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In my magic system, wizards are able to exert a force upon an object. I am trying to ascertain whether this ability could be used to create a nuclear explosion without any preparation, using just raw uranium.

I understand that the basic principle behind any nuclear explosion is to create an exponential chain reaction, and that the Fat Man bomb did this by compressing a plutonium core, causing it to go critical. Based on that simplistic understanding, it sounds plausible that a wizard could simply "squeeze" naturally-occurring uranium and create an explosion.

That sounds like a very simple thing, but the Fat Man bomb was extremely complex. Some of this complexity was required simply to compress the fuel -- which a wizard could do with magic -- or to increase the yield. But is it feasible that a wizard could make do without any of it? Without, say, an initiator, could an explosion even occur at all? Does the compression have to occur at a precise rate?

There's also the matter of purity. Would it be possible to create an explosion using naturally occurring uranium without enriching it first, and what quantity would be required?

For the purposes of this question, let's assume that the yield is not important and that the wizards aren't concerned about surviving the blast.

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  • $\begingroup$ science-based magic is usually a really bad idea. If it's magic, it's magic. Who knows how exactly it pushes? How selective it is? Etc. $\endgroup$ – Mołot Jan 10 '17 at 6:25
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    $\begingroup$ Unless you want a half assed bomb then you should consider super critical mass meaning enriched uranium, this will improve fission rates to a point that we can see a glowing mushroom. If your wizards can summon critters from another world preferably antimatter universe I recommend a pixie for starter... $\endgroup$ – user6760 Jan 10 '17 at 7:16
  • $\begingroup$ Take a look at Verner Vinge’s The Witling. $\endgroup$ – JDługosz Jan 10 '17 at 9:10
  • $\begingroup$ @a4android: You're right, fusion was a typo. Of course I meant fission. $\endgroup$ – jamesqf Jan 10 '17 at 18:08
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    $\begingroup$ Ordinary U-238 doesn't do fission, you need U-235, which is a very small fraction - ~0.7%, IIRC - of natural uranium. The major technical difficulty of the Manhattan Project was enriching this enough to sustain fission. $\endgroup$ – jamesqf Jan 10 '17 at 18:09
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The answer to any question like this is "it depends." Magic can do all sorts of things! However, most likely the demands exceed what most people would think a wizard could do.

The key challenge for the Wizard is to achieve criticality. This is a mixture of many factors such as mass, density, nearby neutron reflectors, and several others. When you achieve criticality it means the neutrons released from the fission of uranium atoms are sufficiently likely to collide with another uranium atom as to cause the entire mass to undergo fision.

This would be terribly hard to do with un-enriched uranium. The U-235 that undergoes fission is relatively low in concentration in naturally occuring uranium. This means you would have to crush the uranium far harder than we had to in an atomic bomb. If the wizards can create a pocket black-hole, they can probably make un-enriched uranium undergo fission. However, if they can make pocket black-holes, one must question if nuclear weapons are even interesting to the wizards!

Assuming they do have enriched uranium, in a suitable configuration, the next step is to crush it together. This is actually quite the dance in real nuclear weapons. Once the reaction starts, it naturally wants to expand. If you don't crush it in just the right shape, it will find a way out and much of the material will never get the chance to undergo fission. The initiators on a nuclear bomb are unique in their precision. They are several order of magnitude more exacting with their timing than any other initiator in the world. They have to be this precise to make sure the many shaped charges layered on top of each other create the proper lensing effects.

Our wizard would need to be able to create a similar level of uniform compression. This compression would need to be held against the nuclear bomb's own explosive forces. This is where believably is tricky. The wizard would certainly not have the timing needed to collapse it perfectly the way we do, so the wizard would have to rely on brute force, holding it together for even longer, while the bomb is exploding. A wizard that can do this can make your head pop off like squeezing a grape.

In the end, it will all come down to Sanderson's First Law:

Sanderson’s First Law of Magics: An author’s ability to solve conflict with magic is DIRECTLY PROPORTIONAL to how well the reader understands said magic.

If you have built up your story such that the reader understands how the wizard could attain such extravagant powers, then by all means have your wizards set off nuclear bombs!

Just brainstorming along the lines of the TV show Lost, perhaps your wizards have nearly limitless power, but are forbidden from directly using these powers to hurt people. Perhaps one evil wizard has found this nuclear bomb trick to be a technicality that skirts the rules.

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  • $\begingroup$ But we cannot.make a perfectly spherical implosion with explosives. Magic, on the other hand, works with mathematical precision not mundane engineering (which mere technology is despised by mages). Were it not for quantum, they would long ago have collapsed the world into a black hole in their arrogance. (I've mashed up a couple of ideas from the late Terry Pratchett here). $\endgroup$ – nigel222 Jan 10 '17 at 22:47
  • $\begingroup$ @nigel222 A magic system which worked with mathematical precision would be intriguing. It'd be an engineer or scientists's best friend. If you can describe the construct with math, it can be produced with magic without any implementation flaws or defects?! That'd be astounding! $\endgroup$ – Cort Ammon Jan 10 '17 at 22:52
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Well, let's suppose that a wizard has worked out a really good magical squeezing process. He's also worked out that diamond is just squeezed carbon. And with a humongous diamond in hand, what girl could possibly deny him?

Unfortunately his magical squeezing spell is a lot more potent than he realizes. Instead of making a diamond he initiates carbon-carbon fusion, normally seen only in the core of very large stars and the gizzards of dragons (which use the same magic rather more successfully).

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Yes and no,

Yes you can create a nuclear explosion with just force, the question is how much you can supply, and how accurately.

If you can supply enough force you can generate a fusion bomb out of thin air by just compressing hydrogen in the atmosphere, (mind you the inside of a star is usually the only place where this much heat and pressure are present).

You can get away with less pressure if you use "enriched hydrogen" deuterium and tritium but then getting this much force and heat fast enough normally requires a fission nuclear bomb).

If you have less energy and sufficient fissionable material you can build a little boy style fission bomb, a sphere of fissionable material with a cone cut out of it. The cone is then shot into the sphere by a cannon setting off the bomb. This requires lots of fissionable material.

If you have lots of precision you can do an implosion sphere style fission bomb, the fat man style. A hollow sphere of fissionable material lined with very carefully machined explosive so it implodes uniformly to a point. This is complicated and difficult as the op notes in his question. This requires less material.

Naturally occurring uranium is stable it would have to be enriched before it could be used.

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  • $\begingroup$ There's also the question of how close the wizard has to be to use this ability. Crispy critter. $\endgroup$ – Cort Ammon Jan 10 '17 at 0:54
  • $\begingroup$ Of course the question then becomes how you find (free) hydrogen in the atmosphere :-) $\endgroup$ – jamesqf Jan 10 '17 at 18:10
  • $\begingroup$ "Hydrogen" fusion bombs require deuterium and/or tritium, compressing ordinary hydrogen in the atmosphere won't do it. Gathering deuterium or tritium from seawater or atmosphere (extremely large quantities of it!) by magical means is certainly possible, but has similar story issues to enriching uranium, except the need to find a uranium mine. $\endgroup$ – Peteris Jan 10 '17 at 22:29
  • $\begingroup$ @Peteris good point will edit (though with sufficient pressure even normal hydrogen and oxygen will go through fusion, though this requires pressure like the inside of the sun) $\endgroup$ – sdrawkcabdear Jan 12 '17 at 0:19

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