successor species, just like the Galapagos ¿ nches. Will that mark the end of
human history?
At larger scales we return to slower and simpler processes, such as the
evolution of the Earth, the Sun, and the Universe. These we can predict with
more con¿ dence. Studying the movement of tectonic plates hints at what the
Earth will look like in 100 or 200 million years’ time. The Atlantic will widen;
the Paci¿ c will narrow, bringing Asia
and North America together; and
eventually a new supercontinent will
emerge. Los Angeles will slide north
and join Canada.
Our Sun is about halfway through
its life. In 4–5 billion years it will
run out of hydrogen, collapse, and
then expand again to form a “red
giant.” The Earth will be vaporized.
Eventually, the Sun will cool and shrink, becoming a “black dwarf.” In its
retirement, it will keep cooling for countless billions of years. Our galaxy,
the “Milky Way,” is on a collision course with its neighbor the Andromeda
galaxy. The two will collide as our Sun enters its death throes, gliding
through each other gracefully, though gravity will introduce some turbulence
as they do so.
How will the Universe evolve? One idea, popular in the late 20th century,
was that the gravitational pull of all the matter and energy in the Universe
would eventually slow expansion until the Universe began to collapse in
on itself. Time would reverse, and the Universe would collapse in a “big
crunch,” to be followed perhaps by a new “big bang,” which would create a
new Universe.
In the late 1990s, astronomers found that the rate of expansion of the Universe
is actually increasing. We do not yet know why. But this suggests the
Universe will keep expanding forever. What will that mean? Eventually, all
stars will use up their fuel and die. The Universe will darken, and black holes
will graze on what’s left for countless billions of years. The space between
In the late 1990s, astronomers
found that the rate of
expansion of the Universe is
actually increasing. We do
not yet know why.