Broca's Brain: The Romance of Science

by Carl Sagan

  FIGURE 1. Microwave brightness temperatures of Venus as a function of time (after a compilation by D. Morrison). There is certainly no evidence of a declining surface temperature. The wavelength of observation is denoted by Λ.

  The high surface temperature of Venus is another of the so-called proofs of the Velikovsky hypothesis. We find that (1) the temperature in question was never specified; (2) the mechanism proposed for providing this temperature is grossly inadequate; (3) the surface of the planet does not cool off with time as advertised; and (4) the idea of a high surface temperature on Venus was published in the dominant astronomical journal of its time and with an essentially correct argument ten years before the publication of Worlds in Collision.

  PROBLEM IX. THE CRATERS AND MOUNTAINS OF VENUS

  IN 1973 AN IMPORTANT aspect of the surface of Venus, verified by many later observations, was discovered by Dr. Richard Goldstein and associates, using the Goldstone radar observatory of the Jet Propulsion Laboratory. They found, from radar that penetrates Venus’ clouds and is reflected off its surface, that the planet is mountainous in places and cratered abundantly; perhaps, like parts of the Moon, saturation-cratered-i.e., so packed with craters that one crater overlaps the other. Because successive volcanic eruptions tend to use the same lava tube, saturation cratering is more characteristic of impact than of volcanic cratering mechanisms. This is not a conclusion predicted by Velikovsky, but that is not my point. These craters, like the craters in the lunar maria (plural for Latin mare, “sea”), on Mercury and in the cratered regions of Mars, are produced almost exclusively by the impact of interplanetary debris. Large crater-forming objects are not dissipated as they enter the Venus atmosphere, despite its high density. Now, the colliding objects cannot have arrived at Venus in the past ten thousand years; otherwise, the Earth would be as plentifully cratered. The most likely source of these collisions is the Apollo objects (asteroids whose orbits cross the orbit of the Earth) and small comets we have already discussed (Appendix 1). But for them to produce as many craters as Venus possesses, the cratering process on Venus must have taken billions of years. Alternatively, the cratering may have occurred more rapidly in the very earliest history of the solar system, when interplanetary debris was much more plentiful. But there is no way for it to have happened recently. On the other hand, if Venus was, several thousand years ago, in the deep interior of Jupiter, there is no way it could have accumulated such impacts there. The clear conclusion from the craters of Venus is, therefore, that Venus has for billions of years been an object exposed to interplanetary collisions-in direct contradiction to the fundamental premise of Velikovsky’s hypothesis.

  The Venus craters are significantly eroded. Some of the rocks on the surface of the planet, as revealed by the Venera 9 and 10 photography, are quite young; others are severely eroded. I have described elsewhere possible mechanisms for erosion on the Venus surface-including chemical weathering and slow deformation at high temperatures (Sagan, 1976). However, these findings have no bearing whatever on the Velikovskian hypotheses: recent volcanic activity on Venus need no more be attributed to a close passage to the Sun or to Venus’ being in some vague sense a “young” planet than recent volcanic activity on Earth.

  In 1967 Velikovsky wrote: “Obviously, if the planet is billions of years old, it could not have preserved its original heat; also, any radioactive process that can produce such heat must be of a very rapid decay [sic], and this again would not square with an age of the planet counted in billions of years.” Unfortunately, Velikovsky has failed to understand two classic and basic geophysical results. Thermal conduction is a much slower process than radiation or convection, and, in the case of the Earth, primordial heat makes a detectable contribution to the geothermal temperature gradient and to the heat flux from the Earth’s interior. The same applies to Venus. Also, the radionuclides responsible for radioactive heating of the Earth’s crust are long-lived isotopes of uranium, thorium and potassium-isotopes with half-lives comparable to the age of the planet. Again, the same applies to Venus.

  If, as Velikovsky believes, Venus were completely molten only a few thousand years ago-from planetary collisions or any other cause-no more than a thin outer crust, at most ~ 100 meters thick, could since have been produced by conductive cooling. But the radar observations reveal enormous linear mountain ranges, ringed basins, and a great rift valley, with dimensions of hundreds to thousands of kilometers. It is very unlikely that such extensive tectonic or impact features could be stably supported over a liquid interior by such a thin and fragile crust.

  PROBLEM X. THE CIRCULARIZATION OF THE ORBIT OF VENUS AND NONGRAVITATIONAL FORCES IN THE SOLAR SYSTEM

  THE IDEA that Venus could have been converted, in a few thousand years, from an object in a highly elongated or eccentric orbit to its present orbit, which is-except for Neptune-the most nearly perfect circular orbit of all the planets, is at odds with what we know about the three-body problem [8] in celestial mechanics. However, it must be admitted that this is not a completely solved problem, and that, while the odds are large, they are not absolutely overwhelming against Velikovsky’s hypothesis on this score. Furthermore, when Velikovsky invokes electrical or magnetic forces, with no effort to calculate their magnitude or describe in detail their effects, we are hard pressed to assess his ideas. However, simple arguments from the required magnetic energy density to circularize a comet show that the field strengths implied are unreasonably high (Appendix 4)-they are counterindicated by studies of rock magnetization.

  We can also approach the problem empirically. Straightforward Newtonian mechanics is able to predict with remarkable accuracy the trajectories of spacecraft-so that, for example, the Viking orbiters were placed within 100 kilometers of their designated orbit; Venera 8 was placed precisely on the sunlit side of the equatorial terminator of Venus; and Voyager 1 was placed in exactly the correct entry corridor in the vicinity of Jupiter to be directed close to Saturn. No mysterious electrical or magnetic influences were encountered. Newtonian mechanics is adequate to predict, with great precision, for example, the exact moment when the Galilean satellites of Jupiter will eclipse each other.

  Comets, it is true, have somewhat less predictable orbits, but this is almost certainly because there is a boiling off of frozen ices as these objects approach the Sun, and a small rocket effect. The cometary incarnation of Venus, if it existed, might also have had such icy vaporization, but there is no way in which the rocket effect would have preferentially brought that comet into close passages with the Earth or Mars. Halley’s comet, which has probably been observed for two thousand years, remains on a highly eccentric orbit and has not been observed to show the slightest tendency toward circularization; yet it is almost as old as Velikovsky’s “comet.” It is extraordinarily unlikely that Velikovsky’s comet, had it ever existed, became the planet Venus.

  SOME OTHER PROBLEMS

  THE PRECEDING ten points are the major scientific flaws in Velikovsky’s argument, as nearly as I can determine. I have discussed earlier some of the difficulties with his approach to ancient writings. Let me here list a few of the miscellaneous other problems I have encountered in reading Worlds in Collision.

  On page 280 the Martian moons Phobos and Deimos are imagined to have “snatched some of Mars’ atmosphere” and to thereby appear very bright. But it is immediately clear that the escape velocity on these objects-perhaps 20 miles per hour-is so small as to make them incapable of retaining even temporarily any atmosphere; close-up Viking photographs show no atmosphere and no frost patches; and they are among the darkest objects in the solar system.

  Beginning on page 281, there is a comparison of the Biblical Book of Joel and a set of Vedic hymns describing “maruts.” Velikovsky believes that the “maruts” were a host of meteorites that preceded and followed Mars during its close approach to Earth, which he also believes is described in Joel. Velikovsky says (page 286): “Joel did not copy from the Vedas nor the Vedas from Joel.” Yet, on pag
e 288, Velikovsky finds it “gratifying” to discover that the words “Mars” and “marut” are cognates. But how, if the stories in Joel and the Vedas are independent, could the two words possibly be cognates?

  On page 307 we find Isaiah making an accurate prediction of the time of the return of Mars for another collision with Earth “based on experience during previous perturbations.” If so, Isaiah must have been able to solve the full three-body problem with electrical and magnetic forces thrown in, and it is a pity that this knowledge was not also passed down to us in the Old Testament.

  On pages 366 and 367 we find an argument that Venus, Mars and Earth, in their interactions, must have exchanged atmospheres. If massive quantities of terrestrial molecular oxygen (20 percent of our atmosphere) were transferred to Mars and Venus 3,500 years ago, they should be there still in massive amounts. The time scale for turnover of O2 in the Earth’s atmosphere is 2,000 years, and that is by a biological process. In the absence of abundant biological respiration, any O2 on Mars and Venus 3,500 years ago should still be there. Yet we know quite definitely from spectroscopy that O2 is at best a tiny constituent of the already extremely thin Martian atmosphere (and is likewise scarce on Venus). Mariner 10 found evidence of oxygen in the atmosphere of Venus-but tiny quantities of atomic oxygen in the upper atmosphere, not massive quantities of molecular oxygen in the lower atmosphere.

  The dearth of O2 on Venus also renders untenable Velikovsky’s belief in petroleum fires in the lower Venus atmosphere-neither the fuel nor the oxidant is present in appreciable amounts. These fires, Velikovsky believed, would produce water, which would be photodissociated, yielding O. Thus Velikovsky requires significant deep atmospheric O2 to account for upper atmospheric O. In fact, the O found is understood very well in terms of the photochemical breakdown of the principal atmospheric constituent, CO2, into CO and O. These distinctions seem to have been lost on some of Velikovsky’s supporters, who seized on the Mariner 10 findings as a vindication of Worlds in Collision.

  Since there is negligible oxygen and water vapor in the Martian atmosphere, Velikovsky argues, some other constituent of the Martian atmosphere must be derived from the Earth. The argument, unfortunately, is a non sequitur. Velikovsky opts for argon and neon, despite the fact that these are quite rare constituents of the Earth’s atmosphere. The first published argument for argon and neon as major constituents of the Martian atmosphere was made by Harrison Brown in the 1940s. More than trace quantities of neon are now excluded; about one percent argon was found by Viking. But even if large quantities of argon had been found on Mars, it would have provided no evidence for a Velikovskian atmospheric exchange-because the most abundant form of argon, 40Ar, is produced by the radioactive decay of potassium 40, which is expected in the crust of Mars.

  A much more serious problem for Velikovsky is the relative absence of N2 (molecular nitrogen) from the Martian atmosphere. The gas is relatively unreactive, does not freeze out at Martian temperatures and cannot rapidly escape from the Martian exosphere. It is the major constituent of the Earth’s atmosphere but comprises only one percent of the Martian atmosphere. If such an exchange of gases occurred, where is all the N2 on Mars? These tests of the assumed gas exchange between Mars and the Earth, which Velikovsky advocates, are poorly thought out in his writings; and the tests contradict his thesis.

  Worlds in Collision is an attempt to validate Biblical and other folklore as history, if not theology. I have tried to approach the book with no prejudgments. I find the mythological concordances fascinating, and worth further investigation, but they are probably explicable on diffusionist or other grounds. The scientific part of the text, despite all the claims of “proofs,” runs into at least ten very grave difficulties.

  Of the ten tests of Velikovsky’s work described above, there is not one case where his ideas are simultaneously original and consistent with simple physical theory and observation. Moreover, many of the objections-especially Problems I, II, III and X-are objections of high weight, based on the motion and conservation laws of physics. In science, an acceptable argument must have a clearly set forth chain of evidence. If a single link in the chain is broken, the argument fails. In the case of Worlds in Collision, we have the opposite case: virtually every link in the chain is broken. To rescue the hypothesis requires special pleading, the vague invention of new physics, and selective inattention to a plethora of conflicting evidence. Accordingly, Velikovsky’s basic thesis seems to me clearly untenable on physical grounds.

  Moreover, there is a dangerous potential problem with the mythological material. The supposed events are reconstructed from legends and folktales. But these global catastrophes are not present in the historical records or folklore of many cultures. Such strange omissions are accounted for, when they are noted at all, by “collective amnesia.” Velikovsky wants it both ways. Where concordances exist, he is prepared to draw the most sweeping conclusions from them. Where concordances do not exist, the difficulty is dismissed by invoking “collective amnesia.” With so lax a standard of evidence, anything can be “proved.”

  I should also point out that a much more plausible explanation exists for most of the events in Exodus that Velikovsky accepts, an explanation that is much more in accord with physics. The Exodus is dated in I Kings as occurring 480 years before the initiation of the construction of the Temple of Solomon. With other supporting calculations, the date for the Biblical Exodus is then computed to be about 1447 B.C. (Covey, 1975). Other Biblical scholars disagree, but this date is consistent with Velikovsky’s chronology, and is astonishingly close to the dates obtained by a variety of scientific methods for the final and colossal volcanic explosion of the island of Thera (or Santorin) which may have destroyed the Minoan civilization in Crete and had profound consequences for Egypt, less than three hundred miles to the south. The best available radiocarbon date for the event, obtained from a tree buried in volcanic ash on Thera, is 1456 B.C. with an error in the method of at least plus or minus forty-three years. The amount of volcanic dust produced is more than adequate to account for three days of darkness in daytime, and accompanying events can explain earthquakes, famine, vermin and a range of familiar Velikovskian catastrophes. It also may have produced an immense Mediterranean tsunami, or tidal wave, which Angelos Galanopoulos (1964)-who is responsible for much of the recent geological and archaeological interest in Thera-believes can account for the parting of the Red Sea as well. [9] In a certain sense, the Galanopoulos explanation of the events in Exodus is even more provocative than the Velikovsky explanation, because Galanopoulos has presented moderately convincing evidence that Thera corresponds in almost all essential details to the legendary civilization of Atlantis. If he is right, it is the destruction of Atlantis rather than the apparition of a comet that permitted the Israelites to leave Egypt.

  There are many strange inconsistencies in Worlds in Collision, but on the next-to-last page of the book, a breathtaking departure from the fundamental thesis is casually introduced. We read of a hoary and erroneous analogy between the structures of solar systems and of atoms. Suddenly we are presented with the hypothesis that the supposed errant motions of the planets, rather than being caused by collisions, are instead the result of changes in the quantum energy levels of planets attendant to the absorption of a photon-or perhaps several. Solar systems are held together by gravitational forces; atoms by electrical forces. While both forces depend on the inverse square of distance, they have totally different characters and magnitudes: as one of many differences, there are positive and negative electrical charges, but only one sign of gravitational mass. We understand both solar systems and atoms well enough to see that Velikovsky’s proposed “quantum jumps” of planets are based on a misunderstanding of both theories and evidence.

  To the best of my knowledge, in Worlds in Collision there is not a single correct astronomical prediction made with sufficient precision for it to be more than a vague lucky guess-and there are, as I have tried to point out, a host of
demonstrably false claims. The existence of strong radio emission from Jupiter is sometimes pointed to as the most striking example of a correct prediction by Velikovsky, but all objects give off radio waves if they are at temperatures above absolute zero. The essential characteristics of the Jovian radio emission-that it is nonthermal, polarized, intermittent radiation, connected with the vast belts of charged particles which surround Jupiter, trapped by its strong magnetic field-are nowhere predicted by Velikovsky. Further, his “prediction” is clearly not linked in its essentials to the fundamental Velikovskian theses.

  Merely guessing something right does not necessarily demonstrate prior knowledge or a correct theory. For example, in an early science-fiction work dated 1949, Max Ehrlich imagined a near-collision of the Earth with another cosmic object, which filled the sky and terrorized the inhabitants of the Earth. Most frightening was the fact that on this passing planet was a natural feature which looked very much like a huge eye. This is one of many fictional and serious antecedents to Velikovsky’s idea that such collisions happen frequently. But that is not my point. In a discussion of how it is that the side of the Moon facing the Earth has large smooth maria while the averted face of the Moon is almost free of them, John Wood of the Smithsonian Astrophysical Observatory proposed that the side of the Moon now turned toward the Earth was once at the edge, or limb, of the Moon, on the leading hemisphere of the Moon’s motion about the Earth. In this position it swept up, billions of years ago, a ring of debris which surrounded the Earth and which may have been involved in the formation of the Earth-Moon system. By Euler’s laws, the Moon must then have altered its rotation axis to correspond to its new principal moment of inertia, so that its leading hemisphere then faced the Earth. The remarkable conclusion is that there would have been a time, according to Wood, when what is now the eastern limb of the Moon would have been facing the Earth. But the eastern limb of the Moon has an enormous collision feature, billions of years old, called Mare Orientale, which looks very much like a giant eye. No one has suggested that Ehrlich was relying upon a racial memory of an event three billion years old when he wrote The Big Eye. It is merely a coincidence. When enough fiction is written and enough scientific hypotheses are proposed, sooner or later there will be accidental concordances.