It took over 2000 years to discover the correct cosmology: the one formulated by Isaac Newton. The features of this cosmology include a heliocentric solar system, a moving earth (diurnal and annual), a unified theory of terrestrial and celestial motion, a universal force of gravity, elliptical orbits, and an account of moons, comets, and satellites. All sorts of contrary ideas were tried out and widely believed during this time of slow discovery, some completely wacky (by modern standards). Mysticism and religion stood in the way of truth. It wasn’t easy to arrive at the correct theory. Why is this—why so difficult? Is it that the theory is extremely complex or requires advanced mathematics or is intrinsically counterintuitive or includes paradoxes (like quantum theory)? No, it is none of these things: it is just that the facts are not open to casual observation. We can’t just look and see. We can’t observe the motion of the earth from our position on its surface; we can’t see what other planets are like from close up; we can’t simply track the elliptical orbits of the planets with our eyes. If we could sense the earth’s motion, we would not need convincing indirect evidence of it; but inertia gets in the way of such observation (we move with the earth so that it seems stationary to us). If we could train our eyes on the planets and observe their likeness to earth, we would immediately conclude that motion has the same causes here and elsewhere; we wouldn’t speak of sublunary and superlunary zones. If we could sit back and watch the planets move, as we watch birds fly, we would see that they move in ellipses not circles. If we could take a trip to outer space, we could see the shape of the earth, its antipodes, and its diurnal rotation—none of these being observable from our earthbound position. The difficulty with arriving at the correct cosmology arises from our location and sensory limits, not from anything intrinsic to the theory. The theory itself is simple, straightforward, and not conceptually problematic (I leave aside the mysterious nature of gravity and confine myself to questions of cosmic architecture). It just so happens that we can’t simply use our senses to get at the truth; in principle, however, the truth is open to sensory observation. The facts are observable facts (macroscopic material bodies moving through space according to normal geometry); it is just that we cannot observe them. It’s really a question of distance and the invisibility of the earth’s motion. The universe itself isn’t intrinsically hard to grasp in the relevant respects; it is actually quite simple, quite transparent, quite commonsensical (ellipses are not less comprehensible than circles). The difficulty of cosmology is entirely observer-relative, and quite adventitious. No doubt Newton was a genius in coming up with the theory, but any ten-year-old can grasp the content of the theory: it’s just not that hard. The earth moves; the sun is stationary; the earth goes round the sun in an elliptical orbit, as do the other planets; the sun exerts a force on the planets causing them do this. What’s not to understand? Suppose people were surrounded by thick clouds all the time. They can’t see what is above them. Occasionally they catch a glimpse of what lies on the other side of the clouds, but nothing very definite. Nevertheless, they formulate theories of their little cosmos; these theories are inevitably pretty wacky, given the slender observational basis (something about a celestial central fire, angels moving ethereal bodies about, that type of thing). Then one day the sky opens up with a clear view of what lies only a short distance above their heads: pieces of paper and dead leaves swirling around in the wind—nothing very spectacular or supernatural or sophisticated. Feeling rather let down, they substitute this new vision for the visions of their imagination in days gone by: this now is their official cosmology—disappointingly mundane but at least true. Well, that is like our position with respect to our (local) cosmos: we couldn’t see it too well, so we invented fanciful theories of what is going on, but now we see that it is nothing very remarkable. Admittedly, it took us 2000 years to arrive at the mundane truth (compared to the mystical mathematical supernatural nonsense concocted earlier), but at least it’s true: bits of rock flying through space, pushed around by gravity, with nary an angel in sight (or even a perfect circle). Not all science is like that: sometimes (often) the correct theory is hard to arrive at not because of human sensory limitations (particularly in regard to distance) but because the theory is genuinely unobvious and taxing even when the observational facts are in. I would say this about atomic theory, big bang cosmology, evolution by natural selection, botany, and chemistry (among others). The theory of photosynthesis, for example, is a complicated and unobvious theory; the difficulty of arriving at it doesn’t derive from a simple sensory limitation (we have the plants right in front of us). Similarly for Darwin’s theory: it takes ingenuity to come up with that; you couldn’t just observe it to be true if your eyes were more capacious. In the case of the atom, we might think that more discerning eyes would reveal the structure of the atom (but could we ever really see an electron?), but it takes more than that to figure out the dynamics of the particles composing an atom. That is, there are real theoretical problems in these areas not just a blanket of clouds or sheer distance. Improved vision wouldn’t make these problems go away. But in astronomy (the part we are concerned with anyway) the theory would be automatic once the senses have done their work: the trouble is the senses can’t do their work. The problem is location not cerebration, physical distance not intellectual depth. Newton’s work on optics falls into this latter class; his work on planetary motion falls into the former class. This is why we all understand the outlines of Newton’s celestial mechanics but we find his work on optics more daunting—because it calls for theoretical understanding. Light is intrinsically hard to understand, but planetary motion is not (it’s just stuff moving through space subject to forces). Philosophical problems lie at the extreme end of the non-observational class of problems: the difficulty of the mind-body problem, say, does not derive from observational paucity due to distance or clouds; it is purely theoretical. We don’t need a better look to solve this problem but better thinking (theory construction). The solution will not be mundane (though hard to arrive at), like Newton’s theory. It won’t take the form of neurons orbiting each other in ellipses, or one part of the brain being stationary while the rest moves, or some such thing. There is something bathetic about Newton’s theory, given the history of astronomy, but surely the solution to the mind-body problem will be anything but bathetic (like concluding that consciousness is a result of neural length). So, there is a contrast between the science of astronomy and other sciences (including philosophy): astronomy up to Newton was hampered by observational limitations, but the other sciences face theoretical problems inherent in their subject matter. Thus, Newton’s theory is easy to grasp though difficult to arrive at, whereas the other theories are not easy to grasp—and hard to arrive at largely for that reason. Of course, discovering and formulating the laws of motion requires theoretical ingenuity, and gravity itself is deeply puzzling, but the basic architecture and dynamics of the solar system are of the same order as ordinary observable phenomena—bodies moving in straight and curved paths through space. The only question was which bodies are moving and along what paths.
 Just how tortuous and faltering it was is brought out in Arthur Koestler’s very thorough The Sleepwalkers (1959).
 The only area I can think of that compares to astronomy is geography. Here too it was millennia before accurate maps of the earth were produced, simply because the layout of the earth is not visible from anywhere on it (even from a mountain top). It was necessary to travel all over the earth to be able to devise adequate maps. In astronomy it wasn’t possible to travel to the stars, but at least you could see them (some of them) from planet earth. Not surprisingly, there wasn’t much variation in different parts of the earth, as there is not much variation between different stars (compared to what used to be believed). The physical universe is pretty homogeneous no matter where you go (it is made of the same stuff after all). A Newton of geography would not have any very remarkable geographical facts to report; that is why geography is a boring subject content-wise. Astronomy is the geography of the skies (also the physics). What it isn’t is a window into the mind of God, or a repository of mathematical and musical harmony, or the basis of astrology.