Home » antimatter


Share This
« Back to Glossary Index

Antimatter is not just the stuff of science fiction. It is as real as ordinary matter. Physicists call the matter that we usually encounter on Earth, “normal matter” or “ordinary matter.” But, all types of ordinary matter particles, for example, electrons and protons, have antimatter counterparts.* Their antimatter counterparts are almost identical but have opposite charge. For example, the electron, which is ordinary matter and has a negative charge, has an antimatter counterpart, the positron, with a positive charge.

In ordinary matter, protons are trapped within the nucleus of the atom and carry a positive charge. This is reversed for antimatter; they are trapped within the nucleus but carry a negative charge. The protons of antimatter are called “antiprotons.”

Antimatter, like matter, is composed of atoms. Theoretically, antimatter could clump together to form objects just like matter does. What would an antimatter chair be like? Scientists haven’t had the opportunity to study one so they’re not sure. Due to some key differences between matter and antimatter, scientists speculate, for example, that the chair held over a balcony might fall up instead of down. Now, that would be a significant difference.

Antimatter-matter annihilation. If an electron approaches a positron (antimatter electron), it will be attracted to it. Their charges are opposite, and opposite charges attract. But get too close, and it’s fatal. On contact, they annihilate each other in the tiniest of explosions. The entire mass of both electron and positron convert to energy, leaving behind no mass at all. However, the mass of these particles is so minuscule that the explosion of a single electron and a single positron would be imperceptible to us without special instruments.

The energy yielded by the explosion of an electron and positron most often takes the form of two gamma rays which shoot out in opposite directions. Gamma rays, a major component of radioactivity, are harmful to humans. When such explosions occur, they contribute to natural low levels of radioactivity on Earth.

PET scans, a technology using antimatter. Positrons, the antimatter version of electrons, are used to see inside the body during PET scans. “PET” stands for “positron emission tomography.” The resulting images are similar to X-ray images in that they show structures inside the body. PET scans allow physicians to search for tumors and other pathologies.

PET scans depend on positrons emitted by a radioactive element such as radioactive carbon. The positrons penetrate the body and then record their travels on a detector.

Antimatter bombs and rocket fuel. The explosiveness of antimatter has given people ideas about creating antimatter bombs. In fact, the U.S. military has been researching this potential for decades. If it were possible to build an antimatter bomb, it could be much more destructive than a nuclear bomb. One gram of antimatter reacting with one gram of matter would have the explosive force of 43 kilotons of TNT. That is, one gram of antimatter (about the weight of a $1 bill) would cause about three times the destruction of the nuclear bomb which destroyed Hiroshima.

Science fiction writers, as well, have long fantasized about antimatter, often as a spaceship fuel. Physicists are currently researching the possibility of turning science fiction into science fact by developing antimatter rocket fuel. However, utilizing antimatter in the amounts needed for either bombs or rocket fuel faces huge obstacles. Read on.

Low availability of antimatter. At this time, physicists cannot obtain antimatter in any quantity. A related obstacle is that working with antimatter is extremely difficult because…well, when it comes in contact with anything made of ordinary matter, it explodes.

Scientists believe that in the early universe, shortly after the Big Bang, our universe included both matter and antimatter in similar amounts. For unknown reasons, the amount of ordinary matter exceeded that of antimatter only slightly. The two annihilated each other in a bloodbath of destruction, yielding vast amounts of energy. The matter in our universe currently is what was left over after the antimatter was largely exhausted.

While scientists don’t observe large quantities of antimatter, tiny quantities are all around us. Positrons fly at the earth from outer space; they are one type of cosmic ray. Another source of positrons is naturally-occurring radioactive elements in the earth such as radioactive carbon and potassium. And let’s not forget bananas. Bananas contain a tiny amount of radioactive potassium which they’ve absorbed from minerals in the soil. As a result, a banana emits one positron about every 75 minutes.

In addition, scientists can create antimatter particles like positrons in particle accelerators like the collider at CERN.

Antimatter cloud at core of the Milky Way. Scientists have long suspected that a large cloud of antimatter surrounds the core of our Milky Way Galaxy. It may be very large—10,000 lightyears across. Recent evidence indicates that the source of such a cloud, assuming it exists, might be stars being torn apart by black holes or by hugely energetic stars.

We don’t have the technology to send space vehicles close to the center of our galaxy. So, for now, any cloud of antimatter near its center is not a resource for those who might be scheming about either antimatter bombs or rocket fuel.

*Quantum particles which have no charge, for example photons, are considered to be their own antimatter particle. In other words, two photons which collide create a collision of matter and antimatter. However, this type of interaction gets into physics and math complexities way beyond my ken.