28 ASTRONOMY • SEPTEMBER 2015
Bursting the bubbles
ighten your seat belt. This odyssey takes us beyond
our universe to a realm of parallel dimensions. We
will not just explore today’s popular multiverses —
theories that suggest ours is one marble in an infinite
bag; we’ll see why some physicists regard them as a
threat to science.
Few scientists would dispute that there’s lots of stuff over
the cosmic horizon, beyond what we can ever see. Light from the
farthest visible objects traveled for more than 13 billion years, from
galaxies currently located some 40 billion light-years away. There’s
no reason for galaxies to simply stop existing at this visible bound-
ary. Moreover, the strong evidence that space is flat on large scales
means that the vast bulk of the universe must lie over the horizon,
beyond where objects recede at light-speed. In fact, many cosmolo-
gists think the overarching universe may be infinite in size and thus
infinite in its inventory of galaxies. (We will return to this “infinite”
business a bit later.)
Since we’ll be forever blind to and ignorant of objects whose light
can never reach Earth, we could call all that stuff a separate uni-
verse. Logically, it has the same physical laws as ours. This is the
most straightforward type of multiverse. As renowned Mass-
achusetts Institute of Technology physicist Max Tegmark notes, “If
you define our universe as everything we can observe, then I’d bet
good money on there being parallel universes.”Bob Berman explores the
strange ideas that drive theorists
to believe in parallel universes.
Multiverses
SCIENCE
OR
SCIENCE FICTION?
Bob Berman is Astronomy’s Strange Universe columnist. His latest book
is ZOOM: How Everything Moves (Little, Brown and Co., 2014).T
ALL ILLUSTRATIONS:ASTRONOMY:ROEN KELLY;ASTRONOMY: WILLIAM ZUBACK (CHILD)