[#26] A Challenge for Humanity: Time Scale Crossing

By Piet Hut

In physics, whenever we confront a new problem, we ask ourselves the question of time scales.  Typically, different processes operate at quite different time scales, but  occasionally time scales cross.  That's when things get really interesting, as in "may you live in interesting times."


To take a simple example: when you walk across a room with a cup of coffee, all is well as long as you walk slowly enough. If the time between two steps is long compared to the time it takes for the coffee to move from left to right in your cup, chances are you'll reach the other side without spilling anything.  However, if you speed up, and the time between steps becomes comparable to the sloshing time, if you're not very careful, chances are that much of the coffee will wind up on the carpet.

Physicists can happily spend years making detailed simulations of such sloshing phenomena (technically speaking: the transition out of a regime where an adiabatic approximation is valid).  And many scientists and engineers do that for a living, since industrial applications are all around us, from designing air flow around airplane wings to making sure fluids flow in the most efficient way through pipes.

But before making any such calculations the first step is always the question: what are your time scales, and how do they compare?  That will determine which process is most relevant on the time scale you are interested in.  And that in turn determines what kind of simulations you want to set up.  Only then does the real work start.

A transonic shockwave

A transonic shockwave

But sometimes there is no dominant time scale.  And when two time scales become similar, we enter into "interesting" regimes that require special attention.  It is at those points that qualitatively new phenomena arise.  For an airplane, the point of reaching the speed of sound; for fluids flowing through pipes, the speed at which there is an onset of turbulence.

In human history, until recently, the time scale for changes in society have typically been much longer than a generation, the thirty years or so in age difference between parents and their children.  The agricultural revolution wasn't much of a revolution; it was a slow cultural and technological evolution in which people began to spend more and more time on cultivating plants, and less and less on hunting and gathering, taking thousands of years to complete.  Even the duration of the industrial revolution spanned several generations.  The spread of book printing with movable types, the general use of trains, or of airplanes, all those developments took much more than thirty years to permeate society.

Picturing ourselves a thousand years into the future, or ten thousand years for that matter, and looking back in time, future historians will note that the year 2000, give or take a decade or so, was a unique turning point.  It was the very first time that the time scale for change had crossed the time scale for human reproduction.  It was the crossover point between biological turnover and technological turnover.  And since technological changes are such an important driver of cultural changes, it was the crossover point between biological and cultural turnover.

For example, facebook, twitter, and smartphones, all of those were introduced only a decade ago, and life has not been the same since.  And in another decade or less, we will again live in a very different time, with forms of augmented reality the impact of which we can't yet dream of.

This time scale crossing has never happened before, so history cannot be a guide. No wonder that coffee is spilling on the carpet, in a grand way; in fact on a planetary scale.


Global warming by a few degrees would be no problem at all if it were to happen on a time scale similar to the time it takes for evolution to adapt.  The problem is that it is now happening on the time scale of a single generation of polar bears, to use an iconic image.  Had it happened over tens or hundreds of thousands of years, polar bears, and the rest of the biosphere, would have found ways to adapt, as has happened so many times in the past.

Locally, the anxiety of children and young adults, seeing role models around them crumble, and having little or nothing to replace them, is another example of the "interesting" effects of time scale crossing.  Adults, too, find themselves disoriented, with jobs for which they were trained rapidly disappearing.  We are not prepared, neither biologically nor culturally, to cope in such a rapidly changing world.  No wonder there is so much appeal in populist demagoguery, harking back to idealized pictures of the past.

However, it is not so much the past that people are nostalgic for, it is the past rate of change, which was slower, providing stability, when sloshing was the exception, rather than the rule.

The big challenge in our times, the most central challenge, is not what to do with specific problems.  It is noble to try to end hunger, end war, end poverty, but attempts in that direction miss the point, two levels deep.

any solution offered today, may not work anymore a decade from now.

First of all, none of these problems can be solved in isolation.  Hunger, war, poverty, and many other problems are so intrinsically intertwined that they can only be approached in an integrated way.  Any attempt to solve just one part of the puzzle in isolation is likely to create more problems for the other parts.

But more importantly, on an even deeper level, any solution that may be offered today, may not work anymore a decade from now. The search for solutions has to take into account the crossover of timescales.  And this in turn requires a different orientation, a cognitive revolution of a kind that humanity has never witnessed before.  In my next few blog posts, I will try to explore some of the contours of such a revolution.

Piet Hut is President of YHouse (where this blog is hosted), Professor of Astrophysics and Head of the Program in Interdisciplinary Studies at the Institute for Advanced Study in Princeton, and a Principal Investigator and Councilor of the Earth-Life Science Institute in the Tokyo Institute of Technology.