Recently I flew from a particularly dire version of Minnesota winter—periodic rain making no dent in the graying heaps of snow, while rendering the smooth ice-covered sidewalks puddle-pocked and slick, so that it was not unusual to find oneself sliding inexorably down an icy slope into four inches of slushy water—into the blush of spring.

This new season was in California, where I was visiting my fiancé for the weekend. (Long-distance relationships are a staple of academia; my Minnesota labmates have significant others in Seattle and India.) Three hours on a plane headed west and I seemed to have jumped forward two months. Puffed-up robins in the snow…

…were replaced with marsh wrens singing furious declarations of their virility.

Bushtits were building their delicate, pendulous nests.

Hummingbirds were squabbling among themselves and gathering nesting materials.

An oak titmouse had filled the bottom of our birdhouse with twigs and was topping that with green grass.

The California ground squirrels were nearly finished with their mating season, but the dregs of the seasonal testosterone surge had males puffing up and wrestling each other.

In among the ground squirrels, a killdeer displayed nervously to draw attention away from his mate’s nest.

The space-for-time substitution in ecology is a method wherein scientists study the effect of a process that takes a long time by studying a spatial gradient that replicates that process in space. For example, ecologists interested in the effects of a century-long reduction in rainfall might study a transect of land with a gradient of decreasing rainfall. This method makes many ecological questions more tractable, particularly those of a predictive nature. Really, just about any alternative to “wait a century and see” is a dramatic improvement in tractability.

My glimpse of spring in California was effectively a space-for-time substitution. The method isn’t perfect: California’s spring has less rain and different species than Minnesota’s will. The two springs will differ in pace, too: California’s spring will be long, blending into summer, while Minnesota’s will be short and intense. California and Minnesota are a more extreme pair than an ecologist would choose, but no space-for-time substition is an exact fit. Scientists use such methods not because they do not care about the inaccuracies, but because there is no perfect way.

There are some situations where the space-for-time substitution loses its potency entirely. I haven’t found any space, however pleasant, that can replicate spending the last seven months with my fiancé instead of hundreds of miles apart. And a space that could tell us what the next two-plus years of long distance will be like—that doesn’t exist either. Like the birds building their nests in what looks to us like a predictable seasonal tradition, but to their short-lived selves must feel sudden and momentous, we just have to see what happens by living. No substitutions.