## Were atoms real?

61 08 December 2010 05:30PM

Related to: Dissolving the Question, Words as Hidden Inferences

In what sense is the world “real”?  What are we asking, when we ask that question?

I don’t know.  But G. Polya recommends that when facing a difficult problem, one look for similar but easier problems that one can solve as warm-ups.  I would like to do one of those warm-ups today; I would like to ask what disguised empirical question scientists were asking were asking in 1860, when they debated (fiercely!) whether atoms were real.[1]

Let’s start by looking at the data that swayed these, and similar, scientists.

Atomic theory:  By 1860, it was clear that atomic theory was a useful pedagogical device.  Atomic theory helped chemists describe several regularities:

• The law of definite proportions (chemicals combining to form a given compound always combine in a fixed ratio)
• The law of multiple proportions (the ratios in which chemicals combine when forming distinct compounds, such as carbon dioxide and carbon monoxide, form simple integer ratios; this holds for many different compounds, including complicated organic compounds).
• If fixed volumes of distinct gases are isolated, at a fixed temperature and pressure, their masses form these same ratios.

Despite this usefulness, there was considerable debate as to whether atoms were “real” or were merely a useful pedagogical device.  Some argued that substances might simply prefer to combine in certain ratios and that such empirical regularities were all there was to atomic theory; it was needless to additionally suppose that matter came in small unbreakable units.

## Disguised Queries

57 09 February 2008 12:05AM

Followup toThe Cluster Structure of Thingspace

Imagine that you have a peculiar job in a peculiar factory:  Your task is to take objects from a mysterious conveyor belt, and sort the objects into two bins.  When you first arrive, Susan the Senior Sorter explains to you that blue egg-shaped objects are called "bleggs" and go in the "blegg bin", while red cubes are called "rubes" and go in the "rube bin".

Once you start working, you notice that bleggs and rubes differ in ways besides color and shape.  Bleggs have fur on their surface, while rubes are smooth.  Bleggs flex slightly to the touch; rubes are hard.  Bleggs are opaque; the rube's surface slightly translucent.

Soon after you begin working, you encounter a blegg shaded an unusually dark blue—in fact, on closer examination, the color proves to be purple, halfway between red and blue.

Yet wait!  Why are you calling this object a "blegg"?  A "blegg" was originally defined as blue and egg-shaped—the qualification of blueness appears in the very name "blegg", in fact.  This object is not blue.  One of the necessary qualifications is missing; you should call this a "purple egg-shaped object", not a "blegg".

But it so happens that, in addition to being purple and egg-shaped, the object is also furred, flexible, and opaque.  So when you saw the object, you thought, "Oh, a strangely colored blegg."  It certainly isn't a rube... right?

Still, you aren't quite sure what to do next.  So you call over Susan the Senior Sorter.

## Words as Hidden Inferences

40 03 February 2008 11:36PM

Followup toThe Parable of Hemlock

Suppose I find a barrel, sealed at the top, but with a hole large enough for a hand.  I reach in, and feel a small, curved object.  I pull the object out, and it's blue—a bluish egg.  Next I reach in and feel something hard and flat, with edges—which, when I extract it, proves to be a red cube.  I pull out 11 eggs and 8 cubes, and every egg is blue, and every cube is red.

Now I reach in and I feel another egg-shaped object.  Before I pull it out and look, I have to guess:  What will it look like?

The evidence doesn't prove that every egg in the barrel is blue, and every cube is red.  The evidence doesn't even argue this all that strongly: 19 is not a large sample size.  Nonetheless, I'll guess that this egg-shaped object is blue—or as a runner-up guess, red.  If I guess anything else, there's as many possibilities as distinguishable colors—and for that matter, who says the egg has to be a single shade?  Maybe it has a picture of a horse painted on.

So I say "blue", with a dutiful patina of humility.  For I am a sophisticated rationalist-type person, and I keep track of my assumptions and dependencies—I guess, but I'm aware that I'm guessing... right?

But when a large yellow striped feline-shaped object leaps out at me from the shadows, I think, "Yikes!  A tiger!"  Not, "Hm... objects with the properties of largeness, yellowness, stripedness, and feline shape, have previously often possessed the properties 'hungry' and 'dangerous', and thus, although it is not logically necessary, it may be an empirically good guess that aaauuughhhh CRUNCH CRUNCH GULP."

The human brain, for some odd reason, seems to have been adapted to make this inference quickly, automatically, and without keeping explicit track of its assumptions.

And if I name the egg-shaped objects "bleggs" (for blue eggs) and the red cubes "rubes", then, when I reach in and feel another egg-shaped object, I may think:  Oh, it's a blegg, rather than considering all that problem-of-induction stuff.