While canvasing LJ for FMA fanfic during the past week or so, I came across granate's fantastic 2005 meta post on flame alchemy. It got me all thinky.
On the third day, I began to wonder whether Roy can make a thermonuclear explosion. He manipulates the hydrogen in water to form diatomic hydrogen gas in Chapter 38, and all alchemists seem to know the chemical and physical composition of whatever it is they're trying to transmute. I thought he might be able to isolate 2H and 3H isotopes—deuterium (D) and tritium (T), respectively—smush the two together into the highly unstable 5He isotope, then let nature take its course with a bang.
Alchemy neatly circumvents the troublesome real-world temperature and pressure requirements; after all, alchemists generally have no problem meeting the energy needs of the chemical reactions they routinely perform. At the same time, because Roy would only be using alchemy to form 5He, which would decay with no alchemical effort on his part, he'd avoid the apparent dissipation of energy produced by transmutations in such a way that it effectively does nothing. Isotopes occur naturally and, IIRC, deuterium is relatively abundant in the ocean (water?). Besides, I don't believe the H-bomb contains that much hydrogen, and it's a slayer of cities. Nuclear fusion is probably more energetic per unit of mass than any other reaction except direct mass to energy conversions; in other words, it shouldn't take much hydrogen to get a big boom. In addition to mass destructive potential, I figure a single D-T reaction would create more than enough energy for Roy to use in sparking his usual fire tricks.
So, why doesn't the Flame Alchemist do D-T reactions? My first thought was that it would require a different array. It's never really been clear to me what Roy can manipulate with his array and to what extent. Obviously, he has some ability to control hydrogen. Enough to fuse hydrogen into helium? I dunno. There's also the speed of the transmutation to consider, IMO. Maybe nuclear fusion is too intricate and too slow to be of practical use. At least by way of alchemy; it's fast enough in the real world.
The more I thought about it, though, the more I felt the problem's greater than the limitations of one array or one transmutation. It seems to me that, of the four major branches of science, physics is the one alchemists know least about. Alchemy clearly has roots in chemistry and biology. Even geology has made an appearance—details about Mei's geomancy, plate tectonics and the planetary dynamo serving as both energy source and, I suspect, ground for transmutations in Chapter 67. Where's the physics, I ask!
Not that I expect Ed to pull M-theory out of thin air but, with alchemists being so well-versed in chemistry, I wonder that nobody seems to know anything about the structure of the atom. I mean, how does a scientific community get far enough along to work out complex chemical reactions without even touching on the mechanisms behind these processes? Not to mention the first stage of alchemy is to understand the structure and properties of whatever's being transmuted. Is alchemical analysis simply not fine enough to pick up on the presence of subatomic particles? That seems reasonable. Yet I find it hard to believe alchemists haven't discovered isotopes. While the isotopes of any given element usually exhibit the same chemical and electrical properties, IIRC, the differences in mass do affect reaction speed. As alchemists have to will reactions to happen, I'd expect them to note such discrepancies. What's more, why haven't alchemists noticed that some elements are radioactive? Carbon-14, for example. Radioactivity was first observed in the real world way back in the 1890's.
This dearth of physics is more puzzling, IMO, in the anime than the manga. The parallel world on the other side of the Gate is well on its way to nuclear weapons while alchemists don't seem to have the slightest inkling that atomic power is possible. In the real world, these sciences are all inextricably linked. Advances in chemistry, in particular, drive advances in atomic and particle physics, and vice versa.
Really, I'm at a loss to understand how, in FMA, one field could've developed so quickly while the other is basically nonexistent. Especially as alchemists, by slapping a hand and (optional) array down on, say, a table, can instantly sift through the chemical and physical makeup of said table. This ability should be invaluable in tracking what happens during reactions and, thus, revealing the atomic and molecular properties that ultimately rule those. From what I can tell, alchemists have an excellent grasp of the molecular level but no idea the atomic level even exists. Do all these obsessively curious people not wonder at all about why elements and molecules behave the way they do? What about the key to most chemistry and electricity—the electron? If alchemists know of electrons, there's absolutely no excuse for not shortly discovering protons. Basic electromagnetism should make it obvious that no two electrons can stay together in so small a space as an atom without something of opposite charge attracting them. The strong nuclear force follows. Why has nobody in FMA, apparently, thought of all this?! I am so confused!
Anybody care to write a long, plotty, AU-ish fic about this? Ed and Al incorporate atomic and particle physics into alchemy! For their first field test, they shanghai Roy into doing a hydrogen-to-helium fusion! After all, hydrogen is the simplest atom! It's all well and good until you blow up the parade ground with Amestris's first thermonuclear explosion! Various parties are exceedingly interested!
hieronymousb, rainbow_cnxn, and I have collectively extended the topic to general speculation about alchemy in FMA. As all three of us have been routinely pushing the LJ comment word limit, I thought it'd be helpful to summarize the discussion thus far. Wild theorizing ahoy! Also, spoilers for the entire anime and manga.
First, rainbow_cnxn's bloody brilliant conception of the alchemist as a human catalyst that wills transmutations to happen at a decent rate and scale. Most of the energy for alchemy is drawn from a nigh-inexhaustible source, which differs from manga to anime and in the various alchemical traditions. The alchemist pays a toll in energy—similar to the activation energy of a chemical reaction in the real world—to harness this power. There are two types of energy available to every alchemist for catalyst purposes—physical and soul. Physical energy is the chemical energy stored naturally by the body; it is renewable, using it leaves the alchemist tired as after normal physical or mental exertion, and it's sufficient to catalyze most transmutations. Soul energy is likely more powerful but using it shortens the alchemist's life.
Because the alchemist is not a perfect catalyst, his personal energy, whether physical or soul, is consumed by the transmutation. The more efficient the alchemist's use of his personal energy, the less it'll cost to perform transmutations. This, in turn, translates into alchemical talent or skill as larger, more complex transmutations are possible per amount of the alchemist's personal energy consumed.
Whereas a real chemist need not add energy for every partial reaction in a reaction chain once the initial activation energy has been supplied, the alchemist may have to sacrifice his energy to catalyze every step as the transmutation would never happen naturally.
The Philosopher's Stone (PS) is essentially concentrated soul energy. It can be used to catalyze transmutations far beyond what the human body can withstand. Finally, human transmutation may be alchemy that requires soul energy as a catalyst, and the greater the attempted feat, the heavier the cost. That is, minor healing alchemy shaves perhaps negligible time off your lifespan, but bringing somebody back from the brink of death might well kill you.
Defined as what happens when an alchemist has enough energy to start a transmutation but not to sustain it. Cornello, after his imperfect PS ran down on energy, is the only example of a rebound not related to human transmutation. His attempted transmutation halted abruptly, and there was a release of wild energy that fused the weapon he was trying to create with his arm. However, Cornello didn't lose any body parts, which is characteristic of failed human transmutation.
This implies that human transmutation may be a special case, and the rebounds suffered while attempting it are not the same as those of other alchemy. Specifically, human transmutation is a powerful multistage reaction, some of which (building organic compounds, shaping the form of the human body) is possible and some of which is the alchemical equivalent of dividing by zero (recreating the minds and souls of the long dead). Even the most talented alchemists might only be capable of limited success in the physical stages before hitting the impossible spiritual stages. The unbalanced transmutation then lashes out for the nearest and quickest source of potential energy—the alchemist—and the Gate (anime) or the Doors of Truth (manga) gets involved. The tendency of alchemists to lose body parts is perhaps the Gate or the Doors of Truth taking the energy toll for the transmutation by direct mass to energy conversion. Such reactions are unparalleled in the amount of energy released but, in the real world, require the gravity of a black hole, the temperatures of the big bang, and other extreme conditions.
Lastly, note that even normal rebounds and the possibility of exhausting your physical strength to the point of death would tend to lethally discourage anyone without a talent for alchemy from pursuing it. The main characters rarely show the effort of doing transmutations despite some being fairly large and intricate because they're just that good.
In addition to all the normal chemical properties, the elements in FMA are accessible as alchemical groups. For instance, hydrogen and oxygen are associated with air, fire, and water, the metals with earth, maybe fire and water, etc. These links allow alchemists to do chemistry using the symbolic representation of alchemy that is the array. While most alchemists need to work through this system in order to manipulate the elements, Ed, Al, and Izumi (the clap-and-slap school of alchemy) might be shortcutting directly to the chemistry.
The best arrays are more flexible than one would assume. Kimbley is the prime example of this. He uses a number of elements, and there seems to be no limits on what he can blow up. Ed analyzes Kimbley's array in Chapter 74. Armstrong also displays flexibility in working with a variety of solids, mostly stone and metal, though his forte may be physical transformations. Roy's array is surprisingly dense, and there's a detailed review somewhere... Anyone have the link?
In the Anime
The last time I watched the anime was two years ago, so my knowledge of it is a little sketchy. Actually, I implore everyone to read mikkeneko's 2005 meta post on the anime homunculi, the Gate, and alchemy: Homunculus 101. My discussion with hieronymousb about how Earth, the world of FMA (Amestris, for brevity), and the Gate are related drew the following conclusions:
There's simply not enough information. However, the two most obvious explanations for the uncanny similarities between Earth and Amestris are that the two were once one world but split or the two are separate worlds that will merge.
Divergent Evolution: The Gate has served as the link between Earth and Amestris since whatever cataclysmic event, perhaps a massive transmutation gone awry, split the two worlds asunder. Alchemy may once have been possible on Earth but, post-split, Amestris has been leeching alchemical (soul) energy from Earth, thus preventing Earth alchemy from ever getting off the ground. A significant decline of alchemy in Amestris may lead to an increase in occult phenomena on Earth.
Convergent Evolution: The Gate is connected to all realities. Because Earth and Amestris are so similar, the link between the two worlds is stronger and maybe more permeable than most. Alchemy was never possible on Earth and may have existed in a different form in Amestris prior to the two worlds becoming close enough for energy transfers. Earth and Amestris might one day merge completely.
The possibilities and variations are practically infinite. I especially like hieronymousb's idea that Earth and Amestris are in a sort of oscillating cycle of attraction and repulsion.
In the Manga
Alchemy comes in two flavors in the manga: renkinjutsu (RKJ), used in Amestris, and rentanjutsu (RTJ), used in Xing.
Renkinjutsu: From Marco and Mei's conversation in Chapter 67, the implication seems to be that Amestrian alchemy was founded by Father and, though alchemists believe they're tapping the enormous energy of plate tectonics, they're in fact skimming energy from either the huge incomplete PS Father and the homunculi have made of the country or Father himself. This explains why Father was able to block all RKJ when Ed et al. confronted him in Chapter 54.
Rentanjutsu: RTJ was quite possibly founded by Hohenheim and draws on the pseudo-chi found in nature. This could be interpreted as the energy of natural forces—gravity, plate tectonics, electromagnetism, and the like. Mei had no trouble using RTJ in Chapter 55.
Scar's Right Arm: The destruction half of a creation-destruction pair of arrays designed by Scar's brother, who is said to have studied, then integrated, RKJ and RTJ. As Scar had no trouble doing transmutations in Chapter 55, like Mei, this hybrid is either drawing on the same power source as RTJ or something else entirely. Assuming this is the influence of Xingese alchemy avoids introducing yet another alchemical energy. Identifying the contribution of RKJ is a bit more difficult because, besides the energy sources and Mei's long-range style, there doesn't seem to be any differences between the two alchemical traditions.