Sky and Telescope - May 2018 - 4

SPECTRUM

by Peter Tyson

A Whale of a Mystery

The Essential Guide to Astronomy
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LAST MONTH I WROTE about how amazing it is that the universe is

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N ASA'S GODDA RD SPACE FLIG H T CEN TER

so transparent that we can perceive galaxies and other objects billions of light-years away. We can see everything!
Except we can't. In fact, we can't see most of what's out there. If
we could plop the universe on a scale, all we can observe with our
eyes and instruments would "weigh" just 5% or so of the total. The rest is stuff
invisible to us - dark matter and dark energy, comprising about 26% and 69%,
respectively. It's like we're peering into a large aquarium and marveling at a
clownﬁsh while somehow missing the giant squid and blue whale right behind it.
We learned the blue whale existed in 1998, when two independent teams
stumbled upon it. They shared the 2011 Nobel Prize in Physics for realizing,
while studying distant supernovae, that the universe's expansion is speeding up.
Something is causing that acceleration, and countering the lassoing effects of
matter, dark and otherwise.
Twenty years after its discovery, we still have few clues as to what dark energy
is. Is it some property intrinsic to space itself that grows as space does? Might
it be a new "ﬁfth force," after gravity, electromagnetism, and the strong and weak nuclear
forces? Does it call for an entirely new understanding of gravity?
Desperate for an answer, researchers have
invoked everything at their disposal to attempt
to pin it down, including such mind-bending
notions as string theory and the multiverse.
From the Big Bang to now: the
universe's expansion in a nutshell
They're trying their utmost to wrap the tightest
constraints they can manage around what this
strange "antigravity" might be, but those bounds remain loose enough that the
whale keeps slipping free, eluding their grasp.
This makes me smile. If there were a Grand Creator (don't worry, I'm not
going there), I can almost imagine it looking on and winking: "You Earthlings
pride yourselves on how much you've ﬁgured out about the cosmos. Congratulations. Now, try your hand at this." That dark energy has stumped our top theorists, at least so far, is a healthy reminder that, clever as we are, we don't know
everything. Do some puzzles actually exceed our ability to solve them?
We could use another Einstein, a galloping genius of an entirely different
stripe. In the meantime, as Marcus Woo explains in our cover story on page 14,
we're doing everything we can to get to the bottom of dark energy. It's rather
consequential: As Woo notes, nothing short of "the characteristics of spacetime, the fate of the universe, even the
nature of reality itself" depend on it.

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Sky and Telescope - May 2018

Table of Contents for the Digital Edition of Sky and Telescope - May 2018