James' World 2

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Why did we take so long to invent civilization? Modern Homo sapiens first evolved roughly 250,000 to 350,000 years ago. But initial steps towards civilization – harvesting, then domestication of crop plants – began only around 10,000 years ago, with the first civilizations appearing 6,400 years ago.

For 95 percent of our species’ history, we didn’t farm, create large settlements or complex political hierarchies. We lived in small, nomadic bands, hunting, and gathering. Then, something changed.

We transitioned from hunter-gatherer life to plant harvesting, then cultivation and, finally, cities. Strikingly, this transition happened only after the ice age megafauna – mammoths, giant ground sloths, giant deer and horses – disappeared. The reasons humans began farming still remain unclear, but the disappearance of the animals we depended on for food may have forced our culture to evolve.

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Photo from Wikimedia Commons/Cloudordinary, CC BY-SA.

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The flashier fruits of Albert Einstein’s century-old insights are by now deeply embedded in the popular imagination: Black holes, time warps, and wormholes show up regularly as plot points in movies, books, TV shows. At the same time, they fuel cutting-edge research, helping physicists pose questions about the nature of space, time, even information itself.

Perhaps ironically, though, what is arguably the most revolutionary part of Einstein’s legacy rarely gets attention. It has none of the splash of gravitational waves, the pull of black holes, or even the charm of quarks. But lurking just behind the curtain of all these exotic phenomena is a deceptively simple idea that pulls the levers, shows how the pieces fit together and lights the path ahead.

The idea is this: Some changes don’t change anything. The most fundamental aspects of nature stay the same even as they seemingly shape-shift in unexpected ways. Einstein’s 1905 papers on relativity led to the unmistakable conclusion, for example, that the relationship between energy and mass is invariant, even though energy and mass themselves can take vastly different forms. Solar energy arrives on Earth and becomes mass in the form of green leaves, creating food we can eat and use as fuel for thought. (“What is this mind of ours: what are these atoms with consciousness?” asked the late Richard Feynman. “Last week’s potatoes!”) That’s the meaning of E = mc². The “c” stands for the speed of light, a very large number, so it doesn’t take much matter to produce an enormous amount of energy; in fact, the sun turns millions of tons of mass into energy each second.

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Credit: Rachel Suggs for Quanta Magazine.

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Water rushes into Venice’s city council chamber just minutes after the local government rejects measures to combat climate change. Wildfires consume eastern Australia as fire danger soars past “severe” and “extreme” to “catastrophic” in parts of New South Wales. Ice levels in the Chukchi Sea, north of Alaska, hit record lows. England sees floods all across the country. And that’s just this week, as I write this.

Human-caused climate change, and the disasters it brings, are here. In fact, they’re just getting started. What will things be like in another decade or century?

It depends on what we do. If our goal is to stop global warming, the best way is to cut carbon emissions now—to zero. The United Kingdom, Denmark, and Norway have passed laws requiring net-zero emissions by 2050. Sweden is aiming at 2045. But the biggest emitters—China, the United States, and India—are dragging their heels. So to keep global warming below 2 degrees Celsius over pre-industrial levels by 2100, it’s becoming more and more likely that we’ll need negative carbon emissions. That is, we’ll need to fix the air. We’ll need to suck more carbon dioxide out of the atmosphere than we put in.

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Photo by Stefano Mazzola.

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