Cosmology is a very active field of research in science today. The
observational data of temperature and polarization anisotropies of the
cosmic microwave background radiation, obtained by the Wilkinson Microwave
Anisotropy Probe (WMAP) mission, still maintains its position as a prime
source of information for cosmologists, which include both astrophysicists
and high-energy physicists.
This paper is one of seven papers describing the data, analysis method,
systematic error limits, foreground emission, basic results, and
cosmological interpretation of the latest WMAP five-year observations.
Demands and appetite for better data and some observational guidance as to
which directions to take next are always very high in the area of
cosmology. I think that such high demands from the cosmology community are
reflected in the citation counts.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
This paper describes the cosmological interpretation of the new WMAP
five-year results, in combination with the latest measurements of
cosmological distances of other astrophysical sources.
Would you summarize the significance of your paper in
Our previous papers on the cosmological interpretations of the cosmic
microwave background data from the WMAP one-year and three-year
observations, as well as other papers on the large-scale structure of the
Universe and supernovae, have established the standard cosmological model;
however, this is a very strange model.
Pie Chart: This chart
According to this model, more than 70% of energy in the present-day
Universe is made by "dark energy," an unknown form of energy which can
cause a repulsive force to accelerate the expansion of the Universe.
While this model is a simple model that has merely six parameters, there
are a lot of unknowns hidden in this phenomenological model: for example,
the nature of dark energy and the nature of dark matter that we know very
little about. Therefore, in this paper, we tried to find evidence for any
deviations from this simple, six-parameter cosmological model.
Despite the unprecedented precision that the five-year WMAP data has
achieved, we could not find any compelling deviations from the simplest
model. This is rather remarkable. The spatial geometry of the Universe
appears to be quite flat—deviation from flat geometry is now
constrained to be less than 1%.
The observed temperature anisotropy seems to obey Gaussian statistics to
high precision— the deviation, called "non-Gaussianity," is less than
0.1%. The nature of dark energy is consistent with a mystical "cosmological
constant" at the level of 10%.
Parity (mirror) symmetry seems respected on the cosmological scales. We
have not seen evidence for the primordial gravitational waves from the
ultra early universe called the era of cosmic inflation—and other
things. The simplest model is full of mystery, but it still remains as the
best phenomenological description of the Universe that fits the data.
How did you become involved in this research, and were
there any problems along the way?
I came to Princeton University as a visiting graduate student from Japan in
1999, hoping to get involved with the WMAP team. Fortunately, my dream has
come true! I would like to thank the PI
(see also |
see also), Johns Hopkins University) and Co-PIs of
the WMAP mission, especially my thesis advisor,
David Spergel, for letting me join the team.
Working on the WMAP data with the team members over the last eight years
has been a fantastic experience. The amount of work was tremendous, and of
course there were many, many difficulties in getting things done correctly,
but all of them were worthwhile.
WMAP's major achievement was to produce high-quality maps of temperature
and polarization anisotropies of the cosmic microwave background, and to
constrain the physical properties of the Universe with the unprecedented
precision and accuracy. To achieve this, many factors had to be kept under
control at the level of 1%, or even at the level of 0.1%. One thing that we
struggled to understand was the noise properties of the polarization
data—various null tests kept failing and it took us quite a while to
figure out what was going on.
Where do you see your research leading in the
I have four items on my agenda. To understand: (i) the nature of dark
energy, (ii) the nature of dark matter, (iii) the physics of cosmic
inflation, and (iv) the emergence and evolution of structures in the
Universe. The WMAP has made a tremendous contribution to advancing our
knowledge on these fundamental questions, and I would like to contribute to
making further, hopefully significant, progress on them.
Both better theoretical understanding of the physics and better
observational data are needed to make progress on any of these items. I am
involved in the University of Texas at Austin and its partner's
"Hobby-Eberly Telescope Dark Energy Experiment
(HETDEX)—a next-generation galaxy survey that
can address all of the above items.
I am excited about the prospect of this experiment. I am also quite excited
about the founding of the Texas Cosmology Center
(TCC) at the University of Texas at Austin, which was
established to foster close collaborations between high-energy
physicists and astrophysicists on the above problems in cosmology.
Do you foresee any social or political implications for
Whenever I give public lectures on cosmology, I always get the following
question, "What is your research good for?" My answer would be, "It
depends." If you have ever looked up the night sky and wondered anything
about the Universe, we can offer you a lot of answers to most of the
questions you might have about the Universe. Some of the answers, which
were derived from scientific observations and experiments, are probably
beyond the wildest imagination.
Questions about the Universe are ultimately related to questions about the
origin of ourselves. In that sense, cosmology has social implications for
how we think about ourselves. On the other hand, if you have never looked
up the night sky and never cared anything about the Universe before, never
mind, and leave us alone!
Texas Cosmology Center
Department of Astronomy
The University of Texas at Austin
Austin, TX, USA Web
Cosmic Pie Chart: This chart shows that the energy density of the Universe
today is mostly dominated by mysterious "dark energy" and "dark matter,"
and the ordinary matter such as atoms makes up only 4.6%. When the Universe
was very young—as young as 380,000 years old—there were
significant contributions also from photons and neutrinos to the energy
density of the Universe.
KEYWORDS: COSMIC MICROWAVE BACKGROUND; COSMOLOGY: OBSERVATIONS;
DARK MATTER; EARLY UNIVERSE; INSTRUMENTATION: DETECTORS; SPACE VEHICLES: