Page 54 - The Creation Of The Universe

52 THE CREATION OF THE UNIVERSE

are what make the elements different from one another.
A crucial rule of (classical) chemistry is that elements cannot be trans-
formed into one another. Changing iron (with twenty-six protons) into sil-
ver (with eighteen) would require removing eight protons from the nucle-
us. But protons are bound together by the strong nuclear force and the
number of protons in a nucleus can be changed only in nuclear reactions.
Yet all the reactions that take place under terrestrial conditions are chemi-
cal reactions that depend on electron exchange and that do not effect the
nucleus.
In the Middle Ages there was a "science" called alchemy–the forerunner
of modern chemistry. Alchemists, unaware of the periodic table or the
atomic structures of the elements, thought it was possible to transform one
element into another. (A favorite object of pursuit, for reasons that should
be apparent, was trying to turn iron into gold.) We now know that what
the alchemists were trying to do is impossible under normal conditions
such as exist on Earth: The temperatures and pressures required for such a
transformation to take place are too enormous to achieve in any terrestrial
laboratory. But it is possible if you have the right place to do it in.
And the right place, it turns out, is in the hearts of stars.

The Universe's Alchemy Labs: Red Giants
The temperature required to overcome the reluctance of nuclei to
change is nearly 10 million degrees Celsius. This is why "alchemy" in the
real sense takes place only in stars. In medium-sized stars like the Sun, the
enormous energy being radiated is the result of hydrogen being fused into
helium.
Keeping this brief review of the chemistry of elements in mind, let us
return to the immediate aftermath of the Big Bang. We mentioned that on-
ly helium and hydrogen atoms existed in the universe after the Big Bang.
Astronomers believe that solar-type stars (of which the Sun is one) are
formed as a result of nebulae (clouds) of hydrogen and helium gas being
compressed until the hydrogen-to-helium thermonuclear reaction gets start-