 |
 |
The Universe Then and Now
The early universe was a very different place from what we see today.
Matter was packed together at temperatures of tens of millions of degrees,
hotter than a nuclear explosion, or the interior of a star.
Everywhere in the universe was the same:
there were no separate galaxies, stars, or planets,
just a featureless expanse of white-hot plasma.
As the universe expanded and cooled,
matter began to clump together,
pulled in by the force of gravity.
Bigger clumps had a larger gravitational pull,
and became even more efficient at pulling in even more "stuff".
Eventually, these clumps of matter grew large enough
to form the familiar stars and galaxies that we observe today.
The oval image at the upper left
shows the distribution of matter and energy
in the Universe
shortly after the Big Bang,
as measured by the
WMAP satellite.
The blue regions represent places
with a tiny (few parts per million) excess of matter.
These "seeds" would later grow to form the
star and galaxies
visible today (lower right).
How did these first stars and galaxies form?
Did stars form first and later cluster together to form galaxies,
or did great sheets of dust and gas
form first and later fragment into individual stars?
Images
of the cosmic microwave background
show us how matter and energy were distributed shortly after the Big Bang.
We can compare these initial conditions
to views of the
modern universe
to try to piece together
how this complex process took place.
ARCADE
measures the slight additional heating of the universe
by the first stars and galaxies to form after the Big Bang.
This heating --
from stars so far away that they can not be seen as individual objects --
will help determine
how the infant universe began the transition
to the familiar universe we see today.
|
|
|
|
|
|
