The Compleat McAndrews

The number of papers written on the subject is huge — Victor Szebehely, in a 1967 book on the topic, listed over 500 references, and restricted himself to only the major source works.

Thanks to the efforts of all these workers, a good deal is known about the possible solutions of the restricted three-body problem. One established fact is that the small object ca

Unfortunately, those arguments ca

So how many rogue planets are there? There could conceivably be as many as there are stars, strewn thick across the Galaxy but completely undetectable to our instruments. Half a dozen may lie closer to us than the nearest star. Or they may be an endangered species, vanishingly rare among the varied bodies that comprise the celestial zoo.

In the seventh chronicle I suggest that they are rather common — and that’s acceptable to me as science fiction. Maybe they are, because certainly planets around other stars seem far more common than we used to think. Up to 1996, there was no evidence at all that even one planet existed around any star other than Sol. Now we know of a dozen or more. Every one is Jupiter’s size or bigger, but that does not imply that most planets in the universe are massive. It merely shows that our detection methods can find only big planets. Possibly there are other, smaller planets in every system where a Jupiter-sized giant has been discovered.

If we ca

The other (and to this date more successful) method of detection relies on the periodic shift in the wavelengths of light that we receive from a star and planet orbiting around their common center of gravity. When the star is approaching us because the planet is moving away from us, the light will be shifted toward the blue. When the star is moving away from us because the planet is approaching us, the star’s light will be shifted toward the red. The tiny difference between these two cases allows us, from the wavelength changes in the star’s light, to infer the existence of a planet in orbit around it.

Since both methods of detection depend for their success on the planet’s mass being an appreciable fraction of the star’s mass, it is no surprise that we are able to detect only the existence of massive planets, Jupiter-sized or bigger. And so far as rogue worlds are concerned, far from any stellar primary, our methods for the detection of extra-solar planets are no use at all.

The solar focus.

We go to general relativity again. According to that theory, the gravitational field of the Sun will bend light beams that pass by it (actually, Newtonian theory also turns out to predict a similar effect, a factor of two less in magnitude). Rays of light coming from a source at infinity and just missing the Sun will be bent the most, and they will converge at a distance from the Sun of 550 astronomical units, which is about 82.5 billion kilometers. To gain a feeling for that number, note that the average distance of the planet Pluto from the Sun is 5.9 billion kilometers; the solar focus, as the convergence point is known, is a fair distance out.

Those numbers apply for a spherical Sun. Since Sol rotates and so has a bulge at its equator, the Sun considered as a lens is slightly astigmatic.

If the source of light (or radio signal, which is simply another form of electromagnetic wave) is not at infinity, but closer, then the rays will still be converged in their passage by the Sun, but they will be drawn to a point at a different location. As McAndrew correctly points out in the eighth chronicle, a standard result in geometrical optics applies. If a lens converges a parallel beam of light at a distance F from the lens, then light starting at a distance S from the lens will be converged at a distance D beyond it, where 1/F = 1/S + 1/D.

This much is straightforward. The more central element of this chronicle involves far more speculation. When, or if you prefer it, if, will it be possible to produce an artificial intelligence, an “AI,” that rivals or surpasses human intelligence?

It depends which writers you believe as to how you answer that question. Some, such as Hans Moravec, have suggested that this will happen in fifty years or less. Others, while not accepting any specific date, still feel that it is sure to come to pass. Our brains are, in Marvin Minsky’s words, “computers made of meat.” It may be difficult and take a long time, but eventually we will have an AI able to think as well or better than we do.

However, not everyone accepts this. Roger Penrose, whom we have already mentioned in co

In a difficult book that was a surprising best-seller, The Emperor’s New Mind (1989), he claimed that some functions of the human brain will never be duplicated by computers developed along today’s lines. The brain, he asserts, performs some functions for which no computer program can be written.

This idea has been received with skepticism and even outrage by many workers in the field of AI and computer science. So what does Penrose say that is so upsetting to so many? He argues that human thought employs physics and procedures drawn from the world of quantum theory. In Penrose’s words, “Might a quantum world be required so that thinking, perceiving creatures, such as ourselves, can be constructed from its substance?”

His answer to his own question is, yes, a quantum world-view is required. In that world, a particle does not necessarily have a well-defined spin, speed, or position. Rather, it has a number of different possible positions or speeds or spins, and until we make an observation of it, all we can know are the probabilities associated with each possible spin, speed, and position. Only when an observation is made does the particle occupy a well-defined state, in which the measured variable is precisely known. This change, from undefined to well-defined status, is called the “collapse of the quantum mechanical wave function.” It is a well-known, if not well-understood, element of standard quantum theory.