The Cosmic Landscape Read Online Free PDF

At the same time, theoretical physicists are proposing theories that demote our ordinary laws of nature to a tiny corner of a gigantic Landscape of mathematical possibilities.
    The word
Landscape,
in the present context, is fewer than three years old, but since I introduced it in 2003, it has become part of the cosmologist’s vocabulary. It denotes a mathematical space representing all of the possible environments that theory allows. Each possible environment has its own Laws of Physics, its own elementary particles, and its own constants of nature. Some environments are similar to our own but slightly different. For example, they may have electrons, quarks, and all the usual particles but with gravity a billion times stronger than ours. Others have gravity like ours but contain electrons that are heavier than atomic nuclei. 5 Still others may resemble our world except for a violent repulsive force (called the cosmological constant) that rips apart galaxies, molecules, and even atoms. Not even the three dimensions of space are sacred; regions of the Landscape describe worlds of four, five, six, and even more dimensions.
    According to modern cosmological theories, the diversity of the Landscape is paralleled by a corresponding diversity in ordinary space. Inflationary cosmology, which is our best theory of the universe, is leading us, sometimes unwillingly, to a concept of a megaverse, filled with a prodigious number of what Alan Guth calls “pocket universes.” Some pockets are microscopically small and never get big. Others are big like ours but totally empty. And each lies in its own little valley of the Landscape. The old twentieth-century question, “What can you find in the universe?” is giving way to, “What can you not find?”
    Man’s place in the universe is also being reexamined and challenged. A megaverse of such diversity is unlikely to support intelligent life anywhere but in a tiny fraction of its expanse. According to this view, many questions such as, “Why is a certain constant of nature one number, instead of another?” will have answers that are entirely different from what physicists had hoped. No unique value will be picked out by mathematical consistency, since the Landscape permits an enormous variety of possible values. Instead, the answer will be, “Somewhere in the megaverse, the constant equals
this
number; somewhere else it is
that
number. We live in one tiny pocket where the value of the constant is consistent with our kind of life. That’s it! That’s all! There is no other answer to the question.”
    Many coincidences occur in the laws and constants of nature that have no explanation other than, “If it were otherwise, intelligent life could not exist.” To some it seems as though the Laws of Physics were chosen, at least in part, to permit our existence. Called the Anthropic Principle
,
this idea is hated by most physicists, as I noted in my introduction. To some it smells of supernatural creation myths, religion, or intelligent design. Others feel that it represents surrender, a giving up of the noble quest for rational answers. But because of unprecedented new developments in physics, astronomy, and cosmology, these same physicists are being forced to reevaluate their prejudices. There are four principal developments driving this sea change: two from theoretical physics and two from observational astronomy. On the theoretical side an outgrowth of inflationary theory called Eternal Inflation is demanding that the world be a megaverse, full of pocket universes that have bubbled up out of inflating space, like bubbles in an uncorked bottle of champagne. At the same time, String Theory is producing a Landscape of enormous diversity. The best estimates are that 10 500 distinct kinds of environments are possible. This number (one followed by five hundred zeros) is far beyond being “unimaginably large,” but even it may not be big enough to count the possibilities.
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