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CHAPTER 9
Far-Out Alternatives

9.1 Problems of interstellar travel. One of the strongest of today's limitations on science fiction writers is the pesky constancy of the speed of light. If you can't go faster than that, light-speed limitation is—to put it mildly—an inconvenience for travel to even the nearest stars.

To many people, travel to the stars may not seem so difficult. After all (the logic goes) a dozen humans have already been to the Moon and back. We have sent landers to Mars, and we plan to do so again. Our unmanned probes have allowed us to take a close look at every planet of the Solar System except Pluto.

After interplanetary travel surely comes interstellar travel. If we have been able to do so much in the forty years since the world's space programs began, shouldn't an interstellar mission be possible in a reasonable time . . . say, thirty or forty years from now?

In a word, no.

For travel on Earth, different transportation systems can be nicely marked by factors of ten. Up to two miles, most of us are (or should be) willing to walk. For two to twenty miles, a bicycle is convenient and reasonable. A car is fine from twenty to two hundred, and above that most of us would rather fly or take a train.

Away from Earth, the factor of ten is no longer convenient. Our closest neighbor in space, the Moon, is about 240,000 miles away, or 400,000 kilometers. A factor of ten does not take us anywhere interesting. Nor does a factor of a hundred. We have to use a factor of 1,000 to take us as far as the Asteroid Belt.

Ten thousand times the distance to the Moon takes us four billion kilometers from Earth, to the outer planets of the Solar System. We are still a long way from the stars. For that we need another factor of 10,000. Forty trillion kilometers is about 4.2 light-years, and that is close to the distance of Alpha Centauri. Thus, the nearest star is about 100,000,000 times as far away as the Moon.

Want to visit the center of our galaxy, a common drop-in point for science fiction travelers? That is almost 10,000 times as far away as Alpha Centauri, a trillion times as far away as the Moon. Getting to the Moon, you may recall, was considered a big deal.

Numbers often have little direct meaning. Perhaps a more significant way of thinking of the distance to the stars is to imagine that we have a super-transportation system, one that can carry a spacecraft and its crew to the Moon in one minute. Anyone interested in solar system development would drool at the very thought of such a device. Yet we will take 190 years to reach Alpha Centauri, and most of the stars that we think of as "famous" are much farther away: 1,300 years trip time to Vega, over 20,000 years to Betelgeuse. Galactic center? Sorry, that's going to take a couple of million years.

We need a faster-than-light drive. But before we consider exotic alternatives, let's take one more look at what we might do within the confines of the laws of physics as they are known today. If nothing can travel faster than light, can we use light itself as our tool?

We can, provided we are willing to send and receive signals, rather than material objects. That is what SETI, the Search for Extraterrestrial Intelligence, is all about.

 

9.2 The Search for Extraterrestrial Intelligence. ET made it look easy. You collect a few bits and pieces of electronics, join them together in some mysterious way, and lo and behold, you have a transmitter that will send a signal to the stars. You switch on, and wait for your friends to show up.

ET did not ask the assistance of Earth scientists in sending his message; but suppose that he had. Suppose that we were asked to send a message to the stars, one that could be received and interpreted many light-years away. What techniques would we choose, and how would we go about it?

The idea of sending messages to beings on other worlds is an old one. In the 1820s, the mathematician Carl Friedrich Gauss proposed to lay out huge geometrical figures on the surface of Earth. He argued that these, seen through telescopes by the inhabitants of other planets, would give proof that Earth harbored intelligent life. The principal pattern, created by the layout of large fields containing crops of different colors, would show a right-angled triangle with each side bordered by squares. We would provide graphic evidence that Earthlings (though not, apparently, many of America's high school students) are familiar with the theorem of Pythagoras.

Gauss had in mind the nearer planets of the solar system, since even with big telescopes the biggest fields on Earth could not be seen from farther away than Mars or Venus. Nonetheless, given its limitations, Gauss's idea is not impossible. It represents wonderfully advanced thinking for its time.

Similar suggestions involving the lighting of great fires in the Sahara Desert were made later in the nineteenth century. By 1900, extraterrestrial communication had become a popular subject. In that year the French Academy of Sciences offered a prize of 100,000 francs to the first person making contact with another world. The planet Mars was specifically excluded, since that was considered too easy.

These early proposals for extraterrestrial communications all had one thing in common: they assumed that visible light would be the best way to communicate over great distances. At first that seems a fair assumption, even when we extend our goal from interplanetary to interstellar space talk. We live on a planet orbiting a fairly typical star. Our eyes have evolved to be sensitive to the light of that star, as modified by passage through the Earth's atmosphere. Other beings, born on planets that circle other stars, are likely to have developed organs of sight. It would be most efficient for them to have developed maximum sensitivity in roughly the same wavelength region as us. Therefore we should be able to communicate by optical techniques, using the part of the electromagnetic spectrum visible to humans.

This sounds reasonable, but it misses a key point. Visible wavelengths are not the best ones for interstellar communication, precisely because visible light is so abundant throughout the universe. We can certainly send a signal, but another being will have trouble distinguishing it from natural signals that every planet, star, and galaxy emits or reflects at the same wavelengths.

Detection would be a formidable task. There is just too much clutter in the spectral window between 0.40 and 0.70 micrometers, where we ourselves see. Our message will be lost in the background noise that Nature is generating all around us.

What we need is a signal that will not be confused by emissions from stars, planets, interstellar dust clouds, galaxies, or any other natural source in the universe. We must find a "quiet" part of the spectrum, in which Nature does not make strong signals of her own; and we need a region where other beings would find logical reasons to send and look for signals.

This sounds like a difficult proposition, but fortunately such a region does exist.

 

9.3 The choice of signal carrier. If we sit down to make a list of the properties that any signalling system should have for communication over interstellar distances, we find that our signal must satisfy these requirements:

1) It should possess characteristics that allow it to be readily distinguished from naturally generated emissions;

2) It should not be easily absorbed by interstellar dust and gas;

3) It should be easy to detect;

4) It should be easy to generate with modest amounts of power;

5) It should travel at high speed.

We assume that no signal can travel faster than the speed of light, so anything traveling at light-speed will be our first preference.

That at once rules out certain signaling methods. For example, the Pioneer 10 and 11 and the Voyager 1 and 2 spacecraft are on trajectories carrying them out of the solar system. They are on their way to the stars, and they even contain messages intended for other beings. However, they travel horribly slowly. It will be hundreds of thousands of years before they reach the nearest stars. Thus they, and any other spacecraft described in Chapter 8, are too slow for interstellar messages.

The speed requirement does nothing to limit our choice within the electromagnetic spectrum. Everything from X-rays and gamma rays to visible light and long-wavelength radio waves travel in vacuum at the same speed; our other four criteria must be employed to select a preferred wavelength.

The first systematic examination of the whole spectrum, to see what is best for interstellar communication, was done by Philip Morrison and Giuseppe Cocconi (Morrison and Cocconi, 1959). As Morrison has remarked, they started out thinking that gamma rays would be the best choice, and only later broadened their viewpoint to include the whole electromagnetic spectrum.

After making their study, they concluded that there are indeed preferred wavelengths for interstellar communication, wavelengths that in fact satisfy all five of the criteria listed above. Morrison and Cocconi also addressed the question of how the signals might be generated and received.

Left out of consideration—deliberately—was the question of who might be sending signals to us. As Morrison put it, informally, "See, you were thinking that in order to call somebody up, you have to have somebody to call. I'm saying that before you call, you have to have a telephone system. We got our initial idea from the telephone system, not from thinking that anyone is there. We don't know how to estimate the probability of extraterrestrial intelligence . . . but if we never try, we'll never find it."

The inability to estimate that probability has not stopped people from trying. Suppose we write an equation giving the number of technologically advanced civilizations sending out messages in our galaxy as a product of seven independent factors: 1) the number of stars in our galaxy; 2) the fraction of such stars with planets; 3) the average number of planets orbiting any star that are suitable for the development of life; 4) the fraction of planets where life actually develops; 5) the fraction of life-bearing planets that develop intelligent life; 6) the fraction of intelligent life forms who actually seek to communicate with other forms; and 7) the fraction of the planet's lifetime occupied in the communicating phase.

This is known as the Drake Equation. It was proposed by Frank Drake, often considered the father of SETI. In 1960, using an 85-foot radio telescope in Green Bank, West Virginia, he was the first person to seek radio signals from extraterrestrial intelligences.

There are a few things to note about this equation. First, it is not a physical law, but merely an enumeration of factors. Second, if any factor is zero, the left hand side and hence the number of signals is zero. Third, only the first factor, the number of stars in our galaxy, is known to even one significant figure. The rest are little more than blind guesses.

Although thousands of pages have been written about the Drake Equation and its factors, I don't think it tells us much. The right attitude was expressed by Freeman Dyson, in his book Disturbing the Universe (Dyson, 1979): "I reject as worthless all attempts to calculate from theoretical principles the frequency of occurrence of intelligent life forms in the universe . . . Nevertheless, there are good scientific reasons to pursue the search for evidence of intelligence. . . ."

Morrison and Cocconi examined the whole electromagnetic spectrum. They reported their results in Nature magazine, and asserted that the microwave region, the one that we use for terrestrial radio and radar, is the best place to put your signal. This wavelength regime is markedly quieter (less cluttered by natural signals) than the gamma ray, X-ray, ultraviolet, visible, or infrared ranges. Nature seems to have overlooked this region for stars and planets, to the point where Earth, with its copious emissions of man-made radar, radio, and television signals, is by far the most powerful source in the solar system. At microwave wavelengths Earth is brighter than Jupiter or even the sun, although the latter is a beacon millions of times brighter at visible wavelengths.

Further, even within the microwave region, there is a definite preferred window, a "quiet spot" between 30 centimeter wavelength (1 gigaHertz frequency) and 0.3 centimeter wavelength (100 gigaHertz frequency). Wavelength and frequency are inversely related, since frequency times wavelength=the speed of light. Thus either wavelength or frequency can be used equally well to define a range of the spectrum. When we speak of radio or radar we usually work in terms of frequencies; for visible or infrared light, we generally use wavelengths.

If we want to send or receive signals from the surface of the Earth, rather than out in space, then the absorption properties of our atmosphere must be taken into account. We also have to note that man-made signals from radio and television and radar form a possible source of noise for external signals. This finally reduces the quietest region to a "terrestrial microwave window" from 1 to 10 gigaHertz (30 to 3 centimeters).

Below 1 gigaHertz, the natural synchrotron radiation of the galaxy provides unwanted noise. Above 20 gigaHertz, the quantum noise of spontaneous emission dominates; but between 1 and 10 gigaHertz the only significant noise is the cosmic background radiation, peaking at a temperature of 2.7 Kelvin and an associated frequency of 25 gigaHertz, but still appreciable between 1 and 10 gigaHertz.

By fortunate coincidence, conveniently within this valley of quiet lie two significant spectral lines: at 1.420 gigaHertz (21 centimeters) we find the radiation emission of neutral hydrogen, and at 1.662 gigaHertz (18 centimeters) the emission of the hydroxyl radical. Together, hydrogen and the hydroxyl radical combine to form water, the basis for all life as we know it. As Project Cyclops, an early study of search methods for extraterrestrial intelligence, stated with memorable imagery:

"Nature has provided us with a rather narrow band in this best part of the spectrum that seems specially marked for interstellar contact. It lies between the spectral lines of hydrogen (1420 megaHertz) and the hydroxyl radical (1662 megaHertz). Standing like the Om and the Um on either side of a gate, these two emissions of the disassociation products of water beckon all water-based life to search for its kind at the age-old meeting place of all species: the water hole" (1972; cited in NASA SP-419, 1977, edited by Philip Morrison).

If we are going to use radiation to send our interstellar signal then this place, the "water hole," provides the best set of frequencies. Moreover, signals in this region can be generated easily, with standard radio equipment; they can be beamed in any direction that we choose; and they will be detectable over stellar distances with the transmission power available to us today.

There is still a problem: deciphering a possible message.

A signal is not acceptable as artificial (remember the pulsars) until it is decoded. Of course, a "message" in the usual sense is not needed; it would be quite sufficient if the pulses that we receive were, say, the prime numbers, or numbers followed by their squares.

In the early days of SETI, Frank Drake devised a short message containing some basic information about us. He sent it to a number of his colleagues, telling them that it was a message and inviting them to decipher it. Not one of them succeeded. Can you? Drake's "message" is given in TABLE 9.1 (p. 246).

The messages sent out on the Voyager spacecraft had the same problem. They included music, the sound of rain and cars, and a statement from President Jimmy Carter; the sign of intelligence, perhaps, but one difficult to interpret, even for its senders.

Note the difference between detecting extraterrestrial signals, and sending signals for others to receive. These two different problems are often confused, but SETI is the search for extraterrestrial intelligence (we sit and listen, but we don't send any signals ourselves), and CETI is communication with extraterrestrial intelligence (we also send our own messages).

The same instruments may be used either to send or to receive signals. A radio telescope can listen, by placing detection equipment at its focal point; or it can send, by placing a transmitter at the same focal point. The signal can be sent to any preferred direction in space.

The 1,000-foot radio telescope at Arecibo in Puerto Rico has been used in both modes; to listen for signals from many places, and to beam a coded signal to the Hercules globular star cluster, M13, 25,000 light-years from Earth. A radio telescope a little bigger than the one at Arecibo Observatory would be able to detect that same signal when it reaches M13, 25,000 years from now.

The big problem with SETI was stated with admirable succinctness by the great Italian scientist, Enrico Fermi: Where are they? If there are extraterrestrial intelligences, some are presumably more advanced than we are. Why haven't they showed up and presented themselves at the United Nations, or sent a proof of their existence that is impossible to miss or deny?

This absence of contact is known as the Fermi Paradox, though it is hardly a paradox. It is simply a good question, to which there is no good answer. Some people suggest that we have not yet found the right radio frequency, or have looked in the wrong direction. Some argue that we are still in too primitive a state of technology, so that our proposed methods of sending or receiving signals are little better than the multicrop agricultural fields proposed by Gauss. And of course there are others who say that aliens don't need to signal, because they visit Earth on a daily basis in UFOs.

But then there is the alternative viewpoint: We are alone, the only intelligent species in our galaxy. It is a waste of time and money scanning the sky for messages, or sending them out to nowhere.

Is SETI a waste of time, as its critics say, because the probability of success is low? Or is it, as its disciples claim, a project that we ought to be engaged in all the time and at an increased level of effort, because the payoff of success could be so enormous?

Although the United States Senate cut off all SETI funding in 1993, the effort continues with private support. The program that used to be at NASA Ames has moved, almost in its entirety, to the SETI Institute in Mountain View, CA. The Planetary Society, in Pasadena, continues an active search under Paul Horowitz at Harvard. A very readable background discussion of the whole subject can be found in The Search for Extraterrestrial Intelligence: Listening for Life in the Cosmos (McDonough, 1987).

In science fiction, SETI has long been an accepted element of the field. Three good and very different examples are The Hercules Text (McDevitt, 1986); Contact (Sagan, 1985); and The Ophiuchi Hotline (Varley, 1977).

 

9.4 Beam me up. We know how to send signals to other civilizations at the speed of light, and we are already looking for messages from them. But do we really need to go in person? Why not transmit a complete signal that represents you or me, and use it to re-create us at the other end? That way, we'll get to the stars as fast as possible, and so far as subjective experience is concerned it will be no time at all.

Put aside for one moment the fact that there is nothing at the other end to put us back together. Ignore also the awkward question of which one is the real you—the one who was scanned back here, or the one who is reconstructed out there. Let us size the problem.

The human body contains about 1028 atoms. To specify the substance of each atom (i.e. the element) needs only two decimal digits, since all atoms of a particular element are identical. However, we also need to specify information where each atom is. That calls for three coordinates, each given to an accuracy of, say, 2x10-10 meters, and with a maximum value of a couple of meters (basketball players have to crouch, or stay home).

Associated with each coordinate we specify a number from 1 to 99 (for the appropriate element) with a zero when a coordinate lies outside your body. A representation of a complete human, down to hair part, birthmarks, and eye color, thus calls for about 1032 separate pieces of information. We assume that we have an understanding, in advance, that the (x,y,z) coordinates of atoms will be given sequentially, in a particular order.

Let's see how long it will take to transmit a person from one place to another (distance is not relevant). A high-speed data link from ground to space is a few hundred million bits per second. We will be generous, and say we have a data link of a billion decimal digits (109) per second. Then the transfer of one human will take 1023 seconds, or 1015 years. The universe is only about 1010 years old. We would be better off using the Post Office.

All right, we will seek economies. First, is it really necessary to send an exact description of every atom? As we know from heart, kidney, and liver transplants, these organs are all functionally similar. Let us send just the information defining the "real you," the brain and maybe a few glands that seem to define our emotions. We do not save very much. The range of each coordinate reduces from 2 meters to 20 centimeters. The transmission time comes down to about 1012 years. Still no good.

How about if we simply regard the brain as a computer, and download the information held in it? This is certainly a popular science fiction device, although Penrose, as we will discuss in some detail in Chapter 13, would argue that it is impossible because the brain is more than a computer.

Let us assume that he is wrong. There are about 1011 neurons in the brain. We number them sequentially, 1, 2, 3 . . . 1011. We make the (disputed) assumption that a neuron is a simple on-off device, so that its information can be represented by a single binary digit. Further, we assume that each neuron connects to an average of 50 other neurons (this is only an average; certain neurons in the cerebellum have up to 80,000 connections). Now we assume that the brain is completely defined by the neuron contents, plus all the neuron-to-neuron connections. For every neuron, we need to specify a binary digit, plus 50 decimal numbers each of which may be up to 11 digits long. Then a human, regarded solely as information, is defined totally by 1014 decimal digits. The transmission time using our billion-digit-a-second transmission system is a little over a day.

This is an acceptable period. Even if we send the signal with triple redundancy, to make sure that the you-that-arrives is not subtly different from the you-that-was-sent, we are talking transmission times of a few days.

Note that you will not exist physically until you have been downloaded from signal form into a clone of your body. That will be grown from your unique DNA description, which requires only about ten billion binary digits (a small fraction of the total signal) and could be sent as a lead file to the main message.

What will we do when it turns out that the SETI signal is not the Encyclopedia Galactica at all, but the exact prescription for some alien interstellar tourist?

 

9.5 A helping hand from relativity. It is Einstein's special theory of relativity that tells us we can never accelerate any object to move faster than the speed of light. The same theory, curiously enough, offers a helping hand when we want to travel long distances.

As we mentioned in Chapter 2, one standard and experimentally tested consequence of relativity is time dilation. Let us recap its effects. When an object (in our case, a spacecraft) moves at close to the speed of light, time as measured onboard the spacecraft feels the same to the passengers, but as far as an external observer is concerned, it is slowed.

The rule is very simple: for an object traveling at a fraction F of the speed of light, when an interval T passes in the rest of the universe, an interval only (1-F2) of T passes in the object's reference frame.

Thus, if a ship travels at 90 percent of light-speed, time onboard relative to the outside universe is slowed by a factor 0.43; when a century passes on Earth, only 43 years pass on the ship. At 99 percent of light-speed, 14 years pass on the ship; at 99.9 percent of light-speed, 4 years pass on board. Clearly, if we can accelerate the ship close enough to light-speed—no mean feat, as we have seen already—then so far as the passengers are concerned, travel time to the stars or even to remote parts of the galaxy can be made tolerable. As an example, the center of the galaxy is about 30,000 light-years away. For a ship that traveled just one hundred meters a second slower than the speed of light, the perceived travel time from here to the galactic center would be only 24 years.

Frank Tipler, grandly dismissing the practical details of ship drive design, has examined travel times for a ship that moves not at constant speed, but at constant acceleration (Tipler, 1996). Setting that acceleration at a comfortable one gee, Tipler finds that a round trip to the center of our galaxy will take about 40 years of shipboard time. The Andromeda Galaxy is about 2.2 million light-years away. A visit to it needs 57 years of ship time. And if we want to take a longer trip, to the Virgo Cluster at 60,000,000 light-years distance, we can expect to be away for about 70 years. As we see, a constant acceleration telescopes almost all distances down to the point where a human lifetime is enough to travel them.

The snag, of course, is that you might go to the center of the galaxy and back in one lifetime; but while you were gone, things here on Earth could be expected to change considerably in your 60,000-year absence. As for a trip to the Virgo Cluster, you could have left Earth when dinosaurs were the dominant land animals, and not be back yet.

 

9.6 Faster than light. Like it or not, we have to explore the possibilities of faster-than-light travel. Without it, all our interstellar empires and intergalactic trade shows are impossible. What's the point of sending your army to quell an uprising when it happened 50 centuries ago, or ordering a piece of furniture that will take a thousand years to be delivered?

We need a loophole. One possibility was suggested in Chapter 2, where the idea of quantum teleportation was explored. To find another one, let us return to Einstein. The assumption that we cannot travel faster than light is usually stated as one of the central elements of the theory of special relativity. In fact, what Einstein said was not quite that. You cannot accelerate an object faster than light, or even as fast as light. As you try to move something faster and faster, the energy needed to do it becomes greater and greater.

However, this does not mean that particles which travel faster than light cannot exist. As one researcher into faster-than-light particles pointed out, that would be like saying that there can be no people north of the Himalayas, since no one can climb over the mountain ranges.

In this case, the mountain range is the speed of light. Although no particle can be accelerated through the barrier, this in no way proves that particles cannot exist on the other side of the barrier.

In 1967, Gerald Feinberg gave a name to hypothetical faster-than-light particles. He called them tachyons, from the Greek word tachys, meaning swift. Richard Tolman, as early as 1917, thought he had proved that the existence of tachyons would allow information transfer to the past, and thus allow history to be changed. For example, a message back to 1963 could in principle have prevented the Kennedy assassination. That possible use of tachyons was explored in the novel Timescape (Benford, 1979). Today, however, Tolman's argument is no longer accepted; Benford's novel remains as fiction.

Tachyons do appear to be permissible within the framework of conventional physics, in that there seems to be no physical or logical law ruling out the possibility of their existence. This has led some writers to argue that tachyons must exist, adopting the rule of the anthill from The Once and Future King (White, 1958): "Everything not forbidden is compulsory."

Suppose for the moment that tachyons are real. Then to see how light speed forms a natural barrier separating bradyons (the familiar "slow" particles of our universe, also known as tardyons) from tachyons, imagine that we accelerate a charged particle faster and faster, for example using an electromagnetic field.

What happens to it? The particle certainly continues to increase in speed, but according to the theory of special relativity as it gets closer to the speed of light it also becomes more massive. As a result it becomes more difficult to accelerate. The mass doubles, then quadruples, and more and more energy is needed to speed it up just a little more.

The process never ends. To accelerate it to the speed of light would take an infinite amount of energy, and is therefore impossible.

In the same way, for a tachyon it takes more and more energy to slow it from above light speed. It would take an infinite amount of energy to slow it to the speed of light. Thus if both bradyons and tachyons exist, each is confined to its own velocity region. The speed of light is a "barrier" that forever separates the world of tachyons from the world of bradyons, and one can never become the other.

This is all logically self-consistent, but a big question remains: How could one detect the presence of a tachyon? It used to be thought that any charged particle traveling faster than light would emit a particular radiation, known as Cherenkov radiation; but this is no longer believed to be the case. The simplest way to detect a tachyon's presence is through a time-of-flight test: if two particle detectors each register an event, and the distance between them is so large and the times so close that only a particle travelling faster than light could cause them both, then we have a candidate tachyon.

This is a suspect mechanism for detection. If two people in a household come down with influenza within an hour of each other, we do not conclude that the incubation time for influenza must be one hour or less. Almost certainly, they both caught the flu from a third party. How would we ever know that a similar underlying cause did not lead to a false inference of tachyon presence?

 

9.7 Wormholes and loopholes. Let us assume that tachyons exist. We then have a possible way of sending messages faster than light. That's useful, but it's not enough. We want to send people between the stars, fast enough to offer the writer some storytelling freedom. Tachyons won't do that, they are signals only. They also have an unfortunate property of allowing those signals to travel backward in time, which might alone be enough reason to avoid them.

Where do we turn for plausible physics, a loophole that will allow us go faster than light without using tachyons or the still-unexplored world of quantum teleportation?

As is so often the case, we turn to the work of Albert Einstein. Thanks to the general theory of relativity, the structure of the universe is not a single, simply-connected region of space and time. As we saw in Chapter 3, no information from inside a black hole can ever reach the rest of the universe. This is still true, even when we allow for the Hawking evaporation process. Thus a black hole provides, in a very real sense, an edge of the universe. If black holes are common, then the whole universe has a curious kind of Swiss-cheese structure of holes and real (i.e. accessible) space.

Furthermore, there are regions close to a rotating black hole where very strange things can happen, at least in theory. Spacetime near the ring singularity of a kernel seems to be multiply connected. In other words, if you go close enough to the singularity, you may suddenly find yourself elsewhere, having been transported through a kind of spacetime tunnel. One problem is that you are likely to appear not only elsewhere, but elsewhen. The transport mechanism may also serve as a time machine.

Other forms of spacetime tunnels, known popularly as "wormholes," have been developed by Kip Thorne and fellow-workers at CalTech. We say "developed," but of course the development so far is purely conceptual. It calls for extracting a minute black hole from the enormous numbers continuously appearing and disappearing at distances of the Planck length (again see Chapter 2). The trick is then to stabilize one—it will try desperately to disappear—and inflate it to a size useful for transmission of human-sized objects. This calls for materials far stronger than anything we have today, although our positronium-positronium bonds of Chapter 5 are taking us in the right direction. The magnified, stabilized wormhole can then serve, like our kernel ring singularity, as a way to travel between distant points without traversing intermediate "normal" space. Again, there seems to be a substantial danger that the traveler will appear in elsewhen.

 

 

 

 

TABLE 9.1 

Frank Drake's proposed message to the stars. 

 

11110000101001000011001000000010000010100
10000011001011001111000001100001101000000
00100000100001000010001010100001000000000
00000000001000100000000001011000000000000
00000001000111011010110101000000000000000
00001001000011101010101000000000101010101
00000000011101010101110101100000001000000
00000000000100000000000001000100111111000
00111010000010110000011100000001000000000
10000000010000000111110000001011000101110
10000000110010111110101111100010011111001
00000000000111110000001011000111111100000
10000011000001100001000011000000011000101
001000111100101111

 

Got it? No, neither could I.

 

 

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