18. From Outer Space To Inner        Space   Previous PageNext Page

The universe beyond our Earth is a study in contrasts of temperature. The center of our sun reaches 40 million degrees, and the fusion reactions in larger stars, discussed in Chapter 8, can reach 2 billion degrees or more. At the other end of the scale, temperature has little meaning in nearly empty space. If we define temperature in terms of the average kinetic energy of molecules, what does temperature mean in a region of outer space that has only one or two atoms per cubic centimeter? Temperature in a vacuum also can be defined in terms of the radiation passing through it, compared with the radiation from a perfectly non-refelective black body of measurable temperature. Interstellar space is filled with microwave radiation in the millimeter wavelength range, corresponding to a black-body temperature of only 3K by this definition. Theoreticians have proposed that this radiation is the last remnant of the primeval "big bang" fireball with which the universe began 15 billion years ago.

The chemistry that we know on Earth is confined to a minute span within this broad range of temperature. At sufficiently high temperatures, electrons are stripped from atoms, and matter exists only as an ionized plasma of electrons and nuclei. In gases the temperature is high enough to overcome the attractions between molecules. In plasmas the temperature is so high that even the attractions between nuclei and electrons are overcome, and neutral atoms no longer exist.

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