March 2020, ScientificAmerican.com 1March 2020VOLUME 322, NUMBER 3Photograph by Matt Nager
COSMOLOGY
30 A Cosmic Crisis
Two divergent measurements of
how fast the universe is expanding
cannot both be right. Something
must give—but what?
By Richard Panek
C H E M I S T R Y
38 The Hidden Toll of Wildfire
As wildfires worsen globally, an
aerial campaign seeks to under-
stand how biomass smoke affects
human health. By Kyle Dickman
ANTISENSE THERAPY
46 Finally Making Sense
A long-disdained therapy that tar-
gets RNA is achieving spectacular
success. By Lydia Denworth
ANTISENSE THERAPY
54 Preventing Prions
Treating susceptible individuals
while they are still healthy
offers the best hope for warding
off a deadly brain disease.
By Sonia Minikel Vallabh and
Eric Vallabh MinikelE C O L O G Y
60 What Is Killing
the Monarchs?
It seemed simple: Roundup herbi-
cide was killing America’s favorite
butterfly. But there may be other
causes, and the way to save the in -
sect is not clear. By Gabriel Popkin
ARCHAEOLOGY
68 The First Story
A cave painting from Sulawesi
is the oldest known example
of narrative art. By Kate WongNEUROBIOLOGY
74 The Brain Learns
in Unexpected Ways
Neuroscientists have discovered
a set of unfamiliar cellular mecha-
nisms for making fresh memories.
By R. Douglas FieldsON ThE cOVEr
The value of the Hubble constant—the rate
of the universe’s expansion—may be the most
important number in all of cosmology. Yet
measurements of it from the “early” universe
shortly after the big bang and the “late”
universe of today disagree. Resolving this
discrepancy could lead to a scientific revolution.
Illustration by Mark Ross Studios.38
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