If you're like most people, you know virtually nothing about antimatter. Perhaps you've heard it name-dropped in science fiction movies or TV shows like Star Trek, but unless you really paid attention in science class you're probably not aware that (a)it exists, (b)it is already in practical use, and (c)its details are rather startling in context. It is the most expensive substance known, and when placed in contact with matter releases a hundred times more energy per unit mass than stellar thermonuclear fusion.
Please feel free to quibble with or correct any of the numbers I provide here if they're wildly off-base, but do understand this is intended to provide a perspective, not a working knowledge.
I. What is antimatter?
The simplest explanation is that antimatter is matter whose component particles have opposite electrical charge to their counterparts in normal matter: Electrons (e-) and positrons (e+) are both low-mass, fast-moving particles that zip around high-mass, lumbering nuclei of opposite charge when combined in atoms with protons and antiprotons, respectively.
When a particle of matter collides with its antimatter counterpart, the mass of the two particles is almost totally converted into energy (along with some exotic particles, such as neutrinos) - a fact that greatly distinguishes this relationship from nuclear fusion, where only a fraction of the mass is converted into energy (because most of the matter is still there).
One of the great mysteries of cosmology is baryogenesis - the process by which there came to be an imbalance (or "asymmetry") between matter and antimatter in the early universe, resulting in the overwhelming abundance of the former relative to the latter - a necessary condition for the existence of the universe as we know it. There is no known specific reason why this should be the case, although theoretical models that attempt to provide a basis using abstruse quantum mechanical models have proliferated.
It may be totally random, or an example of the Anthropic Principle - i.e., these conditions are the only ones in which we could observe them, ergo our observing them is tautologically emergent. Such an explanation would depend on a Multiverse model, and is not yet testable, but will do until more substantive explanations are forthcoming.
II. Perspective
Approximate cost: $62.5 trillion per gram of antihydrogen
Potential energy: 90 quadrillion J/kg --> 25 Terawatt-hours per kg.
To put perspective on these facts, the former means that the entire yearly economic output of the world - $70 trillion (2008) - would create (in a simplistic case, ignoring economies of scale) only slightly more than a gram of antimatter at current costs. But if those costs were progressively brought down over time, the second fact becomes more and more interesting: The mass in antihydrogen of a single, average tank of gasoline could power about 1% of the world. In other words, the parking lot outside Best Buy on a given day would power the entire planet.
Granted, the cost would have to come down an almost unimaginable degree before that would happen...but then everything is unimaginable until it isn't. Specifically, the retail economic value of the electrical energy that could be produced by 1 gram of antimatter (matter-energy conversion is virtually total in particle-antiparticle annihilation, and we can ignore engine efficiency for simplicity) would be about $2 million (DOE retail electricity price table).
But as it inherently takes more energy to create than it releases, the value of antimatter is mainly as a storage medium. About 7 orders of magnitude (x 10 million) in cost reduction would be needed before the production cost entered the magnitude of the retail electricity value, which isn't likely to ever happen, but the case isn't nearly as stark for applications where value is determined by energy-density: E.g., storage or diagnostics.
It is these domains where antimatter has already been applied or will be applied in the future - e.g., in medical scanning technologies (Positron Emission Tomography or PET scan), where compact, highly energetic particles are valuable for their ability to carry significant amounts of energy into the body.
There are also theoretical applications, such as spacecraft propulsion, that hold great promise if the cost of production and safety/efficiency of storage evolve further.
III. Challenges
- Production.
This is obviously the biggest obstacle at the moment. In order to obtain antimatter, there are only two things you can do: Create passive traps and wait a hell of a long time for cosmic rays to penetrate the atmosphere and create some for you, or use a huge amount of energy to collide normal matter particles and create some yourself. The apparatus for either is huge, expensive, and energy-intensive, and results in only miniscule amounts of antimatter over long time periods.
- Storage.
You can't store antimatter like you store matter: If you put it in a container made of normal matter, it would just annihilate and you would (a)lose it, and (b)die in a spectacular fireball if you were working with more than microscopic quantities. The only way to store antimatter is therefore by using energy fields: E.g., positrons, being positively charged, can be contained by having a positively-charged environment that repels them from touching the normal-matter container walls.
This is a simplified statement of what is actually done to contain antimatter - actual containment involves elaborate traps that balance various forces and phenomena, and can be applied also to contain neutral antihydrogen.
Still, it isn't a 100% effective solution - antiparticles still slip through the traps and annihilate at a predictable rate, so you lose your precious antimatter over time if you don't use it quickly.
- Safe use.
Once you can produce and store it efficiently, there is still the problem of using it safely - matter/antimatter annihilation releases extraordinarily high-energy radiant flux, such as γ (gamma) and X rays, and at even higher energies and rates than a fusion reactor would. These rays and the massed particles they energize shred DNA and delicate subcellular structures like bullets through tissue paper, so it's critical to develop shielding technology.
Secondly, one of the most celebrated potential applications is spacecraft propulsion, which brings its own challenges: How do you shield the functional or habitat parts of the spacecraft from the drive section, and what do you do if something penetrates the antimatter containment? Mass and volume are more constrained on a spacecraft, so solutions would need to take that facts into consideration.
IV. Conjectured Solutions
- Production
There is a lot of shared potential between fusion power research and antimatter production - particularly using arrays of relatively cheap lasers (in the million-dollar range each), as opposed to vast magnetic fields, to accelerate and collide particles. Lasers are becoming progressively cheaper, simpler, and more powerful with time, so even if fusion power never proves economically efficient, the research going into it through approaches like inertia confinement fusion may benefit antimatter production technology.
Much further in the future, space-based production plants are envisioned in close solar orbits, making use of the high-energy environment to store great amounts of solar energy in the most potent of all possible material forms and then ship them outward. It is also conceivable to have lenses or mirrors in close solar orbit concentrate the energy, direct it outward, and then have production plants in more distant orbits create the actual antimatter.
- Storage
A number of theoretical possibilities exist for cheap, safe, efficient storage of antimatter. Fortunately, the same advancements in laser technology that may improve production also hold promise for storage: Coherent directed energy can accelerate particles, but it can also hold them in place. Traditional magnetic containment fields could also become substantially cheaper if fusion power is proven effective, since the energy to power them may become much more abundant and economical. These solutions are still quite a ways away, however.
Then there is the geek-favorite question of storage on a spacecraft. Fortunately, being in space creates a lot of options that would be impractical or insane on a planet: Specifically, you have the option of just throwing the antimatter overboard.
It is at least conceivable that a storage system could be engineered to provide passive guarantee of ejection into space if containment were breached - you design the vessel to direct any sudden overabundance of energy into vectors that rip out the fuel section and carry it away from the habitat, with the exhaust directed at angles to the habitat (much like rocket nozzels on a Launch Escape System).
- Safe use.
The basic problem of normal use (once you've managed to at least contain the material safely) is shielding, so the solution will either be massive and dumb - e.g., thick layers of heavy metal - or energetic and complex, such as dynamically-generated shields that direct dangerous exhaust energy away from people and electronics.
V. Potential Benefits
- Microscopic batteries capable of powering human-scale machinery.
- Cell-sized batteries capable of powering artificial organs and prostheses.
- Constant-acceleration manned space travel at one-g through the whole trip (just flip the ship around halfway through and decelerate at the same rate), eliminating the muscle-wasting problem. Makes fractional-c speeds possible with potentially less massive hardware than needed for a fusion reactor.
- Arbitrary-g constant acceleration space travel for unmanned ships, radically reducing robotic transit times to other solar system bodies and allowing for practical supply of colonies.
- Allows for abundant power out to arbitrary distances from the Sun, although RTGs (Radioisotope Thermoelectric Generators) might still be preferable for some or most applications.
VI. Dangers
- Bombs.
The military applications of cheap, practical antimatter are obvious: It's 10 billion times more potent than the most powerful chemical explosive, 10,000 times more potent than a fission nuclear weapon, and hundreds of times more potent than a hydrogen bomb: So potent that, provided the containment technology were sufficiently miniaturized, a bomb sufficient to take out a building could be directed to its target with a remote-controlled insect (a technology already achieved in the laboratory).
- Energy Weapons.
One of the greatest challenges in building directed-energy weapons (AKA, "death rays") is powering them. Progress in laser and microwave technology has given the military and authoritarian police forces lasers that can burn small holes in things, and "pain rays" that can give protesters skin burns, but they still don't have anywhere near the power to destroy things that far simpler projectile weapons provides.
That would change with antimatter: The energy release is such that the scene in Independence Day with skyscrapers being vaporized from above becomes conceivable, and it wouldn't take a ship the size of a mountain to make it happen. Such a weapon wouldn't even necessarily have to be pulsed, but might be swept over a population like a giant magnifying glass over an ant colony - something even more disturbing if you imagine such weaponry ultimately being deployed in satellites. Directed-energy handguns become feasible. But that is at least a century away, so I'm not exactly worried so much as counseling thoughtfulness.
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All in all, antimatter doesn't much attention, but its promise and its peril are both quite extraordinary.
Resources:
Wikipedia
CalculateMe
*Note: I used an online unit-conversion calculator for my numbers, so if anything is wildly off, place the blame squarely where it belongs: Laziness rather than stupidity.