Today, most of us know it as the Sun, but leading physicists around the world regard it with the same sense of awe as our ancient ancestors. This is not because these physicists believe the Sun rides across the sky in a giant reed boat, ready to exact retribution on us mortals at any moment, however. Rather, they know that the Sun harbors the secret to a virtually unlimited source of clean energy.

For the entirety of recorded history, humans have worshipped nuclear fusion. It's gone by different names over the millennia, of course: the Egyptians called it Ra, the Greeks called it Helios, and the Aztecs knew it as Tonatiuh.

If the processes powering the fusion reactor at the Sun's core could be recreated on Earth, it would be one of the most important events in the history of our species. Nuclear fusion power plants could end our dependency on fossil fuels and provide a virtually limitless, highly efficient source of clean energy. They could help end the developing world's energy crisis and lift it from poverty. They could provide the power for large scale desalination plants and end water shortages. They could also change life off Earth, providing power to lunar and Martian colonies, or even interstellar generation ships.

Every second, trillions of hydrogen ions are fusing in the Sun's ultradense 27 million degree core. The crushing weight of the Sun's gravity forces the protons of hydrogen atoms so close together that they combine into a heavier atom (helium) and release an enormous amount of energy: a process called nuclear fusion. Even though the natural fusion reactors at the heart of stars are abundant in the universe, this process has been remarkably hard to replicate on Earth. This is because the Sun's own gravity is able to contain the ultra hot and ultra dense plasma at its core, but trying to contain even small amounts of hydrogen plasma in containers on Earth for a few hundredths of a second has proven to be a difficult challenge for engineers and physicists.

I went to two of the world's leading nuclear fusion research centers—Sandia National Labs in New Mexico and General Fusion outside Vancouver—to see how close we are to bringing the power of the stars down to Earth. At Sandia, many of the physicists see fusion research as an exploratory science and a phenomenon that we're just beginning to understand, even after a half century of research. The researchers at General Fusion, however, are not content to keep waiting for fusion and are actively attempting to harness fusion energy for a practical power plant.

So far, extracting more energy from a fusion system than was used to power it remains a distant goal for these nuclear physicists. The main problem is figuring out how to create and sustain the extreme conditions that make the plasma at the core of fusion reactions possible. Both Sandia and General Fusion have made groundbreaking strides in this direction, and are leading actors in an 80-year drama that began when the Australian physicist Mark Oliphant first achieved man-made nuclear fusion in 1932.

"Fusion will be the source of energy for thousands of years to come. We think we're going to accomplish that in our lifetimes."

Ever since Oliphant's discovery, figuring out how to make a fusion reactor, or a "star in a jar," has been one of the holy grails of physics. It ended up being a more difficult problem than any of the fusion pioneers in the early twentieth century anticipated, which led to a running joke among nuclear physicists: fusion is always 30 years away.

Up until the turn of the millennium, the overwhelming majority of fusion research in the US was conducted by government scientists behind the closed doors of the Department of Energy's national laboratories. Here fusion research was closely linked with national security concerns. Initially, government physicists focused on harnessing fusion energy to make nuclear weapons. Although a pure fusion bomb was never created, fusion energy was integrated into hybrid fission-fusion thermonuclear weapons—colloquially known as hydrogen bombs—which were far more powerful than the fission based predecessors that were dropped on Hiroshima and Nagasaki.

Although fusion helped create the most dangerous weapons on the face of the planet, today publicly funded fusion research in the US is increasingly geared toward the effective stewardship of the stockpile of these nuclear weapons. In the last two decades, however, private money has also been pouring into developing fusion reactors, and a handful of companies are leveraging publicly funded fusion research in a race to develop the first nuclear fusion power plant. The stakes are high—fusion research is incredibly expensive and unlikely to be profitable for decades—but the potential rewards are far higher.

Z MACHINE

On the outskirts of Albuquerque, New Mexico, a sprawling 8,700-acre complex populated with faceless buildings is surrounded by barbed wire fencing and an untold number of other security precautions invisible to the naked eye. Each morning, a line of cars stretches for miles beyond its main entrance gate as employees wait to receive clearance from heavily armed guards.