One of the most famous bets in history was made between Julian Simon and Paul Ehrlich in 1980. Simon, a libertarian economist, let Paul Ehrlich, a "neo-Malthusian" concerned about the rapid growth of population, choose five metals that Ehrlich believed would increase in price over the next decade. If the commodities increased in price, Ehrlich's concern about resource depletion would be vindicated. If not, Simon would be proved correct that technological progress and markets could provide a seemingly unlimited supply of goods. Simon won handily, and Ehrlich sent him a $576.07 check in 1990. (If Ehrlich had specified a longer time period, one lasting until 2011, he would have been vindicated.)

If such a bet were made today, I would be on Ehrlich's side, arguing that we have reached the feasible limits of growth. The Week's John Aziz, on the other hand, would likely side with Simon.

Aziz argues that "those who predict stagnant [economic] growth today due to falling population growth are overlooking the changing technological dynamics of our time." Aziz forecasts that revolutions in robotics and renewable energy will fuel the economy of the future, even as population (and thus the labor force) remains static. I really do hope that Aziz is right. But the realist in me is skeptical. I do not believe that we will be able to continue to enjoy rocket-ship levels of post-war growth, largely because of environmental constraints. And I do not believe robots are as revolutionary as Aziz thinks.

Aziz argues that "while the human population may level off, we are swiftly moving toward a world where humans are not the only productive agents." This is already true, and has been for millennia. Even before the industrial revolution, animals and simple tools have been used by humans to increase their economic output. Indeed, one of the more confusing aspects of the "robot" debate is how utterly banal robots are. Back in 1891 Oscar Wilde noted, "One man owns a machine which does the work of five hundred men." The question now, just as it was back then, is how these benefits are distributed. Wilde writes, "The one man secures the produce of the machine and keeps it, and has five hundred times as much as he should have, and probably, which is of much more importance, a great deal more than he really wants."

This, sadly, is the case now, too. Productivity increases due to technological gains have increasingly accrued to the wealthiest. In fact, the only time that Wilde's observation was not true was in the immediate post-war era, when rapid economic growth, diminished capital stocks, wartime solidarity, massive investment in education and infrastructure, and a powerful left combined to create rapid growth and lowering inequality.

Robots will certainly increase human productivity, supplant much human labor, and perform numerous important tasks. But I still struggle to imagine a world in which they replicate the massive improvements from our first two industrial revolutions: steam, railroads, electricity, internal combustion engine, running water, indoor toilets, communications, entertainment, chemicals, and petroleum. Even if they do, it seems unlikely that these benefits will be broadly shared, given the demise of an organized left and capital's increasingly globalized nature. The robot revolution may well be, like the recovery, one of rabid progress for a small few.

Today, Big Finance has deprived the real economy of much-needed investment. Public infrastructure is in decay, government investment in research and development is reaching historic lows, and state education budgets are being cut. The Financial Times reports that "public investment in the U.S. has hit its lowest level since demobilization" after World War II. Given that many of the most important inventions have been subsidized by either monopolistic companies (Bell Labs) or the government (Human Genome Project, the internet), this low spending is not a harbinger of rapid growth in emerging technologies like robotics and renewables.

At the same time, governments across the world are tightening immigration policies, further slowing growth. Increasingly inequality has sapped consumer demand, further decreasing the possibility of economic growth. Even technological progress seems less amazing than before. The Economist released an issue last year showing a man on the toilet wondering, "Will we ever invent something this useful again?" Robert Gordon, Stephen King (whose work is terrifying for rather different reasons than the horror writer who shares his name) and Tyler Cowen have all presented good reasons to believe that we may not.

But these concerns are dwarfed by the environmental constraints of growth. For many who adopt Aziz's techno-optimist view, Malthus' inaccurate predictions about agricultural returns serve to disprove any environmental concerns of growth. And yet, Jared Diamond has an entire book documenting the many cultures (the Norse, Easter Island, and the Maya, among others) that have grown themselves into economic collapse. Technology does not always come to the rescue.

Aziz brushes this fear aside: "Now, there may be environmental constraints on this new phase of growth. But even if switching from fossil fuels to renewable energy doesn't avert the problem of excessive carbon emissions causing runaway global warming, there already exist technological processes to reduce the greenhouse effect." This ignores the incredibly difficult political problem of switching from a fossil fuel intensive economy to an economy based on solar.

We live in a world where all renewable sources make up a mere 13 percent of the world's primary energy supply (as of 2009). A green economy would require massive infrastructure investment at a time when public spending is widely deplored. The EIA projects renewable energy to be only a mere 16 to 27 percent of U.S. electricity generation in 2040. Even modest proposals to regulate fossil fuels are met with howls from powerful lobbies. A recent study finds that fossil fuels receive almost $1 trillion in implicit economic subsidies worldwide. Since most fossil fuels are already valued by stock markets, wiping them off the balance sheets would require massive write-downs that companies are unlikely to accede to easily.

Can you imagine us living in a country where all of our energy comes from solar and the only concern left is how to scrub up whatever CO2 is left from those nasty fossil fuel days? Me neither. We have the technological capability to fight global warming; we lack the political will.

Natural capital stocks are rapidly declining, too. Developed countries use resources at ten times the rate poor countries do. We use fossil fuels and produce at 32 times the rate that developing nations do (page 504). These numbers point to the sheer impossibility of our maintaining our current growth trajectory, unless we relegate billions of humans to a miserable existence in perpetuity. If developing countries began using resources at the rate we do, the Earth would quickly be depleted. We've already passed several important planetary boundaries, most importantly, biodiversity. Deforestation, depleted aquifers, the collapse of fisheries, and the acidification of the oceans all pose ecological threats. Already a third of the planet's land surface is needed to feed and raise animals for slaughter.

I agree with Aziz that the future will have more solar power and more robots. But sustainable growth should be our goal. We should grow the pie as much as we can within environmental bounds. But the rest of the increase in living standards should come from redistributing what we already have. This will likely be slower than he imagines. And a slower growth world isn't necessarily a bad one.

Humberto Llavador, John Roemer, and Joaquim Silvestre estimate that GDP growth for developed countries like the U.S. must remain at 1 percent per year while those for developing countries must stay at 2.8 percent per year to keep temperatures within a 2 degree Celsius increase (which may still be too high a temperature to risk). The rest of our problems should be solved by redistribution. If the pie were more equally distributed we could all live a better life within planetary boundaries. Charles Kenny estimates that we could end world poverty for only $100 billion.

A world with less growth need not be dystopian. I struggle to see how a world with environmentally unsustainable growth can be anything else.