The Cosmic Landscape (59 page)
J
ust before boarding the giant Hercules aircraft that was to take us to Punta Arenas from the Chilean Antarctic station, I hugged my friend Victor farewell. An emotional and sentimental Russian, Victor was saddened by our leaving. The last thing I said to him before trekking out into the blizzard was, “Victor, don’t you think Antarctica is beautiful?” He was lost in melancholy thought for a brief moment and then quietly smiled and said, “Yes, like some women: beautiful—but cruel.” Had Victor asked me whether I thought our universe and its Laws of Physics are beautiful, I might have answered, “No, not beautiful. But rather friendly.”
Throughout this book I have dismissed beauty, uniqueness, and elegance as false mirages. The Laws of Physics (in the sense that I defined them in chapter 1) are neither unique nor elegant. It seems that the world, or our part of it, is a Rube Goldberg machine. But I confess: I am as vulnerable to the seductive charms of Uniqueness and Elegance as any one of my colleagues. I, too, want to believe that the grand overarching principles that transcend the rules governing any particular pocket of the universe are unique, elegant, and wonderfully simple. But the results of those rules need not be elegant in the least. Quantum mechanics, which rules the microscopic world of atoms, is very elegant—but not everything made of atoms is. The simple laws that give rise to tremendously complicated molecules, liquids, solids, and gases yield stinkweeds as well as roses. I think I might find the universal principles of String Theory most elegant—if I only knew what they were.
I often joke that if the best theories are the ones with the minimum number of defining equations and principles, String Theory is by far the best—no one has ever found even a single defining equation or principle! String Theory gives every indication of being a very elegant mathematical structure with a degree of consistency far beyond any other physical theory. But nobody knows what its defining rules are, nor does anyone know what the basic “building blocks” are.
Remember, building blocks are the simple objects that everything else is made of. For a housing contractor, building blocks may be exactly that—the blocks or bricks that compose the walls and foundation. The relation between building blocks and the composite objects that they compose is very asymmetrical: houses are made of bricks. Only someone with a severe perceptual disorder—perhaps an Oliver Sacks patient, “The Man Who Mistook His House for a Brick”—would get this relationship backward.
The basic building blocks of science depend on context and the state of knowledge at the time. In the nineteenth century the building blocks of matter were the atoms of the periodic table. The same ninety-two elements can be combined into an endless variety of composites called molecules. Later, atoms were discovered to be composite, and they gave way to electrons, protons, and neutrons. The pattern that we have learned to expect is that big things are made up of littler things. For a physicist probing deeper into the laws of nature, this has usually meant uncovering a substructure of smaller building blocks. At the present stage of physics, ordinary matter is believed to be composed of electrons and quarks. The questions that people, both laymen and scientists, often ask is, “Do you think this will go on forever, or do you think there is a smallest building block?” These days the question often takes the form, “Is there anything smaller than the Planck length?” or “Are strings the most fundamental objects or are
they
made of smaller things?”
These may be the wrong questions. The way String Theory seems to work is subtler than this. What we find is that if we focus attention on some particular region of the Landscape, everything is built out of one specific set of building blocks. It may be closed or open strings of some specific type in certain regions. In other regions all matter is composed of D-branes. In yet other parts of the Landscape, objects similar to ordinary field quanta can be assembled into strings, branes, black holes, and more. Whatever is singled out as “most fundamental,” the other objects of the theory behave like composites—composites in the same sense that atoms and molecules are composites of electrons, protons, and neutrons.
But as we move through the Landscape, from one location to another, strange things happen. The building blocks change places with composite objects. Some particular composite shrinks, behaving in a simpler and simpler manner, as if it were becoming an elementary building block. At the same time the original building blocks start to grow and show signs of having the structure of composites. The Landscape is a dreamscape in which, as we move about, bricks and houses gradually exchange their role.
Everything is fundamental, and nothing is fundamental.
What are the basic equations of the theory? Why, they are the equations governing the motion of the basic building blocks, of course. But which building blocks—open strings, closed strings, membranes, D0-branes? The answer depends on the region of the Landscape we are momentarily interested in. What about the regions intermediate between one description and another? In those regions the choice of building blocks and defining equations is ambiguous. We seem to be dealing with a new kind of mathematical theory in which the traditional ideas of fundamental versus derived concepts is maddeningly elusive. Or perhaps ’t Hooft is right, and the true building blocks are more deeply hidden. The bottom line is that we have no clear idea how to describe the entire mathematical structure of String Theory or what building blocks, if any, will win the title of “most fundamental.”
Still, I hope that the principles of String Theory, or whatever underlies it, will have the elegance, simplicity, and beauty that theorists hunger for. But even if the equations satisfy every esthetic criterion that a physicist could hope for, it does not mean that particular solutions of the equations are simple or elegant. The Standard Model is so complicated—with thirty apparently unrelated parameters, unexplained replication of particle types, and forces whose strength vary all over the map—that the String Theory version of it will almost certainly have Rube Goldberg complexity and redundancy.
For my own tastes, elegance and simplicity can sometimes be found in principles that don’t at all lend themselves to equations. I know of no equations that are more elegant than the two principles that underpin Darwin’s theory: random mutation and competition. This book is about an organizing principle that is also powerful and simple. I think it deserves to be called elegant, but again, I don’t know an equation to describe it, only a slogan: “A Landscape of possibilities populated by a megaverse of actualities.”
And what about the biggest questions of all: who or what made the universe and for what reason? Is there a purpose to it all? I don’t pretend to know the answers. Those who would look to the Anthropic Principle as a sign of a benevolent creator have found no comfort in these pages. The laws of gravity, quantum mechanics, and a rich Landscape together with the laws of large numbers are all that’s needed to explain the friendliness of our patch of the universe.
But on the other hand, neither does anything in this book diminish the likelihood that an intelligent agent created the universe for some purpose. The ultimate existential question, “Why is there Something rather than Nothing?” has no more or less of an answer than before anyone had ever heard of String Theory. If there was a moment of creation, it is obscured from our eyes and our telescopes by the veil of explosive Inflation that took place during the prehistory of the Big Bang. If there is a God, she has taken great pains to make herself irrelevant.
Let me then close this book with the words of Pierre-Simon de Laplace that opened it: “I have no need of this hypothesis.”
A Word on the Distinction between
Landscape and Megaverse
The two concepts—
Landscape
and
megaverse
—should not be confused. The Landscape is not a real place. Think of it as a list of all the possible designs of hypothetical universes. Each valley represents one such design. Listing the designs one after another, like names in a telephone book, would not capture the fact that space of designs is multidimensional.
The megaverse, by contrast, is quite real. The pocket universes that fill it are actual existing places, not hypothetical possibilities.
When I first began to write this book, I encountered a problem of terminology that I’m still wrestling with. I didn’t know what to call the new vastness that is replacing the old concept of universe. The term that was (and is) most common is
multiverse.
I have no objection to
multiverse
except that I just don’t like the sound of it. It reminds me of multiplex cinemas, which I try to avoid. I experimented with a number of other possibilities, including
polyverse, googolplexus, polyplexus,
and
googolverse,
without success. I eventually settled on
megaverse,
knowing full well that I was committing the linguistic crime of combining the Greek prefix
mega
with the Latin
verse.
After deciding to use the term
megaverse,
I looked it up on Google and found that I was far from the first to use it. I got 8,700 results for
megaverse.
On the other hand, the same technique applied to
multiverse
got 265,000 results.
Finally, I should add that some of my best friends are users of the term
multiverse,
and so far, we haven’t come to blows over it.
Absorption lines
—Dark lines superimposed on a rainbowlike spectrum of colors. The dark lines are due to absorption of certain colors by gas.
Anthropic Principle
—The principle that requires the laws of nature to be consistent with the existence of intelligent life.
Antiparticle
—The twin of a particle that is identical except with opposite electric charge.
Boson
—A type of particle not constrained by the Pauli exclusion principle. Any number of identical bosons can occupy the same quantum state.
Broken Symmetry
—An approximate symmetry of nature that for some reason is not exact.
Calabi Yau manifold
—The special six-dimensional geometries that String Theory uses to compactify the extra dimensions of space.
Calabi Yau space
—Same as Calabi Yau manifold.
Charge conjugation symmetry
—A (broken) symmetry of nature under which every particle is replaced by its antiparticle.
Compactification
—The rolling up of extra dimensions of String Theory into microscopic spaces.
Cosmic microwave background (CMB)
—The electromagnetic radiation left over from the Big Bang.
Cosmological constant
—The term that Einstein introduced into his equations to counter the effect of gravitational attraction.
Coupling constant
—The constant of nature that determines the probability for an elementary event.
D-brane
—The points or surfaces where the strings of String Theory are allowed to end.
Density contrast
—The variations of energy density in the early universe that eventually evolved into galaxies.
De Sitter space
—The solution to Einstein’s equations with a positive cosmological constant. De Sitter space describes an expanding universe in which space clones itself exponentially.
Domain wall
—The boundary separating two phases of a material such as water and ice.
Doppler shift
—The shift in the frequency of waves due to the relative motion of the source of the waves and the detector of the waves.
Electric field
—The field surrounding charged particles at rest. Along with magnetic fields, electric fields are composed of electromagnetic radiation such as light.
Electron
—Elementary charged particle that makes up electric currents and the outer parts of atoms.
Emergent
—Refers to properties of matter that manifest themselves only when large numbers of atoms behave in a collective or coordinated manner.
Eternal Inflation
—The exponential cloning of space that spawns bubbles, which populate the Landscape.
Exchange diagram
—A Feynman diagram in which a particle such as the photon is emitted by one particle and absorbed by another. Such diagrams are used to explain the forces between objects.
Fermion
—Any particle that is subject to the Pauli exclusion principle. This includes electrons, protons, neutrons, quarks, and neutrinos.
Feynman diagram
—Feynman’s pictorial way of explaining the interactions among elementary particles.
Field
—An invisible influence in space that affects the motion of objects. Examples include the electric, magnetic, and gravitational fields.
Fine structure constant (0.007297351)
—The coupling constant governing the emission of a photon by an electron.
Flux
—One of the many components of a string compactification. A flux is similar to a magnetic field except oriented along the compact directions of space.
Glueball
—Composite particles made out of collections of gluons and having the structure of closed strings.
Gluon
—Particles whose exchange account for the forces between quarks.
Gravitational waves
—Disturbances of the gravitational field that propagate through space with the speed of light.