Our Early Universe: Inflation, or Something
Totally Wacky?
by AMY
SHIRA TEITEL on FEBRUARY
28, 2012
A schematic look at the universe - where it came
from and where it is now. Credit: NASA.
Astronomers generally accept the theory that our
universe looks the way it does because of cosmic inflation —
rapid expansion in the moments after its birth. This explains
the expanse and apparent flat shape of the universe observed
through instruments like NASA’s Wilkinson Microwave Anisotropy
Probe. But inflation isn’t the only model that explains the
early universe. There are others, and they get wacky.
Three physicists from the University at Buffalo —
Ghazal Geshnizjani, Will Kinney and Azadeh Moradinezhad Dizgah —
set out to investigate other cosmic models. Their study titled
“General Conditions for Scale-Invariant Perturbations in an
Expanding Universe” appeared in November in the online Journal
of Cosmology and Astroparticle Physics (not
to be confused with theJournal
of Cosmology) and contained some interesting results.
This picture of the infant universe from NASA's
Wilkinson Microwave Anisotropy Probe (WMAP) reveals 13 billion+
year old temperature fluctuations that correspond to the seeds
that grew to become the galaxies. Credit: NASA Goddard Space
Flight Center.
They stuck with the basics — that the theory of
gravity is correct and that the early universe did rapidly
expand. With these two constraints, the team found that only
three models explain the early universe and the distribution of
matter we observe today. But these models require very strange
physics.
According to their calculations, the early
universe required an accelerated cosmic expansion (inflation), a
speed of sound faster than the speed of light, or extremely high
cosmic energy to end up with our current universe. The third
model actually demands such high energy that scientists would
need to invoke a theory of quantum gravity like string theory to
explain the extra dimensions of space-time that would pop up.
The takeaway message? Inflation turns out to be
the only way to explain the universe within the context of
standard physics, said Kinney. He allows that someone might come
up with exotic physics to explain or create other models, like a
speed of sound faster than that of light, but suspects people
are more comfortable working with models that fit within
commonly accepted laws of particle physics.
The difficulty of explaining other models, said
Kinney, “puts the idea of inflation on a much stronger footing,
because the available alternatives have problems, or weirdnesses,
with them.”
Cosmic inflation incorporates quantum field
theory to explain the distribution of matter in the universe.
Under normal circumstances, particles of matter and antimatter
can pop into existence suddenly before colliding and
annihilating each other instantly. These pairs flew apart so
rapidly after the universe’s birth that they didn’t have a
chance to recombine. The same theory applies to gravitons and
antigravitons, which form gravity waves.
These particles of matter are the basis of all
structure in the universe today. Tiny fluctuations cause matter
to collapse and form stars, planes, and galaxies.
But the hunt for other viable models continues.
Kinney for one isn’t finished exploring other theories,
including those that rely on superluminal sound speeds. There
may yet be some major changes to our understanding of the
cosmos.
Linked
Source: The
University of Buffalo
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