Tonight, as I took a walk, I looked up and watched the clouds and the sky. While I watched, the clouds seemed static. Sure, a couple clouds raced across the sky, but they were the exception.

So, the sky at any given moment, even though I watched, appeared static. But I’d look away - for just a minute - and, I could tell, once I looked back, that the clouds weren’t static at all. They had moved and grown and morphed.

The clouds are always there. But they’re also always changing.

It’s hard to watch clouds in the sky and say, “Aha, right there. That’s when they changed.” But it’s easy to say, “Yes, the sky has definitely changed since a minute ago.” The rate of change for clouds is below my threshold for noticing. So I have an inability to see change as it happens, but have the ability to notice change after it has occurred.

Colors are similar in this regard. Look at a gradient of black to white. At any given point in the gradient, it’s hard to say the color on the left is different from the color on the right. But I can compare the left-most edge to the right-most and see they are clearly different. I have a hard time perceiving the change at any given point, but to contrast the two ends is easy. You can see a live demo of a page slowly fading from black to white that illustrates this effect.

This reminds me of the “heap of sand paradox”. Start with a heap of sand. I can take away one grain of sand and it’s still a heap. But if I apply this same step many, many times, I eventually have only one sand grain left. And a single grain isn’t a heap, is it? But when did the heap become a not-a-heap? This is called the sorites paradox. The sorites paradox, though, stems from the ambiguity of natural language. Whereas the “static sky paradox”, as I’ll call it, stems from my inability to perceive a change below a certain threshold.

Wikipedia again has an interesting article about the just-noticeable difference. It’s “the smallest detectable difference between a starting and secondary level of a particular sensory stimulus”. It’s quite interesting to see these clouds as a real-world way to notice this phenomenon, outside of a controlled test environment.

This observation makes me wonder in what other ways, particularly mental or psychological, am I unable to witness a change (for good or ill) while it happens? Even when I look back, can I see only that something has changed, but not the point at which that change occurred?

Most individual days sit below the difference threshold, such that I can’t pick out on which day something changed… only notice later that it has. Can I become more aware of this fact and lower the threshold so that I can be aware of, observe, and potentially act to affect change as it happens? The alternative is to submit to a force that is inevitable, inescapable, and invisible. And that is hard to swallow.