Sunday, June 6, 2010

Size Matters: The Key to Cosmic Perspective

Cosmic Uroborous

The ancient Egyptian god Nun, the great unknowable and indescribable source of all the other gods, was sometimes portrayed associated with a serpent or even as a serpent. 

There is something about the image of a serpent that has led many cultures to associate it symbolically with the creation of the world and the unity of all things, especially when the serpent is represented as swallowing its own tail. In ordinary speech the word “serpent” is sometimes used interchangeably with “snake,” but a snake is an animal, while a serpent is the symbolic, mythic, sometimes dreamlike representation of that animal. Snakes do not actually swallow their tails, but serpents can do anything humans can imagine. Adapting an idea of Sheldon Glashow, 1979 Nobel laureate in physics, we turn to the multi-thousand year-old symbol of the serpent swallowing its tail and give it a modern interpretation. “Uroboros” is the ancient Greek word for a serpent swallowing its tail. We will call the symbol pictured above the “Cosmic Uroboros.” The tip of the cosmic serpent’s tail represents the smallest possible size scale, the Planck length, and its head represents the largest size scale, the size of the cosmic horizon.

The Cosmic Uroboros represents the universe as a continuity of vastly different size scales. As the image above shows, the diameter of the earth is about two orders of magnitude (10-2) smaller than that of the sun. About sixty orders of magnitude separate the very smallest from the very largest size. Traveling clockwise around the serpent from head to tail, we move from the maximum scale we can see, the size of the cosmic horizon (10-28 cm), down to that of a supercluster of galaxies, down to a single galaxy, to the distance from Earth to the Great Nebula in Orion, to the solar system, to the sun, the earth, a mountain, humans, an ant, a single-celled creature such as the E. coli bacterium, a strand of DNA, an atom, a nucleus, the scale of the weak interactions (carried by the W and Z particles), and approaching the tail the extremely small size scales on which physicists hope to find massive dark matter (DM) particles, and on even smaller scales a Grand Unified Theory (GUT) . The tip of the tail represents the smallest possible scale, the Planck length.  Human beings are just about at the center.

Let’s get oriented on the Cosmic Uroboros.  Most of the time we humans are conscious only of things from about the size of ants to the size of mountains. This range of sizes corresponds to the bottom of the Cosmic Uroboros – if it were a clockface, it would fall approximately between 5 o’clock and 6:30, just about the middle. This is humanity’s native region of the universe, our true homeland.  This is the “reality” in which common sense works and normal physical intuition is reliable. It’s not a geographical location: it’s a point of view. We will name this range of size scales “Midgard,” a name for Earth borrowed from the Norse creation myth, the Edda, in which the world of human beings was seen as midway between the land of the giants and the land of the gods. For much the same reason, the ancient Romans named their sea the Mediterranean, literally “middle of the earth.”  We have chosen the name Midgard for our human-scale homeland in the modern universe not because it is between heaven and hell or any other spiritual dualities, but because it is midway between the largest and smallest sizes. This turns out to be the only size that conscious beings like us could be.

Smaller creatures would not have enough atoms to be sufficiently complex, while larger ones would suffer from slow communication – which would mean that they would effectively be communities rather than individuals, like groups of communicating people, or supercomputers made up of many smaller processors.

Different physical forces control events on different size scales. Electrical and magnetic (electromagnetic) forces control what happens from atoms up to mountains, even though gravity also plays a role.  But around the size scale of mountains, gravity starts to gain the upper hand.  The maximum size of mountains is determined by a competition between electromagnetism and gravity. The electromagnetic force is the glue of the chemical bonds that hold together the atoms that mountains are made of, and the strength of the glue is the same everywhere, regardless of the size of the planet.  But the strength of the gravitational force grows with the increasing mass of the planet or of the mountain.  When the mountain becomes big enough, its gravity overcomes the electromagnetic forces that hold mountains together, and the roots of the mountain flow or break, causing earthquakes. The smaller the mass of the planet, the weaker the gravity pulling the mountain down.  Consequently, mountains can be much higher on smaller planets like Mars than they are on Earth. Since the strength of gravity continues to grow with mass, once we reach that part of the Cosmic Uroboros where gravity controls, all larger scales are also controlled by it and all other forces become less important.

Moving counterclockwise from Midgard up into the larger size scales means adjusting our conscious focus, zooming out to encompass vaster regions, where gravity has counteracted the headlong expansion of the universe by collecting matter in those regions that in the early universe happened to be slightly denser than average. Gravity eventually stopped the cosmic expansion in those regions, and gravity has ever afterward shaped and held everything in the region together in a beautiful, dynamic, yet stable structure – a galaxy, in which stars and planets formed and evolution has had time to work its wonders. The largest structures astronomers see are the great sheets of galaxies known as superclusters. In the old Newtonian view, there was no known object larger than a star, and stars were randomly distributed forever. But in the new cosmology not only are there galaxies, each containing hundreds of billions of stars, but there are superclusters of tens of thousands of galaxies, which astronomers have been mapping since the mid 1980's. That, however, appears to be the end of the line. We see no structures larger than superclusters. On scales much bigger than superclusters, the universe becomes increasingly smooth. If each supercluster were a dot, the visible universe would look much the way Newton expected. He was right about the universe being essentially uniform, but on the wrong scale: he thought the stars were scattered more or less evenly, but instead it’s the superclusters.

Moving clockwise now on the Cosmic Uroboros, zooming way inward past Midgard to the very small, we reach the size scales of subatomic particles.  This is the region controlled by what are called the strong and weak interactions. These forces are active only on scales smaller than atoms. Gravity is of no importance at all on these scales. In fact, gravity’s power fades out at the small end of Midgard. It can’t hurt a mouse. You can drop a mouse down a thousand-yard mine shaft and at the bottom, as long as the ground is soft, it will walk away. Gravity plays virtually no role in the life of bacteria, which are at about 7 o’clock on the Cosmic Uroboros. From there until about 12 o’clock, gravity is completely irrelevant.

But then a strange thing happens. As we continue along the Cosmic Uroboros to the very tip of the tail, gravity becomes extremely powerful again. The reason is that gravity’s strength increases as objects get closer to each other, and at the tip of the tail distances between particles are almost unimaginably small. The Cosmic Serpent swallowing its tail represents the possibility that gravity links the largest and the smallest sizes and thereby unifies the universe. This actually happens in superstring theory, a mathematically beautiful idea which is our best hope for a theory that could unify quantum theory and relativity. In string theory, sizes smaller than the Planck length get remapped into sizes larger than the Planck length.

The latest breakthrough in particle physics was the realization in the 1960s and 1970s that the strong and weak forces are closely related to the electromagnetic force. In the very successful “standard model” of particle physics based on this, elementary particles are treated as if they are points with certain properties. But the standard model cannot be the final word on the subject, since it cannot explain why, for example, electrons and other elementary particles have the masses and other properties that they do. So physicists have been trying for several decades to go beyond the standard model.

The very speculative but promising physics of string theory suggests that not just electrons but all elementary particles might just be the ways a single kind of tiny looped string can vibrate, and in that case an electron would be just a way a string vibrates. An identical string vibrating in a different way would be a different particle. Just as only certain shapes of electron clouds are allowed in atoms, only certain sorts of vibration (and thus of particles) are possible.  An electron is a special sort of vibration: it is the lowest mass vibration having the property of electric charge.  String theory has striking mathematical elegance: it might even be true, and it’s so powerful that it might eventually allow physicists to understand the reason for quantities like the masses of elementary particles. However, string theory only works if you assume a world with ten dimensions – one time and nine space dimensions. No one has figured out what string theory implies for the world of one time and three space dimensions that we actually experience – not only with our senses but with our most sensitive scientific instruments.

Consequently, this beautiful theory has not made a single testable prediction yet (except possibly for the existence of supersymmetric particles like the WIMP dark matter particle), so we don’t yet know how to evaluate its claim that particles are “really” vibrating superstrings.

There is a second meaning to tail-swallowing that may seem strange at first. Swallowing may have existed before the serpent.  At the beginning of the Big Bang, if our present understanding of the laws of physics is right, there was nothing but the head of the Cosmic Uroboros with the tip of the tail in its mouth. There was little of the body because there was little difference between the smallest scale and the largest scale.  The smallest scale is fixed by the constants of nature, and the largest scale, the size of the cosmic horizon, was only a little larger than that because the universe was so young and had not yet had time to expand. The body filled in later as the universe expanded and evolved. Thus tail-swallowing may express a fundamental aspect of the evolution of an expanding universe.

The Cosmic Uroboros represents not only a way to structure the universe but also a dream that has been an underlying personal motivation for many scientists. “What I’m really interested in,” Einstein said, “is whether God could have made the world in a different way; that is, whether the necessity of logical simplicity leaves any freedom at all.” This question is still open. The universe could possibly have been organized in many ways and just happened to end up the way we find it. But it is also possible that there was only one way everything could have worked together. The dream of physicists is to find the theory that answers such questions and ties everything together – a “theory of everything.”

The Cosmic Uroboros swallowing its tail thus symbolizes the dream of a theory of everything, which will tie together our understanding of the universe. Through this dream, physicists are expressing a desire perhaps even more ancient than the uroboros symbol: to feel coherent and at home in the wholeness – to experience reality as One.

Even if there is no success in that quest for years to come, the Cosmic Uroboros can help us right now to appreciate our extraordinary place in Midgard. The centrality of Midgard on the Cosmic Uroboros has nothing to do with the units we choose to measure length. Whether measured in centimeters or light years, Midgard would always fall in the middle. Midgard, as we have said, is not a special location in space – it is a special size scale, and it is everywhere in the universe.

As a serpent, the Cosmic Uroboros is much more than a circle, because every point on it is unique.  There is a head and a tail, and therefore every point in between has a relative position. There is a beginning and an end, even though they overlap and are interdependent and inseparable. On a circle, all points are identical. On the Cosmic Uroboros every point has its own meaning. The uroboros has been used to represent the continuity of whatever universe a tribe or people perceived themselves to be living in.

Something about the serpent swallowing its tail has resonated in the human imagination for thousands of years. We humans are not yet able to explain the perennial attraction of this symbol, and it may be deeper than our conscious understanding. The serpent’s exceedingly simple and flexible body has been endlessly twisted and artistically embellished. It has been seen as both goddess-like and evil, fascinating and repulsive, finite and infinite, yin and yang. None of this rich history would have been implicit in a circle. The uroboros symbol as we interpret it here is capable of representing the modern universe at least as completely as it represented the universes our ancestors imagined. The Cosmic Uroboros resurrects an ancient symbol whose possibilities are by no means exhausted.