In the moment I am writing a story about a post apocalyptic earth where a new, stable society is thriving centuries later. The setting is planned to be an early industrial solar punk world with some futuristic elements due to the fantastical event that caused the apocalypse in the first place.

My question is, what needs to happen physics wise, be it changes in laws of physics or supernaturally, for nuclear weapons, new and old, to not work in the first place without changing the makeup of the world and/or universe drastically? I am looking for a solution that works physics wise even if the why it happens is handwaved.

Edit: My question was a bit vague. What I want to know what laws of physics need to change to make nuclear weapons stop working, preferably atom wise, without changing reality drastically. With magic I meant to inform that the why of it happening could be through magic. There is no need to explain what the magic could be, only how the physics part works.

Note: An earlier question asked how to counter nukes with technology. Please note the tags here, I am changing physics to prevent nuclear weapons rather than designing a defense for them.

  • $\begingroup$ This seems like a question asking for help brainstorming or generating ideas. Broad questions such as this are off topic for this site. $\endgroup$
    – sphennings
    Mar 14 at 16:03
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    $\begingroup$ @sphennings I beg to disagree. This is a specific question that can be given a specific answer (no need for brainstorming). Also, this question might be already answered here: How to make nukes useless?. $\endgroup$
    – Alexander
    Mar 14 at 16:18
  • $\begingroup$ @Alexander If it's a duplicate then you should flag it as such. $\endgroup$
    – sphennings
    Mar 14 at 16:41
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    $\begingroup$ The Laws of Physics are not your biggest problem. The Law of Unintended Consequences will be the one that does you in. Nuclear weapons stop working, so does the sun. $\endgroup$ Mar 14 at 21:53
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    $\begingroup$ Something like some rare astrophysical event where Earth is bombarded by weird neutrinos that provoke the inplace fission of all the heavier nucleii on Earth? $\endgroup$
    – dmcontador
    Mar 15 at 9:04

16 Answers 16


May not need magic

There are a number of factors that definitely will work against having nuclear weapons in a solarpunk society centuries post-apocalypse and more factors that could make them impractical even without changing the laws of physics.

  1. Disregard "old" nukes - Any nuclear weapon over a century old will not detonate, as per the answers to this question. Even nuclear weapons a decade or more old will require regular maintenance and replacement of various precisely-made components, including the explosive lenses that will suffer chemical deterioration.
  2. Who makes new nukes? - Manufacturing nuclear weapons requires a major industrial effort, as witnessed by the mind-boggling size and budget of the original Manhattan Project. Even newer players who can skip all the tedious R&D required for original development still need to invest heavily and/or lean heavily on the existing nuclear power industry for raw materials - in a solarpunk world, would there be a nuclear power industry at all? For starters, uranium needs to be mined and refined. Then the U235 needs to be carefully separated out (it's only about 0.7% of all uranium) using a centrifuge. (Magic option 1 - make it impossible to separate out the U235 to sufficient purity through the existence of a computer virus that gets into the centrifuge controllers and wrecks them any time someone tries to obtain highly enriched uranium or plutonium - magic Stuxnet on steroids. Bonus points if the virus then tells everyone where the naughty person is that's trying to make a nuke.)
  3. Explosive lens fun - assuming that nuclear material can be obtained, explosives are needed to either implode an otherwise sub-critical mass (implosion weapons) or smash two sub-critical masses together (gun-type weapons). Gun-type weapons are relatively hard to mess with because they are so crude and inefficient - with plenty of fissile material and careful machining the sub-critical cylinder could be inserted into the sub-critical sphere by literally lighting a fuse to set off a propellant charge. Fortunately they require a large amount of fissile material and are also considered quite unsafe. Implosion devices, however, require extremely precise machining of the explosive lenses and extremely precise timing on the detonation. (Magic option 2 - make all timing circuits in the vicinity of weapons-grade fissile material develop multi-millisecond glitches that will prevent sufficiently precise detonation for implosion devices. Make timing circuits fail completely in proximity to a total mass of fissile material sufficient for a detonation, even if it is in multiple pieces currently.)

TLDR - build the "magic" into all electronics that are or can be manufactured in this world to ensure that nuclear weapons are either unable to be manufactured (by preventing isotope separation) or unable to be detonated (by preventing the firing circuits working in the vicinity of weapons grade material). This can be either "real" magic or a weakly godlike AI that has inserted its code into all machines that are used to manufacture electronic components.

  • $\begingroup$ On a related note, printers are designed so that it refuses to copy/print something if it detects this pattern. The "virus/magic on electronics" might also work like or draw real-life connection to that.. in addition to what you laid out, of course. $\endgroup$ Mar 15 at 5:01

(this answer is based on a dream I had. This opening allows magic, so let's put the idea...)

How the ICBM issue was solved in the 1980's

Your world is set in the future, my answer is set in the past. It can be solved.

Telekinetic kids

Back in the 1980's, at the time world wide nuclear destruction seemed to be around the corner, millions of youth and their parents hit the street, to protest against nuclear arms. Back then, we felt empowered against the seemingly inevitable destruction of the planet. Many children joined these protests, also the ones who were developing a new talent, later recognized as long range telekinesis.

There has been a limited amount of publications, but at the time, there were many skeptics, who framed these children as superman-wannabees. What they did not know is E.R. Pelinant, a Hungarian physician who fled to the West in 1956, seriously researched these children and measured their abilities. He made an inventory and founded a secret international research organization, that set out to train long range telekinetic abilities. Pelinant's idea was to use telekinetic talents to cause ICBM's to deviate from their path slightly.. preventing cities from being hit.


The talent was very rare, and remains rare today. In a large city like Hong Kong, there existed only 20-25 children able to move objects at a distance. Some of these children could move heavy objects, from very long distances. Pelinant set out to test their capabilities, and made a list.. but he could not devise an early warning system for it. But he did keep in touch, and tried to keep track of where they live.

The early talents are in their 40s now and their number has grown considerably. When internet and cell phones arrived in the 90's, Pelinant set up his web site, which today still exists. The address of this web site is kept secret, to prevent superpowers from hacking it.

Pelinant rejected a secret Nobel Prize in 2002.

Worldwide, the society has more than 6000 capable and motivated members. It has hundreds of professionals, military and non-military, helping them to gather information. There is a map on Pelinant's website, showing locations and projectile paths in real time. Of course, no large scale nuclear conflict ever started.. Pelinant's system was never tested sofar.. but the members spend a lot of free time to study the maps and practice. Some members are activists against all military. They regularly cause military satellites to get lost in orbit, or cause F16 forced landings. To practice, or just for fun..

Swipe it off course

A telekinetic talent in San Francisco recently curved one of Kim Jong Un's missiles into the Pacific, preventing it from hitting a Japanese coral reef. Nowadays, telekinetic folks have a perfect app for this.. when an alarm reaches their cell phone, they get a map and help "swipe" the missile off track.

  • $\begingroup$ This elaborate answer can fail if someone just hack the app or the nuclear attack is launch to some place without telekinetic kids. And what would happen if another "enemy" kid tries to undo the efforts of moving the bomb. A jedi like fight of force? $\endgroup$
    – raulmd13
    Mar 15 at 7:45
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    $\begingroup$ I don't think you can keep a website secret for too long, except for maybe with magic $\endgroup$ Mar 15 at 8:58
  • $\begingroup$ Magic is available.. @raulmd these issues could add to the story, but I did not dream about it.. LaurenceOfDominia should create them, my answer is already too "story based" actually $\endgroup$
    – Goodies
    Mar 15 at 12:10
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    $\begingroup$ If an app is used by all the magic anti-missile defence people, the same app can potentially be used by the other side to track these people and assassinate them with extreme prejudice. $\endgroup$ Mar 16 at 7:00
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    $\begingroup$ "cause F16 forced landings" Seems oddly specific. $\endgroup$
    – Glen Yates
    Mar 16 at 13:58

No changes are required.

Imagine if the apocaliptic event was predicted, and mankind tried to survive it. They build generation ships and stocked them with as much nuclear material they could get their hands on to power and propel them, including some Orion Drives (detonate a nuclear bomb at the right spot to propel the ship). What nuclear material that remained was used to power the bunkers and other survival equipment for decades and centuries.

There is simply not enough fissible material left. What fissible material is left cannot be reached for centuries since the higher tech civilization would have mined it.

Naturally when leaving the predecessor civilization realized the problems of leaving a world without much gas/oil/nuclear resources so they left renewable technologies with those who stayed behind, chief amongst the surviving technologies being solar panels&solar panel fabrication for your solar punk.

Edit: you dont have to take that exact scenario ofcourse. It doesnt matter if some lunatic managed to send all nuclear material into the sun, its all been used or its all hidden somewhere by the pre-apocalipsers. What matters is that there is simply not enough available for building nukes, or at least to test and build enough large nukes to change your setting.

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    $\begingroup$ Fissile material is all over the Earth, just at a very low density. Given the average concentration of uranium in the Earth's crust I once calculated I have enough U-235 for an atom bomb--separating it from the ground it's in is decidedly non-trivial, though, even before you consider the isotope separation. $\endgroup$ Mar 16 at 3:50

Magically change a few first principles

It's a blessing that you chose not to put the hard-science or science-based tags in a question asking to break fusion bombs without breaking reality. Many stars will become vocally upset at what you are about to do, so handling this with the magic tag was a wise choice. Now, magic can safely put a bubble around planet earth that contains our new laws of physics without ripping spacetime asunder. Shields up? Good. We're going in the opposite direction of @Phillipp, because I don't think rapidly reducing the critical mass of every known isotope will stop bomb makers the way you intend. There will be no more bombs being made, I promise you that. Because there will be no one to make them after you cook the universe.

I will draw my answer here from a similar question I posted asking to change the fundamental laws of physics. You need only to rewrite some of the fundamental principles of the metals in the actinide series. And since this experiment is happening in a little bubble around earth, you really only need to worry about some uranium, thorium, and plutonium, since those are the only elements we have in sufficient quantities on earth to talk about regarding atomic weapons. I say atomic weapons specifically, and not thermonuclear weapons, because thermonuclear weapons need atomic bombs to fire them off anyway. Kill the atomic bomb, and you kill all practical and semi-portable means of making atoms go boom on this planet. Technically, if you want perfect and absolute nullification there are 15 actinides which can initiate the big boom. I will only talk about making them practically impossible, because you're not going to get enough lawrencium or fermium to do anything dangerous.

The boom you want to stop comes from neutrons, and neutrons come from atoms that are unstable. That's a colorful name to describe atoms which are not eternal, like most of the ones we know and love. In fact, the actinide series, as it is called, has that name because there is literally no stable element in that block of elements: they are all "radioactive". At some point, all of them will die, falling apart and shooting off some particles. There will be a point some time far down the road that practically no actinides exist at all on earth or the universe, save for what the stars are making now.

Why are actinides special in making a big boom? It's not far off to call it magic, it is essentially just the way the universe was written. Radioactive decay is what is known in physics as a spontaneous event. It means something which causes itself, and no forces or qualities outside the atom can cause it, change it in any way, or stop it from happening. Causality tracks causes and effects by a "light cone," respecting the speed of light in cause-effect relationships. Nothing the universe can do, will cause something else to happen faster than the speed of light. But radioisotopes can ignore this rule becuase they simply have no cause. They just obey their half-life rules absolutley. It just is, and our universe is so much more wonderful and predictable for that (especially science). Let's look at the very wonderful tool of carbon dating that is only possible because of this spontaneous event, for example. For carbon dating, we use carbon-14. Here is the decay chain for it:

$$^{14}_6 \text{C} \rightarrow _7^{14}\text{N} + \text e^- + \overline{v}_e : \lambda = 5,730 \text{years} $$

OK, yes, this is Greek. All you need to know is that any atom of carbon with a six protons and eight neutrons in its nucleus is going to be turning into nitrogen some day, weather it likes it or not. When this will happen is impossible to predict. it is not random, and it is not triggered or caused by anything outside. What we know is simply, that 5,730 years from today, half of all the carbon 14 in the universe today will have turned into nitrogen. Then, in another 5,730 years, half of that remaining carbon 14 will be nitrogen. And so on, forever, never reaching zero. It is a real-world (and true) example of Zeno's dichotomy paradox. Why this is such a great benefit to us, is that it is an absolute reference. We don't need to think about how old the carbon 14 is, or how hot it is, or anything about the pressure. The universe guarantees us absolutely, that it will erase half of it's inventory of carbon 14 in the that amount of time. So with a simple count of this atom in the bones of the fossil, we know exactly when the thing being tested stopped eating forever. Now, there is no need to worry, stars are making more of it all the time. This is why earth is inside a magic bubble, because you are going to just change some of these numbers that never had any rhyme or reason to begin with. Let's start with the most readily available actinide, uranium. The uranium we use in bombs is $^{235}_{92}$U, but we won't play with that just now. What we want to change to neutralize a bomb is the $^{236}_{92}$U that is formed when one of those U-235 atoms picks up a stray neutron to turn it into U-236. Most atoms are pretty happy having an extra neutron, and they just check their schedule to see if they are now stable or not. If not, they wait for their magical clock to strike, and then decay as intended. But $^{236}_{92}$U is what is called a fissionable material. Don't ask why, there is no why. These are just the way atoms work. A fissionable material is an atom nucleus that can be split into two or more pieces by being hit by a neutron, instead of just absorbing it. For example, Actinium-236 is made by smacking Actinium-235 with another neutron. The new atom will hang around for a while, and half of them will decay in about 70 seconds. Then another half of what's left in 70 more, then another half of those leftovers (1/8 of what you started with), and it goes on. But, the actinium-236 won't split apart, even though it's the exact same size as uranium-236. There is no why, and that makes your problem much easier.

If $^{236}_{92}$U were a happy little atom like its neighbor actinium, it would not split in two 80% of the time it got hit. This splitting is where the energy comes from to make the boom. But, nearly 20% of the time, uranium-236 does follow it's decay schedule properly. That looks like this:

$$^{236}_{92} \text{U} \rightarrow _{90}^{232}\text{Th} + \alpha : \lambda = 2.37005 \times 10^7 \text{years} $$

Now you see, if you could make this U-236 atom happy like actinium is, then it would not undergo fission. It would wait around for its time and in 27 thousand years, half of them will have turned to thorium just like the formula above. It makes for a very slow boom that most civilizations would have time to pack there bags and move to another star system before knowing about it. It really is that simple: By decree, U-236 now decays into thorium 100% of the time, like all other well-behaved atoms. You have just broken almost all current nuclear weapons, and nothing on earth breaks. Your story doesn't need an explanation—it can't have one. There is no cause for atoms being fissionable to begin with, so whatever scientific "mumbo jumbo" you invent to explain "why" U-236 works differently is just more magic you need to explain.

OK, ${236}_{92} \text{U}$ is only one problem child in the angry fissionable group. You need to deal with plutonium 240 as well, because that is spontaneously fissionable. Some thorium and americium isotopes will need to be tamed to really shut down mad bombers. but to guarantee earth has no nuclear bombs, just make all fifteen actinide elements magically non-fissionable, which means you just undo the magic that made them fissionable to begin with. And do keep that bubble up like I did in my problem. Bad things will happen in stars if you don't.

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    $\begingroup$ "OK, yes, this is Greek." Well, technically only the alpha and lambda are actually Greek, but we get what you're saying 😁 $\endgroup$
    – Corey
    Mar 15 at 23:29
  • $\begingroup$ Another way to handwave it: Let's change how U-235 and Pu-239 fission slightly. Change some of the prompt neutrons to delayed neutrons (I'm not going to take the time to hunt down the isotopes needed.) Reactors still work but the reaction doesn't go fast enough to make a useful bomb. $\endgroup$ Mar 16 at 4:04
  • $\begingroup$ Or you could tweak the forces so that the actinide series decays to quickly to be of any use, while lead is still happily stable. $\endgroup$
    – EvilSnack
    Mar 16 at 22:05
  • $\begingroup$ @EvilSnack This is sort of Phillips’s answer, but now you have suddenly released heat energy that planned on waiting around for millions of years. Things will be getting hot! And do this through the whole universe??? A Bad Day will be had :( $\endgroup$
    – Vogon Poet
    Mar 16 at 22:14

Cosmic horrors

enter image description here

Humankind was ignorant to the true depths of their hubris when splitting the atom. The alpha and beta particles cast into space by early experiments created a beacon whose strength only intensified as experimentation turned into an industry.

Ripples in existence began to be detected by astronomers. At first they were understood as gravitational waves, but as their intensity grew, it became clear... Einstein was a harbinger priest of that which can only be pronounced by human tongues as Cthulu.

Global leadership united to pool all nuclear resources into a teleporter that would move the planet to a new star system before The Arrival occurred. Once again undetectable in the cosmos, humankind swore to never again light the beacon.

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    $\begingroup$ Your eldritch horrors look like a dance duet. Are you sure we shouldn't invite Cthulhu to a talent show? $\endgroup$ Mar 15 at 22:15
  • $\begingroup$ Huh? I posted a picture of springtime. They say the first stage of The Arrival is hallucinations. Hmm... $\endgroup$
    – Atog
    Mar 16 at 12:54

Alternate History: No Manhattan Project

While the discovery of the theory of nuclear power and weapons was inevitable, their actual implementation was not. With some slight changes to history, you can make it so they remained theoretical.

Actually building nuclear weapons requires a colossal and expensive investment in engineering and infrastructure for the weapon and even more to produce the fissile material. The US undertook this cost in WW2, The Manhattan Project was one of the most expensive projects of the war. Those resources could have been used elsewhere. What if it didn't happen?

To oversimplify it, the Manhattan Project happened because the US thought the Germans were building a bomb. Which they were, however the Germans grossly underestimated what would be involved in a practical nuclear bomb program and never came close. Allied sabotage didn't help.

In this alternate history, the reaction to the Einstein-Szliárd letter warning about the German nuclear program is muted. Rather than creating their own nuclear program, the Allies decide to wait and see and hamper the German program. The war in Europe ends with no nuclear program. The Soviet Invasion of Manchuria, non-stop conventional bombing, and the threat of the revolt of a blockaded, starving population causes Emperor Hirohito to capitulate in Fall 1945.

With the war over, the US slashes its defense budget. The US is rich with oil and coal and has a huge surplus military, it has no reason to spend colossal amounts of money on nuclear power and weapons. Europe and the Soviets are rebuilding, they have better things to spend money on. Fission remains like fusion today: always 10-20 years away, always underfunded. While nuclear power may eventually be successful, it won't come to be in the heady context of a post-WW2 anti-Soviet paranoia with an unlimited, secret military budget. It would come from commercial and scientific endeavors. Huge stockpiles of nuclear weapons would not be integrated into national defense plans, nor to counter the other guy's huge stockpile of nuclear weapons. Rather than being seen as a necessary evil and measure of national prestige, they would be seen as an unthinkable weapon of mass destruction like chemical and biological weapons are today. Some nations might keep small stockpiles, but it would be nothing like the massive glut we have today.


Depends on the time scale

All nuclear weapons use the fission of radioactive heavy elements to produce the bang.

Well, these elements have half lives over which 50% of the radioactive materials decay, typically to more stable elements, reducing potency.

With enough time, all these materials become scarce.

Plutonium-239 halflife is 24 thousand years. Uranium-235 halflife being about 700 million years.

That's not to say something couldn't happen to drastically shorten that time. For each period that occurs though, 50% of the existing material is gone.

If Magic was to specifically target atoms of this weight and isotope, throughout the universe, not much else would change, other than the addition of the byproducts of the decay.

Right now there isn't enough plutonium-239 easily reachable to us to make weapons so we collect it as a waste product in nuclear reactors, then use that to make plutonium bombs.

TL;DR the base material components can decay to where we don't have the materials required, and those already in existence essentially go stale and no longer work.

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    $\begingroup$ Or maybe the societies that went before have mined it all out. There was an old civilization simulation on the early Macs where that could happen. You could grow up a second civilization after your first one had left for the stars, but the planet had no more fissile materials and no more fossil fuels. $\endgroup$
    – Willk
    Mar 15 at 14:05

Neutrino lasers and detectors

Neutrinos take part in many nuclear reactions. As they are almost (but not quite) massless, and pass straight through the Earth without interacting most of the time, we usually ignore them. Nonetheless, the idea that neutrinos could affect the rate of radioactive decay, even on Earth, has been discussed seriously enough to make news, even if it is probably balderdash at the levels we normally encounter.

Your civilization has discovered how to interact normal matter with neutrinos effectively! As a result, you can do two very significant things:

  • You can visualize all of the radioactive material emitting neutrinos everywhere in the world. There's no bunker deep enough, no satellite high enough to keep you from seeing the lump of concentrated nuclear material inside.

  • You can create intense beams of neutrinos. (Calling it a "laser" may be an abuse, but it is at least tightly collimated) These beams are powerful enough to reduce the critical mass of an isotope by a large factor. That means that a nuclear bomb with a sphere or gun of uranium waiting to be put together can now be set off by anyone with a neutrino laser, whenever they want. Even if you make a lump too small for you to set off with the laser ... someone else could make a bigger laser at any time and set it off in your own bunker.

This doesn't completely eliminate the possibility of nuclear attack, but what remains is not very satisfactory. For example, a group of people could carry tiny lumps of a fissible element and throw them all together in a pot for a beam to sweep into and set off. Designing an elegant bomb is no longer needed because the beam itself can trigger an abrupt explosion. However, such methods tend to be suicidal because it is hard to clear to a safe distance before the site is attacked with conventional weapons, and the people smuggling even tiny lumps of isotope will still probably be found and stopped in advance unless there is much chaos already. The explosion produced will likely be small, more "tactical" than "strategic". Enough to remind people the option is out there, but not enough to make it a winning plan.


First, as others have noted, old nuclear weapons do not work without constant maintenance. Especially, but not limited to, the fissile cores.

Secondly, you do not get to have nuclear weapons blipped from the playing field without losing nuclear power (fission) entirely. The processes are similar enough that I can't think of anything that would remove the former without also removing the latter. If the cross sections could somehow change so that the nuclear chain reaction doesn't support explosives, it looks as if you can't do traditional (or even any) reactors at all. Likewise if you start messing with the speed of the neutrons themselves.

So, with those caveats out of the way, what you need is a subtle change in the weak force. Something that drastically alters the decay so that it is unsuitable for nuclear weapons, and there are maybe as many as 5 or 6 isotopes that similar changes have to occur for.

For instance, a suitably altered weak force can reduce the output of neutrons to the point that no chain reaction can be sustained. The decay chain of the isotope changes slightly (I have no idea if you'd want to live in a house with a basement with high radon or not in such a universe), and you might even alter the rate of neutron capture (when instead of splitting, you get U236).

Done correctly, and you still even get to do things like carbon-dating for archaeology. Done poorly, and orthodox chemistry becomes a figment of imagination and all life in the universe ceases to exist.

This change might be done locally, so that aliens millions of light years away still get to nuke each other but your planet is safe. But it's unclear if that's pseudoscience or not... changes to fundamental constants are still assumed to be universal. Though if you're changing them at all we're pretty far into lala land territory, so what's a little extra pseudoscience?


Greatly accelerated radioactive decay.

When radioactive elements decay a lot faster in your world, then any fissile isotopes on Earth would soon decay into stable isotopes. So there would be nothing available to build nuclear bombs with.

When this happened in the distant past, then Earth would be largely look the same as it does today, minus nuclear technology. All the basic building blocks of the planet and its ecosystem are based on stable elements. Radioactive elements don't play an important role on Earth, neither biological nor structurally.

When this change happened in the recent past, then it could very well be the reason for the apocalypse. The reason is that radioactive decay implies decay radiation and decay heat.

  • The fuel rods in all the nuclear reactors would suddenly become a lot more reactive. All nuclear power plants around the world would simultaneously have meltdowns. Their safety measures would probably fail, because they weren't designed to anticipate a scenario which was considered physically impossible.
  • Accelerated radioactive decay would mean that any stockpiles of radioactive isotopes (both nuclear weapons and civil nuclear fuel) would suddenly become very hot and create a lot more radiation. Their casings would melt and their radiation would escape freely.
  • Radioactive ores in Earth's crust would suddenly become hot and very brittle, leading to earthquakes and volcanoes (radioactive volcanoes!).

All of this could probably kill a lot of people and cause the collapse of human civilization. But this apocalypse would be rather short-lived, because the higher the intensity of the radiation of a decaying isotope, the shorter its half-life time. And because this apocalypse would be associated with all nuclear power becoming simultaneously dangerous and unusable, it makes the transition to a new solarpunk civilization even more plausible.


I'm going to interpret the prompt of "nuclear weapons not working" to mean that they can't be built or used as weapons. Making nuclear physics not function at all has too many side effects.

In your pre-apocalypse world, large-scale nuclear war was an imminent threat. One of the factions in that world created a space-based, fully automated nuclear weapon detection and neutralization system. This system has a constellation of satellites that can detect the radiation emitted by any non-trivial quantity of nuclear fuel. Once the location is pinpointed, an orbiting platform will use a laser, kinetic bombardment, or <insert weapon here> to destroy said radioactive object.

This defense system made nuclear weapons unusable. If a military built a nuclear warhead, the defense satellites would attack it within seconds. The weapon would detonate and destroy whoever was trying to use it. Any remaining warheads would be stored in deep underground bunkers. Attempting to bring one to the surface would result in the warhead (and anyone nearby) being destroyed almost instantly.

The system runs completely on autopilot at this point, the ground stations used to control them long gone. Your people are far from technologically advanced enough to disable or destroy the system, perhaps not even advanced enough to understand or see the system. For now, it's as if some unseen magical force will smite anyone foolish enough to try to build or retrieve one of those terrible weapons of old.

The drawback is that this would largely preclude the use of nuclear power as well. Naturally-occurring deposits of radioactive material won't be affected. The defense satellites are smart enough to differentiate between slow changes in radioactivity caused by geology and the relatively fast changes caused by fuel refinement, artificial fission, etc.


The Advent of Weapons with Greater Potential
While quite obvious, and perhaps not the answer you are looking for, more powerful weapons would nullify the use of nuclear weapons, especially if they replace the purpose of nuclear weapons(MAD etc.) , and be significantly more powerful than the nukes.

This would not solve any problems that are related to the existence of nukes, but merely make it so the power of the Greater Weapon is not based on the properties of the nucleus of an atom, but instead some more powerful source, perhaps antimatter, in a controlled and concentrated setting, which I don't think is possible even theoretically, or some sort of quantum disturbance, that erases the Enemies of the Nation from time itself. As long as any replacement fulfills at the idea of MAD, and does it in every way possible better than a nuclear arsenal, for example no wait time between press of button and impact would be a big plus, than nuclear technology would be forever obsolete, in a way that the AK-47 isn't, because any nation still using them would not receive any benefit, since they would be destroyed before impact of their now obsolete rocketry.

In particular I propose the idea of instantaneous destruction, as it most clearly and cleanly replaces the nukes, giving them no power.

  • $\begingroup$ Nothing stopping us from making antimatter bombs except price and time. At the moment antimatter is the most expensive thing we've ever created, by several orders of magnitude - US$1.75e+15 per ounce. If we found a cheap method of creating antiprotons though, there's no reason we couldn't (or wouldn't, for that matter) make bombs out of it. Fortunately to date we've created only a few nanograms worth (less than 20 in total), so it's probably not an immediate problem. $\endgroup$
    – Corey
    Mar 15 at 23:22

Do you need it to be our Earth?

Because, other (probably perfectly habitable planets) may be poor on Uranium and Thorium (and probably also poor on other elements, see the table)

Table: https://en.wikipedia.org/wiki/R-process#/media/File:Nucleosynthesis_periodic_table.svg

(just remove or decrease the violet-colored parts for an image what to expect)

No (or pretty much scarce) natural Uranium and Thorium means no nuclear era until the development of fusion reactors and no bombs (at all).


Fission catalyst (handwavium) particles

It was discovered that by operating a particle accelerator in a particular way, it could be used to generate a beam of Foo particles. (Strangelets? Dark matter? Make it up). These are weakly interacting with normal matter, so they will go through atmosphere or tens of metres of rock without getting absorbed much. However, they act as a catalyst on unstable nuclei, reducing their half-lives by several orders of magnitude.

A nuclear weapon has to contain a high concentration of unstable nuclei.

When hit by a beam of these things, the nuclear materials start decaying with a half-life of days, rather than large numbers of years. The bomb becomes very hot and melts. Not as a useful explosion, just as a fizzle, with its explosives spreading the mess like a mini-Chernobyl.

Instantly, nuclear weapons (and of course nuclear power) have to be abandoned, because the means now exists to make nuclear weapons (and atomic power stations) melt into radioactive slag wherever they might be constructed. Any enriched Uranium (or heaven forbid, Plutonium) has to be buried very deep where such a meltdown won't do any harm. Or quite possibly, diluted in solution and then dumped into the Marianas trench to get very much more diluted in a part of the ocean that we don't really care about.

So there we are. A world without nuclear bombs or nuclear power stations.

You may have noticed that a beam of these particles might also be a ray-gun that works. Everything contains low concentations of unstable nuclei. Being hit by this beam might be like being hit by a small shell, except that a concrete fortification won't save you. You might like to have ray-guns (large, heavy and expensive enough that they don't instantly destroy civilisation.). Otherwise, make the effect mediated by concentration. If its not a macroscopic concentration of nuclear instability (grams or kilograms), the catalytic effect is negligible, so the effect on living organisms is negligible.

This might just something we haven't discovered yet. Very unlikely, but plenty good enough for a McGuffin. (In real life, muons will catalyze nuclear fusion of Deuterium. It's just a shame that we cannot make muons efficiently enough to get fusion power! )


The key lies in your reliance purely on solar power

Making a nuke requires 2 things that a solar society may not have: an advanced understanding of petrochemical compounds required to make the very precise high explosives you need to trigger a Nuke, and the existence of large scale hydro-electric dams capable of filtering the VAST amounts of water you need to get enough heavy water to make one.

Also, there are certain kinds of contamination that can make a river unviable for heavy water refinement. So its also possible that the apocalypses simply contaminated your water sources badly enough with the wrong stuff that refinement is no longer viable even if you do still have the large scale dams to do it with. I do not know what these contaminants are, but it is a known fact that the USA now relies on other countries for heavy water due to contamination of its historical heavy water sites.


Telekinetically-accelerated decay of nuclear weapons

No object in the world is as incredibly fragile and produces as much fear as a nuclear weapon.

As we all know, research into paranormal abilities was at its peak during the Cold War, as the United States and Russia were constantly looking for ways to undermine each other. As we also all know, these programs were complete failures. Nobody actually managed to create or discover anything resembling a useful telepath or telekinetic during this period and the program was dropped, since psychic abilities were obviously not real.

At least, that's what everyone thought.

In reality, the programs did successfully produce several telekinetics - but nobody discovered them for several reasons.

First, telekinesis is subtle. You're not going to get things like floating objects or mind control - the most you could hope for is a slight adjustment of probabilities.

Second, telekinesis is slow. You're not going to see any effect during the duration of a test - but stress and powerful emotions over long-term periods can lead to subtle changes in reality.

Third, the range for telekinesis is, for all intents and purposes, infinite. Since both sides of the Cold War were aiming to produce psychic weapons, their efforts were constantly undermining each other, and the net output of both programs - insofar as undermining each other is concerned - effectively balanced out. Nobody was going to discover anything because the other side was trying their hardest to make sure their enemies didn't discover anything.


The fear of nuclear war and mutually-assured destruction was on everyone's mind, and this included the psychics. When the programs ended and the experimented-on children were released, they continued to project a subtle field over many, many years - a subtle field that was centered on the source of their fear, the bombs themselves. Natural telekinetics all over the world were likewise unconsciously projecting a subtle field that was doing all it could to break down the nuclear weapons.

Nuclear weapons are some of the most fragile objects in the world - a slight change in their structure will cause them to fail. This makes them perfect targets for the subtle psychic pressure of telekinetics around the world, and makes them much more likely to break down over time than anyone would have guessed.

When the time comes to use them, they all turn out to be duds.


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