Matter and Antimatter Help (page 3)

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

Unimaginable Power

If equal masses of matter and antimatter are brought together, in theory, all the mass will be converted to energy. If there happens to be more matter than antimatter, there will be some matter left over after the encounter. Conversely, if there is more antimatter than matter, there will be some antimatter remaining.

In a nuclear reaction, only a tiny fraction of the mass of the constituents is liberated as energy; plenty of matter is left over, although its form has changed. You might push together two chunks of uranium-235, the isotope of uranium whose atomic mass is 235 atomic mass units (amu), and if their combined mass is great enough, an atomic explosion will take place. However, there will still be a considerable amount of matter remaining. We might say that the matter-to-energy conversion efficiency of an atomic explosion is low. Of course, this is a relative thing. Compared with dynamite, an atomic bomb is extremely efficient at converting matter to energy. Compared to an antimatter bomb, however, should one ever be devised, an atomic bomb is inefficient.

In a matter-antimatter reaction, if the masses of the samples are equal, the conversion efficiency is 100 percent. As you can imagine, a matter-antimatter bomb would make a conventional nuclear weapon of the same total mass look like a firecracker by comparison. A single matter-antimatter weapon of modest size easily could wipe out all life on Earth. A big one could shatter or even vaporize the whole planet.

Where Is All The Antimatter?

Why don’t we see antimatter floating around in the Universe? Why, for example, are Earth, Moon, Venus, and Mars all made of matter, not antimatter? (If any celestial object were made of antimatter, then as soon as a spacecraft landed on it, the ship would vanish in a fantastic burst of energy.) This is an interesting question. We are not absolutely certain that all the distant stars and galaxies we see out there consist of matter. We do know, however, that if there were any antimatter in our immediate vicinity, it would have long ago combined with matter and been annihilated. If there were both matter and antimatter in the primordial Solar System, the mass of the matter was greater, for it prevailed after the contest.

Most astronomers are skeptical of the idea that our galaxy contains roughly equal amounts of matter and antimatter. If this were the case, we should expect to see periodic explosions of unimaginable brilliance or else a continuous flow of energy that could not be explained in any way other than matter-antimatter encounters. No one really knows the answers to questions about what comprises the distant galaxies and, in particular, the processes that drive some of the more esoteric objects such as quasars.

Practice problems of this concept can be found at: Extreme Objects in Our Galaxy Practice Problems

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