There is a famous collection of arguments from the pioneering days of computer science to the effect that any device able to carry out every one of the entries on a certain relatively short list of elementary logical operations could, in some finite number of steps, calculate the value of any mathematical function that is calculable at all. Devices like that are called “universal computers.” And what interests Deutsch about these arguments is that they imply that there is a certain definite point, a certain definite moment, in the course of acquiring the capacity to perform more and more of the operations on that list, when such a machine will abruptly become as good a calculator as anything, in principle, can be.My response boils to, "well, maybe." I think this exaggerates the importance of 17th and 18th century science, since our ability to shape the environment did not start with Newton, but I am willing to accept, for the sake of argument, that this was a crucial step in our growing ability to control the world. Where I really beg to differ is in estimating the importance of this development. I mean this in both past and future senses. Science has had a big impact on the world over the past 250 years, but so have other things, such as ideologies like nationalism and communism, and the development of representative democracy. Many social changes that were enabled by science, such as suburbanization, were by no means made inevitable by it, so even where the contribution of science has been crucial (automobiles, modern warfare) it explains little in itself. Deutsch divides our ideas into those that he likes, because they are true or expand our capabilities, and those that he dislikes, because they are false or sterile. Religion and art fall on the wrong side of this divide. I agree that neither has really made any progress in the past 2000 years, but they have certainly been important. Deutsch probably hopes traditional religions will fade away, but I wouldn't bet on it. There is just a lot more to human life than progress and rationality.
Deutsch thinks that such “jumps to universality” must occur not only in the capacity to calculate things, but also in the capacity to understand things, and in the closely related capacity to make things happen. And he thinks that it was precisely such a threshold that was crossed with the invention of the scientific method. There were plenty of things we humans could do, of course, prior to the invention of that method: agriculture, or the domestication of animals, or the design of sundials, or the construction of pyramids. But all of a sudden, with the introduction of that particular habit of concocting and evaluating new hypotheses, there was a sense in which we could do anything. The capacities of a community that has mastered that method to survive, and to learn, and to remake the world according to its inclinations, are (in the long run) literally, mathematically, infinite. And Deutsch is convinced that the tendency of the world to give rise to such communities, more than, say, the force of gravitation, or the second law of thermodynamics, or even the phenomenon of death, is what ultimately gives the world its shape, and what constitutes the genuine essence of nature. “In all cases,” he writes, “the class of transformations that could happen spontaneously — in the absence of knowledge — is negligibly small compared with the class that could be effected artificially by intelligent beings who wanted those transformations to happen. So the explanations of almost all physically possible phenomena are about how knowledge would be applied to bring those phenomena about.” And there is a beautiful and almost mystical irony in all this: that it was precisely by means of the Scientific Revolution, it was precisely by means of accepting that we are not the center of the universe, that we became the center of the universe.
I disagree with Deutsch even more about the future. I am not at all sure that our science is adequate to ever fully understand the universe. Edward Witten and Steven Weinberg, two of our top physicists, have also expressed doubts about our ability to produce a fully complete theory. And even if we do understand the universe fully in theoretical terms, that may only codify our limited ability to change it. The stars are imaginably far away, and if our theories are right, no conceivable technology could make it easy to reach them. I cannot imagine how we would ever go about halting the evolution of our sun, which will eventually make life on our planet's surface impossible.
I expect that scientific progress will continue, and that we will achieve amazing things. But if we are able to reconfigure our genes and give ourselves life expectancies in the thousands of years, I think the result would be boredom, mass despair, and rampant suicide. I do not think we are cut out for lives much longer than the ones we already have. I think, in other words, that we are and will remain subject to limits -- physical, biological, and psychological -- that we will have a very hard time transcending. And while we live out our human lives within those limits, we will keep ourselves going by leaning on those very old pillars of human life: spirituality, art, friendship, love, work, and humor.