Almost all the matter in your life comes

from the hearts of long-dead stars, where intense heat and pressure fused atoms to create everything from the calcium in your bones to the silicon in your computer. But hey, why take my word for it? Try it out for yourself in Fe[26] , the newest iteration of the addictive game 2048.

As in 2048, an Fe[26] player slides squares around on a 4x4 map, pushing like items together. But instead of combining powers of 2, players in Fe[26] try to synthesize heavier and heavier elements with the ultimate goal of creating iron. (Iron has the chemical symbol Fe and 26 protons, hence the name.)

And there are some key gameplay differences that will be initially confusing to anyone who's not a physicist. Only particular squares combine, mimicking which elements will and will not fuse in the real world. Other squares will change into new elements or isotopes after a certain number of terms—the game's version of radioactive decay. And a few elements stick around as dead-ends (I'm looking at you, magnesium).

Make no mistake, this game is fun. It's probably the best of 2048's many, many clones. But if you're like us, you're wondering just how well the game models what really happens inside a star. Dimitar Dimitrov, one of the game's two designers, tells PopMech: "When we were designing the game, we decided on a balance between realism and playability."

So here's what is and isn't accurate:

The fusion pathways in Fe[26], charted out at the bottom of game's webpage, are more-or-less textbook. Just like in real life, two oxygen atoms fuse to form silicon, and that oxygen comes from the merger of carbon and helium. Also dead-on is the different treatment for atomic isotopes—that is, atoms of the same element that have different number of neutrons, such as Helium-3 and Helium-4. And when the game's radioactive elements decay, they do so with proper randomness and change to the proper element.

"But there are a bunch of simplifications," says co-designer Kevin O'Connor, "although many of them were chosen because they support better gameplay." For example, the fusion combinations that create many of the heavier elements in the game (silicon and higher) are much more random in real stars. And when elements in the game decay, Dimitrov says, the game ignores the clusters of protons and neutrons that decay produces.

"Also, magnesium is a dead end in our game, which isn't completely true," O'Connor says. "While it is very stable, mostly we just wanted to add a little bit of challenge to the game."

What do real physicists think of Fe[26]? "Yes, I was really quite surprised when my magnesium was a dead end," says Cole Miller, an astrophysicist and director of the Joint Space-Science Institute at the University of Maryland, who was not involved with the creation of the game. "I kept trying to throw helium-4 at it, and it refused to do anything." Miller applauds the game, saying it could be an interesting and useful teaching tool. But, he says, the game needs a little context.

"Playing the game, you might think you're recreating the processes of what's happening at, say, the center of the Sun," he says. "But the process in this game is will never happen in the Sun—and that doesn't really come across." That's because the pressure and heat required to forge iron could only come about a star at least eight to 10 times as massive as our sun—and even then, only during its final throes.

Nonetheless, "the designers of the game have certainly done their homework," he says. Miller is right in more ways than one. Both O'Connor and Dimitrov, undergraduate computer science majors, designed Fe[26] for an astronomy class at Rensselaer Polytechnic Institute. Even more impressive: Thanks to the open source code of 2048, Fe[26] was built in a day.

And if you're curious why the game's goal is to create iron, and not an even heavier element (such as the deceptively obvious choice of gold) there's a reason.

"In these high-mass stars, once you get to iron, doing fusion actually requires energy," Dimitrov says. "So these stars can't produce enough energy to fuse any elements higher than iron. It's in supernovas where you get all the other elements."

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