David N. Spergel talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of Space
Field: Space Science
Article Title: Three-year Wilkinson Microwave Anisotropy
Probe (WMAP) observations: Implications for
DN;Bean, R;Dore, O;Nolta,
MR;Bennett, CL;Dunkley, J;Hinshaw,
G;Jarosik, N;Komatsu, E;Page, L;Peiris,
HV;Verde, L;Halpern, M;Hill,
RS;Kogut, A;Limon, M;Meyer, SS;Odegard, N;Tucker,
GS;Weiland, JL;Wollack, E;Wright,
Journal: ASTROPHYS J SUPPL SER
Year: JUN 2007
* Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544
* Princeton Univ, Dept Astrophys Sci, Princeton, NJ 08544
(addresses may have been truncated; see full
Why do you think your paper is highly
The paper provides an overview of the current state of cosmology and is of
significant interest to both astronomers interested in the emergence of
galaxies and large-scale structure and particle physicists interested in
the early universe. These are two large and active communities and this
paper has become a standard reference for describing the composition of the
universe and the now "standard cosmology."
Because the paper is a product of the Wilkinson Microwave Anisotropy Probe
science team, I believe that the community views the derived parameters as
reliable. This paper builds on other papers by the WMAP team that describe
the experiment, the detector, the analysis method, and the basic results.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The paper reports new results from the Wilkinson Microwave Anisotropy Probe
and synthesizes the WMAP results with other cosmological data.
Would you summarize the significance of your paper in
"I believe that the recognition
that simple physical models fit the observed universe
have had and will continue to have profound
implications. Copernicus, Galileo, and Newton have
radically altered our world view by showing that the
same laws apply in terrestrial experiments and in
space, while showing that a simple physical model
(Newton’s laws) describe the dynamics of our
solar system. ."
We show that a simple cosmological model, a flat universe filled with
atoms, dark matter, and dark energy and seeded by scale-invariant
primordial fluctuations, fits not only WMAP’s observations of
fluctuations in the microwave background, but also a host of cosmological
With six basic parameters (the age of the universe, the density of matter,
the density of atoms, the amplitude of the initial fluctuations, their
scale dependence and the epoch of the formation of the first stars), we fit
WMAP’s precision measurements of the power spectrum, observations of
galaxy clustering, galaxy lensing, supernova observations, and many other
This model is in some ways very simple and elegant: high school geometry
describes the large-scale shape of the universe and the statistical
properties of the primordial fluctuations seem to be described by only two
numbers. In other ways, it is very bizarre: atoms make up only 4% of the
universe. The next 23% is in the form of dark matter, most likely
sub-atomic particles that couple extremely weakly to ordinary matter and
radiation. Most of the remaining 73% is in the form of dark energy, energy
associated with empty space.
How did you become involved in this research, and were
there any problems along the way?
When Chuck Bennett, the WMAP Principal Investigator, and Lyman Page, the
Princeton experimental lead, were putting together the WMAP team, they
invited me to join as the "house theorist." This was my first deep
involvement with a major experiment; it has been an exciting adventure.
As in any big projects, there were many challenges. For the three-year
analysis, we were able to report the first detection of large-scale
correlations in polarization. The level of this signal was very low, a few
hundred nono-kelvin, far below our design requirements. We had to
understand the instrument very well to be able to report this measurement.
The polarization detection was essential for our ability to constrain
Where do you see your research leading in the
The WMAP experiment is continuing to operate. We hope to
report results from the five-year analysis later this year and results
from the eight-year analysis in either 2010 or 2011.
We are also now operating a new ground-based experiment, the Atacama
Cosmology Telescope (ACT), in the Chilean Atacama desert. This experiment
has a higher resolution than WMAP along with higher sensitivity. We are now
getting our first results and should be able to report new measurements
Do you foresee any social or political implications for
At a superficial level, no. The study of the early universe is far removed
from daily political battles.
At a deeper level, I believe that the recognition that simple physical
models fit the observed universe have had and will continue to have
profound implications. Copernicus, Galileo, and Newton have radically
altered our world view by showing that the same laws apply in terrestrial
experiments and in space, while showing that a simple physical model
(Newton’s laws) describe the dynamics of our solar system. Our work
has been a contribution towards establishing a simple model that appears to
explain the dynamics of the visible universe.
David N. Spergel
Department of Astrophysical Sciences
Princeton Center for Theoretical Physics
Institute for the Physics and Mathematics of the Universe (IPMU)
Princeton, NJ, USA
• David N. Spergel in past
• Charles Bennett in past features;
• Edward L. Wright in past features;
• Licia Verde in a past feature
• SCI-BYTES (archived) as the
Hot Paper in Physics (First-year Wilkinson Microwave
Anisotropy Probe (WMAP) Observations...".
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