Why Does the World Exist: An Existentia - By Jim Holt Page 0,87
to energy, but it gives us no idea of what energy really is—beyond being a numerical quantity that, when calculated correctly, is conserved in all physical processes. As Bertrand Russell noted in his 1927 book, The Analysis of Matter, when it comes to the intrinsic nature of the entities making up the world, science is silent. What it presents us with is one great relational web: all structure, no stuff. The entities making up the physical world are like the pieces in a game of chess: what counts is the role defined for each piece by a system of rules that say how it can move, not the stuff that the piece is made of.
The physicist’s view of reality, by the way, is remarkably akin to the view of language proposed over a century ago by Ferdinand de Saussure, the father of modern linguistics. Language, Saussure maintained, is a purely relational system. Words have no inner essence. The intrinsic character of the noises we make when talking is irrelevant to communication; the important thing is the system of contrasts among those noises. This is what Saussure meant when he wrote that “in language, there are only differences without positive terms.” Saussure’s elevation of structure over stuff was the inspiration for the structuralist movement that swept aside existentialism in France in the late 1950s. It was taken up in anthropology by Claude Lévi-Strauss and in literary theory by Roland Barthes. Its extension to the universe as a whole might well be called “cosmic structuralism.”
If reality were indeed pure structure, that would open up radically new ways of thinking about it. One of these is the way of Penrose and Tegmark. On their view, reality is in essence mathematical. Mathematics, after all, is the science of structure; it neither knows of, nor cares about, stuff. Worlds that are structurally the same but made out of different stuff are identical in the eyes of the mathematician. Such worlds are called “isomorphic,” from the Greek words isos (same) and morphe (form). If the universe is structure all the way down, then it can be exhaustively characterized by mathematics. And if mathematical structures have an objective existence, then the universe must be one of these structures. That, at least, seems to be Tegmark’s meaning when he says that “all mathematical structures exist physically.” If there is no ultimate stuff to reality, then mathematical structure is tantamount to physical existence. Who needs flesh when bones are enough?
A somewhat different take on a stuff-less reality is to see it as consisting not of mathematics but of information. This view is summed up in a slogan coined by the late physicist John Archibald Wheeler: “it from bit.” (Wheeler—who collaborated with Albert Einstein and taught Richard Feynman—had a gift for such coinages; he also gets credit for “black hole,” “wormhole,” and “quantum foam.”)
The it-from-bit story goes as follows. At bottom, science tells us only about differences: how differences in the distribution of mass/energy are associated with differences in the shape of spacetime, for example, or how differences in the charge of a particle are associated with differences in the forces it feels and exerts. States of the universe can thus be seen as pure information states. As the British astrophysicist Sir Arthur Eddington once put it, “Our knowledge of the nature of the objects treated in physics consists solely of readings of pointers on instrument dials.” The “medium” in which these information states are realized, whatever it might be, plays no role at all in the explanation of physical phenomena. Therefore, it can be dispensed with altogether—shaved away by Occam’s razor. The world is nothing but a flux of pure differences, without any underlying substance. Information (“bit”) suffices for existence (“it”).
Some it-from-bit proponents stretch this logic still further. They look on the universe as a giant computer simulation. Among those who have taken this view are Ed Fredkin and Stephen Wolfram, both of whom hypothesize that the universe is a “cellular automaton” that uses a simple program to generate complex physical outcomes. Perhaps the most radical cosmos-as-computer advocate is the American physicist Frank Tipler. The striking thing about Tipler’s vision is that it involves no actual computer: his cosmos is all software, no hardware. A computer simulation, after all, is just the running of a program; and a program, in essence, is a rule that transforms an input string of numbers into an output string of numbers. So any computer simulation—say, the simulation of the physical universe—corresponds to sequences