The Matter / Antimater Imbalance in the Universe

Physicists have long pondered the problem and may have an answer. It seems that just before the universe was one millisecond old, matter and antimatter annihilated each other in a sweeping extinction. But a tiny asymmetry was built into the universe so that matter dominated over antimatter by one part out of 100 billion. Why the built-in asymmetry? In the first 100 billion-billion-billionth of a second of the universe's history, particles called X particles and their antiparticles were create...

 How Radiometric Dating Works

Briefly, a radioactive isotope is a kind of atom which decays into a different kind of atom: for example. one called uranium-238 turns into one called lead-206. Because we know how long this takes to happen, we can think of the isotope as a radioactive clock. Radioactive clocks are rather like the water clocks and candle clocks that people used in the days before pendulum clocks were invented. A tank of water with a hole in the bottom will drain at a measurable rate. If the tank was filled at...