Einstein’s Equation


What does Einstein’s equation, E=mc2  have to do with atomic bombs?


Not a whole lot, really. Albert Einstein wrote his famous equation as an afterthought to his 1905 Theory of Relativity. He discovered that there is an intimate relationship between mass and energy. Energy is the ability to do work and mass is the weight of something- of how much stuff there is.

Mass and energy are interchangeable aspects of the same thing. Scientists refer to it as mass-energy. The equation tells us that even a tiny bit of mass contains a huge amount of energy. The letter m stands for mass and the letter c is the speed of light. The speed of light is a huge number (186,000 miles per second). Even bigger when squared. Mass multiplied by the square of the speed of light yields an unbelievably large figure. Even a tiny bit of mass holds a tremendous amount of energy.

We don’t see that in everyday life. We don’t see that every gram of water or soil or soap contains the energy to run whole cities. It’s like a rich man who doesn’t spend any money. No one can tell how rich he is.  In everyday life our energy-producing activities are chemical processes. From metabolizing food, to burning wood, or gasoline in an engine, or using coal in a power plant.

Want energy? The name of the game is to lose mass. Chemical processes do cause a loss of mass, but it is so tiny, it can hardly be measured. We don’t get much energy from chemical processes, even dynamite or TNT. A pound (454 grams) of TNT gives a loss of mass of only a half a billionth of a gram.

Nuclear processes are quite different than chemical processes. Nuclear means working with the inner core of an atom, the nucleus, and not the electrons going around the nucleus. Atoms of uranium split into two pieces. The two pieces don’t add up the whole piece.

That seems odd at first and defies common sense thinking. Cut a loaf of bread into two pieces, weigh the two pieces on a scale, and we find the two pieces add up what the whole loaf we started with.

That does not happen at the nuclear level. If an atom of uranium is split, the two pieces together weigh less than the whole uranium atom. About a tenth of one percent of the mass is loss. The loss of mass turns into pure energy. How much energy? Einstein’s  E = m c2  tells us how much. A little bit of mass turns into an enormous quantity of energy.

Split a Uranium-235 atom, then particles (neutrons) from that atom split two more atoms, than four more atoms, than eight more atoms, and you have a chain reaction. If that happens in a split second,  it’s an atomic bomb. Slow that chain reaction way down, control it, it’s a nuclear power plant.

However, a nuclear power plant cannot explode like an atomic bomb. The fuel is different. Most reactors use uranium enriched to three percent U-235. An atomic bomb is uranium enriched to ninety percent U-235. The Iran government is accused of trying to do such enrichment.

Einstein’s famous equation is not needed to build an atomic bomb. However, the equation does measure size of the blast.


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