Ali pa osebne impresije Johna Bahcalla z Advanced Study Institute na PrincetonuAncient radiation sheds new light on the universe
11 February 2003
NASA today unveiled the first detailed full-sky map of the cosmic microwave background, the microwave "echo" of the Big Bang. Scientists created the map using data collected by the Wilkinson Microwave Anisotropy Probe satellite (WMAP) over a 12-month period. The results provide further support for the inflationary Big Bang model of the universe and reveal when the first generation of stars was created.
The photons in the cosmic microwave background were created in the Big Bang and then continually scattered by free electrons in the early universe. They were released when the universe had expanded and cooled enough to allow these electrons to combine with protons and form hydrogen atoms. The properties of the photons - which have been stretched to microwave wavelengths by the expansion of the universe -- can therefore be used to study the universe at this "time of last scattering".
A number of experiments have been carried out on the ground and in balloons to study the tiny temperature fluctuations in the microwave background caused by variations in the density of the early universe. WMAP, however, has been able to study these fluctuations in far more detail. And unlike previous experiments, it can record images of the microwave background across the whole sky.
"We've captured the infant universe in sharp focus, and from this portrait we can now describe the universe with unprecedented accuracy," says WMAP Principal Investigator Charles L. Bennett of the Goddard Space Flight Center. "The data are solid, a real gold mine."
The data indicate that the time of last scattering occurred about 380,000 years after the Big Bang and that the Universe is now 13.7 billion years old, give or take 1%. They also reveal that the earliest stars in the universe were created just 200 million years after the Big Bang.
In addition, the results support the idea that the universe underwent a period of rapid expansion when it was very young and that its geometry is flat. The data show that 4% of the universe is ordinary matter, 23% dark matter and 73% dark energy. The NASA researchers say that this dark energy is more likely to resemble Einstein's "cosmological constant" than a negative-pressure energy field called "quintessence", but they do not rule out quintessence.
WMAP is named in honour of David Wilkinson of Princeton University, a project team member who died in September last year. The satellite was launched in June 2001 and now orbits the Lagrange Point, a million miles from Earth. It will continue to observe the cosmic microwave background for another three years.
Edwin Cartlidge is News Editor of Physics World
Homepage MAP-a jeRemarks at the Wilkinson MAP press conference: 02/11/03
by John Bahcall, Institute for Advanced Study, Princeton, NJ
Every astronomer will remember where he or she was when they first heard the WMAP results. I certainly will.
For cosmology, the formal announcement today represents a `rite of passage’ from speculation to precision science.
I am thrilled by the precision of the results we have just heard from Chuck and David.
However, I am astounded by what they mean. Before WMAP, astronomers had assembled an implausible model of the universe with a little bit of ordinary matter; a significant portion of dark matter (whatever that is); and a whole lot of dark energy (another strange beast). I confess; I was skeptical.
But, the WMAP measurements convinced me. The error bars are tiny. There are multiple, redundant checks on the experiment.
The way the world is, is the way WMAP sees the world. We will have to understand this universe. We have no choice.
A natural question, given so many important measurements by WMAP, is: What is the most revolutionary result? In my opinion, the most revolutionary result is that there are no revolutionary results. WMAP has confirmed with exquisite precision the crazy and unlikely scenario that astronomers and physicists cooked up based upon incomplete evidence. Incredibly, everybody got it essentially right.
Lets consider a human analogy to try to appreciate better what WMAP has achieved.
Suppose we equate a 50-year-old man to the current universe, then the analogy is correct if the epoch that is studied by WMAP is a newly born baby, only 12 hours old. . The WMAP scientists have measured for the infant universe the total body weight, the length of the legs, the size of the ears, and the amount of hair
What the WMAP scientists have done is the equivalent of a doctor using the results of an annual physical checkup to infer correctly the detailed physical characteristics of the same individual when he was only 12 hours old.
I have distinguished colleagues, historians, who argue with great erudition about what events occurred a thousand or two thousand years ago. The WMAP results prove that astronomers and physicists know what happened in a broad sense in the universe almost 14 billion years ago.
For me, the bottom line of today’s announcement is that we live in a crazy universe whose defining behavior we know precisely for the last 14 billion years.
The WMAP achievement makes me proud to be an astrophysicist.