Scientific American Space & Physics 2020 06-07.pdf

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JUNE/JULY 2020 | SCIENTIFICAMERICAN.COM
Space
&
Physics
A Lopsided
Universe?
A new x-ray survey of
distant galaxies suggests
that the universe is
expanding unevenly
WITH COVERAGE FROM
Plus:
DOUBTS
ABOUT DARK
MATTER’S
EXISTENCE
IN THE
HEARTS OF
NEUTRON
STARS
APOLLO 13:
50 YEARS
LATER
FROM
THE
EDITOR
&PHYSICS
Your Opinion
Matters!
Help shape the future
of this digital magazine.
Let us know what you
think of the stories within
these pages by emailing us:
editors@sciam.com.
LIZ TORMES
SPACE
The Beautiful, Irregular Universe
On the Cover
A new x-ray survey
of distant galaxies
suggests that the universe
is expanding unevenly
Andrea Gawrylewski
Senior Editor, Collections
editors@sciam.com
ESA AND XMM-NEWTON (X-RAYS); CFHT-LS (OPTICAL); XXL SURVEY
In my eighth-grade science class, our teacher explained to us the Doppler effect: that objects moving away from us
would display stretched-out sound or light waves, whereas objects moving toward us would show crunched-up
sound or light waves. The instructor cited as an example that astronomers could determine whether cosmological
objects are moving toward or away from Earth depending on if their light waves were stretched out (redshifted for
longer wavelengths) or were shorter wavelengths (blueshifted). This captured my imagination immediately, and I
pictured an ever expanding universe spreading out away from Earth evenly like the ripples formed by dropping a
stone in a pond. And indeed, measurements of the cosmic microwave background radiation suggest that the uni-
verse spread evenly following the big bang. But now, as senior editor Lee Billings reports in this issue’s cover story,
the expansion of the universe may not be uniformly distributed but may be occurring more rapidly in certain regions
(see “Do We Live in a Lopsided Universe?”). As with much astronomical research, it sometimes takes years to see
below the surface of what we thought we understood.
Elsewhere in this issue, one candidate source of dark matter is at risk of being ruled out (see “Milky Way Dark Matter
Signals in Doubt after Controversial New Papers”), and be sure to check out some of the Hubble Space Telescope’s
most famous images, such as the Eagle Nebula, the Lagoon Nebular, and others (see “A Birthday Message from the
Hubble Telescope”). Dive in!
2
WHAT’S
INSIDE
June-July 2020
Volume 3
•
No. 3
OPINION
31.
A Sobering
Astronomical
Reminder from
COVID-19
We should be grateful for
the conditions that allow
us to exist at all, because
they won’t last forever
33.
A Birthday
Message from the
Hubble Telescope
I’m turning 30, and it’s
been an amazing journey
so far
38.
Life as We Don’t
Know It
If we’re going to find
extraterrestrials, we need
to stop assuming they’ll
think like humans
40.
Remembering
Freeman Dyson
In our conversations, he
ventured far and wide
across science, literature
and politics, offering
unorthodox ideas with a
bracing self-confidence
PASIEKA
GETTY IMAGES
NEWS
4.
Are We Ready
for Quantum
Computers?
Hardware hasn’t caught
up with theory, but we’re
already lining up many
previously intractable
problems for when
it does
6.
Astronomers May
Have Captured the
First Ever Image of
Nearby Exoplanet
Proxima C
It could be an unpreced-
ented view of a world
in the closest planetary
system to our own,
but uncertainties
aplenty remain
8.
Will String Theory
Finally Be Put to the
Experimental Test?
Physicists have found
a way the theory might
limit the cosmic inflation
that is thought to
have expanded the
early universe
10.
Antimatter
Discovery Reveals
Clues about the
Universe’s Beginning
New evidence from
neutrinos points to one
of several theories
about why the cosmos
is made of matter and
not antimatter
13.
Universe Creates
All Elements in the
Periodic Table in
10 Minutes
Originally published in
July 1948
13.
This Black Hole
Collision Just Made
Gravitational Waves
Even More
Interesting
An unprecedented
signal from unevenly
sized objects gives
astronomers rare insight
into how black holes spin
NASA
FEATURES
15.
Do We Live in a Lopsided Universe?
A new study of galaxy clusters suggests the
cosmos may not be the same in all directions
18.
Milky Way Dark Matter Signals in Doubt
after Controversial New Papers
New analyses question whether mysterious
gamma-ray and x-ray light in the galaxy actually
stems from an invisible mass
21.
The Strange Hearts of Neutron Stars
Space observations are poised to reveal more
about the center of one of the universe’s most
enigmatic objects
27.
Apollo 13
at 50 Years: Looking Back
at the Mission’s Lost Lunar Science
Its commander Jim Lovell and pilot Fred Haise
reflect on their fateful, flawed voyage to the moon
3
NEWS
Hardware hasn’t caught up with
theory, but we’re already lining up
many previously intractable
problems for when it does
YUICHIRO CHINO
GETTY IMAGES
Are We Ready
for Quantum
Computers?
A recent paper by Google claiming
that a quantum computer performed
a specific calculation that would
choke even the world’s fastest
classical supercomputer has raised
many more questions than it an-
swered. Chief among them is this:
When full-fledged quantum comput-
ers arrive, will we be ready?
Google achieved this milestone
against the backdrop of a more
sobering reality: Even the best
gate-based quantum computers today
can only muster around 50 qubits. A
qubit, or quantum bit, is the basic piece
of information in quantum computing,
analogous to a bit in classical comput-
ing but so much more.
Gate-based quantum computers
operate using logic gates, but in
contrast with classical computers,
they exploit inherent properties of
quantum mechanics such as super-
position, interference and entangle-
ment. Current quantum computers
are so noisy and error-prone that the
information in its quantum state is lost
4
NEWS
within tens of microseconds through
a mechanism called decoherence and
through faulty gates.
Still, researchers are making
demonstrable, if slow, progress
toward more usable qubits. Perhaps
in 10 years, or 20, we’ll reach the goal
of reliable, large-scale, error-tolerant
quantum computers that can solve a
wide range of useful problems.
When that day comes, what should
we do with them?
We’ve had decades to prepare.
In the early 1980s American physicist
Paul Benioff published a paper
demonstrating that a quantum-
mechanical model of a Turing ma-
chine—a computer—was theoretically
possible. Around the same time,
Richard Feynman argued that simulat-
ing quantum systems at any useful
scale on classical computers would
always be impossible because the
problem would get far, far too big: the
required memory and time would
increase exponentially with the volume
of the quantum system. On a quantum
computer, the required resources
would scale up far less radically.
Feynman really launched the field
of quantum computing when he
suggested that the best way to study
quantum systems was to simulate
them on quantum computers. Simu-
lating quantum physics is
the
app for
quantum computers. They’re not
going to be helping you stream video
on your smartphone. If large, fault-
tolerant quantum computers can be
built, they will enable us to probe the
strange world of quantum mechanics
to unprecedented depths. It follows
different rules than the world we
observe in our everyday lives and yet
underpins everything.
On a big enough quantum comput-
er, we could simulate quantum field
theories to study the most fundamen-
tal nature of the universe. In chemistry
and nanoscale research, where
quantum effects dominate, we could
investigate the basic properties of
materials and design new ones to
understand mechanisms such as
unconventional superconductivity.
We could simulate and understand
new chemical reactions and new
compounds, which could aid in
drug discovery.
By diving deep into mathematics
and information theory, we already
have developed many theoretical
tools to do these things, and the
algorithms are farther along than the
technology to build the actual ma-
chines. It all starts with a theoretical
Current quantum computers are so noisy
and error-prone that the information
in its quantum state is lost within tens of
microseconds through a mechanism called
decoherence and through faulty gates.
model of the quantum computer,
which establishes how it will harness
quantum mechanics to perform a
useful computation. Researchers
write quantum algorithms to perform
a task or solve a problem using that
model. These are basically a se-
quence of quantum gates together
with a measurement of the quantum
state that provides the desired
classical information.
So, for instance, Grover’s algorithm
shows a way to perform faster
searches. Shor’s algorithm has proved
that large quantum computers will
one day be able to break computer
security systems based on RSA, a
method widely used to protect, for
instance, e-mail and financial Web
sites worldwide.
In my research, my colleagues and
I have demonstrated very efficient
algorithms to perform useful compu-
tations and study physical systems.
We have also demonstrated one of
the methods in one of the first
small-scale quantum simulations
ever done of a system of electrons,
in a nuclear magnetic resonance
quantum information processor.
Others have also followed up on
our work and recently simulated
simple quantum field theories on the
noisy intermediate-scale quantum
computers available today and in
laboratory experiments.
As we wait for the hardware to
catch up with theory, researchers in
quantum information science will
continue to study and implement
quantum algorithms useful for the
currently available noisy, fault-ridden
machines. But many of us are also
taking a longer view, pushing theory
deep into the intersection of quantum
physics, information theory, complexi-
ty and mathematics and opening up
new frontiers to explore, once we
have the quantum computers to take
us there.
—Rolando Somma
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