Borderlands of Science

by Charles Sheffield

  A.11. Accelerating universe. For the past year the astronomers of the world have been in a state of high excitement. Observations of supernovas—exploding stars—billions of light-years away suggest a surprising result: the universe, which since the 1920s has been known to be expanding, is not simply expanding; it's accelerating. Distant galaxies are not only receding from us, they are flying away faster and faster.

  Since these events are taking place at distances so great as to be almost unimaginable, the natural reaction to the new observations might well be, so what? How can things so remote have any possible relevance to human affairs here on Earth?

  To answer that question, we need to explain why it is so surprising for far-off galaxies to be moving away increasingly fast. The place to start is with the "standard model" of the universe, the mental picture of the cosmos that scientists have been developing and testing for the past seventy years. According to that model, our universe began somewhere between twelve and twenty billion years ago, in a "Big Bang" that sent all parts of that original tightly-compressed universe rushing away from each other. We have to point out that it is not that other parts of the universe are receding from us, which would imply we are in some special position. All parts are running away from each other. And the first evidence of this expansion was provided in 1929 by Edwin Hubble, after whom the Hubble Space Telescope is named. All observations since then confirm his result.

  Will the expansion continue forever, or it will it stop at some future time? That question proved difficult to answer. The force of gravity operates on every galaxy, no matter how far away, and it acts to pull them all closer together. Given enough material in the universe, the expansion might one day slow down and even reverse, with everything falling back together to end in a "Big Crunch." Or, with less density of material, the expansion might go on forever, with the force of gravity gradually slowing the expansion rate. But in either case, gravity can only serve to pull things together. It can't push; and a push is what you need in order to explain how the expansion of the universe can possibly be accelerating.

  Where could such a push—a repulsive force between the galaxies—possibly come from? The only possible source, according to today's science, arises from space itself. There must be a "vacuum energy," present even in empty space, and providing an expansion force powerful enough to overcome the attraction of gravity. The idea of such a source of force was introduced by Einstein over eighty years ago, as a so-called "cosmological constant." Einstein used this constant to explain why the universe did not expand (this was before Hubble's observations showing that it did) and Einstein called his failure to imagine an expanding universe the biggest blunder of his life. Until recently, most cosmologists preferred to assume that the value of the cosmological constant was zero, which meant there was no repulsive force associated with space itself.

  The new observations of an accelerating universe imply that this is no longer an option. The cosmological constant can't be equal to zero if space itself is to be the origin of a repulsive force more than strong enough to balance gravitational attraction.

  And now for the so what?: Can such esoteric ideas, originating so far away, have any relevance to everyday life?

  I can't really answer that. But I will point out that the proposed vacuum energy is present here on Earth, as well as in remote locations. And notions equally abstract, published by Einstein in 1905 and concerning the nature of space and time, led very directly to atomic energy and the atomic bomb. That development took less than forty years. If history is any guide, many of us might live to see practical consequences of a non-zero cosmological constant.

  A.12. Nothing but blue skies . . . Let me describe a condition: it is a physical disability that affects more than twenty million Americans; it is usually congenital, and almost always incurable; it is at best a nuisance, and it is at worst life-threatening.

  You might think that such an ailment would be a major item on the agenda of the National Institutes of Health, perhaps even the subject of a Presidential Commission to seek urgent action.

  No such thing. The condition I have described is color blindness. It is strongly sex-linked. One man in every twelve suffers from it to some extent, compared with only one woman in two hundred. And the whole subject enjoys little attention.

  Part of the reason for our lack of emphasis on color blindness is its invisibility. You can't tell that a man has such a disability, though his choice of shirt and matching tie may be a bit of a giveaway. In fact, you may suffer some form of it yourself and become aware of that fact only in special circumstances. In my own case I have difficulty distinguishing blues and greens, but I only notice it when playing "Trivial Pursuit"; then I am never sure if I have a blue or a green question coming.

  A more common—and a more dangerous—form cannot distinguish red from green. John Dalton, the chemist, a colorblind person and one of the first people to write about it, reported that "blood looks like bottle-green and a laurel leaf is a good match for sealing wax." In more modern times, sufferers are forced to distinguish the condition of traffic lights by their vertical placement, and they are at risk in situations where a red "Stop" light or a green "Go" light offers no other information to back it up.

  The problem originates in the retina, at the back of our eyes. The retina contains two different kinds of light-sensitive objects, each microscopic in size. The retinal rods do not perceive color at all, and they are most useful at low light levels. The retinal cones are responsible for all color vision, but they need a higher light level before they become sensitive. Recall that, on a moonlit walk, your surroundings are rendered only in black and white.

  In a person with normal vision, the signals generated by the cones and transmitted by nerve cells to the brain permit all color to be distinguished. If you are color blind, however, certain colors will produce the same signals as each other. Green and red may be confused, or pale green and yellow, or, in my case, certain greens and blues.

  Unlike some other conditions, color blindness has few compensating advantages. In a military situation, a color blind person may detect camouflage which fools ordinary eyes, but in general, color blindness is nothing but a nuisance. So can we do anything about it?

  As I said at the beginning, this disability is usually incurable. It can, however, often be alleviated by the use of special eyeglasses. These contain filters that modify the light passing through them, in such a way that they convert different colors to combinations that the wearer can perceive.

  That's today, and even if impressive it's pretty crude. Twenty years from now we will be able to go much farther, with personalized "false color" eyeglasses. These will employ sensors and displays that transform any light falling on them into color regions for which the wearer's retina is able to generate distinguishable signals.

  You might argue that a person with such eyeglasses is still color blind, because his perception of blue, green, or red will be different from yours. If you make this point, I will ask the question: how do you know that what you perceive when you see colors is at all the same as other people's?

  A.13. Thinking small. The launch of a space shuttle is an impressive event. It is impressively big, impressively noisy, and impressively expensive. During the first few minutes of ascent, energy is used at a rate enough to power the whole United States. Most of us love fireworks, and I have never met anyone who did not enjoy watching this fireworks display on the grandest scale.

  On the other hand, is this a necessary display of size and power? We are in the habit of thinking that sending something into space requires a vast and powerful rocket, but could we be wrong?

  We could, and we are. Most of our preconceived ideas about rocket launches go back to the early days of the "space race" between the United States and the Soviet Union, and in the 1950s and 1960s the name of the game was placing humans into orbit. There were good psychological and practical reasons for wanting to send astronauts and cosmonauts. First, the public is always f
ar more interested in men than in machines; and second, the computers of the early days of the space program were big, primitive and limited in what they could do. People, by contrast, possessed—and possess—far more versatility than any computer, and can perform an endless variety of tasks.

  On the other hand, people come in more-or-less standard sizes. They also need to eat, drink and breathe. Once you decide that humans are necessary in space, you have no alternative to big rockets; but today's applications satellites, for communications, weather observation, and resource mapping, neither need nor want a human presence.

  As computers become smarter and more powerful, they are also shrinking in size and weight. The personal computer in your home today is faster and has far more storage than anything in the Apollo program spacecraft. Other electronics, for observing instruments and for returning data to the ground, is becoming micro-miniaturized. Payloads can weigh less. So how big—or how small—can a useful rocket be?

  We are in the process of finding out. Miniature thrust chambers for rocket engines have already been built, each one smaller and lighter than a dime. A group of about a hundred of these should be able to launch into orbit something about the size of a Coke can. That's more than big enough to house a powerful computer, plus an array of instruments. One of these "microsats" could well become an earth resources or weather observing station.

  We are at the very beginning of thinking small in space. How small might we go? Since our experience with space vehicles is limited, let us draw an analogy with aircraft. Today's aircraft, like today's spacecraft, are designed to carry people. Suppose, however, that we just want a flying machine that can carry a small payload (maybe a few grams, enough for a powerful computer). How small and light can it be? We don't have a final answer to that question, although today a jet engine the size of a shirt button is being built at MIT. However, Nature provides us with an upper limit on size. Swallows, weighing just a few ounces, every year migrate thousands of miles without refueling. We should be able to do at least this well.

  And if you want to think really small, look at what the swallows eat: flying insects, each with its own on-board navigation and observing instruments. Imagine a swarm of space midges, all launched on a rocket no bigger than a waste paper basket, each one observing the Earth or the sky and returning their coordinated observations back to the ground. Imagination could become reality in less than half a century.

  A.14. New maps for old. Map-making in ancient times was not a job for the faint-hearted.

  Even without the early worries of going too far and sailing off the edge of the world, anyone interested in determining the positions of land masses and shore lines had to face the dangers of reefs, shoals, storms at sea, scurvy, shipwreck, and starvation. Perhaps even worse were the hostile natives met along the way, who killed, among others, the famous explorers Ferdinand Magellan and Captain James Cook.

  Mapping the interior of a country was just as difficult. The hardy surveyor had to face deserts, glaciers, avalanches, impassable rivers, infectious diseases, dangerous animals, and still more hostile natives.

  And yet maps were early recognized as vitally important. Within settled countries they were needed to define property ownership, set taxes, measure land use, and establish national boundaries. Farther afield, the lack of good maps and accurate knowledge of position led to countless shipwrecks. In 1707, an English fleet commanded by the splendidly-named Sir Cloudesley Shovel made an error in navigation, ran ashore on the Scilly Isles which they thought were many miles away, and lost more than two thousand sailors.

  Why was map-making so hard? It sounds easy. All you need to define a point on the surface of the Earth uniquely are three numbers: latitude, longitude, and height above some reference surface (usually sea-level). Measure a few thousand or tens of thousands of such points, and you have an accurate map of the Earth.

  Unfortunately, it was difficult verging on impossible to determine absolute locations. The fall-back position was to measure relative locations. Starting with a baseline a few miles long, a distant point was identified, and accurate angles from each end of the baseline were measured. This allowed the other two sides of the triangle to be calculated; from these as new baselines, new angle measurements led to more triangles, which led to still more triangles, until finally the whole country or region was covered by a network. In practice, because there could be small errors in each measurement, all the angles and lengths in the network were adjusted together to produce the most consistent result.

  What we describe sounds straightforward, but the amount of measurement and computation in a large mapping survey was huge. The calculations were, of course, all done by hand. A survey of this type could take years, or even decades. There was also no substitute for going out and making ground measurements. Even fifty years ago, it was possible for a leading expert on maps to declare, with perfect confidence, "there is only one way to compile an accurate map of the earth . . . and that is to go into the field and survey it."

  Today, that is not the case at all. The new generation of map-makers sit in their offices, while far above them, satellites look down on the Earth and send back a continuous stream of images revealing details as small as a few feet across. In perennially cloudy regions, spaceborne radar systems see through to the ground below. The location of the images is known fairly well, but not accurately enough to make good maps. However, the images can be cross-referenced, by identifying common ground features on neighboring and overlapping images. Also, the position of selected points on the ground can be found absolutely, to within a few tens of meters, using another satellite system known as GPS (the Global Positioning System).

  Finally, all the image data and all the cross-reference data can be adjusted simultaneously, in a computer calculation of a size that would have made all early map-makers blench. The result is not just a map of the Earth—it is an accurate map and a recent map, in which a date can be assigned to any observed feature.

  As the people involved in this will tell you, it is still hard work—but it sure beats cannibals and shipwrecks.

  A.15. The ears have it. I am one of those unfortunate people who have trouble singing the "Star-Spangled Banner." It's not that I don't know the tune, it's that my useful vocal range is only about one octave. The National Anthem spans an octave and a half. No matter where I start with "Oh say can you see," by the time I get to "the rockets' red glare" I sound like a wolf baying at the moon.

  I comfort myself with the thought that humans are primarily visual animals. Eighty percent, maybe even ninety percent, of the information that we receive about the world comes to us as visual inputs. Bats, by comparison, depend mainly on sound, "seeing" the world by echolocation of reflected sound signals that they themselves generate. And as for the other senses, any dog owner will tell you that an object without a smell counts as little or nothing in the canine world.

  Being human, we have a tendency to argue for the superiority of "our" primary way of perceiving the world. After all, we have stereoscopic, high-definition, full color vision, and that's a rare ability in the animal kingdom. But would an intelligent bat agree with us, or would it be able to make a good case for its own superior form of perception?

  Let's compare sound and light. They may seem totally different, but they have many similarities. Both travel as wave forms, and both can be resolved into waves of different single frequencies (colors, in the case of light). The note that we hear as middle C has a wavelength of a little more than four feet, whereas what we see as the color yellow has a wavelength of only one twenty-millionth of that. Also, sound waves need something—air, water, metal—to travel through, while light waves travel perfectly well through a vacuum. No bat can ever see the stars. However, I would argue that these are unimportant differences. We have equipment that can readily translate sounds to light, or convert different colored light to sounds.

  Our intelligent bats would agree with all of this; but what they would point out, quite correc
tly, is that our visual senses lack range. We can hear, with no difficulty, sounds that go all the way from thirty cycles a second, the lowest note on a big pipe organ, to fifteen thousand cycles a second, beyond the highest note of the piccolo. That is a span of nine octaves (an octave is just the doubling of the frequency of a note). Compare this with our eyesight. The longest wavelength of visible light (dark red) is not quite twice the wavelength of the shortest light that our eyes can detect (violet). The range of what we can see is less than one octave. If we were to convert "The Star-Spangled Banner" to equivalent light, not a person on earth would be able to see the whole thing.

  Why can we observe such a limited range of wavelengths, while hearing over a vastly greater one? It is a simple matter of the economy of nature. Our eyes have adapted over hundreds of millions of years to be sensitive in just the wavelength region where the sun produces its maximum illumination. The amount of radiation coming from the sun falls off rapidly in the infrared, at wavelengths longer than what we can see, while waves much shorter than violet are absorbed strongly by the atmosphere (lucky for us, or we would fry).

  Of course, being the inventive monkeys that we are, humans have found ways around the natural limitations of our eyes. Today we have equipment that provides pictures using everything from ultra-short X-rays to mile-long radio waves. We roam the universe, from the farthest reaches of space to the insides of our own bodies. With the help of our instruments, we can observe not just nine or ten octaves, but more than forty. Let's see the bats match that one.

  A.16. Memories are made of—what? Over the years I have met many people in many professions: actors, writers, biologists, computer pioneers, artists, astronomers, composers, even a trio of Nobel Prize winners in physics. They had numerous and diverse skills. What none of them had was a good memory. Or rather, what none of them would admit to was a good memory. Their emphasis was the other way round: how hard it was to recall people's faces, or names, or birthdays, or travel directions.