In 1917, a year after his general theory of relativity was
published, Einstein tried to extend his field equation of
gravitation to the universe as a whole. The universe as known at
the time was simply our galaxy—the neighboring Andromeda,
visible to the naked eye from very dark locations, was thought
to be a nebula within our own Milky Way home. Einstein’s
equation told him that the universe was expanding, but
astronomers assured him otherwise (even today, no expansion is
evident within the 2-million-light-year range to Andromeda; in
fact, that galaxy is moving toward us). So Einstein inserted
into his equation a constant now known as “lambda,” for the
Greek letter that denoted it. Lambda, also called “the
cosmological constant,” supplied a kind of force to hold the
universe from expanding and keep it stable within its range.
Then in 1929, Hubble, Humason, and Slipher made their monumental
discovery using the 100-inch Mount Wilson telescope in
California of very distant galaxies and the fact that they were
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