MAXIMA Project's Imaging of Early Universe Agrees It Is Flat, But ... (Forwarded)
Andrew Yee
MAXIMA Project's Imaging of Early Universe Agrees It Is Flat, But ...
By Paul Preuss, paul_...@lbl.gov
May 9, 2000
The results of the first flight of the MAXIMA balloon-borne study of the
cosmic microwave background radiation, released May 9, 2000, agree with
the results of the BOOMERANG Antarctic flight, announced April 26, in the
all-important conclusion that the universe is flat.
"A subset of cosmological theories, those involving inflation, dark matter,
and a cosmological constant, fit our data extremely well," says MAXIMA
team leader Paul L. Richards, a professor of physics at the University of
California at Berkeley and a member of Berkeley Lab's Materials Sciences
Division.
Richards added that MAXIMA's results not only generally agree with
BOOMERANG's but extend them to finer resolution. Moreover, the two
experiments, which differed in many technical and logistic features, also
show intriguing differences in the details of their data analysis.
In its flight on August 2, 1998, MAXIMA (for "millimeter anistropy
experiment imaging array") flew for seven hours over East Texas and
observed a patch of the northern sky about 20 times the size of the full
moon -- three-tenths of a percent of the whole sky -- to a resolution of
one-sixth of a degree.
BOOMERANG (for "balloon observations of millimetric extragalactic
radiation and geophysics") completely circled the South Pole in 10 and
a half days, riding the stratospheric polar vortex and returning to its
starting place (the real meaning of the BOOMERANG acronym) early
in January, 1999, after observing three percent of the whole sky at
somewhat lower resolution.
The goal of both experiments was to take the temperature of the CMB,
whose variations, or anisotropy, amount to a snapshot of the entire
universe 300,000 years after the Big Bang. Before that time the universe
was too hot for atoms to form, and photons were trapped in a dense fog
of electrically charged particles -- so dense that pressure waves
reverberated through the mass like sound waves in water.
When the universe cooled enough for electrons and protons to form neutral
hydrogen atoms -- a moment known as recombination -- highly energetic
photons were freed. In the billions of years since, they have cooled to less
than three degrees Kelvin above absolute zero, equivalent to microwave
frequencies. Slight variations in that remarkably uniform background
temperature, typically only a hundred millionths of a degree, record
the pattern of the "sound waves" at the moment the universe became
transparent.
From their measurements, the CMB experimenters first constructed maps
of the temperature differences in the portions of sky they were studying.
To a practiced investigator of the CMB, a map alone is revealing.
"One can readily see structure in the map on roughly a one-degree angular
scale," says MAXIMA team member George Smoot, of Berkeley Lab's
Physics Division and UC Berkeley, who pioneered studies of CMB
anisotropies with an experiment aboard the COBE satellite in the early
1990s. "Structures in the early universe with a size of nearly one degree
show that the universe has a geometry that is very nearly flat -- the
same geometry, Euclid's, that we all studied in high school."
The best explanation for a flat universe is inflation theory, which posits
that a small, causally connected portion of the entire cosmos expanded
rapidly in the first instant after the Big Bang to form the
almost-but-not-quite perfectly smooth universe we observe today.
Until CMB maps have been analyzed to yield spectra showing the relative
numbers of all features at various angular sizes, however, subtler
information is hidden.
The strongest peak in the CMB power spectrum -- the one at one angular
degree -- represents the fundamental "pitch" of the ringing universe,
directly related to its size at that moment. Just as the tone of a ringing
bell incorporates harmonics -- higher frequency sounds, integer multiples
of the pure pitch -- there should be groups of smaller features in the CMB
yielding a second peak in the power spectrum, a third peak, and so on. Their
frequency and amplitude differ with different models of the early universe.
Much of the analysis for the enormous datasets of both MAXIMA and
BOOMERANG was performed at NERSC. Andrew Jaffe of UC Berkeley and his
colleagues devised an algorithm for finding the most likely map or power
spectrum given the data, an algorithm that was implemented by Julian
Borrill of Berkeley Lab and UC Berkeley, using software he devised called
MADCAP ("microwave anisotropy dataset computational analysis package").
Jaffe and Borrill, who like other MAXIMA and BOOMERANG collaborators are
members of both teams, nevertheless managed to maintain the complete
independence of their results. The differences and similarities in the
spectra from the two experiments raise intriguing questions.
Especially when the CMB measurements are compared with other, wholly
indendent cosmological observations, including estimates of the mass of
galactic clusters and supernova studies indicating that the expansion
of the universe is accelerating, MAXIMA and BOOMERANG agree on the
essentials. Inflation made the universe flat. About a third of its density
is due to matter, most of it dark, and the rest is due to an unknown form
of energy often called the cosmological constant.
One surprise of the BOOMERANG announcement was that its power spectrum
showed no pronounced harmonic at about half an angular degree, where one
would be expected if the most straightforward models of the inflationary
universe are correct. MAXIMA's power spectrum, with higher resolution at
small angles, confirms that there is no sharply defined harmonic at half a
degree, and it allows only a slightly larger harmonic at a third of a degree.
Where are the harmonics? "There are factors that could either distort the
harmonics themselves or the way we see those harmonics today," Smoot
says, naming a number of possibilities including topological defects in
the early universe; a universe that contains more ordinary matter today
than our best estimates; a universe in which some matter decayed before
the moment of recombination; or an unsuspected role for neutrinos. "There
is no agreement on any of these," he says. "It's new physics."
An area where Paul Richards sees a difference between the MAXIMA and
BOOMERANG results is in the calculation of "tilt," which describes the
initial clumping of matter in space on different scales. This clumping
in turn produced the galaxies and clusters of galaxies we see today.
If the amplitude of these tiny, "primordial" perturbations was the same
on all physical scales, leading to the formation of similar structures on
all scales, their spectrum is said to have no tilt. The pattern of clumping
is also reflected in the pattern of the microwave background, and thus in
the angular power spectrum measured by MAXIMA and BOOMERANG.
"Inflationary theories make two main predictions," says Paul Richards.
"One is a flat universe. The other is that the power spectrum has no tilt.
MAXIMA supports both these predictions."
Andrew Jaffe cautions that no tilt "is a very 'natural' value for the
universe's density perturbations at any given time," and -- although a
spectrum with no tilt is predicted by inflation -- "because it is a very
natural spectrum, other possible theories, such as cosmic strings and
other so-called topological defects, are also characterized by no tilt,
although their spectra differ in other ways that our data can probe."
The problem of the "physics of the bumps and wiggles" in the CMB power
spectrum remains.
In close collaboration with their university colleagues, staff scientists
and guests at Berkeley Lab, several with joint appointments at UC Berkeley,
contributed significantly to MAXIMA's experimental hardware as well as
its data processing analysis through programs supported by the Department
of Energy. See http://aether.lbl.gov/ .
Additional Information:
* MAXIMA results are reported in papers submitted 8 May 2000 to
Astrophysical Journal Letters and posted on the web as papers #0005123 and 0005124
[http://xxx.lanl.gov/abs/astro-ph/0005123 and
http://xxx.lanl.gov/abs/astro-ph/0005124] .
* MAXIMA Web site
http://cfpa.berkeley.edu/group/cmb/
* UC Berkeley/University of Minnesota news release
http://www.berkeley.edu/news/media/releases/2000/05/09_maxima.html
* Staff scientists and guests at Berkeley Lab, several with joint
appointments at UC Berkeley, contributed significantly to MAXIMA's
experimental hardware as well as its data processing analysis, in close
collaboration with their university colleagues. See the Berkeley Lab-UC
Berkeley CMB Astrophysics Research Program Web site, http://aether.lbl.gov/ .
* BOOMERANG results were reported in Nature, 27 April 2000, and can be
found on the BOOMERANG Web site,
http://www.physics.ucsb.edu/~boomerang/ .
* The analysis of BOOMERANG data at NERSC
http://www.lbl.gov/Science-Articles/Archive/boomerang-flat.html
IMAGE CAPTIONS:
[http://www.lbl.gov/Science-Articles/Archive/maxima-results.html]
[Image 1]
The Moon, which is 1/2 degree of our sky, is included in this MAXIMA skymap
for scale. MAXIMA's beam resolution is about 1/6 degree or one third the
linear extent of the Moon. And the map itself represents a slice of the sky
some 22 times the size of the Moon or about 500 times its area. What is
most evident about this skymap are the structures roughly twice the size
of the Moon or 1 degree in linear extent. Astrophysicists were surprised at
the paucity of Moon-sized structures.
[Image 2]
The MAXIMA power spectrum compared with the BOOMERANG power spectrum.
The strong peak to the left indicates a flat universe. Both MAXIMA and
BOOMERANG indicate a peak at the first harmonic, and MAXIMA allows for a
third peak, but their weakness means the universe is more complicated than
the simplest models would suggest.
--
Andrew Yee
ay...@nova.astro.utoronto.ca
Ali
just makes the authors less respectable.
The CMBR is the result of Hubble redshift from distant regions of a
homogenious Universe and the clearly Doppler shift Dipole proves that the
Hubble redshift is distance caused.
--
Aladar
http://www2.3dresearch.com/~alistolmar/CMBR.htm
Andrew Yee <ay...@nova.astro.utoronto.ca> wrote in message
news:391A054B...@nova.astro.utoronto.ca...
Jan Panteltje
>hydrogen atoms -- a moment known as recombination -- highly energetic
>photons were freed. In the billions of years since, they have cooled to less
>than three degrees Kelvin above absolute zero, equivalent to microwave
>frequencies.
is he saying the photons redshifted because of TIME?
Jan
Greg Neill
news:958057533.17951....@news.demon.nl...
> >When the universe cooled enough for electrons and protons to form neutral
> >hydrogen atoms -- a moment known as recombination -- highly energetic
> >photons were freed. In the billions of years since, they have cooled to
less
> >than three degrees Kelvin above absolute zero, equivalent to microwave
> >frequencies.
> is he saying the photons redshifted because of TIME?
>
Sort of. A photon travelling through expanding space has its
wavelength stretched. So as the universe expands with time,
the wavelengths of light traversing it are lengthened.
danny boy Mcdonald
Jan Panteltje
>> >hydrogen atoms -- a moment known as recombination -- highly energetic
>> >photons were freed. In the billions of years since, they have cooled to
>less
>> >than three degrees Kelvin above absolute zero, equivalent to microwave
>> >frequencies.
>> is he saying the photons redshifted because of TIME?
>>
>
>Sort of. A photon travelling through expanding space has its
>wavelength stretched. So as the universe expands with time,
>the wavelengths of light traversing it are lengthened.
>
>
>
Thx
Jan