Has the
universe been around forever? If so, possibly it's been bouncing back and forth
in a endless cycle of big bangs in which all matter bubbles out of a
singularity, followed by big crunches, in which all gets swallowed up again to
form that dense point from which the universe is born again. And the cycle carries
on over and over and over.
The math
of those theories, though, has never really worked out in a way that could tell
us whether our universe is repeated or has one beginning and one end. But
recently, a team of researches has invoked the powers of so-called string theory to answer some vital riddles of the early universe. The conclusion could
give us the theoretical push required to build a universe from scratch, and
hence offer support to a repeating universe.
For
example, we know that we live in an ever expanding universe, in which galaxies
and stars are flying away from us at an ever-increasing speed. Researchers can
tell that by using different types of techniques to estimate how fast galaxies
at different distances from us are moving away. We also have pictures of the
baby universe, when it was just 380,000 years old (and I really do mean
"baby," as the universe is currently 13.8 billion years old).
Within
that baby picture, we see remarkable patterns — tiny splotches and blotches
that expose the existence of slight temperature and pressure differences in
that young universe.
We are
able to explain all these observations (and more) with what's called Big Bang
cosmology, plus an additional theory called inflation, which is a process that
we think occurred when the universe was less than a second old. During that
process (which itself lasted for the teensiest sliver of a second), the
universe became much, much larger, taking quantum differences and making them greater
in the process. Those differences ultimately grew, as slightly denser patches
had marginally stronger gravity, making them bigger. With time, those
differences became large enough to imprint themselves as spots in the baby
picture of the universe (and billions of years later, things like stars and
galaxies, but that's a separate story).
Tired of
the Big Bang Theory and want your own version of cosmology? That's fine, but
you'll have to describe things like the expansion of the universe and the spots
in the baby picture of cosmos. In other words, you have to do a better job at clarifying
the universe than inflation does.
This looks
easy, but it isn't. The pressure, density and temperature differences in the universe's
early years has bedeviled many alternate cosmologies, including one of the most
popular let's-go-bigger-than-the-big-bang ideas, called (are you ready for
this), Ekpyrotic universe. The word ekpyrotic comes from the Greek for word for
"conflagration," which refers to an ancient philosophical concept of
a constantly repeating universe.
In the
Ekpyrotic scenario, the universe … constantly repeats. Under that perception,
we are currently in a "bang" phase, which will ultimately (somehow)
slow down, stop, reverse, and crunch back down to extremely high temperatures
and pressures. Then, the universe will (somehow) bounce back and re-ignite in a
new big bang stage.
The
trouble is, it's difficult to repeat the blotches and splotches in the baby
picture of the universe in an Ekpyrotic universe. When we try to put together
some imprecise physics to explain the crunch-bounce-bang cycle (and I do
emphasize "vague" here, because these processes involve energies and
scales that we aren't even coming close to understanding with known physics),
everything just comes out too … easy. No collisions. No wiggles. No splotches.
No differences in temperature, pressure or density.
And that
doesn't just mean the concepts don't match observations of the early universe.
It means that these cosmologies don't result in a universe filled with
galaxies, stars or even people.
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