“Everything ends in plasma!”

The title of this post is a quote from my wife. One morning, I’m sitting on the couch and she comes into the living room and says I “have to read the xkcd book because everything ends in plasma.” For a bit of background, my Ph.D. thesis work was in plasma propulsion a.k.a. electric propulsion. At UAH my research is in more general plasma physics and applications that include propulsion, but also include combustion, materials, and basic science. So anytime plasma is mentioned I perk up. Plasma is known as the 4th state of matter. It is a gas with significant fraction of the particles as ions and electrons. This way it can be affected by an electromagnetic field.

XKCD is a webcomic written and illustrated by Randall Munroe. It has a decidedly science and math bent to its jokes. Over years, xkcd readers have post a bunch of “what if…” questions to him on the forums which he answers in a scientific and humorous manner. Recently he collected the best of them in a book: “What If?: Serious Scientific Answers to Absurd Hypothetical Questions”. I bought this book for my wife for her birthday, thus her reading it.

Now that we’re all caught up, back to the story.

Apparently a number of the what if scenarios in the book pass through or end with the object or scenario in question becoming a plasma. For example, a question is asked in the book about what would happen if you shinned laser pointers at the moon. The answer is not a whole lot. The energy and illumination of laser pointers are tiny compared to the light from the moon and the size of the moon. But the book raises the stakes and keeps ramping up the size of the laser. As the lasers get powerful, and we assume a few million people are pointing at the moon simultaneously, things do start to happen. The final stage is millions of the lasers used at the National Ignition Facility where they do fusion research by shooting lots of high power lasers at a marble. So the what if scenario has the moon being hit with millions of these lasers, and this heats up the moon a lot.

If you heat up a solid material, say with a laser or a super hair dryer, it will first get hot as you energize the molecules that make up the material. Ice is a good example. As the ice gets warm, the bonds holding the water molecules in a solid form break and it becomes a fluid. As the temperature keeps going up, the bonds holding the water molecules together as a liquid break and the water becomes a gas, water vapor. Now if you keep heating it up, you’d likely break the bonds holding water molecule together first. So the bonds between the hydrogen and oxygen would break and you would no longer have water, but a cloud of hydrogen and oxygen. If you keep heating it up, assuming it doesn’t blow up as hydrogen and oxygen are highly combustable, then you would next see the outer electrons in the H and O atoms popping off and escaping for the atom. If a large enough number of the atoms loose an electron, you then have a plasma.

So if you hit the moon with millions of super lasers, first it would go from moon rock to molten moon liquid, then to moon gas, then to basic elemental atoms, and finally those atoms would loose electrons and you’d get a plasma. This would apply to anything if you apply enough heat and energy. So truly, everything does end in plasma, if you try.


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