by Rachel Feltman / illustrations by Alessandro RustighiOVERVIEW18 FALL 2019 • POPSCI.COM
THERE’S NO LIMIT TO
the questions we’d have to
answer to know where, how,
or even if the universe ends.
But all evidence suggests that
we’re not just suspended in
some free-form void: Space
bends around anything with
mass the way a trampoline
sags under a dropped ball;
black holes send out ripples of
gravitational waves like peb-
bles in a cosmic pond; and gaps
between galaxies stretch and
contort over time. All these
distortions give us the spark
of an inkling of how the whole
thing might take shape.stretching might work.CURVATURE
This heavenly Pringle is
the best way to illustrate
a universe that doesn’t
contain enoug
slow the expan
over from the b
Without the de
quired to hold itinward and stret
infinitely. A 2D ske
of this 4D phenom
(don’t forget time
impossible to draw
entirety, but the key
this: Two objects th
set out moving alon
parallel lines will onl
get farther apart as
spacetime warps.POSITIVE
CURVATURE
Our universe might be
as round(ish) as the
globe we call home. In
this reality, moving
in any direction would
eventually bring you
back to your starting
point—like a jaunt
around our equator.
This vision isn’t infinite,
however; you wouldn’t
find endless unexplored
land as you walked.
But since the end
connects seamlessly
to the start, you’d never
arrive at its edge.Based on what we know
about how matter was
distributed in the uni-
verse’s early days and the
density of energy and
matter today, most as-
hysicists believe the
mos is probably flat.
cts moving in parallel
will remain parallel.
don’t despair over
seemingly simple
pe: Just as you can
p paper into a
d-bending Mobius
p, the realm we
bit could do all sorts
multidimensional
sty-turns and still
ain its flatness.A BRIEF
HISTORY
OF SPACE13 billion B.C.
In the beginning,
every thing existed in
one chunk of matter.
The big bang created
the vast nothingness
we have today.1584
Italian theorist Gior-
dano Bruno posited
that our solar system
wasn’t the center of all
existence, but one
cluster amid many.1000s A.D.
In Persia, Abu Rayhan
al-Biruni proposed
Earth’s rotation, which
poked holes in the no-
tion that everything
revolved around us.1929
Edwin Hubble’s tele-
scopic observations of
galactic movements
proved the universe
isn’t static, but is ex-
panding all the time.1964
The U.S. discovery of
cosmic microwave
background radiation
finally convinced most
astronomers of the big
bang theory’s validity.