Picture an object the size of a pencil eraser. For our purposes, we’ll call it “the target.” Now picture 192 precision-guided laser beams focusing all their energy on that target all at once, for just a few billionths of a second.

Now imagine the result: more than two million joules of ultraviolet energy and 500 trillion watts of peak power, temperatures within the target of more than 180 million degrees Fahrenheit, and pressures of more than 100 billion Earth atmospheres. Got it?

If you can imagine those kinds of mind-bending forces at work, then you can imagine nuclear fusion, which is the process by which hydrogen atoms are forced together and release energy in a controlled thermonuclear reaction. It’s also the process by which a star can heat a planet some 93 million miles away from it.

This is the sort of thing that happens at the National Ignition Facility, which is a massive complex at the Lawrence Livermore National Laboratory just across the bay from San Francisco.

Recently, something else happened there at the NIF — something that has the potential to radically change the world by remaking energy as we know it. Scientists announced a significant breakthrough this week, namely the first laboratory fusion reaction that took less energy to create than it yielded.

The reaction, which took place at 1:03 a.m. Pacific Time on Monday, December 5, crossed the threshold of what fusion scientists call “ignition” — which is to say it created more energy than was used by the lasers to generate the reaction. In this case, the fusion reaction appears to have generated 2.5 megajoules of energy while the lasers spent 2.1 megajoules to make it happen.

What does all this mean? Fusion is cleaner than both fossil fuels and uranium-based nuclear energy. In fact, nuclear fusion checks all the boxes — even for the no-nuke zealots, the Chernobylists, and the Three Mile Islanders on the Left. And, like those nuclear power plants, fusion energy is of a density that “green” sources such as wind and solar can’t even dream of.

Now that you’re sufficiently excited, it’s time to tap the breaks. You won’t be able to buy a DIY fusion kit at Home Depot anytime soon.

“Probably decades,” said Kimberly S. Budil, the director of Lawrence Livermore, in response to a question about when fusion might become available on a widespread scale. “Not six decades, I don’t think. I think not five decades, which is what we used to say. I think it’s moving into the foreground and probably, with concerted effort and investment, a few decades of research on the underlying technologies could put us in a position to build a power plant.”

Here’s some more cold water, brought to us by Wilson Ricks, a Ph.D. candidate studying macro energy systems at Princeton: “The fusion power,” he says, “is in the form of heat and radiation, and needs to be converted back to electricity. Assuming a 40 percent steam cycle efficiency, that’s another 2.5x increase in required yield. So we need a fusion reaction 250x more powerful to achieve true electric net gain.”

Summing it up, we still have a long wait ahead of us for practical fusion, but perhaps not as long as we might think. And certainly not as long as, say, fans of the Detroit Lions have been waiting for their team to win an NFL championship. (It’s been 65 years, but who’s counting?)

As for fusion — an abundant energy source that requires no hazardous fuel and generates no hazardous waste — we think it’ll be well worth the wait. And in the meantime, we’ve got an abundance of fossil fuel right beneath our feet.