It is very unlikely that a future terrestrial civilization will pepper the Earth’s surface with LHC-sized accelerators. Almost certainly, antimatter factories will be created in interplanetary space rather than on the Earth.
Although humanity has some significant space accomplishments—lunar landings, Mars rovers, a semi-permanent international space station, extra-solar probes—we are a very long way from having an in-space technological infrastructure capable of tapping cosmic energy sources and converting the energy obtained to quantities of antimatter sufficient for interstellar flight.
The possible development of such an off-planet industrial base might follow the model of the Russian astrophysicist Nikolai Kardashev. Kardashev was interested in the aspects of an extraterrestrial civilization that we might detect over interstellar distances. He hypothesized that ET’s cosmic signature would likely depend on his energy level.
Humanity is now probably about 0.7 on the Kardashev scale. When and if our civilization can utilize all the solar energy striking our planet, then we will have advanced to the point where we will be a Kardashev Type I civilization.
If our economies continue to develop at the current pace, in a few thousand years we might evolve into a Kardashev Type II civilization. At that point, we will control the resources of the solar system and be able to tap the Sun’s entire radiant output.
A Type II civilization would have sufficient energy at its disposal to launch starships on a regular basis to a wide variety of galactic destinations. Over a time scale of millions of years, it could entirely occupy its galaxy and be able to tap the energy output of all stars in its home galaxy. Then it will be a Kardashev Type III civilization.
With such enormous energy reserves, intergalactic travel would ultimately develop. If this civilization continues and expands long enough, it could become the ultimate Type IV civilization that occupies the entire universe and can tap all of its energy.
Clearly, a Kardashev Type IV civilization does not (yet) exist in our universe. If it did, we would be, by definition, part of it. If a Kardashev Type III civilization existed in the Milky Way, we would be part of it as well (unless ET was constrained by some moral code such as Star Trek’s Prime Directive from influencing the development of primitive humanity). So the most energetic extraterrestrial civilizations we can hope to detect are expanding Type IIs.
If humanity evolves into a solar-system wide civilization, it could approach the capabilities of a Kardashev Type II civilization. We might be able to accomplish planetary engineering feats throughout the solar system, such as the terraforming of Mars.
But Mars is not the best location for a huge antimatter factory because it is farther from the Sun than the Earth is and receives about half the solar power. A much better location for a planet-wide antimatter factory is Mercury, the innermost world of our solar system.
Mercury is in a rather elliptical solar orbit with an average distance of 0.39 Astronomical Units (forty percent of Earth’s solar distance) from the Sun. This parched and airless world has a radius thirty-eight percent that of the Earth or about two thousand four hundred forty kilometers. Let us assume that the entire surface of Mercury is covered with solar photovoltaic cells. These supply energy to a gigantic version of the LHC with the single task of creating, decelerating and storing antimatter.
At the Earth’s location in the solar system (1 Astronomical Unit or one hundred fifty million kilometers from the Sun), the amount of solar power striking a surface facing the Sun (called the Solar Constant) is about fourteen hundred watts per square meter. Because solar light intensity varies as the inverse square of solar distance, the Solar Constant at Mercury’s average distance from the Sun is about nine thousand watts per square meter.
The solar power striking Mercury is therefore about 1.7 X 1017 watts, or approximately ten thousand times the total electrical power produced by our global civilization from all sources.
We next assume a twenty percent energy conversion efficiency for the solar cells coating Mercury’s surface. The electrical energy input into the hypothetical antimatter factory constructed on this hot, small planet, is therefore about 3 X 1016 watts.
If our Mercury antimatter factory works continuously and 4 X10-5 of the electrical energy input is converted into matter/antimatter pairs (as in the Tevatron), about 5 X 1018 Joules of energy is converted into antimatter each year. Every year, this antimatter factory will convert about 4 X 1019 Joules of energy into antiprotons.
Optimistically, we assume that all of these can be collected, decelerated, perhaps neutralized with positrons and safely stored until ready for use in the engines of a starship. The total antiproton annual production mass from this hypothetical antimatter factory can be calculated from a variation of Einstein’s famous equation (E = 2Mc2), where the factor 2 accounts for the fact that half the energy (E, in Joules) is converted into protons, M is the antimatter mass in kilograms and c is the speed of light in vacuum (three hundred million meters per second).
Even then, our hypothetical Mercury-based antimatter factory can produce only about five hundred kilograms of anti-hydrogen atoms. If the factory works continuously for a century, about fifty thousand kilograms of antimatter will be produced. This may be hardly enough for Eugen Sanger’s photon rocket, which requires equal amounts of matter and antimatter. But, as we shall see in the section on antimatter rockets below, an operational spacecraft propelled by antimatter/matter-annihilation may function quite well if antimatter is a very small fraction of the total fuel mass.
It should also be mentioned that it is not necessary that our antimatter factory or factories be located on a planet’s surface. Another location would be free space. Here, a huge parabolic, micron-thin reflector might be used to concentrate and focus solar energy on a bank of efficient, hyper-thin and low mass solar photovoltaic cells. Robert Kennedy, Ken Roy and David Fields have suggested that humans may ultimately construct approximately one thousand-kilometer solar-sail sunshades in space to slightly reduce the amount of sunlight striking the Earth and thereby alleviate global warming. Such in-space devices could also be used to concentrate solar energy on Mars. There is no inherent reason why these sunshades or solar concentrators could not serve a dual function and direct sunlight towards in-space antimatter factories.
Also, as Forward speculates, the antiproton conversion efficiency he quotes for the Tevatron may not be the ultimate. There is plenty of room for improvement if some of humanity’s brightest minds turn their attention to the problems of antimatter production and storage.
No matter where the antimatter is produced, the next challenge is the safe storage of the stuff until we are ready to use it in a starship engine. This is especially difficult since antimatter is the most volatile material in the universe and will disappear in a puff of radiation if brought into contact with normal matter.