Matter and Antimatter Help

By — McGraw-Hill Professional
Updated on Sep 17, 2011

Matter And Antimatter

The Cosmos can do strange things to matter. Strange, that is, according to what is considered “normal” here on Earth. Some scientists think that these extreme manifestations—antiparticles, neutron stars, geometric points with infinite density, and such—are as common in the Universe as any other form of matter.

The notion of antimatter is as old as science fiction. You know how this kind of story can go. A space ship lands on a planet that turns out to be made of antimatter, and the journey comes to an unexpected, abrupt, and catastrophic end. A rogue band of space aliens comes to Earth with an antimatter bomb and sells it to the highest bidder. What is the reality of antimatter? Let’s look at the nature of matter first. In simplistic terms, matter consists of three types of particles: the proton , the neutron , and the electron .

The Proton

Protons are too small to be observed directly, even with the most powerful microscopes. All protons carry a positive electrical charge. The charge on every proton is the same as the charge on every other. Every proton at rest has the same mass as every other proton at rest. Most scientists accept the proposition that all protons are identical, at least in our part of the Universe, although they, like all other particles, gain mass if accelerated to extreme speeds. This increase in mass takes place because of relativistic effects; you’ll learn about this later.

While an individual proton is invisible and not massive enough to make much of an impact all by itself, a high-speed barrage of them can have considerable effects on matter. Protons are incredibly dense. If you could scoop up a level teaspoonful of protons the way you scoop up a teaspoonful of sugar—with the protons packed tightly together like the sugar crystals—the resulting sample would weigh tons in Earth’s gravitational field. A little ball made of solid protons would fall into the Earth and cut through the crustal rocks like a lead shot falls through the air.

The Neutron

A neutron has a mass slightly greater than that of a proton. Neutrons have no electrical charge, and they are roughly as dense as protons. However, while protons last for a long time all by themselves in free space, neutrons do not. The mean life of a neutron is only about 15 minutes. This means that if you gathered up a batch of, say, 1 million neutrons and let them float around in space, you would have about 500,000 neutrons left after 15 minutes. After 30 minutes, you would have approximately 250,000 neutrons remaining; after 45 minutes, there would be about 125,000 neutrons left.

Neutrons can last a long time when they are in the nuclei of atoms. This is a fortunate thing because if it weren’t true, matter as we know it could not exist. Neutrons also can survive for a long time when a huge number of them are tightly squeezed together. This happens when large stars explode and then the remaining matter collapses under its own gravitation.

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