A Wild Profusion
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A Wild Profusion

The idea that the universe was made just for us—known as the anthropic principle—debuted in 1973 when Brandon Carter, then a physicist at Cambridge University, spoke at a conference in Poland honoring Copernicus, the 16th-century astronomer who said that the sun, not Earth, was the hub of the universe. Carter proposed two interpretations of the anthropic principle.

The “weak” anthropic principle simply says that we are living in a special time and place in the universe where life is possible. Life couldn’t have survived in the very early universe before stars formed, so the universe had to have reached a certain age and stage of evolution before life could arise.

The “strong” anthropic principle makes a much bolder statement. It asserts that the laws of physics themselves are biased toward life. To quote Freeman Dyson, a renowned physicist at the Institute for Advanced Study in Princeton, the strong anthropic principle implies that “the universe knew we were coming.”

A Wild Profusion

The anthropic principle languished on the fringes of science for years. Physicists regarded it as an interesting idea, but the real action in the field lay elsewhere. And in the late 1970s, Linde, then a professor at the prestigious Lebedev Physical Institute in Moscow, was in the thick of that action. At the time, he wasn’t interested in the anthropic principle at all; he was trying to understand the physics of the Big Bang. Linde and other researchers knew that something was missing from the conventional theory of the Big Bang, because it couldn’t explain a key puzzling fact about the universe: its remarkable uniformity.

Strikingly, the temperature of space is everywhere the same, just 2.7 degrees Celsius above absolute zero. How could different regions of the universe, separated by such enormous distances, all have the same temperature?

In the standard version of the Big Bang, they couldn’t. The universe as a whole has been cooling ever since it emerged from the fireball of the Big Bang. But there’s a problem: For all of it to reach the same temperature, different regions of the universe would have to exchange heat, just as ice cubes and hot tea have to meet to reach the uniform temperature of iced tea? But as Einstein proved, nothing—including heat—can travel faster than the speed of light. In the conventional theory of the Big Bang, there simply hasn’t been enough time since the universe was born for every part of the cosmos to have connected with every other part and cooled to the same temperature.

MIT physicist Alan Guth found a viable, but flawed, solution to the puzzle in 1981. Linde shored up that work shortly thereafter, making improvements to overcome those flaws. In a nutshell, Guth and Linde proposed that the universe underwent a colossal growth spasm in the first instants of its existence, a phenomenon called inflation. Today widely accepted as the standard version of the Big Bang theory, inflation holds that regions of the universe that are currently separated by many billions of light-years were once close enough to each other that they could exchange heat and reach the same temperature before they were wildly super-sized. Problem solved.

Linde has spent much of the past 20 years refining that idea, showing that each new universe is likely to have laws of physics that are completely different from our own. The latest iteration of his theory provides a natural explanation for the anthropic principle. If there are vast numbers of other universes, all with different properties, by pure odds at least one of them ought to have the right combination of conditions to bring forth stars, planets, and living things.

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