Explanation of Isotopes

The number of neutrons in an atom's nucleus is less fixed than the number of protons: many elements have different versions, called isotopes, with different numbers of neutrons. For example, there are three isotopes of carbon, called Carbon-12, Carbon-13 and Carbon-14. The numbers refer to the mass of the atom, which is the sum of the protons and neutrons. Each of the three has six protons. Carbon-12 has six neutrons. Carbon-13 has seven neutrons and Carbon-14 has eight neutrons. Some isotope...

 The Precarious Laws of Nature

By examining the model universes we generate when the theories of physics are altered in certain ways, one can study the effect of changes to physical law in a methodical manner. It turns out that it is not only the strengths of the strong nuclear force and the electromagnetic force that are made to order for our existence. Most of the fundamental constants in our theories appear fine tuned in the sense that if they were altered by only modest amounts, the universe would be qualitatively diff...

 The Four Forces of Nature

1. Gravity. This is the weakest of the four, but it is a long-range force and acts on everything in the universe as an attraction. This means that for large bodies the gravitational forces all add up and can dominate over all other forces. 2. Electromagnetism. This is also long-range and is much stronger than gravity, but it acts only on particles with an electric charge. being repulsive between charges of the same sign and attractive between charges of the opposite sign. This means the ele...