One hundred years ago a Scientific American article about the history and large-scale structure of the universe would have been almost completely wrong. In 1908 scientists thought our galaxy constituted the entire universe. They considered it an “island universe,” an isolated cluster of stars surrounded by an infinite void. We now know that our galaxy is one of more than 400 billion galaxies in the observable universe. In 1908 the scientific consensus was that the universe was static and eternal. The beginning of the universe in a fiery big bang was not even remotely suspected. The synthesis of elements in the first few moments of the big bang and inside the cores of stars was not understood. The expansion of space and its possible curvature in response to matter was not dreamed of. Recognition of the fact that all of space is bathed in radiation, providing a ghostly image of the cool afterglow of creation, would have to await the development of modern technologies designed not to explore eternity but to allow humans to phone home.

It is hard to think of an area of intellectual inquiry that has changed more in the past century than cosmology, and the shift has transformed how we view the world. But must science in the future always reflect more empirical knowledge than existed in the past? Our recent work suggests that on cosmic timescales, the answer is no. We may be living in the only epoch in the history of the universe when scientists can achieve an accurate understanding of the true nature of the universe.

A dramatic discovery almost a decade ago motivated our study. Two different groups of astronomers traced the expansion of the universe over the past five billion years and found that it appears to be speeding up. The source of this cosmic antigravity is thought to be some new form of “dark energy” associated with empty space. Some theorists, including one of us (Krauss), had actually anticipated this new result based on indirect measurements, but in physics it is direct observations that count. The acceleration of the universe implies that empty space contains almost three times as much energy as all the cosmic structures we observe today: galaxies, clusters and superclusters of galaxies. Ironically, Albert Einstein first postulated such a form of energy to keep the universe static. He called it the cosmological constant [see “Cosmological Antigravity,” by Lawrence M. Krauss; Scientific American, January 1999].

Dark energy will have an enormous impact on the future of the universe. With cosmologist Glenn Starkman of Case Western Reserve University, Krauss explored the implications for the fate of life in a universe with a cosmological constant. The prognosis: not good. Such a universe becomes a very inhospitable place. The cosmological constant produces a fixed “event horizon,” an imaginary surface beyond which no matter or radiation can reach us. The universe comes to resemble an inside-out black hole, with matter and radiation trapped outside the horizon rather than inside it. This finding means that the observable universe contains only a finite amount of information, so information processing (and life) cannot endure forever [see “The Fate of Life in the Universe,” by Lawrence M. Krauss and Glenn D. Starkman; Scientific American, November 1999].

Long before this information limit becomes a problem, all the expanding matter in the universe will be driven outside the event horizon. This process has been studied by Abraham Loeb and Kentaro Nagamine, both then at Harvard University, who found that our so-called Local Group of galaxies (the Milky Way, Andromeda and a host of orbiting dwarf galaxies) will collapse into a single enormous supercluster of stars. All the other galaxies will disappear into the oblivion beyond the event horizon. This process takes about 100 billion years, which may seem long but is fairly short compared to the wilderness of eternity.

Collapsing Pillars
What will astronomers of the far future, living in this supercluster, conclude about the history of the universe? To think about this question, recall the pillars on which our current understanding of the big bang is based.

The first is Einstein’s general theory of relativity. For nearly 300 years Newton’s theory of universal gravitation served as the basis for almost all of astronomy. Newton’s theory does an excellent job of predicting the motions of objects on scales from the terrestrial to the galactic, but it is completely incapable of dealing with infinitely large collections of matter. General relativity overcomes this limitation. Shortly after Einstein published the theory in 1916, Dutch physicist Willem de Sitter solved the equations of general relativity for a simplified universe incorporating Einstein’s cosmological constant. De Sitter’s work appeared to reproduce the prevailing view of the universe at the time: an island galaxy embedded in a largely empty, static void.

Cosmologists soon realized that the stasis was a misinterpretation. In fact, the de Sitter universe is eternally expanding. As Belgian physicist Georges Lemaître later made clear, Einstein’s equations predict that an infinite, homogeneous, static universe is impossible. The universe has to expand or contract. From this realization, the big bang theory, as it would later be called, was born.

The next pillar came in the 1920s, when astronomers detected the expansion of the universe. The first person to provide observational evidence for expansion was American astronomer Vesto Slipher, who used the spectra of stars to measure the velocities of nearby galaxies. Waves of light from a star moving toward Earth are compressed, shortening the wavelength and making the light bluer. Light waves from an object moving away from us are stretched, making the wavelength longer and the light redder. By measuring the lengthening or compression of the light waves from distant galaxies, Slipher was able to determine whether they were moving toward us or away from us and at what speed. (At the time, astronomers were not even sure whether the fuzzy patches of light that we call “galaxies” were actually independent bodies of stars or simply gas clouds inside our own galaxy.) Slipher found that almost all these galaxies were moving away from us. We seemed to be sitting at the center of a runaway expansion.

The person who is generally credited for discovering the expansion of the universe is not Slipher but American astronomer Edwin Hubble. (When was the last time you read about the Slipher Space Telescope?) Hubble determined not just the velocities of nearby galaxies but also their distances. His measurements led to two conclusions that justify his fame. First, Hubble showed that galaxies were so far away that they really were independent collections of stars, just like our own galaxy. Second, he discovered a simple relation between the distance to galaxies and their velocities. The velocity was directly proportional to its distance from us: a galaxy twice as far away as another was moving twice as fast. This relation between distance and velocity is exactly what happens when the universe is expanding. Hubble’s measurements have since been refined, most recently by the observations of distant supernovae, which led to the discovery of dark energy.

The third pillar is the faint glow of the cosmic microwave background, discovered serendipitously in 1965 by Bell Labs physicists Arno Penzias and Robert Wilson as they tracked down sources of radio interference. This radiation was quickly recognized to be a relic left over from the early stages of the expansion of the universe. It indicates that the universe began hot and dense and has since cooled and thinned out.

The final observational pillar of the big bang is that the hot, dense early universe was a perfect location for nuclear fusion. When the temperature of the universe was one billion to 10 billion kelvins, lighter nuclei could fuse into heavier nuclei, a process known as big bang nucleosynthesis. This process can occur for only a few minutes as the universe expands and cools, so fusion was limited to the lightest elements. Most of the helium in the universe was produced then, as was deuterium, or heavy hydrogen. The measured abundances of helium and deuterium match the predictions of big bang nucleosynthesis, providing further evidence for the theory as well as an accurate estimate of the abundance of protons and neutrons in the universe.

Dark Skies
What will the scientists of the future see as they peer into the skies 100 billion years from now? Without telescopes, they will see pretty much what we see today: the stars of our galaxy. The largest and brightest stars will have burned up their nuclear fuel, but plenty of smaller stars will still light up the night sky. The big difference will occur when these future scientists build telescopes capable of detecting galaxies outside our own. They won’t see any! The nearby galaxies will have merged with the Milky Way to form one large galaxy, and essentially all the other galaxies will be long gone, having escaped beyond the event horizon.

The disappearance of distant galaxies is not immediate but gradual. The redshift of these galaxies becomes infinitely large as they approach the horizon. Krauss and Starkman calculated that this redshift will exceed 5,000 for all galaxies by 100 billion years, rising to an unfathomable 1053 by 10 trillion years—at which time even the highest-energy cosmic rays will have redshifted so much that their wavelength will be larger than the horizon size. These objects will then be truly and completely invisible to us.

As a result, Hubble’s crucial discovery of the expanding universe will become irreproducible. All the expanding matter in the universe will have visually disappeared beyond the horizon, and everything remaining will be part of a gravitationally bound cluster of stars. For these future astronomers, the observable universe will closely resemble the “island universe” of 1908: a single enormous collection of stars, static and eternal, surrounded by empty space.

Our own experience demonstrates that even when we have data, the correct cosmological model is not so obvious. For example, from the 1940s to the mid-1960s, with the edifice of observational cosmology resting only on Hubble’s discovery of the expanding universe, some astrophysicists resurrected the idea of an eternal universe: the steady-state universe, in which matter is created as the universe expands, so that the universe as a whole does not really change with time. This idea proved to be an intellectual dead end, but it does demonstrate the kind of mistaken notion that can develop in the absence of adequate observational data.

Where else might astronomers of the future search for evidence of the big bang? Would the cosmic microwave background allow them to probe the dynamics of the universe? Alas, no. As the universe expands, the wavelengths of the background radiation stretch and the radiation becomes more diffuse. When the universe is 100 billion years old, the peak wavelengths of the microwave radiation will be on the scale of meters, corresponding to radio waves instead of microwaves. The intensity of the radiation will be diluted by a factor of one trillion and might never be seen.

Even further into the future, the cosmic background will become truly unobservable. The space between stars in our galaxy is filled with an ionized gas of electrons. Low-frequency radio waves cannot penetrate such a gas; they are absorbed or reflected. A similar effect is the reason that AM radio stations can be picked up far from their cities of origin at night; the radio waves reflect off the ionosphere and back down to the ground. The interstellar medium can be thought of as one big ionosphere filling the galaxy. Any radio waves with frequencies below about one kilohertz (a wavelength of greater than 300 kilometers) cannot penetrate into our galaxy. Radio astronomy below one kilohertz is forever impossible inside our galaxy. When the universe is about 25 times its present age, the microwave background will be stretched beyond this wavelength and become undetectable to the residents of the galaxy. Even before then, the subtle patterns in this background radiation, which have provided so much useful information to today’s cosmologists, will become too muted to study.

Burning Up
Would observations of the abundances of chemical elements lead cosmologists of the distant future to a knowledge of the big bang? Once again, the answer is likely to be no. The problem is that our ability to probe big bang nucleosynthesis hinges on the fact that the abundances of deuterium and helium have not evolved very much since they were produced 14 billion years ago. Helium produced in the early universe, for example, makes up about 24 percent of the total matter. Although stars produce helium in the course of their fusion reactions, they have increased this abundance by no more than a few percent. Astronomers Fred Adams and Gregory Laughlin of the University of Michigan at Ann Arbor have suggested that this fraction could increase to as much as 60 percent after many generations of stars. An observer in the distant future would find the primordial helium swamped by the helium produced in later generations of stars.

Currently the cleanest probe of big bang nucleosynthesis is the abundance of deuterium. Our best measurements of the primordial deuterium abundance come from observations of hydrogen clouds backlit by quasars, extremely distant and bright beacons thought to be powered by black holes. In the far future of the universe, however, both these hydrogen clouds and quasars will have passed beyond the event horizon and will be forever lost to view. Only galactic deuterium might be observable. But stars destroy deuterium, and little will survive. Even if astronomers of the future observe deuterium, they might not ascribe it to the big bang. Nuclear reactions involving high-energy cosmic rays, which have been studied today as a possible source of at least some of the observed deuterium, might seem more plausible.

Although the observational abundance of light elements will not provide any direct evidence for a fiery big bang, it will nonetheless make one aspect of future cosmology different from the illusory cosmology of a century ago. Astronomers and physicists who develop an understanding of nuclear physics will correctly conclude that stars burn nuclear fuel. If they then conclude (incorrectly) that all the helium they observe was produced in earlier generations of stars, they will be able to place an upper limit on the age of the universe. These scientists will thus correctly infer that their galactic universe is not eternal but has a finite age. Yet the origin of the matter they observe will remain shrouded in mystery.

What about the idea with which we began this article, namely that Einstein’s theory of relativity predicts an expanding universe and therefore a big bang? The denizens of the far future of the universe should be able to discover the theory of general relativity from precision measurements of gravity in their own solar system. Using this theory to infer a big bang, however, rests on observations about the large-scale structure of the universe. Einstein’s theory predicts an expanding universe only if the universe is homogeneous. The universe that our descendants survey will be anything but homogeneous. It will consist of an island of stars embedded in a vast emptiness. It will, in fact, resemble de Sitter’s island universe. The ultimate future of the observable universe is to collapse into a black hole, precisely what will in fact occur to our galaxy in the distant future.

Alone in the Void
Is there no way at all for our descendants to perceive an expanding universe? One telltale effect of acceleration would indeed remain within our observational horizon, at least according to our current understanding of general relativity. Just as the event horizon of a black hole emits radiation, so, too, does our cosmological event horizon. Yet the temperature associated with this radiation is unmeasurably small, about 10–30 kelvin. Even if astronomers were able to detect it, they would probably attribute it to some other, far larger local source of noise.

Ambitious future observers might also send out probes that escape the supergalaxy and could serve as reference points for detecting a possible cosmic expansion. Whether it would occur to them to do so seems unlikely, but in any event it would take billions of years at the very least for the probe to reach the point where the expansion noticeably affected its velocity, and the probe would need the energy output comparable to that of a star to communicate back to its builders from such a great distance. That the science-funding agencies of the future would support such a shot-in-the-dark is unlikely, at least if our own experience is any guide.

Thus, observers of the future are likely to predict that the universe ultimately ends with a localized big crunch, rather than the eternal expansion that the cosmological constant produces. Instead of a whimper, their limited universe will end with a bang.

We are led inexorably to a very strange conclusion. The window during which intelligent observers can deduce the true nature of our expanding universe might be very short indeed. Some civilizations might hold on to deep historical archives, and this very article might appear in one—if it can survive billions of years of wars, supernovae, black holes and countless other perils. Whether they will believe it is another question. Civilizations that lack such archives might be doomed to remain forever ignorant of the big bang.

Why is the present universe so special? Many researchers have tried to argue that the existence of life provides a selection effect that might explain the coincidences associated with the present time [see “The Anthropic Principle,” by George Gale; Scientific American, December 1981]. We take different lessons from our work.

First, this would quite likely not be the first time that information about the universe would be lost because of an accelerating expansion. If a period of inflation occurred in the very early universe, then the rapid expansion during this era drove away almost all details of the preexisting matter and energy out of what is now our observable universe. Indeed, one of the original motivations for inflationary models was to rid the universe of pesky cosmological objects such as magnetic monopoles that may once have existed in profusion.

More important, although we are certainly fortunate to live at a time when the observational pillars of the big bang are all detectable, we can easily envisage that other fundamental aspects of the universe are unobservable today. What have we already lost? Rather than being self-satisfied, we should feel humble. Perhaps someday we will find that our current careful and apparently complete understanding of the universe is seriously wanting.

 
An image of a Martian terraced fan taken by a camera on board the Mars Odyssey spacecraft.

To figure out an odd landscape feature on Mars, play in a big sandbox.

Enlist some high school students, too.

That’s what some scientists at the Utrecht University in the Netherlands did, and they believe they now know how sediment deposits spilling out of the mouth of some water channels on Mars were shaped in a series of terraces that look like terraced rice paddies.

But no similar natural formations have been seen in river deltas on Earth. Usually river sediments spill out in a smooth, sloping fan like the Mississippi delta.

Planetary geologists have been speculating about the terraced fans since they were first spotted by NASA’s Mars Global Surveyor eight years ago. About 10 stepped fans have been identified, most at the base of a steep slope emptying into a basin like an impact crater. (Most of the 200 sediment fans seen on Mars do not have the stepped structure. Another mystery is why many of the river channels seem to have no sediment deposit at all.)

Some scientists suggested the terraced fans were the result of repeated shore erosion as a lake in the basin dried up. Others thought repeated landslides might have formed the steps.

The sandbox experiment, reported in Thursday’s issue of the journal Nature, supports a third notion. The terraces form by the interaction of the sediment flow with the water’s edge, which is rising as the basin fills.

“Where that’s happening, you’re getting a little lip,” said Erin R. Kraal, the lead author of the Nature paper. Pulses of flow and sediment produced multiple terraces. “They’re just stacking one atop the other,” she said.

While a postdoctoral researcher at Utrecht, Dr. Kraal became intrigued by the terraced fans and mentioned them to her colleagues there. Utrecht has a set-up known as Eurotank, essentially a 16- by 40-foot sandbox for studying sedimentary dynamics.

High school students visiting the laboratory as part of an educational project saw the Mars pictures on the laboratory walls and were interested in helping on an experiment, which eventually turned into a short educational movie about the Martian fans.

The students dug a crater in the sandbox and shaped a water channel. Then they sent water down the channel — and the result was a terraced fan, just as on Mars.

“We didn’t expect it to be so successful the first time,” said Dr. Kraal, now a research scientist at Virginia Polytechnic Institute and State University. “We were really surprised they formed so quickly and so easily.”

Dr. Kraal and her colleagues, Maurits van Dijk, George Postma and Maarten G. Kleinhans later repeated the experiments more rigorously so they could correlate their sandbox results with the Martian terrain.

They estimate that the water necessary to form one of the Martian fans, which measure up to a dozen miles wide, would equal 10 years of Mississippi River flow. The whole structure appears to have formed in one event lasting perhaps tens of years, they said.

“It does look like she’s experimentally shown here that this type of deposit can form in a single event type of discharge,” said Rossman P. Irwin III, a geologist at the Smithsonian Institute’s Center for Earth and Planetary Studies who has also studied the terraced fans. “It offers some good experimental support for a type of feature that is basically unique to Mars and really was not well understood.”

About one-130-millionth of an ounce of force pushes a cobalt atom across a smooth, flat piece of platinum.

Pushing the same atom along a copper surface is easier, just one-1,600-millionth of an ounce of force.

The scientists report these minuscule findings in Friday’s issue of the journal Science.

I.B.M. scientists have been pushing atoms around for some time, since Donald M. Eigler of the company’s Almaden Research Center in San Jose, Calif., spelled “IBM” using 35 xenon atoms in 1989. Since then, researchers at the company have continued to explore how they might be able to construct structures and electronic components out of individual atoms.

Knowing the precise forces required to move atoms “helps us to understand what is possible and what is not possible,” said Andreas J. Heinrich, a physicist at Almaden and an author of the new Science paper. “It’s a stepping stone for us, but it’s by no means the end goal.”

In the experiment, Dr. Heinrich and his collaborators at Almaden and the University of Regensburg in Germany used the sharp tip of an atomic force microscope to push a single atom. To measure the force, the tip was attached to a small tuning fork, the same kind that is found in a quartz wristwatch. In fact, in the first prototype, Franz J. Giessibl, a scientist at Regensburg who was a pioneer in the use of atomic force microscopes, bought an inexpensive watch and pulled out the quartz tuning fork for use in the experiment.

The tip vibrates 20,000 times a second until it comes into contact with an atom. As the tip pushes, the tuning fork bends, like a diving board, and the vibration frequency dips.

A single atom does not roll, and even a perfectly smooth surface is not perfectly smooth. Instead, the atom rests in small indentations in the lattice, in effect like an egg in an egg carton. The resistance — what becomes friction when multiplied by millions and billions of atoms — comes from the energy needed to rearrange the bonds between the cobalt atom and surface.

When the tip pushes hard enough, the atom hops, almost instantaneously to the next indentation. “It’s not smooth,” said Markus Ternes, another Almaden scientist working on the research. “It’s faster than we can detect.”

From the changes in the frequency of the tuning fork vibrations, the scientists calculated the force that the tip applied to the cobalt atom.

Copper is less sticky than platinum, because of differences between the underlying bonds, and hence allowed the greater ease is pushing the cobalt atom along.

 
DIFFERENT STROKES: Rats given neural tissue derived from human embryonic stem cells were able to recover from an induced stroke that hampered their exploration of a tube in the lab. It ought to work for cardboard tubes, too.

In a new study, rats were spared the limb-weakening effects of a stroke if they were treated with brain tissue cultivated from human embryonic stem cells. But unlike similar experiments, the transplanted cells gave no sign of causing tumors, according to a report this week in the online journal PLoS One.

Researchers say that if they can build a string of such successes in a range of animal models, they can make a stronger case for testing the cells in people. "This is really exciting, just to overcome this obstacle of tumorigenicity," says Stanford University stem cell biologist Marcel Daadi, a co-author of the study.

Investigators have had success of late creating stem cells, or cells very similar to them, from new sources such as adult human tissue. But the ongoing scientific challenge is to harness those cells' ability to morph into the different adult cell types and thereby develop new treatments for debilitating diseases such as stroke, which strikes about 700,000 Americans every year, according to the U.S. Centers for Disease Control and Prevention.

Daadi and his colleagues transplanted specially grown human neural stem cells—precursors of neurons and other neural cell types—into the brains of rats made to suffer a stroke in the right hemisphere of the brain, which had sapped the strength from their front left paws. Rats that received the transplant recovered strength in the impaired limbs, as judged by a test in which the rodents explore a tube. Animals given a sham injection regained little or none of the lost strength, the group reports.

The researchers found no sign of tumor growth in the brains of the healed rats or after stem cell injections into the bodies of healthy rats. Daadi attributes the success to their way of harvesting neural stem cells from human embryonic stem cells, which he says weeded out unwanted cell types that might grow into tumors.

An application for early human testing of a stroke treatment using cells derived from human fetal brain tissue, developed by the Guildford, England–based stem cell company ReNeuron Group, PLC, is currently on hold with the Food and Drug Administration, pending additional data.

How did you first become interested in artificial intelligence (AI)?
Everything happened almost by accident. I learned to play chess by eight—it was my big passion in high school and university. In my last year at university, I came across a thing called a computer. I heard about it, but knew nothing about it. They were incredibly primitive then—they didn't run on transistors, but on vacuum tubes. I got interested in computer programming through programming games. Then I head about a subject called AI, which people in Edinburgh were working on, such as Donald Michie, the head of the department of machine intelligence at the University of Edinburgh, who worked with Alan Turing on breaking German codes. Donald Michie was an amazing guy who was killed just recently in a car crash. He was the founding father of AI in the U.K. and introduced me and others to AI.

So your interest in chess programs led you to computers and, ultimately, artificial intelligence?
Back then, people wrote chess programs to simulate human thought processes. It turned out in time that approach didn't work, that chess programs would use completely different techniques that are not humanlike at all. But I was still left interested in simulating human thought processes and emotions and personality. I thought, "Wouldn't it be interesting if there were artificial people we could talk to?" So that started me thinking even more about the way humans interact with computers—not just by typing on a keyboard, but how people could interact with computers in a humanlike way. I funded a project for three years that won the Loebner Prize in 1997, a world championship for conversational computer programs decided by a Turing test–type conversation.

In other words, the program's responses tried as much as possible to be indistinguishable from those of a human, and in Turing's conception, the machine could be said to think. So, moving on from mere conversation, you began researching how, um, far interaction between humans and robots could go?
Around the year 2003, I started researching this topic very seriously. I was writing a book, Robots Unlimited, with a couple of chapters on robot emotion—love, even sex. I found so much material that when I finished that book, I wanted to look even more deeply in human emotional relationships with computers, with the possibility of sexual relations. I decided to call the book I wrote Love and Sex with Robots.

Did any of the research you found prove especially memorable?
The one single thing that made me go into this subject deeply was when I read a book by Sherry Turkle, The Second Self. In there, she wrote about some students she interviewed in her attempts to figure out how people related to computers. In one anecdote with a student dubbed "Anthony," he tried having girlfriends but preferred relationships with computers. With girls, he wasn't sure how to react; but with computers, he knew how to react. I thought that was so fascinating. And there are loads of Anthonys out there who find it difficult to, or can't form satisfying relationships with, humans. I dedicated my book Love and Sex with Robots to Anthony and all the other Anthonys before and since of both sexes—to all those who feel lost and hopeless without relationships, to let them know there will come a time when they can form relationships with robots.

So what was it like researching the possibility of sex with robots? You ended up writing a lot about sex dolls—did you know about sex dolls before you wrote your book?
I hadn't thought about them beforehand at all. It was absolutely fascinating doing the research. Then I got the idea that sex with dolls is like sex with prostitutes—you know the prostitute doesn't love you and care for you, is only interested in the size of your wallet. So I think robots can simulate love, but even if they can't, so what? People pay prostitutes millions and millions for regular services. I thought prostitution was a very good analogy.

And, as you mention in Love and Sex with Robots, brothels in Japan and South Korea already offer sex with dolls for the same rates they would charge for human prostitutes. So in studying sex with prostitutes, you figured you might begin to understand what the thinking behind sex with robots would be.
I started analyzing the psychology of clients of prostitutes. One of the most common reasons people pay for sex was that people wanted variety in sex partners. And with robots, you could have a blonde robot today or a brunette or a redhead. Or people want different sexual experiences. Or they don't want to commit to a relationship, but just to have a sexual relationship bound in time. All those reasons that people want to have sex with prostitutes could also apply to sex with robots.

But sex with robots won't just be a guy thing?
When I started, the research was almost entirely on male clients, but the number of women who pay for sex is on the increase, although there's not much published on the subject. That shows both sexes are interested and willing and desirous to get sex they paid for. Heidi Fleiss is proposing to open a brothel in Nevada where all the sex workers are male and the clients are female. You already have something similar in Spain.

If people fall in love with robots, aren't they just falling in love with an algorithm?
It's not that people will fall in love with an algorithm, but that people will fall in love with a convincing simulation of a human being, and convincing simulations can have a remarkable effect on people.

When I was 10, I was in Madame Tussauds waxworks in London with my aunt. I wanted to find someone to get to some part of the exhibition and I saw someone, and it didn't dawn on me for a few seconds that that person was a waxwork. It had a profound effect on me—that not everything is as it seems, and that simulations can be very convincing. And that was just a simple waxwork.

And if you or others could be taken in just by a wax figure, even for a moment, imagine what a realistic robotic simulation of a person would do. But if people are aware that a robot's just electronics, won't that be an obstacle to true love?
By 40 or 50 years, everyone of a marriageable age will have grown up with electronics all around them at home, and not see them as abnormal. People who grow up with all sorts of electronic gizmos will find android robots to be fairly normal as friends, partners, lovers.

Now did science fiction inspire you at all? Because science fiction is naturally one of the first things that leapt to my mind when I think of a society with robots in it.
I don't read science fiction at all. The only sci-fi book I ever read was as a favor to a publisher who wanted a quote from me on the back cover, but the book was so dreadful that I couldn't support it.

Are advances in robotics really going to happen that fast? Wouldn't the technology take up rooms of electronics?
Computer technology is getting faster and more powerful and smaller all the time. What fits in a backpack now could fit in a matchbook in 30 years' time.

If we don't yet completely understand humans, how can we make a humanlike robot?
It will be an iterative process, to be sure. But while we don't understand humans perfectly, we know quite a bit now about human behavior and psychology, and we could program that in.

Isn't your prediction about humans marrying robots in 50 years optimistic?
If you went back 100 years, if you proposed the idea that men would be marrying men, you'd be locked up in the loony bin. And it was only in the second half of the 20th century that you had the U.S. federal government repealing laws in about 12 states that said marriage across racial boundaries was illegal. That's how much the nature of marriage has changed.

I think the nature of marriage in the future is that it will be what we want it to be. If you and your partner decide to be married, you decide what the bounds are, what its purpose is to you.

Would people really want a robot that agreed with everything you wanted or were completely predictable?
I do think there is often a need for friction in relationships. You wouldn't actually want a robot that does everything you want. Most people might want robots that sometimes say, "I don't really want to do that," that rejects certain requests from time to time. So you could program that in, the level of disagreement you want.

And you could program a robot to have different tastes from you. I personally find it very beneficial that my wife has interests that I do not. You could find it fascinating, for instance, that your robot knows a lot about 19th-century South African stamps or the like.

How might human–robot relationships alter human society?
I don't think the advent of emotional and sexual relationships with robots with end or damage human–human relationships. People will still love people and have sex with people. But I think there are people who feel a void in their emotional and sex lives for any number of reasons who could benefit from robots. Other people might try out a relationship with a robot out of curiosity, or be fascinated by what's written in the media. And there are always people who want to keep up with the neighbors.

One point a friend made to me was that there will be people who say, "Oh, you're only a robot." But I also think there will be people who take the view, "Oh, you're only a human."

Isn't falling in love with a robot reminiscent of falling in love in a chat room?
I think it's a very small step at the end of the day—if you are sitting at home talking in a chat room with someone who purports to be a 26-year-old female—between that person being a human or a robot. It's a kind of Turing test. So many people nowadays are developing strong emotional attachments across the Internet, even agreeing to marry, that I think it doesn't matter what's on the other end of the line. It just matters what you experience and perceive.

Do you think others will follow this field?
I was actually recently contacted by a woman at the University of Washington, who wants to write a thesis on human–robot relationships.

What directions will you pursue now?
I'm writing an academic paper on the ethical treatment of robots. Not just the ethics of designing robots to do certain things—people write about whether we should design robots to go into combat and kill people, for instance—but should we be treating robots in an ethical way. If we treat robots in an unethical way, would that be a very bad lesson for other people and children? If it's seen as okay to maltreat robots, would that send a message about living creatures? Robots can certainly have a semblance of being alive.

What does your wife think?
She has a different slant from me. She's not a science person at all—her background's in English and drama; she's not interested in computers or robots or AI. She was totally skeptical of the idea that humans would fall in love with robots. She's still fairly skeptical, but she's beginning to appreciate something like this will happen.

What happens if 50 years from now your predictions have not proved true, and humans and robots don't marry?
I know some people think the idea is totally outlandish. But I am totally convinced it's inevitable. I would be absolutely astounded if I'm proven wrong—not if I'm a few years off, but if I'm proven completely wrong.

 
TO SCALE: A new planetary system contains two planets that closely resemble Jupiter and Saturn in their relative mass and distance to their star.

Astronomers have discovered a pair of planets around a star 5,000 light-years away that resemble smaller versions of Jupiter and Saturn, hinting that solar systems like ours may be unexpectedly common. As in our own solar system, the closer of the two planets to their star is the larger one, 70 percent as massive as Jupiter; the more distant planet has 90 percent the mass of Saturn.

The star itself, dubbed OGLE-2006-BLG-109L, is dimmer than our sun and is only half its size. But the ratios between the two planets' masses and that of their star as well as their relative orbital distances are very similar to those of Jupiter and Saturn. "Basically what we found is a scaled-down analog of our solar system," says Scott Gaudi, an assistant professor of astronomy at The Ohio State University and lead author of the study published this week in Science.

Gaudi and his colleagues discovered the planets over a two-week period in early spring 2006, when their stellar parent crossed in front of a more distant star. Due to an effect called gravitational microlensing, the gravity of the nearer star magnified the light 500-fold from the more distant one. The motions of the planets caused periodic spikes in the brightness of the magnified light, which allowed the team to calculate the size of the planets and their distances from the star. The Optical Gravitational Lensing Experiment (OGLE) at the Las Campanas Observatory in Chile first detected the event.

Researchers know of other multiplanet systems, but in those systems the planets are huddled close to their stars. Microlensing events reveal planets in orbits that are more distant from their stars.

Previous to this discovery, microlensing had turned up four planets, two of them Jupiter-size. But this crossing was the first one that happened to have the right conditions to reveal the presence of smaller planets. "The first time we could find a Jupiter-–Saturn analogue, we did," Gaudis says. "And that provides us a hint ... that these kind of solar system analogues might be quite common."