Nobel Lecture: Cosmic microwave background radiation anisotropies: Their discovery and utilization^*

Figure 1

Summary of CMB temperature measurements as a function of redshift. The filled dot is from COBE (70). The squares are upper limits obtained on the C I or C II from 119, 120; S), 63; L), and 38; G). Combes et al. is the filled triangle. The line is the ($1+z$) expected variation. From Combes et al., 1999.

Figure 2

(Color) A space-time diagram in units of conformal time (vertical) $\eta =\int cdt∕a\left(t\right)$, where $a\left(t\right)$ is the scale factor of the universe, and comoving coordinates which are converted to physical distance by multiplying by the scale factor $a\left(t\right)$. In these coordinates light travels on a 45° angle. The line in the center is our matter’s path through time shown with no peculiar motion (very small in practice). The universe is shown opaque until the last scattering surface from either the end of the inflationary epoch or the big bang singularity. The thickness of this is shown exaggerated relative to the subsequent elapsed time until the present (now) so as to show the causal horizon (distance that could be covered by the speed of light $d=3ct$ in physical units) and the sound horizon (distance that would be covered by speed of sound in the early universe). These two horizons have special imprint upon the physical structures in the universe.

Figure 3

(Color) Dipole anisotropy measured by U2 flight experiment (1976). Top panel: Sky covered by U2 flight experiments in northern and southern hemispheres. Bottom panel: The dipole map made by U2 experiments. The red spot centered near the constellation Leo indicates $+3.5\mathrm{mK}$ from the median background temperature and the blue spot centered near the Aquarius is $-3.5\mathrm{mK}$ region (115; 39).

Figure 4

Dipole anisotropy results from the sum of many components of velocity due to gravitational attraction of various mass concentrations.

Figure 5

(Color) Selected observations of the CMB frequency spectrum.

Figure 6

(Color) Photograph of the COBE Science Working Group (minus Eli Dwek) taken during a meeting in 1988. From left to right, back row: Ed Cheng, Rick Schafer, Stephan Meyer, Mike Janssen, John Mather, Ned Wright, George Smoot, Tom Kelsall; middle row: Dave Wilkinson, Tom Murdock, Chuck Bennett, Bob Silverberg, Harvey Moseley, Michael Hauser, Rainer Weiss; front row: Nancy Boggess, Sam Gulkis, Phil Lubin.

Figure 7

(Color) The DMR instrument design. Left, photograph of the DMR instrument; right, schematic of the DMR. The DMR has played a key role in the CMB anisotropy experiments, including the U2 flight experiments and the COBE DMR. The WMAP also adopted differential radiometers as the basic apparatus for the CMB observations (http://lambda.gsfc.nasa.gov/product/cobe/).

Figure 8

(Color) The solid (blue) curve shows the expected intensity from a single temperature blackbody spectrum, as predicted by the hot big bang theory. The FIRAS data fit with the expected blackbody curve with $T=2.726\mathrm{K}$ so precisely that the uncertainties are smaller than the width of the blackbody curve, the data points are covered by the curve and not visible (70).

Figure 9

(Color) False-color image of the near-infrared sky map (1.25, 2.2, and $3.5\mathrm{\mu }\mathrm{m}$ composited) mapped by DIRBE. The dominant sources of infrared light at these wavelengths are stars in the Milky Way, as shown by the thin disk and the bulge at the center. Scattered bright sources can also be seen off the galactic disk (http://lambda.gsfc.nasa.gov/product/cobe/).

Figure 10

(Color) The breakdown of the CMB sky map produced by COBE DMR (http://lambda.gsfc.nasa.gov/product/cobe/), monopole (top), dipole (middle), and multipole (bottom). At $T\sim 3\mathrm{K}$ level (top), we have uniform radiation from every direction. When the sensitivity is changed to $\sim \mathrm{mK}$ level, the dipole pattern shows up, which is due to the peculiar motion of our solar system relative to the CMB rest frame. As the scale is refined to $\mathrm{\Delta }T\sim 10\mathrm{\mu }\mathrm{K}$, after removal of the dipole, the multipole features of anisotropy become evident. These very tiny fluctuations give us information about the early universe.

Figure 11

(Color) By 2001 the first acoustic peak was observed and there was evidence mounting for a second peak in the CMB angular power spectrum based upon the observations obtained from COBE DMR, MAXIMA, BOOMERanG, DASI, and CBI. In a couple more years much more data were available and the WMAP first year data then traced out the plateau and first peaks. The solid blue line is the prediction curve of a model with $n=1$, $H=50\mathrm{km}∕\mathrm{s}\mathrm{Mpc}$ and cold dark matter (http://cosmas.lbl.gov/).

Figure 12

(Color) The best fit curve (orange) of small-scale angular power spectrum for $\Lambda \mathrm{CDM}$ model estimated with WMAP data and measurements carried out by ground-based and balloon-borne CMB experiments (122). Notice that this shows the greater details of angular power spectrum at the range $l\ge 300$.

Figure 13

(Color) Flat or Euclidean geometry.

Figure 14

(Color) Closed or positively curved geometry.

Figure 15

(Color) Open or negatively curved geometry.

Figure 16

(Color) A visual comparison of COBE DMR and WMAP. The COBE was able to show only the superhorizon scale $(\sim 10°)$ structures while the WMAP has sufficient angular resolution to show more detailed structures down to subhorizon scale $(\sim 0.3°)$.

Figure 17

(Color) Power spectrum predicted by $\Lambda \mathrm{CDM}$ model and plots by WMAP 3-year data experiments, ACBAR and BOOMERANG03. Solid (yellow) curve is the predicted power spectrum of $\Lambda \mathrm{CDM}$ model.

Figure 18

(Color) An artist’s rendering of the Planck satellite in space (http://www.rssd.esa.int/planck/).

Figure 19

(Color) The progression of satellite CMB map resolutions going from the COBE DMR discovery maps to the WMAP and anticipated Planck map (http://www.rssd.esa.int/planck/).