Sky & Telescope - September 2016 - 4

Peter Tyson
Spectrum
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Beating Down
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EDITORIAL

Editor in Chief Peter Tyson
Senior Editors J. Kelly Beatty, Alan M. MacRobert
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Observing Editor S. N. Johnson-Roehr
Project Coordinator Bud Sadler

In the context of science, I have always liked the verb
"to constrain." I have a visceral response to it, as if I can feel the word going
about its business of squeezing a value to bring it within speciﬁed limits.
(It comes from the Latin constringere, to constrict or bind tightly together.)
Like a good piece of writing, which casts out the unnecessary and gets
straight to the point, the word neatly describes the process astronomers and
other scientists use to zero in on a hypothesis that ﬁts the evidence.
Two of the meatiest cosmological enigmas in need of proper constraint
are dark energy and dark matter. Current models of cosmology require the
existence of these two glaring unknowns, which together make up roughly
95% of everything in the universe. Yet we have no clear idea what either
one is. Until we do, we won't have a basic
understanding of our cosmos, including
the growth of large-scale structure or the
cause of its accelerating expansion.
In their attempts to rein in these two
elephants in the room, astronomers
employ various techniques or "probes."
One such probe is weak gravitational
lensing (see our cover story on page
34). Strong and cluster lensing serve as
probes too. So do Type Ia supernovae,
the cosmic background radiation, and
Dark matter (mapped in blue) in a
baryon acoustic oscillations (S&T: Apr.
Hubble galaxy-cluster image
2016, p. 22). Our best hope of yielding
the necessary precision to distinguish among models of dark energy and
dark matter lies in using these and other such tools in combination, as well
as in maximizing their potential.
To do that, astronomers need more data - heaps more. Fortunately,
we'll soon have enormously data-rich wide-ﬁeld surveys like the Large
Synoptic Survey Telescope, Euclid, and the Wide Field Infrared Survey Telescope. Astronomy is entering a new arena - that of "big data" (see article
on page 14) - which will be challenging to manage but promises to open
new windows on the universe's constituents and properties.
Who knows? Maybe we'll even succeed in constraining theories and
models of dark energy and dark matter thoroughly enough not only to
grasp what they are, but also to devise a fundamental theory of physics for
our universe. Until now, both have been frustratingly elusive. Astronomers,
constrain away. ✦

Senior Contributing Editors Robert Naeye, Roger W. Sinnott
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Schaaf, Govert Schilling, William Sheehan, Mike Simmons, Mathew
Wedel, Alan Whitman, Charles A. Wood, Robert Zimmerman
Contributing Photographers P. K. Chen, Akira Fujii, Robert Gendler,
Babak Tafreshi
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IMAGE: NASA / ESA, D. HARVEY (ÉCOLE POLYTECHNIQUE FÉDÉRALE DE
LAUSANNE, SWITZERLAND) / R. MASSEY (DURHAM UNIVERSITY, UK) /
THE HUBBLE SM4 ERO TEAM / ST-ECF / ESO / D. COE (STSCI) / J. MERTEN
(HEIDELBERG/BOLOGNA) / HST FRONTIER FIELDS / HARALD EBELING (UNIVERSITY OF HAWAI'I AT MANOA) / JEAN-PAUL KNEIB (LAM) AND JOHAN
RICHARD (CALTECH, USA)

September 2016 sky & telescope

Editor in
Edi
i Chi
Chieff

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Sky & Telescope - September 2016

Table of Contents for the Digital Edition of Sky & Telescope - September 2016