Is The Universe A Computer Program ?

Is The Universe A Computer Program ?

by : Aria Ratmandanu 

       John Wheeler believed that all physical reality could be reduced to pure information. Bekenstein takes the idea of black hole information one step further into uncharted waters by asking the question: is the entire universe a computer program ? Are we just bits on a cosmic CD ?

        The question of whether we are living in a computer program was brought brilliantly to the silver screen in the movie The Matrix, where aliens have reduced all physical reality to a computer program. Billions of humans think that they are leading everyday lives, oblivious of the fact that all this is a computer-generated fantasy, while their real bodies are asleep in pods, where the aliens use them as a power source.

         In the movie, it is possible to run smaller computer programs that can create artificial minirealities. If one wants to become a kung fu master or a helicopter pilot, one just inserts a CD into a computer, the program is fed into our brain, and presto! one instantly learns these complicated skills. As the CD is run, a whole new subreality is created. But it raises an intriguing question: can all of reality be placed on a CD ? The computer power necessary to simulate reality for billions of sleeping humans is truly staggering. But in theory: can the entire universe be digitalized in a finite computer program ?

           The roots of this question go back to Newton’s laws of motion, with very practical applications for commerce and our lives. Mark Twain was famous for stating, “Everyone complains about the weather, but no one ever does anything about it.” Modern civilization cannot change the course of even a single thunderstorm, but physicists have asked a more modest question : can we predict the weather ? Can a computer program be devised that will predict the course of complex weather patterns on Earth ? This has very practical applications for everyone concerned about the weather, from farmers wanting to know when to harvest their crops to meteorologists wanting to know the course of global warming in this century.

          In principle, computers can use Newton’s laws of motion to compute with almost arbitrary accuracy the course of molecules that make up the weather. But in practice, computer programs are extremely crude and are not reliable at predicting the weather beyond a few days or so, at best. To predict the weather, one would need to determine the motion of every air molecule—something that is magnitudes beyond our most powerful computer; there is also the problem of chaos theory and the “butterfly effect,” where even the tiniest vibration from a butterfly’s wing can cause a ripple effect that, at key junctures, may decisively change the weather hundreds of miles away.

          Mathematicians summarize this situation by stating that the smallest model that can accurately describe the weather is the weather itself. Rather than microanalyzing each molecule, the best we can do is to look for estimates of tomorrow’s weather and also larger trends and patterns (such as the greenhouse effect).

         So it is exceedingly difficult for a Newtonian world to be reduced to a computer program, since there are too many variables and too many “butterflies.” But in the quantum world, strange things happen. Bekenstein, as we saw, showed that the total information content of a black hole is proportional to the surface area of its event horizon. There is an intuitive way of seeing this. Many physicists believe that the smallest possible distance is the Planck length of 10-33 cm. At this incredibly small distance, space-time is no longer smooth but becomes “foamy,” resembling a froth of bubbles. We can divide up the spherical surface of the horizon into tiny squares, each one the size of the Planck length. If each of these squares contains one bit of information, and we add up all the squares, we find roughly the total information content of the black hole. This seems to indicate that each of these “Planck squares” is the smallest unit of information. If this is true, then Bekenstein claims that perhaps information is the true language of physics, not field theory. As he puts it, “Field theory, with its infinity, cannot be the final story.

          Ever since the work of Michael Faraday in the nineteenth century, physics has been formulated in the language of fields, which are smooth and continuous, and which measure the strength of magnetism, electricity, gravity, and so on at any point in space-time. But field theory is based on continuous structures, not digitalized ones. A field can occupy any value, while a digitalized number can only represent discrete numbers based on 0 s and 1s. This is the difference, for example, between a smooth rubber sheet found in Einstein’s theory and a fine wire mesh. The rubber sheet can be divided up into an infinite number of points, while a wire mesh has a smallest distance, the mesh length. Bekenstein suggests that “a final theory must be concerned not with fields, not even with spacetime, but rather with information exchange among physical processes.

         If the universe can be digitalized and reduced to 0 s and 1 s, then what is the total information content of the universe? Bekenstein es- timates that a black hole about a centimeter across could contain 1066 bits of information. But if an object a centimeter in size can hold that many bits of information, then he estimates that the visible universe probably contains much more information, no less than 10100 bits of information (which can in principle be squeezed into a sphere a tenth of a light-year across. This colossal number, 1 followed by 100 zeros, is called a google.)

        If this picture is correct, we have a strange situation. It might mean that while a Newtonian world cannot be simulated by com- puters (or can only be simulated by a system as large as itself), in a quantum world, perhaps the universe itself can be put onto a CD! In theory, if we can put 10100 bits of information on a CD, we can watch any event in our universe unfold in our living room. In principle, one could arrange or reprogram the bits on this CD, so that physical reality proceeds in a different fashion. In some sense, one would have a God-like ability to rewrite the script. (Bekenstein also admits that the total information content of the universe could be much larger than that. In fact, the smallest volume that can contain the information of the universe may be the size of the universe itself. If this is true, then we are back to where we started: the smallest system that can model the universe is the universe itself.)

        String theory, however, offers a slightly different interpretation of the “smallest distance” and whether we can digitalize the universe on a CD. M-theory possesses what is called T-duality. Recall that the Greek philosopher Zeno thought that a line could be divided into an infinite number of points, without limit. Today, quantum physicists like Bekenstein believe that the smallest distance may be the Planck distance of 10-33 centimeters, where the fabric of space-time becomes foamy and bubbly. But M-theory gives us a new twist to this. Let’s say that we take a string theory and wrap up one dimension into a circle of radius R. Then we take another string and wrap up one dimension into a circle of radius 1/R. By comparing these two quite different theories, we find that they are exactly the same.

        Now let R become extremely small, much smaller than the Planck length. This means that the physics within the Planck length is identical to the physics outside the Planck length. At the Planck length, space-time may become lumpy and foamy, but the physics inside the Planck length and the physics at very large distances can be smooth and in fact are identical.

       This duality was first found in 1984 by Keiji Kikkawa and his student Masami Yamasaki, of Osaka University. Although string theory apparently concludes that there is a “smallest distance,” the Planck length, physics does not abruptly end at the Planck length. The new twist is that physics smaller than the Planck length is equivalent to physics larger than the Planck length.

      If this rather topsy-turvy interpretation is correct, then it means that even within the “smallest distance” of string theory, an entire universe can exist. In other words, we can still use field theory, with its continuous (not digitalized) structures to describe the universe even to distances well inside the Planck energy. So perhaps the universe is not a computer program at all. In any event, since this is a well-defined problem, time will tell. (This T-duality is the justification for the “pre–big bang” scenario of Veneziano. In that model, a black hole collapses down to the Planck length and then “bounces” back into the big bang. This bounce is not an abrupt event but the smooth T-duality between a black hole smaller than the Planck length and an expanding universe larger than the Planck length.)