# Sustainability: The Clue That Could Solve Fermi’s Paradox

If civilizations can’t grow exponentially, that might explain why we don’t see any signs of ET.

While lunching with colleagues at the Los Alamos National Labs in 1950, Enrico Fermi began a discussion about the likelihood of intelligent life existing elsewhere in the universe. The size and age of the universe makes it seem probable that many advanced societies ought to exist. But if they did, where are they? he asked.

This problem has since become known as the Fermi Paradox, and many a canteen lunch has been spent discussing its resolution (we discussed one possible solution a few months back).

Today, Jacob Haqq-Misra and Seth Baum at Pennsylvania State University put forward another idea. They point out that the Fermi Paradox assumes an exponential spread of civilizations across galaxies. Such an expansion must be closely linked with expansion in population, environmental impact, and the consumption of resources.

The problem is that this kind of growth may not be possible, and they look at Earth as an example. For any expansion to be sustainable, the growth in resource consumption cannot exceed the growth in resource production. And since Earth’s resources are finite, and it has a finite mass and receives solar radiation at a constant rate, human civilization cannot sustain an indefinite, exponential growth.

So we’ll have trouble colonizing the galaxy, if we ever decide that’s necessary. At the very least, the spread of our civilization will not be exponential, if it is possible at all.

Haqq-Misra and Baum say that this argument means that any extraterrestrial civilization must be similarly constrained.

The Fermi Paradox often leads to the conclusion that other advanced civilizations do not exist. Haqq-Misra and Baum say that this is unduly pessimistic. What the Fermi Paradox implies is that intelligent civilizations capable of exponential expansion do not exist.

And that’s a very different proposition.

Ref: arxiv.org/abs/0906.0568: The Sustainability Solution to the Fermi Paradox