Thoughts on nuclear technology in my two favorite sci-fi games (Halo and Mass Effect)

[Kolby Jack]

First in Halo: Did the Forerunners never invent nuclear technology? The Covenant don't have nukes, nor do they seem to understand them very well outside "make big boom, yea yea yea." The Forerunners don't seem to have them either. At least I've never heard of them using nuclear bombs, or even nuclear reactors for that matter. Add in the fact that nuclear explosions seem to be the most effective means of destroying both Covenant and Forerunner things (during the war, before Humanity made it's non-nuclear tech WAY more powerful) and it seems like Humanity was the only species to split the atom, or at least utilize it to it's fullest extent.

I suppose you could hypothesize that the Forerunners considered it a crude technology with many drawbacks in atmosphere, but in space nukes are pretty much awesome and have virtually no negative effects. It seems more plausible that they simply didn't grasp it rather than they deliberately ignored it, considering it's also a damn good way of killing the Flood. They seemed pretty smart though, so they probably new about fusion at least considering that's what stars are made of, but maybe they couldn't figure out how to replicate it like we did.

And something that occurred to me in Mass Effect 3: When you see the flashbacks of the Reapers invading Prothean Eden Prime, Javik's little AI buddy activates something called a "neutron purge," the implication being that it's a hugely destructive weapon that would destroy all the enemies in the area but also just about everything else except the highly fortified bunker the scene takes place in. All we see of it is the sound of muffled explosions and brief tremors. "Neutron Purge" sounds like science-fiction mumbo-jumbo, but thinking about it, I think it's just what the Protheans called nuclear weapons (at least fission ones). Neutrons are the key element in fission reactions, and given that it's mentioned that the Reapers deliberately targeted Earth's nuclear stockpile before we could use it, it seems to me they fear the destructive potential of nuclear bombs. Kinetic barriers don't do jack against heat, after all. Given that eezo basically replaced the need for most applications of nuclear technology, I think it's highly possible that the Protheans discovered how to split the atom but bypassed learning how to fuse it and utilized fission warheads for their "neutron purge."

These are just hypotheses, of course. I may have overlooked several details. Still, thoughts?

 

[Altorin]

there's a neutron purge in Noveria... so it's not a nuclear weapon (even though it is probably a "nuclear" weapon as Neutrons are in the nucleus of the atom). It is highly devastating though. It's enough to destroy the entire lower half of the laboratory that's been overrun by Rachni (it's not accessible in the game but it's described by the russian guy)

Nuclear weapons as we see them are mostly described in their use by the Krogans. Tuchanka has suffered a nuclear winter due to their use of fission bombs. On the galactic theater though, conventional nuclear weapons are actually much less devastating then the other options available. The Citadel version of the geneva conventions classify nuclear weapons as medium threats. The weapons they're more concerned with biological weapons and kinetic drops, where asteroids or large space stations are dropped onto planets. Using those weapons is deemed a warcrime. Nukes are just big bombs when compared to those.

 

[Kolby Jack]

there's a neutron purge in Noveria... so it's not a nuclear weapon (even though it is probably a "nuclear" weapon as Neutrons are in the nucleus of the atom). It is highly devastating though. It's enough to destroy the entire lower half of the laboratory that's been overrun by Rachni (it's not accessible in the game but it's described by the russian guy)

Nuclear weapons as we see them are mostly described in their use by the Krogans. Tuchanka has suffered a nuclear winter due to their use of fission bombs. On the galactic theater though, conventional nuclear weapons are actually much less devastating then the other options available. The Citadel version of the geneva conventions classify nuclear weapons as medium threats. The weapons they're more concerned with biological weapons and kinetic drops, where asteroids or large space stations are dropped onto planets. Using those weapons is deemed a warcrime. Nukes are just big bombs when compared to those.

Hmmm. Then why did they mention that the Reapers made sure to neutralize our nuclear stockpile first? As for the Noveria purge, I had forgotten about that. I'm not entirely convinced it completely disproves my theory because they still don't explain what exactly a neutron purge IS (which stands out since this series explains almost everything about its technology), but it's something to consider.

 

[TheVampwizimp_v1legacy]

I think you're generally correct about what a neutron purge is. The difference, I imagine, is that where a nuclear fission bomb splits atoms to create a runaway chain reaction resulting in an explosion, the neutron purge is actually a much more controlled fission reaction, creating more of a lethal wave of radiation than a sudden explosion.

I'm not sure about this, as they never explain it, but that's what it sounds like to me. Detonating a nuclear fission bomb under the scientific compound on Noveria would have blown the entire mountain apart, which obviously didn't happen, so the most logical thing to infer would be that the purge releases a massive burst of pure neutrons, creating a radiation field that instantly kills any lifeform caught in the way, but does not destroy physical objects like walls and rock formations.

Secondly, I believe the reason the reapers would bother to destroy our nukes is because they have methods of delivery that more conventional weapons (for the time) do not. Kinetic impactors are much more dangerous as they release more energy, but to use one you have to have a functional gun mounted on something that can aim it. To use a nuclear bomb, all you need is a detonator and some way to get it in proximity of the target. What it comes down to is, once the reapers had eliminated the top of the line defenses of earth, i.e., their space ships and antiaircraft guns, the next biggest threat to them would be someone sneaking up close with a nuke and detonating it.

 

[skywolfblue]

First in Halo: Did the Forerunners never invent nuclear technology? The Covenant don't have nukes, nor do they seem to understand them very well outside "make big boom, yea yea yea." The Forerunners don't seem to have them either. At least I've never heard of them using nuclear bombs, or even nuclear reactors for that matter. Add in the fact that nuclear explosions seem to be the most effective means of destroying both Covenant and Forerunner things (during the war, before Humanity made it's non-nuclear tech WAY more powerful) and it seems like Humanity was the only species to split the atom, or at least utilize it to it's fullest extent.

I suppose you could hypothesize that the Forerunners considered it a crude technology with many drawbacks in atmosphere, but in space nukes are pretty much awesome and have virtually no negative effects. It seems more plausible that they simply didn't grasp it rather than they deliberately ignored it, considering it's also a damn good way of killing the Flood. They seemed pretty smart though, so they probably new about fusion at least considering that's what stars are made of, but maybe they couldn't figure out how to replicate it like we did.

Isn't the plasma weaponry of the Halo universe a lot more powerful then nukes anyway? Especially when it comes to ship to ship combat.

I think in Halo:CE Cortana mentions the Covenant using antimatter, which would really put nukes to shame in any environment.

I think the Covenant and Forerunners have at least an understanding of how Fusion/Fission operates, they just don't bother with it anymore because they have better.

 

[mad825]

And something that occurred to me in Mass Effect 3: When you see the flashbacks of the Reapers invading Prothean Eden Prime, Javik's little AI buddy activates something called a "neutron purge," the implication being that it's a hugely destructive weapon that would destroy all the enemies in the area but also just about everything else except the highly fortified bunker the scene takes place in. All we see of it is the sound of muffled explosions and brief tremors. "Neutron Purge" sounds like science-fiction mumbo-jumbo, but thinking about it, I think it's just what the Protheans called nuclear weapons (at least fission ones). Neutrons are the key element in fission reactions, and given that it's mentioned that the Reapers deliberately targeted Earth's nuclear stockpile before we could use it, it seems to me they fear the destructive potential of nuclear bombs. Kinetic barriers don't do jack against heat, after all. Given that eezo basically replaced the need for most applications of nuclear technology, I think it's highly possible that the Protheans discovered how to split the atom but bypassed learning how to fuse it and utilized fission warheads for their "neutron purge."

It's "The neutron bomb" in other words and if the current generation of species could master this tech I'm sure the Protheans would've as well.

 

[Gatx]

there's a neutron purge in Noveria... so it's not a nuclear weapon (even though it is probably a "nuclear" weapon as Neutrons are in the nucleus of the atom). It is highly devastating though. It's enough to destroy the entire lower half of the laboratory that's been overrun by Rachni (it's not accessible in the game but it's described by the russian guy)

Nuclear weapons as we see them are mostly described in their use by the Krogans. Tuchanka has suffered a nuclear winter due to their use of fission bombs. On the galactic theater though, conventional nuclear weapons are actually much less devastating then the other options available. The Citadel version of the geneva conventions classify nuclear weapons as medium threats. The weapons they're more concerned with biological weapons and kinetic drops, where asteroids or large space stations are dropped onto planets. Using those weapons is deemed a warcrime. Nukes are just big bombs when compared to those.

Hmmm. Then why did they mention that the Reapers made sure to neutralize our nuclear stockpile first? As for the Noveria purge, I had forgotten about that. I'm not entirely convinced it completely disproves my theory because they still don't explain what exactly a neutron purge IS (which stands out since this series explains almost everything about its technology), but it's something to consider.

Throwing an asteroid or space station onto a planet (huge target moving in a predictable path) is a lot easier than trying to hit a Reaper (actual living, moving thing, much smaller than a planet) with it. An asteroid drop would cause a ton of devastation for a planet for sure, enough to categorize them above nukes, but nukes would be a more immediate threat to Reapers.

 

[Whateveralot]

there's a neutron purge in Noveria... so it's not a nuclear weapon (even though it is probably a "nuclear" weapon as Neutrons are in the nucleus of the atom). It is highly devastating though. It's enough to destroy the entire lower half of the laboratory that's been overrun by Rachni (it's not accessible in the game but it's described by the russian guy)

Nuclear weapons as we see them are mostly described in their use by the Krogans. Tuchanka has suffered a nuclear winter due to their use of fission bombs. On the galactic theater though, conventional nuclear weapons are actually much less devastating then the other options available. The Citadel version of the geneva conventions classify nuclear weapons as medium threats. The weapons they're more concerned with biological weapons and kinetic drops, where asteroids or large space stations are dropped onto planets. Using those weapons is deemed a warcrime. Nukes are just big bombs when compared to those.

Hmmm. Then why did they mention that the Reapers made sure to neutralize our nuclear stockpile first? As for the Noveria purge, I had forgotten about that. I'm not entirely convinced it completely disproves my theory because they still don't explain what exactly a neutron purge IS (which stands out since this series explains almost everything about its technology), but it's something to consider.

Throwing an asteroid or space station onto a planet (huge target moving in a predictable path) is a lot easier than trying to hit a Reaper (actual living, moving thing, much smaller than a planet) with it. An asteroid drop would cause a ton of devastation for a planet for sure, enough to categorize them above nukes, but nukes would be a more immediate threat to Reapers.

That would be THE renegade option though. Lure all (if not most) of the reapers into earth's atmosphere and then crash a giant asteroid into this (at FTL speed, shot off by one of the Mass Relays).

 

[OneCatch]

First in Halo: Did the Forerunners never invent nuclear technology? The Covenant don't have nukes, nor do they seem to understand them very well outside "make big boom, yea yea yea." The Forerunners don't seem to have them either. At least I've never heard of them using nuclear bombs, or even nuclear reactors for that matter. Add in the fact that nuclear explosions seem to be the most effective means of destroying both Covenant and Forerunner things (during the war, before Humanity made it's non-nuclear tech WAY more powerful) and it seems like Humanity was the only species to split the atom, or at least utilize it to it's fullest extent.

I suppose you could hypothesize that the Forerunners considered it a crude technology with many drawbacks in atmosphere, but in space nukes are pretty much awesome and have virtually no negative effects. It seems more plausible that they simply didn't grasp it rather than they deliberately ignored it, considering it's also a damn good way of killing the Flood. They seemed pretty smart though, so they probably new about fusion at least considering that's what stars are made of, but maybe they couldn't figure out how to replicate it like we did.

Isn't the plasma weaponry of the Halo universe a lot more powerful then nukes anyway? Especially when it comes to ship to ship combat.

I think in Halo:CE Cortana mentions the Covenant using antimatter, which would really put nukes to shame in any environment.

I think the Covenant and Forerunners have at least an understanding of how Fusion/Fission operates, they just don't bother with it anymore because they have better.

That was my understanding of it as well. Even the standard ship based MAC guns in Halo are about as big as average yield nukes, and the bigger orbital defence platforms are about 4 orders of magnitude above (therefore about 10,000 times as powerful) the highest yield fusion nukes [https://en.wikipedia.org/wiki/Tsar_Bomba].

We're looking at roughly stages 2-4.5 on this page [http://what-if.xkcd.com/20/] for the MACs.

And the Covenant and Forerunners are even further beyond that. Hell, IIRC Covenant hand-held plasma weapons use fusion to generate the plasma.
And their ships manage to glass entire planets without too much difficulty, which puts their energy generation a few magnitudes higher again (probably the energy of stage 5 on the link, but spread out better)

And yeah, the Covenant bomb early in Halo 2 uses antimatter (and makes a surprisingly small bang [http://www.youtube.com/watch?v=SmsqEtq3sp8], even if you handwave by saying that most of the mass [http://www.edwardmuller.com/right17.htm?Weight=Kilograms&Amount=25] of the bomb was containment not actual antimatter).

All this aside, any society that could develop planetary megastructures would pretty much have to be way beyond mere fission for any kind of technological consistency. To say otherwise would be like suggesting that the Romans developed the internet without needing any of the transient development, and without ever developing an understanding of, i dunno, molecular chemistry.

EDIT; correcting derped figures

 

[Da Orky Man]

Snippity snip!

I didn't play a great deal of Halo, so I'm not sure about that/ However, as for the neutron purge...

Neutrons are extremely damaging to organic matter. Not only are they highly ionisng, but they also penetrate sufficienty into the body to cause real damage. Not onl that, but neutrons even make whatever they hit radioactive due to neutron absorption and later emitting. So yeah, a sufficient amount of neutron radiation would kill nay living thing.

Now then, we currently do posses neutron bombs which are essentially a kind of low-yield nuke which relies on a high neutron count to do damage. Thhey were made in order to effectively kill tanks/warships, as they are surprisingly resilient to normal nukes, and to be able to wipe out the population of a city without destroying it, allowing for capture and usage later.

So yeah, I'm betting that the neutron purge was a set of rather advanced neutron warheads spread around the chamber.

 

[TheCommanders]

Secondly, I believe the reason the reapers would bother to destroy our nukes is because they have methods of delivery that more conventional weapons (for the time) do not. Kinetic impactors are much more dangerous as they release more energy, but to use one you have to have a functional gun mounted on something that can aim it. To use a nuclear bomb, all you need is a detonator and some way to get it in proximity of the target. What it comes down to is, once the reapers had eliminated the top of the line defenses of earth, i.e., their space ships and antiaircraft guns, the next biggest threat to them would be someone sneaking up close with a nuke and detonating it.

Interestingly, part of the "Miracle at Palaven" codex entry shows combined turian and krogan forces doing exactly that, so I think you might be on to something. I had always thought that a pretty tried and true strategy when it came to enemy forces that were larger (speaking of physical size), but fewer in number the best tactic wouldn't be to engage them directly, and clearly it worked (for a while).

Spoiler: spoilered for length

The turian and krogan counterattack on Palaven combined deception, courage, and tenacity. First, the turians leaked a false battle plan that drew on the same tactics they used at beginning of the assault on Palaven. Then the dreadnought Indomitable faked a problem with its drive core, coming out of FTL near Palaven's moon, Menae. Three other dreadnoughts and their attendant fleets deployed to assist Indomitable, a tempting target that drew the Reaper capital ships away from Palaven. Turian troop transports then entered Palaven's atmosphere to release shuttles, gliders, and individual soldier capsules.
The Reapers did not understand the seriousness of the threat at first--those that detected the landing crafts sent husks and Collector swarms to intercept them, but little more. This allowed krogan commandos to link up with Palaven's resistance and hand off their payloads--warp bombs and fission weapons.

In simultaneous strikes across the globe, Reaper ships began to explode. Turian resistance members had managed to smuggle the bombs inside when the Reaper processing ships, troop transports, and even destroyers and capital ships had opened their structures to indoctrinated turian leaders.

Large swaths of territory fell back into turian and krogan control. News of the victory gave a much-needed boost to the morale of the turian resistance and the galactic public.

But the action was not without sacrifice. Turian insurgents gave their lives to ensure the explosives detonated, and the processing centers they destroyed were full of civilians who died just as surely as if they had been harvested. Of the dead, General Minin Resvirix said, "Whatever they were in life, their deaths had no equal. They are worthy of joining the spirit of Palaven itself."

 

[TheVampwizimp_v1legacy]

Secondly, I believe the reason the reapers would bother to destroy our nukes is because they have methods of delivery that more conventional weapons (for the time) do not. Kinetic impactors are much more dangerous as they release more energy, but to use one you have to have a functional gun mounted on something that can aim it. To use a nuclear bomb, all you need is a detonator and some way to get it in proximity of the target. What it comes down to is, once the reapers had eliminated the top of the line defenses of earth, i.e., their space ships and antiaircraft guns, the next biggest threat to them would be someone sneaking up close with a nuke and detonating it.

Interestingly, part of the "Miracle at Palaven" codex entry shows combined turian and krogan forces doing exactly that, so I think you might be on to something. I had always thought that a pretty tried and true strategy when it came to enemy forces that were larger (speaking of physical size), but fewer in number the best tactic wouldn't be to engage them directly, and clearly it worked (for a while).

Spoiler: spoilered for length

The turian and krogan counterattack on Palaven combined deception, courage, and tenacity. First, the turians leaked a false battle plan that drew on the same tactics they used at beginning of the assault on Palaven. Then the dreadnought Indomitable faked a problem with its drive core, coming out of FTL near Palaven's moon, Menae. Three other dreadnoughts and their attendant fleets deployed to assist Indomitable, a tempting target that drew the Reaper capital ships away from Palaven. Turian troop transports then entered Palaven's atmosphere to release shuttles, gliders, and individual soldier capsules.
The Reapers did not understand the seriousness of the threat at first--those that detected the landing crafts sent husks and Collector swarms to intercept them, but little more. This allowed krogan commandos to link up with Palaven's resistance and hand off their payloads--warp bombs and fission weapons.

In simultaneous strikes across the globe, Reaper ships began to explode. Turian resistance members had managed to smuggle the bombs inside when the Reaper processing ships, troop transports, and even destroyers and capital ships had opened their structures to indoctrinated turian leaders.

Large swaths of territory fell back into turian and krogan control. News of the victory gave a much-needed boost to the morale of the turian resistance and the galactic public.

But the action was not without sacrifice. Turian insurgents gave their lives to ensure the explosives detonated, and the processing centers they destroyed were full of civilians who died just as surely as if they had been harvested. Of the dead, General Minin Resvirix said, "Whatever they were in life, their deaths had no equal. They are worthy of joining the spirit of Palaven itself."

That's exactly the codex entry that led me to this train of thought.

 

[oreso]

Some great stuff here.

I would only add that I don't think nukes are that awesome in space. Without the atmosphere, it's just a flash of radiation, which dissipates quickly over distance, and spreads its damage over the entire surface of the craft. Compare to kinetic weapons, which maintain their energy at any distance, focuses all of its energy at a single point and can still be devastating at relativistic speeds.

There have been other ideas though. David Weber's Honorverse has 'bomb-pumped lasers' as the payload of its missiles. As the missile explodes, the energy is channelled into an x-ray laser. It still explodes, but a significant portion of the energy is directed in a single direction, and this energy doesn't dissipate nearly as much.

 

[Dirty Hipsters]

And their ships manage to glass entire planets without too much difficulty, which puts their energy generation a few magnitudes higher again (probably the energy of stage 5 on the link, but spread out better)

That's actually not true. In Halo Reach you learn that the Covenant never had the capability to glass an entire planet from the 10th data log that you collect:

[Minutes, working session, Committee of Minds for Security]

[^] Directly preceding their assault on the colony world of Biko, the Covenant transmitted a message to its surface. Within this message was a bold claim: 'your world will burn until its surface is but glass' - a claim that clearly indicates the Covenant leadership believes they possess the power to literally reduce a planet?s surface to a molten state. [^]

[^] Assuming they have the wherewithal to back-up such a claim, the dangers to our creators are obvious.

The implications for their own internal politics are also instructive e.g., what effect might the Covenant leadership's assertion have on any client species in their coalition? We aren't the only beings that would be terrified by the idea of absolute destruction of a planet's surface - nor would we be the only ones to realize the futility of attempting to resist a force that has such power at its disposal. [^]

[^] Moving forward, this Committee recommends the formal adoption of the descriptor 'glassing' to portray the aftermath of planetary assault by the Covenant. It is the opinion of this Committee that this term will capitalize on the three weaknesses evident in the majority of our creators: passive curiosity, absence of a solid methodological foundation, and the inability to grasp even simple phenomena when applied on a planetary scale. [^]

[^] In short: 'glassing' will magnify the horror of the Covenant?s capabilities. And as such, this Committee believes targeted dissemination of this terminology will help galvanize our creators in their current struggle. [^]

[^] Importantly, the Covenant does not possess the capacity to accomplish 'glassing' on a global scale and wage a multisystem war simultaneously. This is reinforced by hard data regarding their capabilities revealed during fleet engagements with the UNSC. A single Covenant capital ship (CCS-class) is capable of 'glassing' approximately one acre of a planet's surface after an average of fifteen seconds of sustained fire. Understandably this action takes considerably less time when applied to open desert, and considerably longer when applied to deep ocean (> 1.8 km) [^]

[^] Earth, one of the smaller planets inhabited by our creators, has one hundred and thirty billion acres of surface area. Thus, assuming the Covenant possesses a number of ships equal to that of the UNSC, and assuming that all of those ships are capable of generating and discharging the required power non-stop for the duration of the process, it would necessitate the combined efforts of their ships in toto for a minimum of 30.3801 years to 'glass' the entire surface of Earth. Myriad other variables which were not applied to this equation suggest this number would be far greater. [^]

[^] Of course, dissemination of this analysis to our creators would undermine the utility of 'glassing' as a galvanizing concept, and should be suppressed. [^]

According to that data log, the covenant saying that they could "glass" a planet was simply an attempt at scaring humans into surrendering to them, and that it would in fact take an entire covenant fleet over 30 years to glass a planet like Earth.

http://halo.wikia.com/wiki/Data_pads

 

[Souplex]

A "Neutron purge" is probably most similar to a neutron bomb which is almost entirely radiation, rather than explosive force.
http://en.wikipedia.org/wiki/Neutron_bomb

 

[Kolby Jack]

Haven't played either of those games, but here's some Science we can fan-wank.

Atomic-powered technology relies upon heavy elements. If you look at stellar nucleosynthesis, you'll see that solar fusion stops with iron. So where to the heavier elements (like Uranium) come from? Well... supernovae, primarily.

So, in order to have atomic tech, you need to evolve and develop in a region of space that had sufficient supernovae in the past yet still retained the ability to develop life-sustaining planetary systems. It could be that humanity has the nuke simply due to growing up in the right neighborhood.

"But, Minion? What about fusion bombs?" Good question. But if you look at our current hydrogen bomb technology, you'll find that we use atomic bombs as a triggering device to start hydrogen-isotope fusion. Again, the tech (as we know it) relies upon ready access to sufficient trans-ferrous elements.

So far as the effectiveness of nukes in space, well... they're not as great as sci-fi would lead us to believe. Most of an nuke's effect comes from the shock wave. In space, there simply isn't any medium for the shock wave to propagate. And given the already high EMR flux outside of a planetary magnetosphere, the radiation effect of a nuke really isn't effective against the shielding you have to have in deep space anyway.

So, you're talking about direct hits or very near misses to make nukes worthwhile. But nukes, being made of matter, travel at a relatively (ba dum chh) slow speeds and can be easily intercepted and destroyed by directed energy weaponry.

TL;DR: Humans are lucky to have uranium, but nukes aren't much use in space anyway.

Well said, but I think you're wrong about the effectiveness of nukes in space. Keep in mind, nukes are not conventional explosives, which are caused by chemical reactions. In atmosphere, they have similar, if dramatically greater, effects to chemical explosives, but where chemical explosives rely on unstable bonds rapidly breaking down, nuclear energy comes from the direct conversion of matter TO energy. It may not sound like a difference maker, but in actuality this means that while atmosphere greatly increases the kinetic effects of a nuclear explosion, it greatly REDUCES the radiation effects. A nuclear reaction is pure energy; atmosphere does nothing but contain it. So in space, a nuclear explosion would not cause shockwaves, but the amount of energy generated would still be equivalent to that of a small star and would still be spread over a huge area rapidly, and almost NONE of it would be "spent" as heat until it made contact with something. Using a nuke in space would essentially microwave any ships even remotely "near" (which in space is pretty far) to it, only instead of sparks and a little melting, you get absolute destruction because it's exponentially more energy than a simple microwave.

The science isn't completely concrete on this, mind you, as shooting nukes into space is frowned upon and getting a nuke far enough away from Earth to really test it is pretty hard to do. But yea, contrary to how it may seem, atmosphere disperses energy so it doesn't go nearly as far. Space... doesn't.

 

[RJ 17]

First in Halo: Did the Forerunners never invent nuclear technology? The Covenant don't have nukes, nor do they seem to understand them very well outside "make big boom, yea yea yea." The Forerunners don't seem to have them either. At least I've never heard of them using nuclear bombs, or even nuclear reactors for that matter. Add in the fact that nuclear explosions seem to be the most effective means of destroying both Covenant and Forerunner things (during the war, before Humanity made it's non-nuclear tech WAY more powerful) and it seems like Humanity was the only species to split the atom, or at least utilize it to it's fullest extent.

I suppose you could hypothesize that the Forerunners considered it a crude technology with many drawbacks in atmosphere, but in space nukes are pretty much awesome and have virtually no negative effects. It seems more plausible that they simply didn't grasp it rather than they deliberately ignored it, considering it's also a damn good way of killing the Flood. They seemed pretty smart though, so they probably new about fusion at least considering that's what stars are made of, but maybe they couldn't figure out how to replicate it like we did.

And something that occurred to me in Mass Effect 3: When you see the flashbacks of the Reapers invading Prothean Eden Prime, Javik's little AI buddy activates something called a "neutron purge," the implication being that it's a hugely destructive weapon that would destroy all the enemies in the area but also just about everything else except the highly fortified bunker the scene takes place in. All we see of it is the sound of muffled explosions and brief tremors. "Neutron Purge" sounds like science-fiction mumbo-jumbo, but thinking about it, I think it's just what the Protheans called nuclear weapons (at least fission ones). Neutrons are the key element in fission reactions, and given that it's mentioned that the Reapers deliberately targeted Earth's nuclear stockpile before we could use it, it seems to me they fear the destructive potential of nuclear bombs. Kinetic barriers don't do jack against heat, after all. Given that eezo basically replaced the need for most applications of nuclear technology, I think it's highly possible that the Protheans discovered how to split the atom but bypassed learning how to fuse it and utilized fission warheads for their "neutron purge."

These are just hypotheses, of course. I may have overlooked several details. Still, thoughts?

Well that's certainly an...interesting take on those two scenarios.

As for Halo: it's been implied in a lot of sci-fi stories that nuclear technology is pretty primitive compared to other forms of harvesting energy. It's very likely that they've developed high tech "magic space-science" that's far more advanced and efficient than nuclear reactors. Given how highly advanced the Covvies and Forerunners are compared to Humanity, it's very likely their means of energy production is far more advanced. The Forerunners built giant space station ring-worlds that have the power of releasing an energy pulse capable of wiping out all organic life in the entire galaxy...a nuclear bomb to them would be like a blackcat firecracker. As for the Covvies, they have a reputation for "glassing" entire worlds, so clearly they have their own form of (likely plasma-based) WMD's that burn so hot and are so powerful they convert a planet's surface to glass.

As for ME: sure, why the hell not? It's stated that all the cycles are essentially the same, just slightly different variations in evolution. To say the Protheans had access to nukes really isn't that far of a stretch. Hell, the Krogan nuked their planet into a radioactive hell-hole. On Virmire in ME1, you set up ship's power core to cause a nuclear explosion to destroy Saren's base. On Jack's loyalty mission in ME2, the bomb you use certainly seems to have a massive nuclear explosion. So yeah, nukes are very prevalent in the ME universe, they're just highly frowned upon by Council authorities.