by Carl Sagan
There is an alternative explanation, which derives from the fact that there are not a whole number of lunations in a solar year, nor a whole number of days in a lunation. These incommensurabilities will be galling to a culture that has recently invented arithmetic but has not yet gotten as far as large numbers or fractions. As an inconvenience, these incommensurabilities are felt even today by religious Muslims and Jews who discover that Ramadan and Passover, respectively, occur from year to year on rather different days of the solar calendar. There is a clear whole-number chauvinism in human affairs, most easily discerned in discussing arithmetic with four-year-olds; and this seems to be a much more plausible explanation of these calendrical irregularities, if they existed.
Three hundred and sixty days a year provides an obvious (temporary) convenience for a civilization with base-60 arithmetic, as the Sumerian, Akkadian, Assyrian and Babylonian cultures. Likewise, thirty days per month or ten months per year might be attractive to enthusiasts of base-10 arithmetic. I wonder if we do not see here an echo of the collision between chauvinists of base-60 arithmetic and chauvinists of base-10 arithmetic, rather than a collision of Mars with Earth. It is true that the tribe of ancient astrologers may have been dramatically depleted as the various calendars rapidly slipped out of phase, but that was an occupational hazard, and at least it removed the mental agony of dealing with fractions. In fact, sloppy quantitative thinking appears to be the hallmark of this whole subject.
An expert on early time-reckoning (Leach, 1957) points out that in ancient cultures the first eight or ten months of the year are named, but the last few months, because of their economic unimportance in an agricultural society, are not. Our month December, named after the Latin decem, means the tenth, not the twelfth, month. (September = seventh, October = eighth, November = ninth, as well.) Because of the large numbers involved, prescientific peoples characteristically do not count days of the year, although they are assiduous in counting months. A leading historian of ancient science and mathematics, Otto Neugebauer (1957), remarks that, both in Mesopotamia and in Egypt, two separate and mutually exclusive calendars were maintained: a civil calendar whose hallmark was computational convenience, and a frequently updated agricultural calendar—messier to deal with, but much closer to the seasonal and astronomical realities. Many ancient cultures solved the two-calendar problem by simply adding a five-day holiday on at the end of the year. I hardly think that the existence of 360-day years in the calendrical conventions of prescientific peoples is compelling evidence that then there really were 360 rather than 365¼ rotations in one revolution of Earth about the Sun.
This question can, in principle, be resolved by examining coral growth rings, which are now known to show with some accuracy the number of days per month and the number of days per year, the former only for intertidal corals. There appears to be no sign of major excursions in recent times from the present number of days in a lunation or a year, and the gradual shortening (not lengthening) of the day and the month with respect to the year as we go back in time is found to be consistent with tidal theory and the conservation of energy and angular momentum within the Earth-Moon system, without appeal to cometary or other exogenous intervention.
Another problem with Velikovsky’s method is the suspicion that vaguely similar stories may refer to quite different periods. This question of the synchronism of legends is almost entirely ignored in Worlds in Collision, although it is treated in some of Velikovsky’s later works. For example (page 31), Velikovsky notes that the idea of four ancient ages terminated by catastrophe is common to Indian as well as to Western sacred writing. However, in the Bhagavad Gita and in the Vedas, widely divergent numbers of such ages, including an infinity of them, are given; but, more interesting, the duration of the ages between major catastrophes is specified (see, for example, Campbell, 1974) as billions of years. This does not match very well Velikovsky’s chronology, which requires hundreds or thousands of years. Here Velikovsky’s hypothesis and the data that purport to support it differ by a factor of about a million. Or (page 91) vaguely similar discussions of vulcanism and lava flows in Greek, Mexican and Biblical traditions are quoted. There is no attempt made to show that they refer to even approximately comparable times and, since lava has flowed in historical times in all three areas, no common exogenous event is necessary to interpret such stories.
Despite copious references, there also seem to me to be a large number of critical and undemonstrated assumptions in Velikovsky’s argument. Let me mention just a few of them. There is the very interesting idea that any mythological references by any people to any god that also corresponds to a celestial body represents in fact a direct observation of that celestial body. It is a daring hypothesis, although I am not sure what one is to do with Jupiter appearing as a swan to Leda, and as a shower of gold to Danaë. On page 247 the hypothesis that gods and planets are identical is used to date the time of Homer. In any case, when Hesiod and Homer refer to Athena being born full-grown from the head of Zeus, Velikovsky takes Hesiod and Homer at their word and assumes that the celestial body Athena was ejected by the planet Jupiter. But what is the celestial body Athena? Repeatedly it is identified with the planet Venus (Part 1, Chapter 9, and many other places in the text). One would scarcely guess from reading Worlds in Collision that the Greeks characteristically identified Aphrodite with Venus, and Athena with no celestial body whatever. What is more, Athena and Aphrodite were “contemporaneous” goddesses, both being born at the time Zeus was king of the gods. On page 251 Velikovsky notes that Lucian “is unaware that Athene is the goddess of the planet Venus.” Poor Lucian seems to be under the misconception that Aphrodite is the goddess of the planet Venus. But in the footnote on page 361 there appears to be a slip, and here Velikovsky for the first and only time uses the form “Venus (Aphrodite).” On page 247 we hear of Aphrodite, the goddess of the Moon. Who, then, was Artemis, the sister of Apollo the Sun, or, earlier, Selene? There may be good justification, for all I know, in identifying Athena with Venus, but it is far from the prevailing wisdom either now or two thousand years ago, and it is central to Velikovsky’s argument. It does not increase our confidence in the presentation of less familiar myths when the celestial identification of Athena is glossed over so lightly.
Other critical statements which are given extremely inadequate justification, and which are central to one or more of Velikovsky’s major themes, are: the statement (page 283) that “Meteorites, when entering the earth’s atmosphere, make a frightful din,” when they are generally observed to be silent; the statement (page 114) that “a thunderbolt, when striking a magnet, reverses the poles of the magnet”; the translation (page 51) of “Barad” as meteorites; and the contention (page 85) “as is known, Pallas was another name for Typhon.” On page 179 a principle is implied that when two gods are hyphenated in a joint name, it indicates an attribute of a celestial body—as, for example, Ashteroth-Karnaim, a horned Venus, which Velikovsky interprets as a crescent Venus and evidence that Venus was once close enough to Earth to have its phases discernible to the naked eye. But what does this principle imply, for example, for the god Ammon-Ra? Did the Egyptians see the sun (Ra) as a ram (Ammon)?
There is a contention (page 63) that instead of the tenth plague of Exodus killing the “first born” of Egypt, what is intended is the killing of the “chosen.” This is a rather serious matter and at least raises the suspicion that where the Bible is inconsistent with Velikovsky’s hypothesis, Velikovsky retranslates the Bible. The foregoing queries may all have simple answers, but the answers are not to be found easily in Worlds in Collision.
I do not mean to suggest that all of Velikovsky’s legendary concordances and ancient scholarship are similarly flawed, but many of them seem to be, and the remainder may well have alternative, for example diffusionist, origins.
With the situation in legend and myth as fuzzy as this, any corroboratory evidence from other sources would be welcomed by those who support Velikovsky’s argumen
t. I am struck by the absence of any confirming evidence in art. There is a wide range of paintings, bas-reliefs, cylinder seals and other objets d’art produced by humanity and going back to at least 10,000 B.C. They represent all of the subjects, especially mythological subjects, important to the cultures that created them. Astronomical events are not uncommon in such works of art. Recently (Brandt, et al., 1974), impressive evidence has been uncovered in cave paintings in the American Southwest of contemporary observations of the Crab Supernova event of the year 1054, which was also recorded in Chinese, Japanese and Arab annals. Appeals have been made to archaeologists for information on cave painting representations of the earlier Gum Supernova (Brandt, et al., 1971). But supernova events are not nearly so impressive as the close approach of another planet with attendant interplanetary tendrils and lightning discharges connecting it to Earth. There are many unflooded caves at high altitudes, distant from the sea. If the Velikovskian catastrophes occurred, why are there no contemporary graphic records of them?
I therefore cannot find the legendary base of Velikovsky’s hypothesis at all compelling. If, nevertheless, his notion of recent planetary collisions and global catastrophism were strongly supported by physical evidence, we might be tempted to give it some credence. If the physical evidence is not, however, very strong, the mythological evidence will surely not stand by itself.
LET ME GIVE a short summary of my understanding of the basic features of Velikovsky’s principal hypothesis. I will relate it to the events described in the Book of Exodus, although the stories of many other cultures are said to be consistent with the events described in Exodus:
The planet Jupiter disgorged a large comet, which made a grazing collision with Earth around 1500 B.C. The various plagues and Pharaonic tribulations of the Book of Exodus all derive directly or indirectly from this cometary encounter. Material which made the river Nile turn to blood drops from the comet. The vermin described in Exodus are produced by the comet—flies and perhaps scarabs drop out of the comet, while indigenous terrestrial frogs are induced by the heat of the comet to multiply. Earthquakes produced by the comet level Egyptian but not Hebrew dwellings. (The only thing that does not seem to drop from the comet is cholesterol to harden Pharaoh’s heart.)
All this evidently falls from the coma of the comet, because at the moment that Moses lifts his rod and stretches out his hand, the “Red Sea” parts—due either to the gravitational tidal field of the comet or to some unspecified electrical or magnetic interaction between the comet and the “Red Sea.” Then, when the Hebrews have successfully crossed, the comet has evidently passed sufficiently farther on for the parted waters to flow back and drown the host of Pharaoh. The Children of Israel during their subsequent forty years of wandering in the Wilderness of Sin are nourished by manna from heaven, which turns out to be hydrocarbons (or carbohydrates) from the tail of the comet.
Another reading of Worlds in Collision makes it appear that the plagues and the Red Sea events represent two different passages of the comet, separated by a month or two. Then after the death of Moses and the passing of the mantle of leadership to Joshua, the same comet comes screeching back for another grazing collision with the Earth. At the moment that Joshua says “Sun, stand thou still upon Gibeon; and thou, Moon, in the valley of Ajalon,” the Earth—perhaps because of tidal interaction again, or perhaps because of an unspecified magnetic induction in the crust of the Earth—obligingly ceases its rotation, to permit Joshua victory in battle. The comet then makes a near-collision with Mars, so violent as to eject it out of its orbit so it makes two near-collisions with the Earth which destroy the army of Sennacherib, the Assyrian king, as he was making life miserable for some subsequent generation of Israelites. The net result was to eject Mars into its present orbit and the comet into a circular orbit around the Sun, where it became the planet Venus—which previously, Velikovsky believes, did not exist. The Earth meantime had somehow begun rotating again at almost exactly the same rate as before these encounters. No subsequent aberrant planetary behavior has occurred since about the seventh century B.C., although it might have been common in the Second Millennium.
That this is a remarkable story no one—proponents and opponents alike—will disagree. Whether it is a likely story is, fortunately, amenable to scientific inquiry. Velikovsky’s hypothesis makes certain predictions and deductions: that comets are ejected from planets; that comets are likely to make near or grazing collisions with planets; that vermin live in comets and in the atmospheres of Jupiter and Venus; that carbohydrates can be found in the same places; that enough carbohydrates fell in the Sinai peninsula for nourishment during forty years of wandering in the desert; that eccentric cometary or planetary orbits can be circularized in a period of hundreds of years; that volcanic and tectonic events on Earth and impact events on the Moon were contemporaneous with these catastrophes; and so on. I will discuss each of these ideas, as well as some others—for example, that the surface of Venus is hot, which is clearly less central to his hypothesis, but which has been widely advertised as powerful post hoc support of it. I will also examine an occasional additional “prediction” of Velikovsky—for example, that the Martian polar caps are carbon or carbohydrates. My conclusion is that when Velikovsky is original he is very likely wrong, and that when he is right the idea has been pre-empted by earlier workers. There are also a large number of cases where he is neither right nor original. The question of originality is important because of circumstances—for example, the high surface temperature of Venus-which are said to have been predicted by Velikovsky at a time when everyone else was imagining something very different. As we shall see, this is not quite the case.
In the following discussion, I will try to use simple quantitative reasoning as much as possible. Quantitative arguments are obviously a finer mesh with which to sift hypotheses than qualitative arguments. For example, if I say that a large tidal wave engulfed the Earth, there is a wide range of catastrophes—from the flooding of littoral regions to global inundation—which might be pointed to as support for my contention. But if I specify a tide 100 miles high, I must be talking about the latter, and moreover, there might be some critical evidence to counterindicate or support a tide of such dimensions. However, so as to make the quantitative arguments tractable to the reader who is not very familiar with elementary physics, I have tried, particularly in the Appendices (following the References), to state all the essential steps in the quantitative development, using the simplest arguments that preserve the essential physics. Perhaps I need not mention that such quantitative testing of hypotheses is entirely routine in the physical and biological sciences today. By rejecting the hypotheses that do not meet these standards of analysis, we are able to move swiftly to hypotheses in better concordance with the facts.
There is one further point about scientific method that must be made. Not all scientific statements have equal weight. Newtonian dynamics and the laws of conservation of energy and angular momentum are on extremely firm footing. Literally millions of separate experiments have been performed on their validity—not just on Earth, but, using the observational techniques of modern astrophysics, elsewhere in the solar system, in other star systems, and even in other galaxies. On the other hand, questions on the nature of planetary surfaces, atmospheres and interiors are on much weaker footing, as the substantial debates on these matters by planetary scientists in recent years clearly indicate. A good example of this distinction is the appearance 1975 of Comet Kohoutek. This comet had first been observed at a great distance from the Sun. On the basis of the early observations, two predictions were made. The first concerned the orbit of Comet Kohoutek—where it would be found at future times, when it would be observable from the Earth before sunrise, when after sunset—predictions based on Newtonian dynamics. These predictions were correct to within a gnat’s eyelash. The second prediction concerned the brightness of the comet. This was based on the guessed rate of vaporization of cometary ices to make a large cometary t
ail which brightly reflects sunlight. This prediction was painfully in error, and the comet—far from rivaling Venus in brightness—could not be seen at all by most naked-eye observers. But vaporization rates depend on the detailed chemistry and geometrical form of the comet, which we know poorly at best. The same distinction between well-founded scientific arguments, and arguments based on a physics or chemistry that we do not fully understand, must be borne in mind in any analysis of Worlds in Collision. Arguments based on Newtonian dynamics or the conservation laws of physics must be given very great weight. Arguments based on planetary surface properties, for example, must have correspondingly lesser weights. We will find that Velikovsky’s arguments run into extremely grave difficulties on both these scores, but the one set of difficulties is far more damaging than the other.
PROBLEM I
THE EJECTION OF VENUS
BY JUPITER
VELIKOVSKY’S hypothesis begins with an event that has never been observed by astronomers and that is inconsistent with much that we know about planetary and cometary physics, namely, the ejection of an object of planetary dimensions from Jupiter, perhaps by its collision with some other giant planet. Such a propagation of catastrophes, Velikovsky promised, would be “the theme of the sequel to Worlds in Collision” (page 373). Thirty years later, no sequel of this description has appeared. From the fact that the aphelia (the greatest distances from the Sun) of the orbits of short-period comets have a statistical tendency to lie near Jupiter, Laplace and other early astronomers hypothesized that Jupiter was the source of such comets. This is an unnecessary hypothesis because we now know that long-period comets may be transferred to short-period trajectories by the perturbations of Jupiter; this view has not been advocated for a century or two except by the Soviet astronomer V. S. Vsekhsviatsky, who seems to believe that the moons of Jupiter eject comets out of giant volcanoes.