Dark energy has captured the imagination of scientists
because it must be very different from anything we know. In
order to understand it, we would have to have a much better understanding
of how space, time, and matter are related. This is
the kind of challenge that drives revolutions in science.
There are subtle questions as well. What is the purpose of dark
energy? What role does it play in the unfolding universe? Such
questions may seem unscientific, yet scientists continue to be
astonished at the connections and relatedness within the physical
world – a kind of "ecology of the universe." It
would be surprising indeed if dark energy were an afterthought
on nature's part.
One of the most perplexing questions is why the universe we observe
today should contain an amount of dark energy comparable to the
amount of normal matter. Why not much more or much less? What is
special about this near-balance between dark energy and normal
matter? No one knows yet.
It seems curious that dark energy should be discovered at just
that time in history when we thought we had finally answered the
ancient Greek question, "what is the world made of?" It
took two thousand years to answer that question. First, we had
to invent science along the way. Finally, we have studied and understood
all of the chemical elements and many of the fundamental particles
of which they are made. We have periodic tables and textbooks
crammed with lists fundamental particles. Yet now we find that
most of the universe is made of something completely unknown. It
is as though we are now the ancients, asking questions of nature
that we do not yet know how to answer.
This great dialogue with nature seems to keep going. Where it
is going no one really knows yet; the next generations will have
a better idea. But what a marvelous journey!