Ask a Physicist: Can I build a doomsday device using neutrinos?

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In this week's "Ask a Physicist," I get counter-factual and imagine what would happen if we had perfect control over neutrinos. Would we build a death ray? Escape from an Inception dreamscape? Here's what would really happen - sort of.

I've known I wanted to do a bit on neutrinos for a while now, and at first, I thought of inventing a reader, but figured that you guys would think a question from a Mr. H. Jablomie would be a bit low class. I decided instead to cheat somewhat less, and prompt our editors, Charlie Jane Anders and Annalee Newitz, to feed me a question. Consider this all the more incentive for you to send me questions. Here's what they came up with:

What could we do if we could completely control the behavior of neutrinos?

What does it mean to to completely control the behavior of neutrinos? Make a high-intensity neutrino beam? Harness the neutrino flux from the sun? I generally try to stay away from counter-factual questions. After all, we can't completely control neutrinos. However, I decided to make an exception in this case.


Why? Because it's pretty clear that Charlie Jane and Annalee are in line to join the Evil League of Evil, and would like my help in designing a doomsday device. And I have no problem with that.

I'm going to look at a few neutrino powered scifi devices later, but first we should probably say a few things about how neutrinos work. They are perfectly ordinary particles in lots of ways. Except for the fact that they don't have any electrical charge, they're almost identical to electrons, but much much less massive. Because they are both low-mass and neutral, they are very hard to detect. In fact, they interact with other matter almost entirely via the weak nuclear force. They interact so weakly, in fact, that you could shoot a neutrino through about a light-year's worth of lead and only have about a 5% chance that the neutrino hits anything en route.


Wolfgang Pauli realized way back in 1930 that neutrinos must exist, because when neutrons decay, the resulting protons and electrons recoil in such a way that it was very clear that there was some sort of missing particle. The neutrinos weren't detected experimentally for more than 25 years after that. I bring this up just to point out that it's very possible to theorize (correctly) that a particle exists long before the particle itself is ever detected. I'm just saying.


I was desperate for a good, solid neutrino question because they are awesome. For instance, they played a major role in determining how much of each kind of element we have in the universe today, an effect I describe in some detail in the "User's Guide to the Universe."


But there are many other awesome things about neutrinos. In no particular order:

  • They help to make the sun shine.
  • Strange but true, the nuclear fusion in the sun is governed by the weak nuclear force, not the strong one. As a result, when hydrogen fuses into helium (think of the They Might be Giants song) neutrinos are created in tremendous numbers. Literally billions of them are emitted from every square centimeter of the sun every second, and the amount of neutrino power is comparable to that of light.
  • You're soaking in them.
  • Neutrinos, as I've mentioned, were a big player in the early universe. You couldn't move a micron without some neutrino or another smacking you in the face. As the universe cooled down, neutrinos calmed down a bit, but they didn't go anywhere. To this day, for every ordinary atom in the universe, there's something like a billion neutrinos or anti-neutrinos flying around.
  • They have an identity crisis.
  • In the 1960's a number of people were building big underground pools of cleaning fluid to try to detect neutrinos from the sun. But something was wrong. We only got about a third of what we expected! As it turns out, there are three different types of neutrinos and they have no compunction at all about turning into one another. Electron neutrinos turn into mu and tau neutrinos, and vice-versa. If you're looking for a core concept to guide you in this strangeness, the "oscillations" between flavors of neutrinos is very similar to the uncertainty guiding the collapse of a quantum mechanical wave-function.
  • Despite what Ye Olde textbooks say, they aren't massless.
  • Remember when we talked about what happens when you approach the speed of light? Time slows down compared to other observers. No time at all seems to pass for something moving at the speed of light. But the only particles that move the speed of light are massless ones.
  • So (and the reasoning gets tricky here) in order for neutrinos to have the time to oscillate from one flavor to another, —they need to experience time themselves—, and therefore they need to be going less than the speed of light. Therefore, they have mass. Get it? Only, the current constraints on their masses are tiny. How tiny? Well, we're not really sure because we don't actually measure the masses of the different types of neutrinos, just the difference of the squares of their masses. Yeah, I know. It's a ridiculously circuitous thing to measure. Screw you, universe.
  • It's only in the last dozen years that we've actually been sure that neutrinos have mass at all, and not to sound like an old man about it, but in my day, neutrinos were massless. They may not be massless, but they are insanely light. A reasonable estimate of the heaviest neutrino is still only about one ten-millionth of that of an electron. This is too small, unfortunately, to do a very good job accounting for the missing dark matter in the universe.
  • They know left from right.
  • In my last column, on monopoles, I talked a bit about symmetries in physics. Physics generally doesn't care very much about the difference between left and right. The big exception is neutrinos. Neutrinos spin, just like electrons. As it happens, if I fire a neutrino at you, it will always spin clockwise as seen head-on. Anti-neutrinos always spin counter-clockwise. So if you are a particle physicist and want to construct an Inception-style totem, might I suggest making a counter-clockwise neutrino?

Neutrinos aren't normally on the supply side of, say, power generators or weapons, but they do get created in great abundance. As a result a number of big neutrino detectors are intentionally built near nuclear reactors. But let's be creative. How might we use these buggers to take over the world? I'm not as evil a scientist as I'd like to be, but fortunately, others have thought this out for me.

1. In 2012, solar neutrinos are apparently destined to melt the earth's core. I say, "apparently" because I'm basing this on wikipedia. I'm devoted to you as my readers, but nothing could induce me to actually see the movie.


Could it work? In the real world, absolutely not, since neutrinos can (and do) pass right through the earth with virtually no impact. But okay io9, I'll play your game. Suppose you could make the core suck up the full energy of the solar neutrinos, maybe with some giant parabolic neutrino mirror (which, I remind you, does not exist). These neutrinos are essentially at temperatures of a hundred million degrees. It might take a while, but since we'd essentially double the amount of energy being absorbed by the earth, it would ultimately be bad news for us.


2. Twitter follower Dan Tannenbaum (whose example you should totally follow, by the way) suggested the Metalunan's neutrino ray — a death ray made of neutrinos — from This Island Earth. I'm pretty sure this is just the sort of thing Charlie Jane and Annalee were thinking of in the first place.

Would it work? This one does slightly better, but it would require a crapload of neutrino flux. In principle if you could collect enough high-energy neutrinos (far more than could be created by any sort of normal weapon) then they could be used to turn your innards into all the wrong elements. This is, by the way, one of the ways that neutrino detectors work. In some of them, chlorine gets turned into argon. That sort of thing will kill you pretty darn quick. Even a few of your genes being mutated by such a process might do you in, but that could take a bit longer.


I'd point out that the interocitor is also supposed to be used as some sort of communication device. But it seems to me a pretty bad one. Even under the best of circumstances, neutrinos only travel at the speed of light. It seems easier to me to just use light, but I guess I'm just lazy.

3. I know I was specifically commissioned to build weapons here, but we can also find potentially peaceful uses for sci-fi neutrinos. In the Stargate Universe, the Asgard use a neutrino-ion generator to power their ships.


Would it work? Nah. In fact, I'd be happy if anyone could just explain how this is supposed to work.

But I'm sure I've missed a bunch. So describe your favorite neutrino-based sci-fi weapons, energy sources, communication devices or propulsion systems below, and the io9 community and I will figure out how to build them. And nothing from Dimension X, please.


Dave Goldberg is the author, with Jeff Blomquist, of "A User's Guide to the Universe: Surviving the Perils of Black Holes, Time Paradoxes, and Quantum Uncertainty." (follow us on facebook or twitter.) He is an Associate Professor of Physics at Drexel University. Feel free to send email to with any questions about the universe.