Again, we are at the point where the science fiction enters. If the vacuum state has an energy associated with it, I assume that this energy is capable of being tapped. Doesn’t this then, according to relativity (E =mc2), suggest that there is also mass associated with the vacuum, contrary to what we think of as vacuum? Yes, it does, and I’m sorry about that, but the paradox is not of my creation. It is implicit in the contradictions that arise as soon as you try to put general relativity and quantum theory together.
Richard Feynman, one of the founders of quantum electrodynamics, addressed the question of the vacuum energy, and computed an estimate for the equivalent mass per unit volume. The estimate came out to two billion tons per cubic centimeter. The energy in two billion tons of matter is more than enough to boil all Earth’s oceans (powerful stuff, vacuum). Feynman, commenting on his vacuum energy estimate, remarks:
“Such a mass density would, at first sight at least, be expected to produce very large gravitational effects which are not observed. It is possible that we are calculating in a naive manner, and, if all of the consequences of the general theory of relativity (such as the gravitational effects produced by the large stresses implied here) were included, the effects might cancel out; but nobody has worked all this out yet. It is possible that some cutoff procedure that not only yields a finite energy for the vacuum state but also provides relativistic invariance may be found. The implications of such a result are at present completely unknown.”
With that degree of uncertainty at the highest levels of present-day physics, I feel not at all uncomfortable in exploiting the troublesome vacuum energy to service McAndrew’s drive.
The third chronicle introduces two other ideas that are definitely science fiction today, even if they become science fact a few years from now. If there are ways to isolate the human central nervous system and keep it alive independently of the body, we certainly don’t know much about them. On the other hand, I see nothing that suggests this idea is impossible in principle — heart transplants were not feasible forty years ago, and until this century blood transfusions were rare and highly dangerous. A century hence, today’s medical impossibilities should be routine.
The Sturm Invocation for vacuum survival is also invented, but I believe that it, like the Izaak Walton introduced in the seventh chronicle, is a logical component of any space-oriented future. Neither calls for technology beyond what we have today. The hypnotic control implied in the Invocation, though advanced for most practitioners, could already be achieved. And any competent engineering shop could build a Walton for you in a few weeks — I am tempted to patent the idea, but fear that it would be rejected as too obvious or inevitable a development.
Life in space and the Oort cloud.
Most chronicles take place at least partly in the Halo, or the Outer Solar System, which I define to extend from the distance of Pluto from the Sun, out to a little over a light-year. Within this radius, the Sun is still the primary gravitational influence, and controls the orbits of objects moving out there.
To give an idea of the size of the Halo, we note that Pluto lies at an average distance of about 6 billion kilometers from the Sun. This is about forty astronomical units, where the astronomical unit, usually abbreviated to AU, is defined as the mean distance of the Earth from the Sun. The AU provides a convenient yardstick for measurements within the Solar System. One light-year is about 63,000 AU (inches in a mile, is how I remember it). So the volume of space in the Halo is 4 billion times as large as the sphere enclosing the nine known planets.
By Solar System standards, the Halo is thus a huge region. But beyond Neptune and Pluto, we know little about it. There are a number of “trans-Neptunian objects,” but no one knows how many. Some of them may be big enough to qualify as planets. The search for Pluto was inspired early this century by differences between theory and observation in the orbits of Uranus and Neptune. When Pluto was found, it soon became clear that it was not nearly heavy enough to produce the observed irregularities. The obvious explanation is yet another planet, farther out than the ones we know.
Calculations of the orbit and size of a tenth planet needed to reconcile observation and theory for Uranus and Neptune suggest a rather improbable object, out of the orbital plane that all the other planets move in and about seventy times the mass of the Earth. I don’t believe this particular object exists.
On the other hand, observational equipment and techniques for faint objects are improving rapidly. The number of known trans-Neptunian objects increases almost every month.
The other thing we know for sure about the Halo is that it is populated by comets. The Halo is often called the Oort cloud, since the Dutch astronomer Oort suggested thirty years ago that the entire Solar System is enveloped by a cloud of cometary material, to a radius of perhaps a light-year. He regarded this region as a “cometary reservoir,” containing perhaps a hundred billion comets. Close encounters between comets out in the Halo would occasionally disturb the orbit of one of them enough to divert it to the Inner System, where it would appear as a long-period comet when it came close enough to the Sun. Further interactions with Jupiter and the other planets would then sometimes convert the long-period comet to a short-period comet, such as Halley’s or Encke’s comet, which we observe repeatedly each time they swing by close to the Sun.
Most comets, however, continue their lonely orbits out in the cloud, never approaching the Inner System. They do not have to be small to be invisible to us. The amount of sunlight a body receives is inversely proportional to the square of its distance from the Sun; the apparent area it presents to our telescopes is also inversely proportional to the square of its distance from Earth. For bodies in the Halo, the reflected light that we receive from them thus varies as the inverse fourth power of their distance from the Sun. A planet with the size and composition of Uranus, but half a light-year away, would be seven trillion times as faint. And we should remember that Uranus itself is faint enough that it was not discovered until 1781, when high-quality telescopes were available. So far as present-day detection powers are concerned, there could be almost anything out there in the Halo.
One of the things that may be there is life. In a carefully argued but controversial theory developed over the past thirty years, Hoyle and Wickramasinghe have advanced the idea that space is the natural place for the creation of “pre-biotic” molecules in large quantities. Pre-biotic molecules are compounds such as carbohydrates, amino acids, and chlorophyll, which form the necessary building blocks for the development of life. Simpler organic molecules, such as methyl cyanide and ethanol, have already been observed in interstellar clouds.
Hoyle and Wickramasinghe go further. They state explicitly: “We shall argue that primitive living organisms evolve in the mixture of organic molecules, ices and silicate smoke which make up a comet’s head.”
The science fiction of the fourth chronicle consists of these two assumptions:
1. The complex organic molecules described by Hoyle and Wickramasinghe are located in a particular region of the Halo, a “life ring” that lies between 3,200 and 4,000 AU from the Sun;
2. The “primitive living organism” have evolved quite a bit further than Hoyle and Wickramasinghe expected, on at least one body of the Oort cloud.