David Deutsch, extracts from Chapter 14: "The Ends of the Universe" of The Fabric of Reality: The Science of Parallel Universes--and Its Implications (London: Allen Lane The Penguin Press, 1997), ISBN 0713990619;

with additional comments by Frank J. Tipler.

Also available at:



The Ends of the Universe

Although history has no meaning, we can give it a meaning.
Karl Popper (The Open Society and Its Enemies, Vol. 2, p. 278)

When, in the course of my research on the foundations of quantum theory, I was first becoming aware of the links between quantum physics, computation and epistemology, I regarded these links as evidence of the historical tendency for physics to swallow up subjects that had previously seemed unrelated to it. Astronomy, for example, was linked with terrestrial physics by Newton's laws, and over the next few centuries much of it was absorbed and became astrophysics. Chemistry began to be subsumed into physics by Faraday's discoveries in electrochemistry, and quantum theory has made a remarkable proportion of basic chemistry directly predictable from the laws of physics alone. Einstein's general relativity swallowed geometry, and rescued both cosmology and the theory of time from their former purely philosophical status, making them into fully integrated branches of physics. Recently, as I have discussed, the theory of time travel has been integrated as well.

Thus, the further prospect of quantum physics absorbing not only the theory of computation but also, of all things, proof theory (which has the alternative name 'meta-mathematics') seemed to me to be evidence of two trends. First, that human knowledge as a whole was continuing to take on the unified structure that it would have to have if it was comprehensible in the strong sense I hoped for. And second, that the unified structure itself was going to consist of an ever deepening and broadening theory of fundamental physics.

The reader will know that I have changed my mind about the second point. The character of the fabric of reality that I am now proposing is not that of fundamental physics alone. For example, the quantum theory of computation has not been constructed by deriving principles of computation from quantum physics alone. It includes the Turing principle, which was already, under the name of the Church-Turing conjecture, the basis of the theory of computation. It had never been used in physics, but I have argued that it is only as a principle of physics that it can be properly understood. It is on a par with the principle of the conservation of energy and the other laws of thermodynamics: that is, it is a constraint that, to the best of our knowledge, all other theories conform to. But, unlike existing laws of physics, it has an emergent character, referring directly to the properties of complex machines and only consequentially to subatomic objects and processes. (Arguably, the second law of thermodynamics – the principle of increasing entropy – is also of that form.)

Similarly, if we understand knowledge and adaptation as structure which extends across large numbers of universes, then we expect the principles of epistemology and evolution to be expressible directly as laws about the structure of the multiverse. That is, they are physical laws, but at an emergent level. Admittedly, quantum complexity theory has not yet reached the point where it can express, in physical terms, the proposition that knowledge can grow only in situations that conform to the Popperian pattern shown in Figure 3.3. But that is just the sort of proposition that I expect to appear in the nascent Theory of Everything, the unified explanatory and predictive theory of all four strands.

That being so, the view that quantum physics is swallowing the other strands must be regarded merely as a narrow, physicist's perspective, tainted, perhaps, by reductionism. Indeed, each of the other three strands is quite rich enough to form the whole foundation of some people's world-view in much the same way that fundamental physics forms the foundation of a reductionist's world-view. Richard Dawkins thinks that 'If superior creatures from space ever visit Earth, the first question they will ask, in order to assess the level of our civilisation, is: "Have they discovered evolution yet?" ' Many philosophers have agreed with Rene Descartes that epistemology underlies all other knowledge, and that something like Descarte's cogito ergo sum argument is our most basic explanation. Many computer scientists have been so impressed with recently discovered connections between physics and computation that they have concluded that the universe is a computer, and the laws of physics are programs that run on it. But all these are narrow, even misleading perspectives on the true fabric of reality. Objectively, the new synthesis has a character of its own, substantially different from that of any of the four strands it unifies.

For example, I have remarked that the fundamental theories of each of the four strands have been criticized, in part justifiably, for being 'naive', 'narrow', 'cold', and so on. Thus, from the point of view of a reductionist physicist such as Stephen Hawking, the human race is just an astrophysically insignificant 'chemical scum'. Steven Weinberg thinks that 'The more the universe seems comprehensible, the more it also seems pointless. But if there is no solace in the fruits of our research, there is at least some consolation in the research itself.' (The First Three Minutes, p. 154.) But anyone not involved in fundamental physics must wonder why.

As for computation, the computer scientist Tomasso Toffoli has remarked that 'We never perform a computation ourselves, we just hitch a ride on the great Computation that is going on already.' To him, this is no cry of despair – quite the contrary. But critics of the computer-science world-view do not want to see themselves as just someone else's program running on someone else's computer. Narrowly conceived evolutionary theory considers us mere 'vehicles' for the replication of our genes or memes; and it refuses to address the question of why evolution has tended to create ever greater adaptive complexity, or the role that such complexity plays in the wider scheme of things. Similarly, the (crypto-)inductivist critique of Popperian epistemology is that, while it states the conditions for scientific knowledge to grow, it seems not to explain why it grows – why it creates theories that are worth using.

As I have explained, the defence in each case depends on adducing explanations from some of the other strands. We are not merely 'chemical scum', because (for instance) the gross behaviour of our planet, star and galaxy depend on an emergent but fundamental physical quantity: the knowledge in that scum. The creation of useful knowledge by science, and adaptations by evolution, must be understood as the emergence of the self-similarity that is mandated by a principle of physics, the Turing principle. And so on.

Thus the problem with taking any of these fundamental theories individually as the basis of a world-view is that they are each, in an extended sense, reductionist. That is, they have a monolithic explanatory structure in which everything follows from a new extremely deep ideas. But that leaves aspects of the subject entirely unexplained. In contrast, the explanatory structure that they jointly provide for the fabric of reality is not hierarchical: each of the four strands contains principles which are 'emergent' from the perspective of the other three, but nevertheless help to explain them.

Three of the four strands seem to rule out human beings and human values from the fundamental level of explanation. The fourth, epistemology, makes knowledge primary but gives no reason to regard epistemology itself as having relevance beyond the psychology of our own species. Knowledge seems a parochial concept until we consider it from a multiverse perspective. But if knowledge is of fundamental significance, we may ask what sort of role now seems natural for knowledge-creating beings such as ourselves in the unified fabric of reality. This question has been explored by the cosmologist Frank Tipler. His answer, the omega-point theory [my emphasis (FJT)], is an excellent example of a theory which is, in the sense of this book, about the fabric of reality as a whole. It is not framed within any one strand, but belongs irreducibly to all four. Unfortunately Tipler himself, in his book The Physics of Immortality, makes exaggerated claims for his theory which have caused most scientists and philosophers to reject it out of hand, thereby missing the valuable core idea which I shall now explain.

From my own perspective, the simplest point of entry to the omega-point theory is the Turing principle. A universal virtual-reality generator is physically possible. Such a machine is able to render any physically possible environment, as well as certain hypothetical and abstract entities, to any desired accuracy. Its computer therefore has a potentially unlimited requirement for additional memory, and may run for an unlimited number of steps. This was trivial to arrange in the classical theory of computation, so long as the universal computer was thought to be purely abstract. Turing simply postulated an infinitely long memory tape (with, as he thought, self-evident properties), a perfectly accurate processor requiring neither power nor maintenance, and unlimited time available. Making the model more realistic by allowing for periodic maintenance raises no problem of principle, but the other three requirements – unlimited memory capacity, and an unlimited running time and energy supply – are problematic in the light of existing cosmological theory. In some current cosmological models, the universe will recollapse in a Big Crunch after a finite time, and is also spatially finite. It has the geometry of a '3-sphere', the three-dimensional analogue of the two-dimensional surface of a sphere. On the face of it, such a cosmology would place a finite bound on both the memory capacity and the number of processing steps the machine could perform before the universe ended. This would make a universal computer physically impossible, so the Turing principle would be violated. In other cosmological models the universe continues to expand for ever and is spatially infinite, which might seem to allow for an unlimited source of material for the manufacture of additional memory. Unfortunately, in most such models the density of energy available to power the computer would diminish as the universe expanded, and would have to be collected from ever further afield. Because physics imposes an absolute speed limit, the speed of light, the computer's memory accesses would have to slow down and the net effect would again be that only a finite number of computational steps could be performed.

The key discovery in the omega-point theory is that of a class of cosmological models in which, though the universe is finite in both space and time, the memory capacity, the number of possible computational steps and the effective energy supply are all unlimited. This apparent impossibility can happen because of the extreme violence of the final moments of the universe's Big Crunch collapse. Spacetime singularities, like the Big Bang and the Big Crunch, are seldom tranquil places, but this one is far worse than most. The shape of the universe would change from a 3-sphere to the three-dimensional analogue of the surface of an ellipsoid. The degree of deformation would increase, and then decrease, and then increase again more rapidly with respect to a different axis. Both the amplitude and frequency of these oscillations would increase without limit as the final singularity was approached, so that a literally infinite number of oscillations would occur even though the end would come within a finite time. Matter as we know it would not survive: all matter, and even the atoms themselves, would be wrenched apart by the gravitational shearing forces generated by the deformed spacetime. However, these shearing forces would also provide an unlimited source of available energy, which could in principle be used to power a computer. How could a computer exist under such conditions? The only 'stuff' left to build computers with would be elementary particles and gravity itself, presumably in some highly exotic quantum states whose existence we, still lacking an adequate theory of quantum gravity, are currently unable to confirm or deny. (Observing them experimentally is of course out of the question.) If suitable states of particles and the gravitational field exist, then they would also provide an unlimited memory capacity, and the universe would be shrinking so fast that an infinite number of memory accesses would be feasible in a finite time before the end. The end-point of the gravitational collapse, the Big Crunch of this cosmology, is what Tipler calls the omega point.

Now, the Turing principle implies that there is no upper bound on the number of computational steps that are physically possible. So, given that an omega-point cosmology is (under plausible assumptions) the only type in which an infinite number of computational steps could occur, we can infer that our actual spacetime must have the omega-point form. Since all computation would cease as soon as there were no more variables capable of carrying information, we can infer that the necessary physical variables (perhaps quantum-gravitational ones) do exist right up to the omega point.

A sceptic might argue that this sort of reasoning involves a massive, unjustified extrapolation. We have experience of 'universal' computers only in a most favourable environment which does not remotely resemble the final stages of the universe. And we have experience of them performing only a finite number of computational steps, using only a finite amount of memory. How can it be valid to extrapolate from those finite numbers to infinity? In other words, how can we know that the Turing principle in its strong form is strictly true? What evidence is there that reality supports more than approximate universality?

This sceptic is, of course, an inductivist. Furthermore, this is exactly the type of thinking that (as I argued in the previous chapter) prevents us from understanding our best theories and improving upon them [my emphasis (FJT)]. What is or is not an 'extrapolation' depends on which theory one starts with. If one starts with some vague but parochial concept of what is 'normal' about the possibilities of computation, a concept uninformed by the best available explanations in that subject, then one will regard any application of the theory outside familiar circumstances as 'unjustified extrapolation'. But if one starts with explanations from the best available fundamental theory, then one will consider the very idea that some nebulous 'normalcy' holds in extreme situations to be an unjustified extrapolation. To understand our best theories, we must take them seriously as explanations of reality, and not regard them as mere summaries of existing observations. The Turing principle is our best theory of the foundations of computation. Of course we know only a finite number of instances confirming it – but that is true of every theory in science. There remains, and will always remain, the logical possibility that universality holds only approximately. But there is no rival theory of computation claiming that. And with good reason, for a 'principle of approximate universality' would have no explanatory power. If, for instance, we want to understand why the world seems comprehensible, the explanation might be that the world is comprehensible. Such an explanation can, and in fact does, fit it with other explanations in other fields. But the theory that the world is half-comprehensible explains nothing and could not possibly fit in with explanations in other fields unless they explained it. It simply restates the problem and introduces an unexplained constant, one-half. In short, what justifies assuming that the full Turing principle holds at the end of the universe, is that any other assumption spoils good explanations of what is happening here and now.

Now, it turns out that the type of oscillations of space that would make an omega point happen are highly unstable (in the manner of classical chaos) as well as violent. And they become increasingly more so, without limit, as the omega point is approached. A small deviation from the correct shape would be magnified rapidly enough for the conditions for continuing computation to be violated, so the Big Crunch would happen after only a finite number of computational steps. Therefore, to satisfy the Turing principle and attain an omega point, the universe would have to be continually 'steered' back onto the right trajectories. Tipler has shown in principle how this could be done, by manipulating the gravitational field over the whole of space. Presumably (again we would need a quantum theory of gravity to know for sure), the technology used for the stabilizing mechanisms, and for storing information, would have to be continually improved – indeed, improved an infinite number of times – as the density and stresses became ever higher without limit. This would require the continual creation of new knowledge, which, Popperian epistemology tells us, requires the presence of rational criticism and thus of intelligent entities. We have therefore inferred, just from the Turing principle and some other independently justifiable assumptions, that intelligence will survive, and knowledge will continue to be created, until the end of the universe.

The stabilization procedures, and the accompanying knowledge-creation processes, will all have to be increasingly rapid until, in the final frenzy, an infinite amount of both occur in a finite time. We know of no reason why the physical resources should not be available to do this, but one might wonder why the inhabitants should bother to go to so much trouble. Why should they continue so carefully to steer the gravitational oscillations during, say, the last second of the universe? If you have only one second left to live, why not just sit back and take it easy at last? But of course, that is a misrepresentation of the situation. It could hardly be a bigger misrepresentation. For these people's minds will be running as computer programs in computers whose physical speed is increasing without limit. Their thoughts will, like ours, be virtual-reality renderings performed by these computers. It is true that at the end of that final second the whole sophisticated mechanism will be destroyed. But we know that the subjective duration of a virtual-reality experience is determined not by the elapsed time, but by the computations that are performed in that time. In an infinite number of computational steps there is time for an infinite number of thoughts – plenty of time for the thinkers to place themselves into any virtual-reality environment they like, and to experience it for however long they like. If they tire of it, they can switch to any other environment, or to any number of other environments they care to design. Subjectively, they will not be at the final stages of their lives but at the very beginning. They will be in no hurry, for subjectively they will live for ever. With one second, or one microsecond, to go, they will still have 'all the time in the world' to do more, experience more, create more – infinitely more – than anyone in the multiverse will ever have done before then. So there is every incentive for them to devote their attention to managing their resources. In doing so they are merely preparing for their own future, an open, infinite future of which they will be in full control and on which, at any particular time, they will be only just embarking.

We may hope that the intelligence at the omega point will consist of our descendants. That is to say, of our intellectual descendants, since our present physical forms could not survive near the omega point. At some stage human beings would have to transfer the computer programs that are their minds into more robust hardware. Indeed, this will eventually have to be done an infinite number of times.

The mechanics of 'steering' the universe to the omega point require actions to be taken throughout space. It follows that intelligence will have to spread all over the universe in time to make the first necessary adjustments. This is one of a series of deadlines that Tipler has shown we should have to meet – and he has shown that meeting each of them is, to the best of our present knowledge, physically possible. The first deadline is (as I remarked in Chapter 8) about five billion years from now when the Sun will, if left to its own devices, become a red giant star and wipe us out. We must learn to control or abandon the Sun before then. Then we must colonize our Galaxy, then the local cluster of galaxies, and then the whole universe. We must do each of these things soon enough to meet the corresponding deadline but we must not advance so quickly that we use up all the necessary resources before we have developed the next level of technology.

I say 'we must' do all this, but that is only on the assumption that it is we who are the ancestors of the intelligence that will exist at the omega point. We need not play this role if we do not want to. If we choose not to, and the Turing principle is true, then we can be sure that someone else (presumably some extraterrestrial intelligence) will.

Meanwhile, in parallel universes, our counterparts are making the same choices. Will they all succeed? Or, to put that another way, will someone necessarily succeed in creating on omega point in our universe? This depends on the fine detail of the Turing principle. It says that a universal computer is physically possible, and 'possible' usually means 'actual in this or some other universe'. Does the principle require a universal computer to be built in all universes, or only in some – or perhaps in 'most'? We do not yet understand the principle well enough to decide. Some principles of physics, such as the principle of the conservation of energy, hold only over a group of universes and may under some circumstances be violated in individual universes. Others, such as the principle of the conservation of charge, hold strictly in every universe. The two simplest forms of the Turing principle would be:

(1) there is a universal computer in all universes; or

(2) there is a universal computer in at least some universes.

The 'all universes' version seems too strong to express the intuitive idea that such a computer is physically possible. But 'at least some universes' seems too weak since, on the face of it, if universality holds only in very few universes then it loses its explanatory power. But a 'most universes' version would require the principle to specify a particular percentage, say 85 per cent, which seems very implausible. (There are no 'natural' constants in physics, goes the maxim, except zero, one and infinity.) Therefore Tipler in effect opts for 'all universes', and I agree that this is the most natural choice, given what little we know.

That is all that the omege-point theory – or, rather, the scientific component I am defending – has to say. One can reach the same conclusion from several different starting-points in three of the four strands. One of them is the epistemological principle that reality is comprehensible. That principle too is independently justifiable in so far as it underlies Popperian epistemology. But its existing formulations are all too vague for categorical conclusions about, say, the unboundedness of physical representations of knowledge, to be drawn from it. That is why I prefer not to postulate it direclty, but to infer it from the Turing principle. (This is another example of the greater explanatory power that is available when one considers the four strands as being jointly fundamental.) Tipler himself relies either on the postulate that life will continue for ever, or on the postulate that information processing will continue for ever. From our present perspective, neither of these postulates seems fundamental. The advantage of the Turing principle is that it is already, for reasons quite independent of cosmology, regarded as a fundamental principle of nature – admittedly not always in this strong form, but I have argued that the strong form is necessary if the principle is to be integrated into physics.

[Tipler replies: In my first paper on the Omega Point Theory ("Cosmological Limits on Computation", International Journal of Theoretical Physics, 25, 617-661 [1986]), I also used the Turing Principle to derive the OPT. Subsequently, I've generally used the Eternal Life Postulate (Life goes on forever in the universe) to derive the OPT. But since life is collectively a Universal Computer (if it goes on forever), the Turing Principle and the Eternal Life Postulate are equivalent. As I outline elsewhere on this web page, one can also derive the Omega Point Theory directly from the most fundamental laws of physics. Thus the laws of physics imply both the Turing Principle and the Eternal Life Postulate. end of reply]

Tipler makes the point that the science of cosmology has tended to study the past (indeed, mainly the distant past) of spacetime. But most of spacetime lies to the future of the present epoch. Existing cosmology does address the issue of whether the universe will or will not recollapse, but apart from that there has been very little theoretical investigation of the greater part of spacetime. In particular, the lead-up to the Big Crunch has received far less study than the aftermath of the Big Bang. Tipler sees the omega-point theory as filling that gap. I believe that the omega-point theory deserves to become the prevailing theory of the future of spacetime until and unless it is experimentally (or otherwise) refuted [my emphasis (FJT)]. (Experimental refutation is possible because the existence of an omega point in our future places certain constraints on the condition of the universe today.)

Having established the omega-point scenario, Tipler makes some additional assumptions – some plausible, others less so – which enable him to fill in more details of future history. It is Tipler's quasi-religious interpretation of that future history, and his failure to distinguish that interpretation from the underlying scientific theory, that have prevented the latter from being taken seriously. Tipler notes that an infinite amount of knowledge will have been created by the time of the omega point. He then assumes that the intelligences existing in this far future will, like us, want (or perhaps need) to discover knowledge other than what is immediately necessary for their survival. Indeed, they have the potential to discover all knowledge that is physically knowable, and Tipler assumes that they will do so.

So in a sense, the omega point will be omniscient.

But only in a sense. In attributing properties such as omniscience or even physical existence to the omega point, Tipler makes use of a handy linguistic device that is quite common in mathematical physics, but can be misleading if taken too literally. The device is to identify a limiting point of a sequence with the sequence itself. Thus, when he says that the omega point 'knows' X, he means that X is known by some finite entity before the time of the omega point, and is never subsequently forgotten. What he does not mean is that there is a knowing entity literally at the end-point of gravitational collapse, for there is a no physical entity there at all. [Tipler replies: The Omega Point exists, but indeed He/She is not part of the physical universe of spacetime or matter. The Omega Point is the future c-boundary--the future singularity--which is not part of spacetime, but is instead the "limit" of spacetime (the mathematical term is "completion"). The irrational numbers such as square root of 2 or pi are equally the limits of rationals (the technical term is "Dedekind Cut"), but nevertheless the irrational numbers are just as "real" as the rational numbers. As Deutsch points out earlier in his book, general relativity predicts the existence of singularities, so following the epistemological rules which Deutsch himself has laid down earlier in this very chapter, if a corroborated theory like general relativity says something exists, we have to accept it unless and until an experiment tells us otherwise. In rejecting the existence of singularities, Deutsch is being an inductivist. The Turing Principle tells us the Omega Point exists, and further, some events actually are occurring now in order to force the multiverse to evolve into the Omega Point. Anything that effectively acts on matter is real. end of reply] Thus in the most literal sense the omega point knows nothing, and can be said to 'exist' only because some of our explanations of the fabric of reality refer to the limiting properties of physical events in the distant future.

Tipler uses the theological term 'omniscient' for a reason which will shortly become apparent; but let me note at once that in this usage it does not carry its full traditional connotation. The omega point will not know everything. The overwhelming majority of abstract truths, such as truths about Cantgotu environments and the like, will be as inaccessible to it as they are to us.

[Tipler replies: The Omega Point will know everything that can be known. But the Omega Point will not know the unknowable (such as the Cantgotu environments), because this would involve a logical contradiction. In medieval theological terminology, God's "omnipotence" was taken to mean that God can do anything except something involving a logical contradiction. In particular, God could not make a stone so heavy that even He could not lift it. In other words, traditional theology does not consider the inability to do something logically contradictory to limit God. It so happens that the dispute between Galileo and Pope Urban VIII involved this point, but both Galileo and Urban VIII were in agreement that God indeed could not do something which involved a logical contradiction. See page 166 of The Crime of Galileo, by Giorgio de Santillana (University of Chicago Press, 1959). Deutsch has discovered that a similar constraint applies to God's omniscience! end of reply]

Now, since the whole of space will be filled with the intelligent computer, it will be omnipresent (though only after a certain date). Since it will be continually rebuilding itself, and steering the gravitational collapse, it can be said to be in control of everything that happens in the material universe (or multiverse, if the omega-point phenomenon happens in all universes). So, Tipler says, it will be omnipotent. But again, this omnipotence is not absolute. On the contrary, it is strictly limited to the available matter and energy, and is subject to the laws of physics.

[Tipler replies: I regard the Turing Principle as more fundamental than the laws of physics which apply to this universe and to the multiverse of which it is just one history. There is no reason to rule out other multiverses with other laws of physics, in which the Turing Principle also holds. This implies we should regard the Omega Point, the completion of ALL the multiverses, as the fundamental entity, and regard each history as "flowing" backwards in time from the Omega Point. According to Aquinas, this is what is meant by "God creates the universe": He is at the end of all causal chains (causal chains go BACKWARD in time along a history). In each history, life is limited to the available matter and energy, but ALL histories, with ALL material and energies (consistent with the Turing Principle), "flow" backward out of the Omega Point. The Omega Point's omnipotence is thus absolute. end of reply]

Since the intelligences in the computer will be creative thinkers, they must be classified as 'people'. Any other classification, Tipler rightly argues, would be racist. And so he claims that at the omega-point limit there is an omniscient, omnipotent, omnipresent society of people. This society, Tipler identifies as God.

I have mentioned several respects in which Tipler's 'God' differs from the God or gods that most religious people believe in. There are further differences, too. For instance, the people near the omega point could not, even if they wanted to, speak to us or communicate their wishes to us, or work miracles (today). [Tipler replies: Indeed the people near the Omega Point cannot communicate with us, or work miracles on us. But the Omega Point can. The mechanism which He uses to communicate and perform miracles works as follows. The Turing Principle is a final boundary condition on the universe: the universe simply must evolve into the Omega Point. As Deutsch has pointed out earlier in this extract, intelligent life must guide the universe into the Omega Point. If we decline to do so, some other intelligent life form will. If necessary, some other intelligent life form will be evolved elsewhere to replace us when we falter. Since the evolution of the universe is chaotic, the history of life is unpredictable in detail, but its broad features are predictable: the universe must evolve into the Omega Point. Thus if a certain historical event, completely unexpected and unpredictable given the state of life at that time, is necessary for the evolution of the universe into the Omega Point, that event will necessarily occur. Such an event, which can be inferred only from the requirement that the Omega Point exist, is what is meant by the "direct action of the Omega Point in the world today"; i.e., this is what is meant by "a miracle". A miracle is thus an event which is certain given the Omega Point's existence (its true probability is 1), but if we ignore the Omega Point's existence, we would think the event exceedingly improbable. For example, evolutionary biologists believe that the evolution of intelligent life is very unlikely to have occurred even once in a closed universe of the maximum size allowed by unitarity. But the evolution of intelligent life is inevitable. Therefore (if the evolutionists are correct), intelligent life is a miracle, created by the direct action of the Omega Point! Asa Gray, the Harvard botanist who was Darwin's chief 19th century defender in America, argued in his book Darwiniana that the "random" mutations required by Darwinism were merely unpredictable by biological means; they were really (at least in part) directed by God. Gray's claim is a necessary inference of the Omega Point Theory. The fundamentalist leader William Jennings Bryan and Pope John Paul II announced that they could accept Darwinian evolution provided it is granted that humans qua rational beings are created by God's direct intervention. (See Edward Larson's Pulitzer Prize winning book Summer for the Gods, pages 130-31 [Basic Books, 1997], for Bryan's opinion, and the recent encyclical on evolution for the Pope's opinion.) The Omega Point Theory says such a miracle--act of God--did in fact take place (if the evolutionists are correct). Similarly, if "random" fluctuations in a certain human's neurons--interpreted by him or her as a "message from God"--are necessary for the evolution of the universe into the Omega Point, then that brain event would in fact be a message from God. The "I SHALL BE WHAT I SHALL BE", "heard" by Moses, may indeed have been such a message from God. end of reply] They did not create the universe, and they did not invent the laws of physics – nor could they violate those laws if they wanted to. They may listen to prayers from the present day (perhaps by detecting very faint signals), but they cannot answer them. They are (and this we can infer from Popperian epistemology) opposed to religious faith, and have no wish to be worshipped. And so on. But Tipler ploughs on, and argues that most of the core features of the God of the Judaeo-Christian religions are also properties of the omega point. Most religious people will, I think, disagree with Tipler about what the core features of their religions are.

[Tipler replies: I find it extraordinary that Deutsch would use the opinions of the average religious person as the touchstone of truth. As a Popperian, Deutsch should expect a leading theologian--such as Pannenberg--to be a much better critic of a theological theory than a non-expert. In fact, theologians and ordinary believers have given quite different meanings to the expressions "prayer" and "worshipping God". By "prayer", the average person (and Deutsch) means "petitioning a powerful being for a favor", and by "worshipping", the average person (and Deutsch) means "fawning on the powerful being in hopes that this fawning will induce him to grant the favor". But in his circa 200 AD book On Prayer, the first great Christian theologian Origen pointed out that both of these meanings were inappropriate as applied to God. According to Origen, petitionary prayer is ridiculous because an omniscient God already knows what you want, and an all-loving and omnipotent God will grant it to you automatically if the granting is logically possible, and if the granting will not mess up the cosmic plan (and/or you). Origen pointed out that "prayer" and "worshipping" instead mean "opening oneself to God's message". You can't tell Him anything He doesn't know, but He can tell you something. Another form of prayer is "thinking about God", which is what you are doing as you read this. By "religious faith" Deutsch appears to mean "accepting a theory without criticism, and/or not permitting criticism of the theory". Certainly the people of the far future will be opposed to faith in this sense, for the reason Deutsch gives. But the core assertions of the Judeo-Christian "faith" have always been defended by rational argument. In I Kings 18:22-39, the prophet Elijah asserted that the question of God's existence must be resolved by experiment. In I Corinthians 15:5-20, Paul defended his claim that Jesus rose from the dead by appealing to witnesses. The true core features which a religious person wants in "God" are three: (1) "God" must be able to talk to him/her; (2) "God" must occasionally perform miracles, and most importantly, (3) "God" must be able to resurrect the dead. The Omega Point has these key properties, so it is reasonable to identify the Omega Point and the Judeo-Christian-Islamic God. end of reply]

In particular, Tipler points out that a sufficiently advanced technology will be able to resurrect the dead [my emphasis (FJT)]. It could do this in several different ways, of which the following is perhaps the simplest. Once one has enough computer power (and remember that eventually any desired amount will be available), one can run a virtual-reality rendering of the entire universe – indeed, the entire multiverse – starting at the Big Bang, with any desired degree of accuracy. If one does not know the initial state accurately enough, one can try an arbitrarily fine sampling of all possible initial states, and render them all simultaneously. The rendering may have to pause, for reasons of complexity, if the epoch being rendered gets too close to the actual time at which the rendering is being performed. But it will soon be able to continue as more computer power comes on line. To the omega-point computers, nothing is intractable. There is only 'computable' and 'non-computable', and rendering real physical environments definitely comes into the 'computable' category. In the course of this rendering, the planet Earth and many variants of it will appear. Life, and eventually human beings, will evolve. All the human beings who have ever lived anywhere in the multiverse (that is, all those whose existence was physically possible) will appear somewhere in this vast rendering. So will every extraterrestrial and artificial intelligence that could ever have existed. The controlling program can look out for these intelligent beings and, if it wants to, place them in a better virtual environment – one, perhaps, in which they will not die again, and will have all their wishes granted (or at least, all wishes that a given, unimaginably high, level of computing resources can meet). Why would it do that? One reason might be a moral one: by the standards of the distant future, the environment we live in today is extremely harsh and we suffer atrociously. It may be considered unethical not to rescue such people and give them a chance of a better life. But it would be counter-productive to place them immediately in contact with the contemporary culture at the time of resurrection: they would be instantly confused, humiliated and overwhelmed. Therefore, Tipler says, we can expect to be resurrected in an environment of a type that is essentially familiar to us, except that every unpleasant element will have been removed, and many extremely pleasant elements will have been added. In other words, heaven.

Tipler goes on in this manner to reconstitute many other aspects of the traditional religious landscape by redefining them as physical entities or processes that can plausibly be expected to exist near the omega point. Now, let us set aside the question whether the reconstituted versions are true to their religious analogues. The whole story about what these far-future intelligences will or will not do is based on a string of assumptions. Even if we concede that these assumptions are individually plausible, the overall conclusions cannot really claim to be more than informed speculation. Such speculations are worth making, but it is important to distinguish them from the argument for the existence of the omega point itself, and from the theory of the omega point's physical and epistemological properties. For those arguments assume no more than that the fabric of reality does indeed conform to our best theories, and assumption that can be independently justified.

As a warning against the unreliability of even informed speculation, let me revisit the ancient master builder of Chapter I, with his pre-scientific knowledge of architecture and engineering. We are separated from him by so large a cultural gap that it would be extremely difficult for him to conceive a workable picture of our civilization. But we and he are almost contemporaries in comparison with the tremendous gap between us and the earliest possible moment of Tiplerian resurrection. Now, suppose that the master builder is speculating about the distant future of the building industry, and that by some extraordinary fluke he happens upon a perfectly accurate assessment of the technology of the present day. Then he will know, among other things, that we are capable of building structures far vaster and more impressive than the greatest cathedrals of his day. We could build a cathedral a mile high if we chose to. And we could do it using a far smaller proportion of our wealth, and less time and human effort, than he would have needed to build even a modest cathedral. So he would have been confident in predicting that by the year 2000 there would be mile-high cathedrals. He would be mistaken, and badly so, for though we have the technology to build such structures, we have chosen not to. Indeed, it now seems unlikely that such a cathedral will ever be built. Even though we supposed our near-contemporary to be right about our technology, he would have been quite wrong about our preferences. He would have been wrong because some of his most unquestioned assumptions about human motivations have become obsolete after only a few centuries.

Similarly, it may seem natural to us that the omega-point intelligences, for reasons of historical or archaeological research, or compassion, or moral duty, or mere whimsy, will eventually create virtual-reality renderings of us, and that when their experiment is over they will grant us the piffling computational resources we would require to live for ever in 'heaven'. (I myself would prefer to be allowed gradually to join their culture.) But we cannot know what they will want. Indeed, no attempt to prophesy future large-scale developments in human (or superhuman) affairs can produce reliable results. As Popper has pointed out, the future course of human affairs depends on the future growth of knowledge. And we cannot predict what specific knowledge will be created in the future – because if we could, we should by definition already possess that knowledge in the present.

[Tipler replies: Deutsch's mile-high cathedral is poor choice for a counter-example, because the cost of such a building relative to our current resources is much too high. Given the fact that no government or commercial mile-high building has yet been built, in spite of the obvious prestige going to the builder--and dictators like Saddam like to build monuments to themselves, and have billions of dollars available for this purpose--it is clear that constructing a mile-high building would be at the very limits of current technology. It might even be beyond us today. But eventually that mile-high cathedral will be built. When he is resurrected, Deutsch's ancient master builder could do it himself--as an inexpensive spare time hobby. end of reply]

. . .

Tipler's overconfidence in predicting people's motives near the omega point has caused him to underrate an important implication of the omega-point theory for the role of intelligence in the multiverse. It is that intelligence is not only there to control physical events on the largest scale, it is also there to choose what will happen. The ends of the universe are, as Popper said, for us to choose. Indeed, to a large extent the content of future intelligent thoughts is what will happen, for in the end the whole of space and its contents will be the computer. The universe will in the end consist, literally, of intelligent thought-processes. Somewhere towards the far end of these materialized thoughts lies, perhaps, all physically possible knowledge, expressed in physical patterns.

. . .

In his enthusiasm (in the original sense of the word!), Tipler has neglected part of the Popperian lesson about what the growth of knowledge must look like. If the omega point exists, and if it will be created in the way that Tipler has set out, then the late universe will indeed consist of embodied thoughts of inconceivable wisdom, creativity and sheer numbers. But thought is problem-solving, and problem-solving means rival conjectures, errors, criticism, refutation and backtracking. Admittedly, in the limit (which no one experiences), at the instant when the universe ends, everything that is comprehensible may have been understood. But at every finite point our descendants' knowledge will be riddled with errors. Their knowledge will be greater, deeper and broader than we can imagine, but they will make mistakes on a correspondingly titanic scale too.

[Tipler replies: At every finite point, Deutsch is completely correct. But at the Omega Point, which is the completion of all knowledge growth, where all criticism has been completed, knowledge is perfect: everything which can be known, will be known. The Omega Point is omniscient! end of reply]

Like us, they will never know certainty or physical security, for their survival, like ours, will depend on their creating a continuous stream of new knowledge. If ever they fail, even once, to discover a way to increase their computing speed and memory capacity within the period available to them, as determined by inexorable physical law, the sky will fall in on them and they will die. Their culture will presumably be peaceful and benevolent beyond our wildest dreams, yet it will not be tranquil. It will be embarked upon the solution of tremendous problems and will be split by passionate controversies. For this reason it seems unlikely that it could usefully be regarded as a 'person'. Rather, it will be a vast number of people interacting at many levels and in many different ways, but disagreeing. They will not speak with one voice, any more than present-day scientists at a research seminar speak with one voice. Even when, by chance, they do happen to agree, they will often be mistaken, and many of their mistakes will remain uncorrected for arbitrarily long periods (subjectively). Nor will the culture ever become morally homogeneous, for the same reason. Nothing will be sacred (another difference, surely, from conventional religion!), and people will continually be questioning assumptions that other people consider to be fundamental moral truths. Of course, morality, being real, is comprehensible by the methods of reason, and so every particular controversy will be resolved. But it will be replaced by further, even more exciting and fundamental controversies. Such a discordant yet progressive collection of overlapping communities is very different from the God in whom religious people believe. But it, or rather some subculture within it, is what will be resurrecting us if Tipler is right.

In view of all the unifying ideas that I have discussed, such as quantum computation, evolutionary epistemology, and the multiverse conceptions of knowledge, free will and time, it seems clear to me that the present trend in our overall understanding of reality is just as I, as a child, hoped it would be. Our knowledge is becoming both broader and deeper, and, as I put it in Chapter I, depth is winning. But I have claimed more than that in this book. I have been advocating a particular unified world-view based on the four strands: the quantum physics of the multiverse, Popperian epistemology, the Darwin-Dawkins theory of evolution and a strengthened version of Turing's theory of universal computation. It seems to me that at the current state of our scientific knowledge, this is the 'natural' view to hold. It is the conservative view, the one that does not propose any startling change in our best fundamental explanations. Therefore it ought to be the prevailing view, the one against which proposed innovations are judged. That is the role I am advocating for it. I am not hoping to create a new orthodoxy; far from it. As I have said, I think it is time to move on. But we can move to better theories only if we take our best existing theories seriously, as explanations of the world.

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