Copernicus and revolutions

Before Copernicus, everyone thought that the earth was the center of the universe.  Then Copernicus, in De Revolutionibus Orbium Coelestium, said that planets, including the earth, revolved around the sun.  Thus did science triumph over tradition and superstition.

Well, that's the Short Attention Span Theater version.  It has the advantage of being short and memorable, and the disadvantage of not being particularly near reality.  Yes, Copernicus did write De Revolutionibus, and yes, it did have the earth revolving around the sun, but heliocentric theories go back at least to Aristarchus of Samos, and it took another 200 years after Copernicus for the idea to take really firm hold in the scientific community (a somewhat anachronistic term in itself, but never mind).

Much has been made of controversy with the Church over the theory, but that came later.  Copernicus published the book with the aid of his friend Bishop Giese and dedicated it to Pope Paul III.  Nor does De Revolutionibus usher in a fully-formed modern view of the universe.  Copernicus postulates eight celestial spheres, with the fixed stars in the outermost, each planet moving in a perfect circle.

Copernicus does not present new data that can't be made to fit with the older geocentric view.  He reanalyzes centuries of observations that had been explained by a fairly complex system of cycles and epicycles, explaining them by a somewhat simpler system of cycles and epicycles.  The infamous epicycles are still needed because the planets don't actually move in perfect circles.



Copernicus's work is often considered important because it regards the earth not as the center of the universe, that is, as a special, distinguished place, but as a part of it, a planet on an equal standing with the other planets.  This notion that we do not occupy a special place is central to modern cosmology, extending even to the notion that the particular universe we occupy is not necessarily special, despite possessing such apparently unlikely features as solid matter and cosmologists.  In this view of science as the great dethroner of humanity, Darwin delivered a final insult by arguing that we are not even special among animals, but rather Just Another Ape.

There is merit in this view, even though (or maybe because) the notion that we are special creatures in a special place remains quite popular.  However, the Copernican shift can also be seen as one of a long line of cases where a simple and reasonable assumption turned out not to be true.  For example

• That the earth is not flat but an enormously large globe (enormous on a human scale, at least)
• That the earth revolves around the sun and not the other way around
• That the other planets are not points of light, but worlds at least somewhat like ours, most with their own moons
• That the stars are not points of light, but suns like our own
• That the Milky Way is a vast collection of stars, of which our own sun and the stars we see at night are part
• That "spiral nebulae" also consist of large numbers of stars and are indeed galaxies like our own.
• That the planets do not move in perfectly circular orbits, but ellipses
• That there are many, many objects in the solar system that are not planets (in the famous case of Pluto, something we had considered a planet looks to be better described as something else)
• That not everything in the solar system moves like a planet; for example, some objects move from an inner orbit to an outer one and back over time.
• That what appear to be single stars are often systems of two or more stars
• That the the fixed stars are actually not fixed, but moving
• That stars are not eternal, but are born and die

In many of these cases, but not all, the new view does make our position less special.  The driving force behind these shifts, however, isn't a desire to make humanity less special, but a desire to find simple, coherent explanations that fit the facts.  It's striking that many, but again not all, of the shifts listed above are toward a more uniform view -- the earth is of a kind with the other planets, the sun with other stars, the Milky Way with other galaxies.  Such a shift makes our place less special, but more as a side effect than as a specific aim. 

The most uniform explanation is not always right, though.  Stars like our sun are relatively rare.  Most stars are significantly larger or smaller, hotter or cooler.  Single-star systems are a majority, but stars in multiple systems constitute a significant minority.  Of the planets in our solar system, only one has significant liquid surface water.  There are many more Kuiper Belt objects than proper planets.  Even neglecting KBOs, asteroids, comets and such, there are many more moons in the solar system than planets.  Putting it all together, a rocky planet with liquid surface water orbiting a single star is almost certainly fairly rare, even if planets in general are abundant.

In the early 20th century it was discovered that distant objects are moving away from us, and the more distant the object, the faster it is moving.  The effect is uniform in all directions, within the limits of measurement [once you subtract out the dipole anisotropy -- like pretty much everything else, we are moving slightly, relative to the general expansion of the universe -- but that's a subtle effect and wasn't discovered until much later -- D.H.].  The conclusion is obvious: We are at the center of the universe, a unique spot whence everything else recedes.  This conclusion was rejected in favor of one which does not require us to sit in a special place: The entire universe is expanding and, other factors being equal, everything is moving away from everything else.  Again, this is the more uniform view, and evidence has borne it out over the decades.

How might I add that to the list above?

• That the universe is not static, but expanding?
• That our solar system is not the center of the universe, but just another part of it?

The first, I think, more closely reflects the actual development of thought.  The second fits the Copernican revolution model, but only by setting up a strawman.  By the time the Hubble expansion was discovered, it was already a given that our place is not special, so much so that what might have been taken as game-changing new evidence of our special place was quickly interpreted as just the opposite.

Pitting rational science against irrational human egocentricity makes a good story, but there's a more mundane reading to be found:  Science likes uniformity, and it likes uniformity so much that a nicely uniform explanation of known facts will eventually push aside our natural, egocentric concepts.

Put briefly and in retrospect, many of the shifts listed above seem blindingly obvious.  Why assume that the sun is different from other stars?  Why assume that ours is the only galaxy?  But this forgets the flip side of uniformity:  The most natural assumption is that things which appear different really are different. 

The earth appears to us as a huge surface with many features.  The other planets appear to us as tiny lights in the sky.  The sun is a blindingly bright ball.  The stars are more tiny lights in the sky.  The Milky Way is a huge swatch through the sky.  Spiral nebulae are tiny, in almost all cases much too small to be seen by the naked eye.  And, in the most famous case, planets really do appear to move around us in the sky, with occasional backtracking.  We're down here, they're up there.  The geocentric view, however egocentric it might be, was also the most natural and prudent until a more compelling story came along.

Navigating underground

I've always loved subways/undergrounds.  Even packed cheek-to-jowl into an un-air-conditioned Circle or District line car in the middle of the (then) hottest summer on record, in a suit, I still loved the posters and ads, the station architecture and decor, the endless parade of passengers, the nearly endless escalators, the tabloid news stands, the surprising variety of little shops tucked away ... even the names of the stations, the sound of the wheels and the brakes, the generally indecipherable announcements and the sheer urban gothiness of the tunnels themselves.  Sort of like an old-fashioned carnival funhouse ride but way, way cooler.

But there is another, more practical reason that I love subway systems: They make navigating a strange city nearly foolproof.  You only need to know two things: What stop your destination is at, and how to get to and from the system.  If you're just seeing the major sites, both of those are generally dead easy: the names of the stops are invariably listed in the guide book, and guess what -- stations tend to be built right by major landmarks.  Even if you're not visiting a major landmark, chances are whomever you're visiting will tell you the name of their station and the same technique will work.

All you really have to do is follow the greatly-simplified system map, make the right transfers and avoid Baker Street.  Unless you're on a tight schedule, you can essentially treat the whole system as a single point.  Your route is Point A -- subway -- Point B.

Such conceptual simplicity is so handy that one can spend months in many cities without learning more than the bare rudiments of the above-ground layout.  This is not entirely a good thing.  Apart from missing the richness of sights to be encountered by straying into this side-street or that arcade (but not that one; the less said about it the better), there are surprisingly many cases where it would be faster just to walk.

An underground transit system has a cognitive character all of its own.  Traveling above ground, you can generally see where you're going and gauge turns and distances reasonably well.  Underground, after several twists and turns of stairways and corridors, lurching starts and stops, and a few subtle or not-so-subtle bends, I personally find I might as well be playing pin-the-tail-on-the-donkey.

And yet the human brain, adapted to navigating outdoors and on foot, seems to cope reasonably well with the time-passes-and-then-you're-elsewhere nature of subway riding, even when the mental map of the territory above is largely blank.  A mental map developed solely from underground transit will have significant distortions, of course, but these don't seem to hurt much.  Once the real landscape becomes familiar, this more accurate view tends to supplant the earlier one (at least in my experience) and the below-ground journey starts to make a bit more sense.

The brain is used to meshing different sets of information, so perhaps this isn't surprising, but I get the definite feeling that more is going on here beneath the surface (so to speak) than one might think.