Universe Awash in a Sea of
Cosmic Neutrinos
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New data has shed new light on our understanding of the universe and its
early development.
The data, which was collected over a five year period by the Wilkinson
Microwave Anisotropy Probe (WMAP), gives new evidence that a sea of
cosmic neutrinos permeates the universe.
Neutrinos are almost weightless sub-atomic particles that zip around at
nearly the speed of light. Millions of these cosmic particles pass through our
bodies every second.
"A block of lead the size of our entire solar system wouldn't even come close
to stopping a cosmic neutrino," said science team member Eiichiro Komatsu
of the University of Texas at Austin.
WMAP found evidence for this so-called "cosmic neutrino background" from
the early universe. Neutrinos made up a much larger part of the early universe
than they do today.
Microwave light seen by WMAP from when the universe was only 380,000
years old, shows that, at the time, neutrinos made up 10% of the universe,
atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible.
In contrast, estimates from WMAP data show the current universe consists of
4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1
percent neutrinos.
Cosmic neutrinos existed in such huge numbers that they affected the
universe's early development. That, in turn, influenced the microwaves that
WMAP observes.
The new data suggest, with greater than 99.5% confidence, the existence of
the cosmic neutrino background - the first time this evidence has been
gleaned from the cosmic microwaves.
Much of what WMAP reveals about the universe is because of the patterns in
its sky maps. The patterns arise from sound waves in the early universe. As
with the sound from a plucked guitar string, there is a primary note and a
series of harmonics, or overtones. The third overtone, now clearly captured by
WMAP, helps to provide the evidence for the neutrinos.
The hot and dense young universe was a nuclear reactor that produced
helium. Theories based on the amount of helium seen today predict a sea of
neutrinos should have been present when helium was made.
The new data agree with that prediction, along with precise measurements of
neutrino properties made by Earth-bound particle colliders
"We are living in an extraordinary time," said Gary Hinshaw of NASA's
Goddard Space Flight Center in Greenbelt, Md. "Ours is the first generation in
human history to make such detailed and far-reaching measurements of our
universe."
Another breakthrough derived from WMAP data is clear evidence the first stars
took more than a half-billion years to create a cosmic fog. The data provide
crucial new insights into the end of the "dark ages," when the first generation
of stars began to shine.
The glow from these stars created a thin fog of electrons in the surrounding
gas that scatters microwaves, in much the same way fog scatters the beams
from a car's headlights.
"We now have evidence that the creation of this fog was a drawn-out process,
starting when the universe was about 400 million years old and lasting for
half a billion years," said WMAP team member Joanna Dunkley of the
University of Oxford in the U.K. and Princeton University in Princeton, N.J.
"These measurements are currently possible only with WMAP."
A third major finding arising from the new WMAP data places tight constraints
on the astonishing burst of growth in the first trillionth of a second of the
universe, called "inflation", when ripples in the very fabric of space may have
been created. Some versions of the inflation theory now are eliminated.
Others have picked up new support.
"The new WMAP data rule out many mainstream ideas that seek to describe
the growth burst in the early universe," said WMAP principal investigator,
Charles Bennett, of The Johns Hopkins University in Baltimore, Md. "It is
astonishing that bold predictions of events in the first moments of the
universe now can be confronted with solid measurements."
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