Earlier this year (2003), the Wilkinson Microwave Anisotropy (pronounced an-eye-SOT-tro-pee) Probe, whose acronym is WMAP, reported its first results after one year of taking data. Launched on June 30, 2001, WMAP is an instrument designed to measure the cosmic microwave background radiation to unprecedented precision. It is the sequel to the Cosmic Background Explorer (COBE) satellite. It performs its measurements in outer space 1.5 million kilometers (one million miles) from Earth!
For the definitions of terms such as cosmic microwave background radiation and for other information on cosmology, see Jupiter Scientific's earlier report entitled "The Changing View of Our Universe." For more information on inflation, read the review of Alan Guth's book. Dark matter is discussed at the webpage entitled "The Dark Matter Mystery".
Like COBE, WMAP measures the current temperature variations of the cosmic microwave background radiation. In doing so, it provides a portrait of the Universe in its infancy when it was only 380,000 years old. The word "infancy" is quite appropriate: If the Universe were a middle-aged 40-year old person, then 380,000 years would correspond to when the person was a 10-hour-old, new-born baby!
The thermal variations that WMAP detects are very small of the order of one-ten-thousandth (10-5) of a degree Kelvin. The variations in temperature also correspond to fluctuations in density with warmer spots being denser. Such denser regions became the galaxy clusters of today. In the following image adapted from NASA's page http://map.gsfc.nasa.gov/m_mm.html, blue corresponds to cooler and red corresponds to warmer:
WMAP has allowed astronomers to determine the parameters that characterize the Universe. Here are the main results:
(1) To within 1%, the age of the Universe is 13.7 billion years.
(2) The material in the Universe consists of 4% ordinary matter (atoms and nuclei), of 23% cold dark matter and of 73% dark energy.
(3) The present value of the Hubble constant is 71 km/sec per Megaparsec with a margin of error of around 5%.
(4) The ratio, W, of the mass density of the Universe to its critical value, is one to within 2%.
(5) The first stars appeared at around 200 million years after the Big Bang.
(6) The current average temperature of the cosmic microwave background radiation is about halfway between 2.72 and 2.73 degrees Kelvin.
(7) The period of recombination during which atoms form ended 380,000 years after the Big Bang.
(8) Polarization measurements are consistent with predictions from the inflation theory.
Let us comment on the above seven results. (1) Although astronomers now claim to know the age of the Universe to within 200 million years, they assume that the Universe evolves precisely according to the Standard Model of Cosmology. Given our lack of understanding of dark matter and dark energy and the possibility of some small surprises or modifications to the Standard Model, Jupiter Scientific believes that the accuracy is overstated. It is probably safe to say that the age of the Universe is 14 billion years plus or minus one billion.
Result (2) means that 96% of matter is of an unknown type that does not interact electromagnetically thereby rendering it invisible. Dark matter and dark energy are sensed through their gravitational effects and their influence on the expansion of the Universe. Another result of WMAP is that a cosmological constant is favored over quintessence as the source of dark energy although the latter is still not ruled out.
(3) The Hubble constant is a measure of the current expansion rate of the Universe. When space expands, galaxies move apart from one another. A value of 71 km/sec per Megaparsec for the Hubble constant means that a galaxy that is one Megaparsec from us moves away from the Earth at 71 kilometers per second (about 45 miles per second) and that a galaxy that is two Megaparsecs from us moves away at 142 kilometers per second, and so on. A Megaparsec is a million parsecs, which is about 3.3 million light years or 30 million-trillion kilometers.
(4) The result W = 1 means that space is flat. See Jupiter Scientific's report on "The Changing View of Our Universe."
(5) Previously, cosmologists believed that the first stars appeared at around 500 million years after the Big Bang. WMAP indicates that star formation began earlier.
(6) When the cosmic microwave background radiation was emitted during atom formation 300,000 years after the Big Bang, its temperature was several thousand degrees and the light was in the visible part of the electromagnetic spectrum. As the Universe expanded, it cooled and the visible light first became infrared radiation then microwaves. The temperature of the Universe now is a frigid 2.725 degrees about absolute zero.
(7) During the period in which atoms were forming and earlier, the Universe was opaque in the sense that light could not travel any appreciable distance. It was as though the Universe was "in a fog." At 380,000 years, recombination was essentially completed: Each proton had paired up with an electron to form a hydrogen atom. Light was liberated. The Universe cleared and the cosmic background radiation has traveled undisturbed ever since. When WMAP makes its measurements, it captures some of the radiation that has been traveling uninterrupted for almost 14 billion years.
(8) Inflation is the idea that space underwent a tremendous expansion during the very earliest moments of the Big Bang. Polarization refers to the manner in which the electric and magnetic fields oscillate in the microwaves.
MAP was renamed WMAP in honor of David Wilkinson, who was one of the founders of the microwave anisotropy probe and who died on September 5, 2002. He was a renowned cosmologist and professor of Princeton University. It was he along with Robert Dicke, James Peebles and Peter Roll who explained the reason for the noise in the Bell Labs radio dish that had perplexed Arno Penzias and Robert Wilson so much in 1964 and 1965. The later two received the Nobel Prize in physics for their discovery: The noise was actually the cosmic microwave background radiation. Curiously, David Wilkinson and Peter Roll were building a microwave device to detect the same thing but were scooped by Penzias and Wilson.
This page was created by the staff of
an organization devoted to the promotion of
science and scientific education through books, the Internet
and other means of communication.
This web page and its contents may NOT be copied onto other web
sites, but other sites may link to this page.