“It sounds great, Orin. Although I don't look forward to rehab.
“By the way, could you put in an order for three more tripods in the next supply run? There was a programming glitch and a couple seem to have wandered off.”
(c)Copyright 2006 by Henry Melton
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* * *
The Universe of Choice:
The Alternate View by John G. Cramer
Our universe supports life because of some rather remarkable coincidences. If the values of the physical constants that govern the fundamental forces and interactions in our universe were just a bit different, then life (or at least, life as we know it) would be impossible. I devoted a previous column ("The ‘Real World’ and The Standard Model", Analog, May 1996) to a discussion of some of the consequences of tinkering with some of the physical constants, but let me give some further examples here.
If gravity were a bit stronger, the universe would have long since collapsed to a black hole. If gravity were a bit weaker, galaxies would never have formed. If either the strong or electromagnetic forces were a bit different in strength, the neutron would be less massive than the proton, and the universe would be filled with neutrons and neutron stars, with few atoms or nuclei. If the 7.654-MeV energy level in carbon-12 was not precisely where it is, the nuclei of carbon and the heavier elements could not have formed from helium in burned-out stars and supernovas, and there would be no heavy elements to make planets and people. And so on...
The most recent realization that our universe is “special” comes from the observation (see “Our Runaway Universe and Einstein's Cosmological Constant", Analog, May 1999) that the rate of expansion of the universe is itself accelerating. This implies that Einstein's cosmological constant is not zero: in other words, that there is a small but non-zero density of “dark” energy in the vacuum itself, which creates a negative pressure driving the accelerating expansion. Cosmologists are coming to realize that the remarkably small but non-zero size of this vacuum energy is another “accident” that makes life in our universe possible.
It's fair to ask (while difficult to answer) the question of whether the values of the fundamental constants, including the cosmological constant, are just lucky accidents, or whether there is some mechanism that arranged them to make life in the universe possible. One way providing an answer to this question is through the Anthropic Principle. The Anthropic Principle asserts that since we, as living beings, are present to measure the fundamental constants and ask where they come from, they must be arranged to make living beings possible. Otherwise, there would be nobody around to ask the question. This is an answer of sorts, but it is not a very satisfying one.
This situation in cosmology is a bit like the theology of the middle ages, which insisted that the Earth was the center of the universe because God made it that way. Galileo got in a lot of trouble for discovering the moons of Jupiter, a planetary system in miniature visible with his newly invented telescope, and suggesting that by analogy the Earth might be just a satellite orbiting the Sun, as Copernicus had previously claimed, rather than the center of the universe.
As long as there was only one Planet Earth and we were living on it, it appeared that divine intervention was required to make things come out the way they are. However, we now know that there are a huge number of galaxies in our universe, a huge number of stars in each galaxy, and that most of those star probably have planets orbiting them. From such a cosmic perspective, the Earth is a much less special place, perhaps just one of a very large number of planets in the universe that can support life, perhaps including intelligent life. Earth has been demoted from the center of the universe to the sidelines.
(c)Copyright 2006 by John G. Cramer
* * * *
Illo. by Wolf A. Read
* * * *
Prof. Leonard Susskind of Stanford University has recently proposed a view that resembles this cosmic perspective, but as applied to universes rather than planets. This perspective comes from string theory, an area of theoretical physics that has for the past decade been the intellectual focus of major theoretical activity in the physics community. String theorists have been exploring a mathematics that describes fundamental particles (quarks, leptons...) as vibrational standing waves on hyperdimensional strings. The string theory variants that describe such a worldview, as they have developed, were found to be divisible into five different string theory classes. Later, new insights regrouped them into “M-theory,” within which the five separate string theories were special cases, special solutions of a master theory. However, there is one problem in comparing our universe with all of those “universes” described by string theory variants. All of the string-theory universes have a zero cosmological constant. The problem is that the master theory is too symmetric—there is a boson for every fermion—and this symmetry sets the cosmological constant to zero.
Susskind deals with this problem by asserting that there must be “islands” of reduced symmetry lying “off the coast” of the super-symmetric main body of string theory. And he further asserts that the number of such islands must be extremely large, numbering far more than the number of electrons in our universe.
What distinguishes these islands (which can be thought of as universes) from one another is the value of the cosmological constant (which has an indirect effect on some of the other fundamental constants) within them. Susskind calls the ensemble of such string theory universes “the landscape of string theory.” This landscape is populated by a vast number of universes, each with a different “ground state vacuum,” in other words, with a different cosmological constant and amount of dark energy in a given volume of vacuum.
The observed value of the cosmological constant constitutes a difficult puzzle. The difficulty for both orthodox quantum chromodynamics (QCD) and the more speculative string theory with the density of vacuum energy in our universe is that it is very small, but not zero. These theories were well prepared to explain either a zero vacuum energy (e.g., with supersymmetry) or a very large vacuum energy (e.g., with standard QCD). However, a small-but-not-zero vacuum energy density is far more difficult, because it requires “fine tuning” to get the vacuum energy “just right” to make a universe like ours. This is sometimes called “the Goldilocks Problem.” Up to now, cosmological theorists have been unable to suggest a mechanism that could solve the Goldilocks Problem. Susskind is attempting to supply such a mechanism by invoking the Anthropic Principle, as applied to universes.
Basically, he argues that of all the universes populating the string-theory landscape, at least one must have a ground state vacuum that has a “just-right” amount of dark energy in the vacuum—small, but not zero. In that universe, life would be possible. The vast majority of other universes would be lifeless. Therefore, since we exist as living beings, we must reside in that just-right universe. In other words, the dark energy in the vacuum is small, not because some fine tuning set it that way, but because our universe in one of the few populating the string theory landscape in which in which it is low enough to make life possible.
In the Susskind scenario, the Big Bang created a vast quantity of “bubble” universes. The vacuum of each of these universes was initially filled with dark energy, driving the superluminal expansion we call inflation. At the end of the inflation period, the vacuum energy density dropped until it reached a bottom level, a vacuum energy ground state. And because of the vast number of islands in the landscape of string theory, there was enormous variation from universe to universe in the value of the ground state energy. Thus, if our universe has low ground state energy, it should be no surprise, because some universe should have such a situation.
Susskind's scenario tells us, therefore, that most of these universes will be lifeless and inhospitable to visitors, perhaps empty of stars, perhaps empty of matter, perhaps the site of a black hole collapse or a Big Rip super expansion.
* * * *
What are the science fiction
applications of Susskind's ideas? Obviously, the idea of a multitude of universes, parallel or otherwise, has been written about many times. Steven Baxter, in his novel Raft, hypothesized a universe in which the gravitational force was much stronger than in our universe and in which castaway humans struggled for survival in an alien and hostile universe, into which they have somehow been deposited.
My own novel Einstein's Bridge is built on the assumption that there is a multiplicity of separated “bubble universes,” and that wormholes (in the physics literature, originally called “Einstein-Rosen Bridges") could be use to communicate and travel from one such universe to another.
In Susskind's scenario, universes containing life as we know it would be few and far between. The average universe would have a large vacuum energy, which would cause it to have accelerated expansion to a state where it was essentially empty. Universe hopping would be a lonely business, with a very low probability of finding anything interesting. Explorers would need some advance signal of the presence of intelligent life (see, for example, Einstein's Bridge) to make it worth expending the resources to make contact with another universe.
* * * *
Is Susskind's scenario viable? Time will tell. It requires some advances in string theory to verify his speculation of “islands” with varying cosmological constants. From another perspective, it may have a problem with Occam's Razor, since it justifies the state of our present observable universe by hypothesizing that it must have a very large number of unobservable siblings. It therefore suffers from the same malady as the rest of string theory, in that untestable hypotheses, particularly those making spectacular claims, are not subject to testing and improvement through the use of the scientific method.
But in any case, it's an interesting idea that may be worth consideration by writers of science fiction.
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* * *
AV Columns Online: Electronic reprints of over 120 “The Alternate View” columns by John G. Cramer, previously published in Analog, are available online at: www.npl.washington.edu/av. The preprints referenced below can be obtained at: www.arxiv.org.
* * * *
References:
“The Anthropic Landscape of String Theory", Leonard Susskind, (2003), preprint hep-th/0302219;
“Supersymmetry Breaking in the Anthropic Landscape", Leonard Susskind, (2004), preprint hep-th/0405189.
[Back to Table of Contents]
* * *
Playhouse
by Larry Niven
Illustration by John Allemand
* * * *
And you thought babysitting for one species was hard?
* * * *
Day Zero
Long View reached lunar orbit as so many Chirpsithra-manned passenger ships had done before, but faster, skipping steps. There was a curtness to their negotiations with United Nations traffic control. The lander turned loose from the big ship before its orbit about the Moon was well established.
I was spending a few weeks with Jehanneh and Walt in Saddam Hussein's palace in Tikrit. The army had turned some of his old palaces into hotels back in the Twenty Zeros. Amenities were primitive and the fad had wilted, so it wasn't that expensive, considering. Saddam had had lots of interesting playground equipment ... for adults, of course, but Walt was having a good time too.
Then the liner hove into view near the Moon and I was called back. I left Walt and Jehanneh there. The Draco Tavern was no place for a two-and-a-half-year-old boy.
Day One
I got there ahead of my crew.
Reworking the Draco Tavern to accommodate new species takes a lot of preparation. I spent a few hours looking around the tavern, then called the ship to learn what kind of visitors to expect. I was waiting on the line, chatting with the translator device, when four Chirpsithra filed through the tall and narrow airlock.
Chirpsithra stand eleven feet tall. They're exoskeletal creatures, usually wearing tools and pouches and rank marks attached to their scarlet chitin shells. I've learned to recognize some of the marks. Three were ranking officers. The fourth wore a sigil I'd never seen before: a triangle with curved edges. They looked around, chattering to each other with their translators turned off.
I pointed at a sparker. Want this? The triangle-bearer spoke in Lottl, and I heard, “Rejected with thanks. Rick Schumann?”
“That's right.”
“Proprietor of this?”
“Yes, the Draco Tavern. Welcome.”
“Thank you. I am Queeblishiz, Matriarch of Lifesystem Support. We have a—” The translator hesitated. “—situation.”
Running this world's only interspecies bar for nearly forty years, I've seen more “situations” than I could count. I said, “See if you can describe it.”
“Our cold sleep facilities have failed.”
“Oh boy,” I said, before my mind quite caught up. How many extra visitors—? “Just a minute. Don't most of your passengers come down anyway? The Draco Tavern is popular. So's Earth.”
“Passengers, yes,” Queeblishiz said.
Still speculating, I said, “You'd have to fix what's broken before you can leave. You'll play hell finding tools for spacecraft on Earth.” We'd abandoned the Moon more than forty years before the first interstellar liner showed up. “How long?”
“Perhaps forty days. We carry tools to make tools.”
That didn't sound bad. But the other Chirp officers were still chattering at her, and she turned off her translator and chattered back. Then, “Barman, we must upgrade your facilities, particularly your defenses.”
“Defenses?” Ohmygod. Sooner or later it had to happen. “What is Long View, a prison ship?”
“Close. Unlucky guess. Long View is not unusual, a typical passenger liner with cold sleep facilities for prey animals, pets, and children. These are breaking down. The ship is too small, massively too small. We'll go insane if we can't set some of our children free on Earth.”
“And prey animals too? Do you plan to run hunts through my place?”
“Those we may slaughter and clone again later. We may require the owners to care for their pets, or slaughter them too. Our concerns are for the children. We have four varieties awake.”
“That doesn't sound too bad,” I said.
“Yes, but we must begin at once. We must childproof the Tavern.”
* * * *
I phoned Arlan and Genevieve and told them the situation.
Staff at the Draco Tavern are always volunteers; they're scientists come to interact with unearthly intelligences and alien disciplines. Children were not of interest. They both bowed out.
* * * *
Children and pets are normally barred from the tavern. Variety in adult tool users has always caused problems enough.
The Chirps put electronic locks on the airlocks and toilets. I worried: what if a child was locked out? Queeblishiz reassured me. The children would have bar codes tattooed on their hides. Only the appropriate locks and toilets would open for them ... and they wouldn't lock with a child inside.
Hah, that lesson must be universal! Walt hasn't locked us out of a bathroom yet, but it's a basic intelligence test for grown-ups.
The first child was already down. Djil was a streamlined humanoid massing around two hundred kilos. Most of a human's features were in place, but she had lids over everything: eyelids, earlids, no nose, no hair, a gristly filter behind the lips, and no obvious openings that a human would cover with clothing. I pictured her as coming from a windy, sandy world.
We put her in a shirt and jeans. She didn't object.
Djil explored the Draco Tavern and watched Queeblishiz impose childproofing changes. I watched it all carefully. Fragile stuff out of reach or locked away. Stairs blocked with a repel field keyed to the bar codes. Odd chemicals kept out of sight and touch, and that included everything behind and beneath my bar. Most of what I serve is lethal to something.
When a party of anthropologists showed up, Djil
served their drinks, then got into an intense discussion of experimental methods.
“Her parents are too big to travel,” Queeblishiz said. “They can arrest the development of children for a time. Djil is nearly seventy years old by your counting. She can babysit, but she must be watched.”
“Why? She sounds like an adult to all intents and purposes.”
“Watch her. Tend her. Djil's brain has not reached full weight, and she is as self-centered as any child.”
Day Two
We barred humans from the tavern. Protests came from various directions. Sooner or later ... but first we'd better see just how much of a problem the children were.
“There's no need to think of me as a child,” Djil told me. “I'm older than you. My parents are excessively protective. They tried to stop me from leaving. We reached a compromise. I'm listed as a child, with fewer rights than a passenger.”
“That's a pity,” I said. “But why were you chosen to guard the younger children?”
“I'm an available sitter, and barred from roaming at will through Long View. The Chirpsithra are economical.”
I'd still keep a watch on her. She was too big to be taken lightly.
Day Three
After two days of work, Matriarch Queeblishiz brought down the children.
The Rainbow Wyrms were snakes, six of them. They were caged when Queeblishiz brought them in on a heavy lift platform. When the field was switched off, they were gone too fast to be visible. For an hour they buzzed around the Tavern, bouncing off the lock fields whenever they got near the bar. They couldn't fly, but they could jump like coiled springs. They buzzed into corners and under booths, chasing down the mice.
A few minutes wore them out, and they slowed down. They were glittering orange and green, each half a man's weight, each about three meters long. You could see a fringe of little limbs growing down the ventral line. They slept a lot, usually wrapped in knots around each other. They were friendly to visitors; I could wear one wrapped around my shoulders and neck. They ate small mammals taken from another failing freezer. Visitors would have to be marked with bar codes; any rats and mice in the tavern were on their own.
Analog SFF, March 2006 Page 12
