THE BIG BANG OPENS THE DOOR TO THE MULTIVERSE
The new Gravitational waves detected in the aftermath of
the Big Bang may open the possibility of the existence of the Multiverse:
“Gravitational waves rippling through the aftermath of the cosmic fireball,
physicists suggest, point to us inhabiting a multiverse, a universe filled with
many universes. (See: "Big Bang's 'Smoking Gun' Confirms Early Universe's
Exponential Growth.")
That's because those gravitational wave results point to a particularly prolific
and potent kind of "inflation" of the early universe, an exponential
expansion of the dimensions of space to many times the size of our own cosmos
in the first fraction of a second of the Big Bang, some 13.82 billion years
ago.
"In most models, if you have inflation, then you have a
multiverse," said Stanford physicist Andrei Linde. Linde, one of
cosmological inflation's inventors, spoke on Monday at the Harvard-Smithsonian Center for Astrophysics event where the BICEP2
astrophysics team unveiled the gravitational wave results.
Essentially, in the models favored by the BICEP2 team's observations, the
process that inflates a universe looks just too potent to happen only once;
rather, once a Big Bang starts, the process would happen repeatedly and in
multiple ways. (Learn more about how universes form in "Cosmic Dawn" on the National
Geographic website.)
"A multiverse offers one good possible explanation for a lot of the
unique observations we have made about our universe," says MIT physicist Alan Guth, who first wrote about inflation theory in 1980. "Life being here,
for example."
The Big Bang and inflation make the universe look like the ultimate free
lunch, Guth has suggested, where we have received something for nothing.
But Linde takes this even further, suggesting the universe is a
smorgasbord stuffed with every possible free lunch imaginable.
That means every kind of cosmos is out there in the aftermath of the Big
Bang, from our familiar universe chock full of stars and planets to
extravaganzas that encompass many more dimensions, but are devoid of such
mundane things as atoms or photons of light.
In this multiverse spawned by "chaotic" inflation, the Big Bang
is just a starting point, giving rise to multiple universes (including ours)
separated by unimaginable gulfs of distance. How far does the multiverse
stretch? Perhaps to infinity, suggests MIT physicist Max Tegmark, writing for Scientific American.
That means that spread across space at distances far larger than the roughly 92 billion light-year width of the universe that we
can observe, other universes reside, some with many more dimensions and
different physical properties and trajectories. (While the light from the most
distant stuff we can see started out around 14 billion light-years away, the
universe is expanding at an accelerating rate, stretching the boundaries of the
observable universe since then.)
"I'm a fan of the multiverse, but I wouldn't claim it is true,"
says Guth. Nevertheless, he adds, a multiverse explains a lot of things that now confuse
cosmologists about our universe.
For example, there is the 1998 discovery that galaxies in our universe seem
to be spreading apart at an accelerating rate, when their mutual gravitational
attraction should be slowing them down. This discovery, which garnered the 2011 Nobel Prize in physics, is generally thought to imply the
existence of a "dark energy" that counteracts gravity on cosmic
scales. Its nature is a profound mystery. About the only thing we understand
about dark energy, physicists such as Michael Turner of the University of Chicago have long said, is its
name.
"There is a tremendous mismatch between what we calculate [dark
energy] ought to be and what we observe," Guth says. According to quantum
theory, subatomic particles are constantly popping into existence and vanishing
again in the vacuum of space, which should endow it with energy—but that vacuum
energy, according to theoretical calculations, would be 120 orders of magnitude
(a 1 followed by 120 zeroes) too large to explain the galaxy observations. The
discrepancy has been a great source of embarrassment to physicists.
A multiverse could wipe the cosmic egg off their faces. On the bell curve
of all possible universes spawned by inflation, our universe might just happen
to be one of the few universes in which the dark energy is relatively lame. In
others, the antigravity force might conform to physicists' expectations and be
strong enough to rip all matter apart.
A multiverse might also explain away another embarrassment: the number of
dimensions predicted by modern "superstring" theory. String theory
describes subatomic particles as being composed of tiny strings of energy, but
it requires there to be 11 dimensions instead of the four we actually observe.
Maybe it's just describing all possible universes instead of our own. (It
suggests there could be a staggeringly large number of possibilities—a 1 with
500 zeroes after it.)
Join the "multiverse club," Linde wrote in a March 9 review of inflationary
cosmology, and what looks like a series of mathematical embarrassments
disappears in a cloud of explanation. In a multiverse, there can be more things
dreamt of in physicists' philosophy than happen to be found in our sad little
heaven and earth.
The multiverse may even help explain one of the more vexing
paradoxes about our world, sometimes called the "anthropic"
principle: the fact that we are here to observe it.
To cosmologists, our universe looks disturbingly fine-tuned for life.
Without its Goldilocks-perfect alignment of the physical constants—everything
from the strength of the force attaching electrons to atoms to the relative
weakness of gravity—planets and suns, biochemistry, and life itself would be
impossible. Atoms wouldn't stick together in a universe with more than four
dimensions, Guth notes.
If ours was the only cosmos spawned by a Big Bang, these life-friendly
properties would seem impossibly unlikely. But in a multiverse containing
zillions of universes, a small number of life-friendly ones would arise by
chance—and we could just happen to reside in one of them.
"Life may have formed in the small number of vacua
where it was possible, in a multiverse," says Guth. "That's why we
are seeing what we are seeing. Not because we are special, but because we
can."
(National Geographic,
2014)
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