Fission, Fusion, Hot and Cold

It’s always a great episode when we get to open with a clip from Back to the Future.

In the final scene from the 1985 film, Christopher Lloyd’s Doc Brown arrives from 2015 to take Marty McFly and Jennifer Parker back to the future. As he attempts to wrangle the surprised duo, he fuels his Delorean’s Mr. Fusion Home Energy Reactor with banana peels and beer. 

Doc Brown utilizes the power of the stars, also known as nuclear fusion.

From Star Wars to Star Trek and in countless science-fiction tales, we have employed the notion of nuclear fusion to propel us to the deep reaches of the cosmos.

The reason nuclear fusion is such a powerful plot device is nuclear energy is an extraordinarily powerful technology. Ever since Albert Einstein gifted the world with his famous equation – E = mc– we have understood the massive power that resides within all matter. In the equation, the energy within each bit of mass is equal to that mass multiplied by the square of the speed of light, which is a gargantuan number. The implication is that small amounts of mass can produce energy on nearly unfathomable scales.

So, Doc Brown could power his car with trash, we could power our infrastructure with tiny amounts of fuel, or we could develop weapons of planet-level destruction with elemental mass that can fit in a suitcase.

In the video above, you can see the stark difference between an explosion using TNT and a nuclear bomb.

The terrifying weapons we developed during and after World War II harnessed the power of the stars just like Doc Brown, though the methodology is different. Our current bomb technologies are based on nuclear fission.

In fission, atoms are split; during the process, smaller atoms emerge plus a slew of destructive energy or, in the case of nuclear power plants, a lot of energy and some radioactive leftovers. Conversely, in fusion, we attempt to fuse atoms together; during this process, atoms become heated and fuse into larger atoms, which also releases abundant energy.

We largely mastered the chain reactions of fission in the 20th century. To date, however, we have not been able to mimic the fusion reactor we see every day: the sun. Fusion requires an extremely high amount of heat and pressure to pull off. The sun has no problem with that prerequisite.

Since nuclear bombs were developed, scientists have viewed fusion as something like a holy grail.

Where fission needs heavy, rare elements to work well and produces radioactive waste as a byproduct, fusion takes abundant elements, namely hydrogen, and creates another safe atom in helium. If we could somehow ape our space heater, we could tap into the universe’s ultimate clean and efficient energy source.

As we noted before, though, the energy needed to produce sufficient heat and pressure to fuse atoms is exorbitant. So exorbitant that efforts to do so cost more energy than the output of the reaction, rendering fusion an inefficient scientific experiment instead of a revolutionary power source.

Until now.

A fusion chamber at at the Lawrence Livermore National Laboratory - photo by Philip Saltonstall

In December 2022, researchers at the National Ignition Facility at the Lawrence Livermore National Laboratory in California announced they made a breakthrough in nuclear fusion.

For the first time, more energy came out of a fusion reaction than went into it.

As you might expect, this first step was not a Neil-Armstrong giant leap but a baby step. The experiment cost $3.5 billion and it produced enough heat to boil 15 to 20 kettles of water! Still, this result is perhaps the most significant scientific achievement in many moons.

Scientists shone a 192-beam laser onto a clump of hydrogen the size of a peppercorn. The robust laser heated the hydrogen to 100 million degrees Celsius – hotter than the center of the sun – and compressed it more than 100 billion times what Earth’s atmosphere could achieve. The hydrogen atoms fused and a whole lotta heat seeped.

We have a long way to go to match our prime nuclear reactor - image from NASA

Though exciting, this development will not change our lives immediately. To go from boiling kettles of water to heating our homes or powering space flights will require many years of development and investment. Further, though the energy used by the lasers was smaller than the energy output of the reactions, we still operated at an overall loss if we consider the energy required to power the lasers. The arc of scientific achievement is long and the iterative steps are many.

In other words, Doc Brown’s fusion reactor from 2015 is currently a long way off.

Farther off than even our investigation today might lead you to believe. Though many view fusion as the holy grail, the holiest grail might be something called cold fusion. In this theoretical reaction, fusion would not require the extreme heat and pressure of regular fusion, hence the frosty nomenclature.

Some scientists hypothesize that chemical reactions might enable elements to kickstart a fusion reaction, even at room temperature. So, for example, one could toss a few banana peels into a reactor on one’s car and zoom into other dimensions without burning at the temperatures of the sun.

Though many scientists doubt cold fusion is possible, if we could one day conjure such magic, Doc Brown might offer one mighty “Great Scott!”

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