This is a post about physics and engineering: do you think you can handle it? I hope so! I promise that it’s immensely important for understanding the effects of contemplation, the results of Transfiguration of the body, and the links between action and contemplation.

Did that get your attention? Good, because it wasn’t a lie. ^^

Following Dionysius, Saint Thomas teaches that “good is of itself diffusive”, bonum diffisivum sui. This principle appears, crops up, illuminates, obscures, and wanders through the writings of many, many saints and spiritual writers. For example, Saint Hildegard tell us of “universal faith, diffused round the whole ambit of the earth and originating in the bright splendour of the first dawn”. Saint John of the Cross tells us of qualities that are more “diffusive and communicative”, the more they are “subtle and delicate” like the Word. And so on. We could multiply examples. Good is diffusive.

Actually, the principle is that the higher the good is, the more it is by its nature tending to diffuse to other goods. That is a more precise formula. God, who is Goodness Itself, is supremely diffusive; this happens both within the Trinity and without. God, in a free choice of Love, communicates being and good.

Now… What is diffusion? How does modern science understand it? This analogy can take us a long way towards understanding the meaning of bonum diffisivum sui.

Let’s say I dropped a gallon of one chemical into a big lake. At the point where I dropped it, the concentration of the chemical would jump up initially. But then, with time, it would spread out. The shape of the spreading-out curve is given by a “diffusion equation”: the chemical diffuses through the water in the lake. In one dimension, what I just described in words looks like this on a graph:

There’s a bell-shaped curve that gets lower and broader as time goes on [click the picture for more details]. The concentration peak drops, but it spreads over more distance.

Now, that’s the case of just dropping a momentary burst into the lake.

What happens if we don’t have a momentary burst? What happens if we have a constant source of chemical at a fixed point? Around it, the concentration starts to go up:

And the higher the concentration at the fixed point, the more the concentration is raised around the point. If the peak gets taller, everything gets taller. And broader. Taller and broader [click the picture for more details].

That’s what diffusion really is like. This is what the saints, spiritual writers, and Doctors of the Church are getting at. Of course, if God throws a certain amount of interior goodness into a soul, it is concentrated in that soul. He can throw a series of bursts; that’s like the burst of chemical (one gallon). Or he may come to dwell in the soul interiorly and more and more consciously; that’s more like the constant source of chemical. In either cases, or in an overlapping combination of cases, the good diffuses outwardly.

(Of course, material goods and spiritual goods are gained and lost differently. I’m not saying that we lose spiritual goods by diffusion. That would be silly. Please don’t let that part of the analogy be confusing!)

The higher the good, the more it spreads to those around us. The world is like a series of interacting bell curves, growing, overlapping, fortifying one another, taking external good into the interior, throwing the concentration of interior good into the world…

Throwing the interior good into the world… How does good spread? Well, analogies to physics and mathematics are not going to be very helpful here. We need to return to the spiritual question. How does good spread? Gestures, looks, touches, words, hidden things unperceived by the conscious mind but taken in unconsciously: all of this, all of these poor, weak means. Good is carried by a transfigured, divinely lit smile; good is carried by a word of truth spoken in love.

Thus taught the chemical engineer: “Good is of itself diffusive”, bonum diffisivum sui. ^^