My grandmother used to stop me, as a child, from swatting at flies that came too close to her prayer corner, not because she loved insects particularly but because she said you never know what a small thing carries. I didn't understand it then and used the sentence mostly as evidence that grown-ups made rules out of nothing. I understand it a little better now, though not in the way she meant it, and not by the route I expected.
There is a story, often repeated and often garbled, about a scientist running a weather simulation who once re-entered a number with a few digits trimmed off, expecting no real difference, and watched the forecast diverge completely from the first run within a matter of simulated days. Whatever the precise details of how the observation was first made, the underlying finding is well established and has a name: sensitivity to initial conditions. In certain systems, weather among them, a tiny difference in the starting numbers doesn't stay tiny. It compounds, and compounds again, until two nearly identical starting points produce wildly different outcomes not much later. This got shortened, in popular telling, into the image of a butterfly's wingbeat somewhere setting off a hurricane somewhere else. It's a vivid image and, taken literally, a bad one. No one has traced an actual hurricane to an actual butterfly, and no meteorologist believes they could, even in principle, given how many other tiny disturbances are also churning through the same air at the same moment. What the image is really pointing at is not causation you could follow link by link. It's a property of the system: unpredictability that grows from below the threshold of what we can measure, not a chain of blame running from wing to storm.
Karma, in the traditions that use the word most carefully, is often explained with a comparable intuition, that small actions have consequences reaching further than their apparent size would suggest, rippling outward through a life or beyond it in ways too tangled to trace back individually. I want to hold this next to the wingbeat carefully rather than fuse them, because they are answering different questions. Chaos theory describes a physical system's sensitivity, a mathematical fact about how small numerical differences amplify under certain kinds of dynamics, water and air obeying equations that make long range prediction impossible past a certain horizon, regardless of anyone's intentions. It is not making a claim about fairness, or about actions returning to their doer, or about any moral ledger being kept. A pebble kicked into a river doesn't owe the riverbank anything and isn't owed anything back. Karma, as it's usually meant, is precisely a claim about that kind of return, about intention and consequence bound together in a way that physics, describing weather or any other blind system, has no mechanism for and doesn't attempt to supply.
What they share, I think, is narrower and more useful than a secret equivalence: both are correctives to a particular kind of arrogance, the assumption that a thing's size tells you its reach. Weather systems humble the forecaster who assumes rounding errors don't matter. The idea of karma humbles whoever assumes an unwitnessed unkindness, a door held shut, a rumor passed along without much thought, simply ends where its immediate effect ends. Neither claim requires the other to be true. You can accept full atmospheric sensitivity to initial conditions and hold no view whatsoever about moral consequence, and you can believe firmly in consequence returning to its source without needing weather equations to back you up.
My grandmother's fly, all these years later, seems less like a category error and more like an early, imprecise gesture at something I keep circling from different directions: that the visible size of an action is a bad guide to its true extent, in a river or a life, for reasons that have nothing to do with each other and every reason to be taken seriously on their own separate terms.