4 IPMU News No. 10 June 2010
How did the universe begin? What happened
in its first moments? How did the rich structure
of galaxies, stars and planets emerge out of
nothingness? While humans have been asking
these questions for millennia, we can now directly
observe physical processes that occurred in the first
moments of the universe.
Because light travels at a finite speed, when we
look out in space, we look back in time. Since it
takes light eight minutes to travel from the Sun
to the Earth, we observe the Sun as it was eight
minutes ago. We see Jupiter as it was 30 minutes
ago and see nearby stars as they were 5 or 100
years ago. When the Subaru telescope observes a
distant galaxy, it sees light that left the galaxy 12
billion years ago.
Einsteinʼs theory of General Relativity (together
with our observations of the properties of the
universe) implies that our current universe began
13.7 Billion years ago. Today, the universe is filled
with cosmic microwave background radiation
(CMBR), the leftover heat from the
Big Bang.
Today, the temperature of the CMBR is only 3
degrees above absolute zero. However, when the
universe was younger, the CMBR was much hotter.
Three hundred and eighty thousand years after
Principal Investigator David N. Spergel
Research Area
：
Astrophysics
FE ATURE
How Did the Universe Begin?
the big bang, the temperature of the CMBR was
3000 degrees above absolute zero, roughly half
the temperature of the surface of the Sun. At this
temperature, the CMBR was hot enough to ionize
most of the hydrogen in the universe, so space was
filled with a dense plasma of electrons and protons.
The CMBR cannot penetrate this thick fog, so when
we look out in space, this is as far as we can see
back in time.
Over the past 15 years, most of my research has
focused on interpretation of tiny fluctuations in
the temperature of the CMBR measured by the
Wilkinson Microwave Anisotropy Probe (WMAP).
WMAP is a NASA satellite that orbits the Earth and
Sun at four times the distance of the moon where it
characterizes the CMBR.
Our observations have found a pattern of CMBR
temperature fluctuations consistent with a very
simple cosmological model characterized by only
five basic numbers: the age of the universe, the
mean density of atoms in the universe, the mean
density of matter in the universe, the amplitude
of fluctuations in the density of the universe and
the scale-dependence of these fluctuations (see
Figure 2). Not only does this model fit our data, but
The universe is filled with CMBR,
the leftover heat from the Big Bang
A simple model explains
cosmological observations
