the fundamental units of our
world." I have also added a paragraph in which I attempt to make explicit the
correspondences of the metaphor.
Lastly, the notion that one measurement erases previous quantities is not quite correct. It is true
that one can not simultaneously determine conjugate variables but this is subtly different from the
idea that one has erased something, commuting variables could both be measured without any
effect on each other. This is not so much an erasing as it is a recognition that one simply cannot
know all this even if one wishes to.
I compliment the author for struggling with difficult issues but suggest that this work needs a bit
- The author responds: If I understand this comment correctly, the reviewer is saying
two things: first, that "erasing" is not a good description of the effect of measuring one
complementary property on its partner; and second, that measuring one property (which
happens to have a complementary property) may have no effect whatsoever on other
properties which are not complementary to that property.
- To the first comment, my use of the word "erasing" was limited in a strict sense to
the situation where the complementary properties being measured are quantized in an
either/or relationship. Thus, I speak of measuring spin and thereby losing all definiteness
regarding a previous measurement of angular momentum. If one has lost all definiteness
regarding previously acquired knowledge, one must make a new measurement which will
bear no relation to the previous measurement of the same property of the same quantum
unit. This seems equivalent to erasure in the computer analogy, but perhaps there is a
distinction to be made. Discretion being the better part of valor, I have revised the
essay to erase the reference to "erasing effect," substituting an allusion to "the inconstant
qualities of computer variables." I hope this addresses the reviewer's concern.
- To the second comment, I do not see any conflict between my reference to one
aspect of QM (the measurement effect with respect to complementary properties), and an
altogether different aspect (the lack of a measurement effect with respect to other
properties). Perhaps the reviewer felt that my statement implied a broader application than
intended. In any event, I hope that removing the reference to "erasing" will eliminate the
|E. Wigner, "Remarks on the Mind-body Question," in The Scientist Speculates, I.J. Good, ed. (Basic
Books, New York 1961); also reprinted in J.A. Wheeler and W.H. Zurek, eds., below.|
|J. Wheeler and W. Zurek, ed., Quantum theory and measurement (Princeton University Press, 1983).|
|J.C. Polkinghorne, The Quantum World (Princeton Univ. Press 1984) at 64-67.|
|R. Penrose, Shadows of the Mind (Oxford Univ. Press 1994).|
|Tom Ostoma and Mike Trushyk, "Cellular Automata Theory and Physics: A New Paradigm For The
Unification of Physics," Los Alamos National Laboratory e-Print archive (1999).
|"Pick a Number From 1 to 2^32," Science, vol. 289 no. 5476 (7 July 2000) at 7.|
|T. Toffolli, "Non-Conventional Computers" in J. Webster, ed., Encyclopedia of Electrical and
Electronics Engineering, John Wiley & Sons (New York 1998).|
|Jim Calfas (comment in Digital Physics e-mail list, July 3, 2000). I am indebted to the members
of the Digital Physics mailing list for their comments on this question.|
|E.g., N. Bohr ("The entire formalism is to be regarded as a tool for deriving predictions, of definite or
statistical character, as regards information obtainable under experimental conditions described in
classical terms"), quoted in J.C. Polkinghorne, The Quantum World at 79 (citing M. Jammer, The
Philosophy of Quantum Mechanics); N. Herbert, Quantum Reality at 95 ("Most physicists treat the
wave function as a mere calculation device, not as a real wave located somewhere in space"); but see
J.C. Polkinghorne, The Quantum World at 80-81 ("[I]t is . . . difficult to think of a wavefunction as
a mere calculational device . . .. [The waveform] is certainly the object of quantum mechanical
discourse and, for all the peculiarity of its collapse, its subtle essence may be the form that reality
has to take on the atomic scale and below").|
|My thinking on this owes much to the discussion by David Z. Albert in the first chapter of his
book, Quantum Mechanics and Experience. If Mr. Albert has simplified the physics for the purpose
of illustration, then I may well have simplified the concept in a way that is subtly different, perhaps
even wrong. (Mr. Albert does not himself suggest erasure as an explanation.)|
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