The setting is Earth in 2021 OTL. An invisible space station of an arbitrarily advanced alien civilization is orbiting around Earth keeping watch on humanity. The aliens have determined that nuclear technology is something that humanity should not have at this stage of development. It's like children playing with fire, has the potential to create mutually assured destruction. Although the aliens have otherwise has a noninterference policy regarding the Earth, they see humanity as something too precious to waste. So in order to keep them from destroying themselves, the aliens decide to magically remove all nuclear everything from human civilization.

So instantaneously all radioactive elements and compounds including uranium, radium, plutonium, thorium, etc ... are replaced with pure silver. An atom of the radioactive element is literally replaced with an atom or ordinary silver, every single atom, affecting the mass of the object. This affects all such radioactive elements in nuclear weapons, power plants, toxic waste dumps, mines, under ground deposits, and just scattered throughout the environment.

It is worth noting that the aliens performed this replacement affecting under ground deposits only within the outer layer of the Earth, that humans can feasibly get to with modern or near future equipment. Any radioactive elements deep inside the Earth are untouched, so the Earth's magnetic fields would continue to work normally.

There are no visual effects or anything associated with the replacement, it is all silent. This occurs without any warning, and humans are initially unaware of what happened.


I do apologize as this is a multi-part question, but never the less I will ask it. I would like to know what happens after this instantaneous replacement takes place? Obviously all nuclear power plants will cease working because all radioactive elements will have been replaced with silver, but will they gradually cool down, or have a sudden failure? Would humans be able to detect what happened?

What will happen within a few hours of the great replacement? A few days? Weeks? Months? Years?

How soon might humans, such as employees of nuclear power plants notice that something is amiss? Would their equipment even tell them that? What about smaller reactors such as in nuclear powered ships and submarines? Would CERN be able to detect anything? And how soon would they come to the conclusion that all nuclear reactors around the world have been disabled?

Also, how soon would the militaries realize that their nuclear weapons no longer work as intended? Essentially they are now reduced to using conventional non-nuclear weapons. Specifically the main question is, how would this realization affect global geopolitics? I mean to say that there are some countries in the world who only wield the thread of nuclear weapons to scare their foes. Without nuclear weapons such countries wouldn't be able to stake their claims with their regular army and economy alone. It would be good if at least one of the answer would mention which are those countries in particular and what would happen to them after the great replacement?

As I understand in addition to carrying the threat of mutual destruction, nuclear weapons also keep the rival militaries scared of each other, and not bold enough to start a hot war. In short it also is a bad way of guaranteeing peace. Once the militaries find out that no one has nuclear weapons anymore, would they start a war? Would some countries try to conquer the territories of other countries, because their military is weak without having the nuclear weapons anymore?

So I am asking about both the short term, medium term, and long term consequences of the sudden great replacement of radioactive elements into pure silver at the same time everywhere on Earth.

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    $\begingroup$ The French will be really , really upset. But no-one will hear them, as they will have no electric power to run their phones, computers or tv stations to tell anyone about it. $\endgroup$
    – PcMan
    Jan 16, 2021 at 20:09
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    $\begingroup$ Re: "So instantaneously all radioactive elements and compounds ... are replaced with pure silver", well, all animals and humans die within a few days because the potassium within their bodies is a significantly radioactive element. See en.wikipedia.org/wiki/Potassium-40#Banana_equivalent_dose $\endgroup$ Jan 16, 2021 at 20:25
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    $\begingroup$ @GrumpyYoungMan K40 is a pretty insignificant fraction of total potassium. Might be enough to cause illness, but most potassium would be perfectly fine. $\endgroup$
    – Sol
    Jan 16, 2021 at 21:10
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    $\begingroup$ All the people that need nuclear medicine, such as cancer patients, may die. $\endgroup$
    – NomadMaker
    Jan 16, 2021 at 22:18
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    $\begingroup$ One interesting thing I've heard is that coal plants release more radioactive byproducts than a decently designed nuclear plant. $\endgroup$
    – NomadMaker
    Jan 16, 2021 at 22:19

6 Answers 6


This is a bit too much for a comment so here it is as an answer.

I agree with most of what everyone else has said, with one caveat. This is an event that would redefine the term "global terrorism."

The nuclear weapons going cold isn't a major issue, to be honest. While it's true that we still plan for and how to counter a nuclear exchange, the bigger concern is the weapons falling into the hands of terrorists. So this just simplified that problem. The major disruption will come from the disruption of the power grid, medical and everyday devices, and economic depression as others have said in their answers. We're talking millions dead, all because these aliens think they know better and have the moral right (them seeing humanity as precious is suspicious in its own right...) to interfere with our development.

Assuming we survive the coming issues with intact governments, we (the world as a whole) would now have incontrovertible proof that someone/thing was out there and that they have essentially propagated an act of war against the entire globe. That they did it in secret and without a declaration of any sort will just be further proof of their hostile intentions. Not the best first impression for a species to make.

Yes, we have been set back rather significantly by what they have done, but now we know it's possible to do something like that. We will catch up tech-wise, eventually. Everything these meddling aliens have done in the meantime (because they've done it once already, whats to stop them from doing it a second, or third time) will be remembered. Our entrance onto the galactic stage will be bright, violent, and vengeful. I'd like to imagine at least one world leader giving an Independence Day style speech as we set off into the void.

It may also be short-lived, but the aliens would know of our displeasure at being toyed with.

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    $\begingroup$ Now to take your idea further, how would knowing that there is a god-like alien power that can do something like this on such scale, impact on the mentality of humanity, particularly politicians and military? Would they be scared and stop fighting amongst themselves in order to better organize and work together instead to counter such an alien power? $\endgroup$
    – Galaxy
    Jan 16, 2021 at 22:41
  • $\begingroup$ Also along the same topic, if other than the great replacement, the aliens would give no signs of their presence, would humanity necessarily assume that some alien species did it? Or would they think that God did it? Or some paranormal activity? $\endgroup$
    – Galaxy
    Jan 16, 2021 at 22:50
  • $\begingroup$ I don't really have enough faith in humanity as a whole to believe that we would suddenly adapt a one world government without a lot of bloodshed. That isn't to say we wouldn't pull together as allies though, even if temporary. The politicos, well a few months ago I may have given them a chance to unite and work towards the same goal, now, eh, I doubt it. Not unless they can get something out of it themselves. The military mentality is more simple, there is a threat, find it, neutralize it. Individuals would certainly be scared, opt to hide or advocate world peace, even capitulation. Cont> $\endgroup$
    – Teak
    Jan 16, 2021 at 23:11
  • $\begingroup$ But it wouldn't last overall. Eventually, somebody would discover what or who had done it, and the wrath of humanity would be pointed straight at them. As for the aliens/god part? There will always be signs, we simply may not be able to detect them, yet. And yes, many would assume everything from aliens to hollow-earthers to a deity of xyz religion as responsible. And there will be individuals/organizations that take advantage of those beliefs. But in the end we'd find an errant heat signature in orbit, an isotope that shouldn't be there, or a new satellite will hit "something" and we'll know. $\endgroup$
    – Teak
    Jan 16, 2021 at 23:22
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    $\begingroup$ @Teak - sustained fusion, by definition, doesn't involve fissile material. Very brief fusion does. $\endgroup$
    – jdunlop
    Jan 16, 2021 at 23:58

I can't address the geopolitics, but in terms of the pure technical, any operating reactor would notice immediately. Power level is monitored by detecting neutrons from fission, and the power suddenly dropping to zero would be very obvious.

Based on what I know from working at a research reactor, this would probably lead to: SCRAM the reactor immediately -> contact the supervisor -> contact the director -> contact the NRC (Nuclear Regulatory Commission). This would probably lead to a flood of messages at the NRC. It would probably be pretty quick to determine that it wasn't a safety issue, after which there would be widespread head-scratching, physicists having existential crises, and general confusion.


The immediate effect, as others have mentioned, is that all nuclear reactors start cooling down and there are catastrophic power outages across large parts of the planet. In addition to the civilian misery, businesses have their supply chains disrupted, aggravating the situation. Overall, this causes an immense economic depression to occur which causes civil/political unrest. Pollution increases drastically in the short term (5-10 years) as fossil-fuel powerplants and generators are reactivated and run at maximum capacity to make up for the shortfall until enough renewable power sources can be brought online.

All civilian, commercial/industrial, medical, and scientific uses of radioactives are wiped out. Americium based smoke detectors are non-functional, radiopharmaceuticals used for cancer treatment and medical imaging are gone, pacemakers with radioactive-powered batteries fail, other industrial uses for radioactives are also non-functional, no RTGs for spacecraft, etc. This causes additional significant loss of life, supply chain disruption, and consequent economic damage.

Even after recovering from the immediate disruption, geopolitics is significantly altered. Nations with weak militaries that depended on MAD to deter stronger nations either begin beefing up their conventional forces or looking into banned WMDs (e.g. biological weapons for low-tech countries or orbital kinetic bombardment weapons for high-tech countries) as a replacement deterrent. This triggers a new arms race with nations with stronger militaries. Coupled with the political unrest caused by the depression, the risk of wars breaking out significantly increases.



I'll try to answer the questions in the order they were made:

How soon might humans notice that something is amiss?

Immediately. Within instants. Possibly faster than humans can react, as automated systems measuring radiation and heat output in nuclear reactors start screaming that they've either failed or something is terribly wrong. The thousands of scientists who are this moment examining transuranic elements. The thousands of students holding a Geiger counter over a piece of feldspar at this very moment.

How soon would they realize that the effect was global?

Within a day. The first hour or so would be spent verifying the readings they were getting, then they'd consult coworkers, then they'd consult colleagues elsewhere. It wouldn't take more than a day. (Also, France's electrical grid would have crashed.)

Which countries would be abruptly opportunistic?

Honestly, probably none. The whole point of MAD wasn't to persuade people not to go to war (if it were, Ukraine would still be whole, for example) but to persuade them that using nuclear weapons is suicidal. The Chinese shelled Taiwan for years and engaged in air combat despite the presence of nuclear and thermonuclear weapons in the arsenal of Taiwan's allies.

Long term

There would be at least a temporary increase in emissions, as fossil fuel plants were brought online to replace 400 GW of generative capacity lost when nuclear reactors stopped working. Cancer treatments would suffer. It would be impossible to judge the age of biological artifacts. Medical diagnostics would suffer. A bunch of far-north lighthouses would stop working. Many millions of smoke detectors would stop working.

  • $\begingroup$ I specifically mentioned that only the radioactive elements within the outer layer of the Earth within the range that humans could reach would be converted. The inside the Earth would remain untouched. $\endgroup$
    – Galaxy
    Jan 16, 2021 at 21:10
  • $\begingroup$ @Galaxy - so noted, removed the Extremely Long Term consequences. $\endgroup$
    – jdunlop
    Jan 17, 2021 at 0:04

Every other answer regarding power and geopolitics is basically right, so I wont repeat them.

Some other things to consider:

  • Nuclear medicine. We have radioactive chemicals in our body when were getting medical imagining, when were treating certain cancers, or dealing with thyroid conditions. Having this lifesaving medicine turn to silver is a death sentance.
  • much of some nations military depends on nuclear propulsion. Nuclear submarines will be able to surface but will be adrift on emergency battery power. Air craft carriers will be useless. The US navy could loose all its flagships.
  • Changing uranium deposits to silver deposits is going to cause hills to collapse. The materials have different mass, density, strength, compressibility, etc. Many landscapes will have landslides. Many miners will die in mines.
  • Every space probe not using solar panels just stops working. They rely on radioactive isotopes for power generation in cases when solar power is insignificant. The Mars rovers will be idle. New horizons will loose contact.

Noticed instantly and war

Alarms went off.

Of course, there's nothing special about alarms going off in the control room of a nuclear power station. They do it all the time. It is because there are many dials and meters and things that something important might not get noticed if it doesn't at least beep.


Horace Gander looked at the flashing red lights. Then he looked at some dials. Then he looked at the faces of his fellow workers. Then he raised his eyes to the big dial at the far end of the room. Four hundred and twenty practically dependable and very nearly cheap megawatts were leaving the station. According to other dials, nothing was producing them. <...>

"Alf, you'd better ring the station manager."Three crowded hours went past. They involved a lot of phone calls, telexes and faxes. Twenty-seven people were got out of bed in quick succession and they got another fifty-three out of bed, because if there is one thing a man wants to know when he's woken up in a panic at 4.00 a.m., it's that he's not alone.

Anyway, you need all sorts of permissions before they let you unscrew the lid of a nuclear reactor and look inside. They got them. They unscrewed it. They had a look inside.

Horace Gander said, "There's got to be a sensible reason for this. Five hundred tons of uranium don't just get up and walk away." A meter in his hand should have been screaming. Instead, it let out the occasional halfhearted tick. Where the reactor should have been was an empty space. You could have had quite a nice game of squash in it.

Right at the bottom, all alone in the centre of the bright cold floor,l was a lemon sherbet.

- From 'Good Omens', Terry Pratchett and Neild Gaiman.

Illustrated might not completely fit the story, but one thing is for sure. If your radioactive material suddenly vanishes, you'll notice instantly. The nuclear reactor will most likely stop harmlessly, not including the ones in submarines for example. However, nuclear power plants wouldn't be the only thing to stop working.

Radioactive material is everywhere. Even if we discount that even the most mundane thing is radioactive in some way, if you remove the dangerous stuff lots will happen. From the dials on many watches stopping to glow in the dark, to medical equipment not running, therapies not working, to airport security not being able to scan. Radioactive materials are used a surprising amount.

This makes the conclusion quite easy. Something has happened to all radioactive materials. The moment this is understood, they'll check the nuclear weapons to see if their capabilities are in tact. I expect that this would be less than a day.


Now the problems really start. As suggested before, we use nuclear material in a great deal of things. But losing the reactors will leave a large hole in our energy budget. We'll make a quick grab to whatever is available to fill this gap. Most likely fossil fuels.

However, there is a finite amount we're producing. The immediate scarcity of fossil fuels will increase tensions a great deal. Enough that nations are willing to use force to secure enough for themselves. Military intervention already happened with many oil countries that became unstable due to civil unrest. Now we have a world in chaos due to many services like healthcare and stable energy supply falling apart. They'll clamber over each other to protect their lifestyle.

The problem is we will lack nuclear weapons. Currently we know that using nuclear weapons will not be good for any party. But even if you can't use it, the threat is there. You don't want to risk any military action that would conceivably force the enemy to use such a weapon, because they feel threatened. Without these weapons, nations would test to see how far they can go with their military actions close to other nations. This will eventually escalate and become a war.

Even if you only remove the 'dangerous' radioactive materials in the bombs and the nuclear power plants, it might escalate to a full blown war just for the battle for energy.

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    $\begingroup$ The fossil fuels used for power generation are almost entirely coal and natural gas, both of which are plentiful across the globe. See eia.gov/tools/faqs/faq.php?id=427&t=3 There's no reason for war over that. $\endgroup$ Jan 16, 2021 at 21:40
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    $\begingroup$ @GrumpyYoungMan I'll need a bit more evidence than a random link to a USA usage to believe gas is globally easily available and won't inspire wars and change my answer. I mean the Ukraine conflict was in part due to the gas and the gas pipelines. I don’t see how all fossil fuels will be 'no biggy' if we lose our nuclear power. $\endgroup$
    – Trioxidane
    Jan 16, 2021 at 21:59
  • $\begingroup$ britannica.com/science/coal-fossil-fuel/… and pmfias.com/… $\endgroup$ Jan 16, 2021 at 22:42
  • $\begingroup$ Healthcare, while hampered by a lack of radioactives, wouldn't "fall apart". Chemo would remain totally viable, and medical imaging would be fine. You wouldn't be able to use radiotherapy or radioactive tracers, but that's a subset of medicine. (Also, watch dials haven't been radioactive since the 60s, since people don't like getting burns on their wrists.) $\endgroup$
    – jdunlop
    Jan 17, 2021 at 0:03

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