4. The Efficiency of Hydrogen Fusion

In stars, the pressure of gravitational attraction is so strong that nuclear reactions start to occur, and hydrogen is transmuted into helium through fusion. The amount of energy released in this process is given by Einstein's famous equation E = mc2. But only 0.7 percent of the hydrogen initially present actually becomes energy. Expressed as a decimal, this number is 0.007. This is the efficiency of hydrogen fusion, and the presence of life in the universe is determined by this number.

3. The Chandrasekhar Limit

A supernova explosion produces all those heavier elements and scatters them throughout the universe, enabling planets to form and life to evolve. The size of a star determines its fate. Stars slightly larger than the sun become white dwarves, intensely hot but small stars cools slowly and die. However, if a star exceeds a certain mass—the Chandrasekhar limit—then it is destined to become a supernova.  This limit is approximately 1.4 times the mass of the sun.