WMAP (formerly known as MAP, see below)

Acronym standing for Wilkinson Microwave Anisotropy Probe. A probe launched by the NASA on June 30 2001 to study the Cosmic Microwave Background (CMB) radiation. Its mission is meant to last 27 months.

The purpose of this probe, as its name implies, is to measure the background radiation temperature of the universe also referred to as the birth cry of the universe. (Talking about the temperature of a radiation refers to the temperature at which a perfect black body would need to be heated at to emit such radiation.)

This background radiation is the remnant of the light that first travelled the universe a few hundred thousand years after the Big Bang. Before that time the universe was so hot that all it contained were elementary particles and a handful of atomic nuclei. The electrons were not bound to atoms and since the photons scatter or bounces off electrons the universe was completely opaque for the first 400 000 years of its existence. The "light" that travels from that time is hence very faint and not visible to the human eye but is found in the microwave part of the electromagnetic spectrum.

"The cosmic microwave light is a fossil. Just as we can study dinosaur bones and reconstruct their lives of millions of years ago, we can probe this ancient light and reconstruct the Universe as it was about 14 billion years ago."

Professor David T. Wilkinson,Princeton University, Princeton, NJ.

Because this light was created so long ago, studying it is equivalent to looking at the universe almost 14 billions years ago, and since this radiation is not uniform as the COBE(Cosmic Background Explorer) probe showed already, reading these fluctuations in the pattern of the CMB gives clues on how the universe has expanded and what its future might be. MAP will give answers to many questions and clarify some theories on the evolution of the universe but, as always, it is likely to create twice as many new ones.

Some of the questions MAP will try to answer include:

- Will the universe expand forever or collapse at some point?
- Is the universe dominated by exotic dark matter?
- How and when did the galaxies form?

For instance MAP will allow scientists to have a better understanding of the structure of the universe as the CMB carries an imprint of the density fluctuations of the early universe in the form of temperature variations. The differences in density explains why such objects as galaxies exist in our universe instead of a uniform repartition of the particles throughout space. If you take the universe as the water inside a boiling pan and the galaxies as the bubbles it would fall down as to ask why the bubbles were able to exist (In a boiling pan it is mainly because of defect on the surface of the pan). These temperature fluctuations are very minute though. The COBE satellite reported variation as small as 0.0001 degree Kelvin and MAP is able to measure differences of a millionth of a Kelvin.

One of the most exciting aspects of the MAP mission is that it will be able to test the validity of the inflation theory. This theory tries to explain some facts such as:

- The high number of photons in the universe.
- The unexpected uniformity of the universe on large scale.
- The universe expansion that seems to accelerate instead of slowing down.
- and some others...

The interesting thing about the last point is that it gives a new ground to what is known as the greatest blunder of Albert Einstein, The cosmological constant. In this theory the constant would act as a sort of anti gravity factor that acts only on large distance.

And all of this in the attempt to know where we come from and where we are going. Again.

Update : february 11, 2003

Here we are, Science at work: the first results from the WMAP mission.

Theses first results are the analysis of the first full sky scan that WMAP completed in April 2002. In a nutshell these first results confirm the Big Bang theory and the Inflation Theory.

A few more things this probe elucidates:

- The age of the Universe : 13.8 billion years old (with a 1% accuracy).
- The universe is "flat" as opposed to being "open" or "closed". It means that the Universe will expand forever.
- The first stars in the universe appeared only 200 millions years after the Big Bang, which is earlier than most scientists expected.
- "Baryonic" matter, ie normal matter makes only 4% ( yes you read correctly: f-o-u-r per cent ) of the universe, 23% is an exotic version of matter they call cold dark matter and 73% is even more mysterious dark energy that could account for the loss of effect of gravity over large distances.

"These numbers represent a milestone in how we view our Universe. This is a true turning point for cosmology."
Dr. Anne Kinney, NASA director for astronomy and physics.
This dark energy is more likely to be of a cosmological constant type rather than an energy field acting in opposition to gravity. This finding is a step toward rehabilitating what Einstein himself described as his greatest blunder.

Update : march 16, 2006

The results of the first year of observation have been confirmed after the third full sky scan. WMAP successor, the Planck probe, is planned to be launched in 2007 by the ESA (European Space Agency) and will have ten times as much sensitivy than WMAP.

WMAP is named in honor of David Wilkinson of Princeton University,
a world renowned cosmologist and WMAP team member who died in September 2002.

WMAP home page : http://map.gsfc.nasa.gov
Goddard Space flight center : http://www.gsfc.nasa.gov/topstory/2003/0206mapresults.html

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