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10/10/2000
Snapshot of Our Roots
Remember that I said Pittsburgh was an underrated city? Well,
my man Al, from Mars, has informed me of the happenings after
the very last Pirate game played in the about-to-be-imploded
Three Rivers Stadium. He tells me that fireworks and other
hoopla accompanied the game but the piece de resistance was
what happened to home plate. It was removed from the ground
and given to a daring guy equipped with jetpack. This guy flew
up and out of Three Rivers and deposited home plate in the new
baseball stadium to be opened next year. Is that class or what?
For those who might question the reliability of someone from
Mars as a news source, I have confirmed Al''s account with our
Lamb creator, who knows someone who actually attended the
game in question.
While I was quite impressed with this bit of space travel, I''m
afraid it pales when compared with the planned insertion of a
NASA spacecraft into an orbit between the earth and the sun a
million miles from earth next year. But it''s not the distance that
impresses me, it''s the mission. Indeed, in the May 2000 issue of
Discover magazine Tim Folger calls it "The Magnificent
Mission". The spacecraft is called MAP, which stands for
Microwave Anisotropy Probe, a somewhat daunting name. It
might sound a bit less formidable if I tell you that MAP is a
space probe designed simply to measure temperature.
Admittedly, it''s a pretty sensitive thermometer that will be
measuring rather cold temperatures only 2.7 Kelvin, 5 degrees
Fahrenheit above absolute zero. (Absolute zero is the lowest
temperature we can measure, some 460 degrees Fahrenheit
below our Fahrenheit zero.) Actually, MAP''s mission is to
measure temperature differences of one part in a hundred
thousand through sophisticated microwave measurements.
You may think that sounds impressive but not "magnificent". I
hope you''ll change your mind when you hear some of the
questions MAP may answer. How fast is the universe
expanding? What is the shape of the universe? How did
galaxies first form and when? Will our universe go on
expanding forever or come back together in a Big Crunch? And,
a real far out possibility, are we essentially seeing ourselves a
few billion years ago somewhere out there in the heavens?
What does all this have to do with microwaves? Last week I
mentioned that the long wavelength infrared photons coming
from the sun are felt as heat. Without going into the math (I
wouldn''t want to be accused of fuzzy math!), each wavelength
corresponds to a certain energy or to an equivalent temperature.
It turns out that the wavelengths corresponding to the region of
2.7 degrees Kelvin lie in the millimeter range, out beyond the
infrared in the microwave range.
If you''re into the origin of our universe, you already know that
2.7 degrees Kelvin is the temperature of the radiation or heat left
over from the Big Bang. I have to admit that I have an ulterior
motive when I write about such things as the Big Bang or black
holes. I feel that if I write about them often enough, I''ll convince
myself that I actually understand them and I''ll die a happy man!
So, here I go again. To understand the Bang, you first have to
accept that you can make something out of nothing, or at least
what we think of as nothing. Today, physicists are comfortable
with the idea that in a vacuum, particles are continually blinking
into and out of existence. I try to convince myself that this is
reasonable by realizing that a vacuum is not really nothing, not
even in outer space. There are all kinds of electrical and
magnetic fields, neutrinos, photons, gravity waves and maybe
WIMPs. Probably, none of these sorts of things are involved in
the blinking particles we''re talking about, but it consoles me to
know a vacuum contains energy and stuff I can''t see or feel.
Now that we''ve accepted blinking particles, albeit reluctantly,
let''s go to the Big One. Our universe started out with a
tremendous amount of energy concentrated in a volume smaller
than a proton. Current thinking is that within some ridiculously
small fraction of a second, our teensy little universe inflated like
a balloon to roughly the size of our earth. In the process, zillions
and zillions of particles, especially quarks and gluons, blinked
into existence. This time, however, the energies were so great
they didn''t blink out as particles are doing today. This was
certainly a good thing since we wouldn''t be here today had they
blinked out! Now we have the quark-gluon "soup" that workers
in Switzerland think they duplicated recently, as I discussed in a
recent column.
Well, this quark-gluon soup kept expanding and cooling down
and, before you knew it, the quarks and gluons had gotten
together to form protons and electrons and various charged
particles. There were also lots of photons of light but they kept
bumping into the protons and electrons and were scattered
around, sort of like light is scattered in a cloud of water droplets.
For 300,000 years you had this expanding, very hot foggy mix of
photons, protons and electrons. After 300,000 years, however,
the mix had cooled down to the point that the electrons and
protons started sticking together, forming hydrogen (1 electron
and 1 proton). But hydrogen is transparent to light and suddenly
everything changed. Those scattered photons were now free to
spread throughout the universe at, what else, the speed of light.
Over time, those hot photons have cooled down as the universe
kept expanding. Those 2.7 degree Kelvin microwave photons
are the remnants of that time 300,000 years after the Big Bang
when the universe really followed the "Let there be light"
scenario. It was the discovery of this cosmic background
radiation in 1965 that won Arno Penzias and Robert Wilson of
Bell Labs the Nobel Prize.
After this discovery, there was naturally a huge amount of
interest in the properties of this window to our universe as it was
some 13 billion years ago. One problem that worried scientists
was how the stars and galaxies came into being if conditions
were uniform in the proton-electron soup and the resulting
hydrogen universe. It seemed that no matter where in the sky
one looked, the temperature of the background radiation was the
same. Then, in 1992, NASA''s COBE (Cosmic Background
Explorer) satellite reported tiny fluctuations (anisotropy) in the
cosmic microwave background. One area of the sky, for
example, had a temperature of 2.7281 Kelvin, another 2.7280
Kelvin. This difference of only 0.0001 degree doesn''t seem like
much but cosmological types were ecstatic. One of the mission
scientists, George Smoot, even proclaimed that finding these
little heat differences was "like looking at God".
Why the excitement? The temperature differences, though small,
showed that at the time the universe lit up, everything wasn''t
uniform. There were regions in which the densities of hydrogen
were larger and than in surrounding regions. Our own Milky
Way would have been one of those denser regions. What
depends on density? Gravity. The dense region, through its
larger mass, attracts more hydrogen and grows and grows and
grows. Finally, there''s enough hydrogen to form clouds of gas
and then stars and galaxies. How did the fluctuations arise? Go
back to the beginning when those particles blinked into being. In
that soupy mix, the effect of more particles coming into the
picture was like tossing stones into a lake. Ripples are formed
and pressure waves spread out. Pressure waves through a gas are
sound waves and according to Folger''s article, the whole
universe rang like a bell! When the photons were free to travel
the pressure waves stopped. It was sort of like freezing a pond or
ocean instantaneously to preserve the wave patterns. In this case
what was frozen was the pattern of the photons in the cosmic
microwave background.
So where does MAP come into the picture? COBE was a pretty
crude instrument, "a real pile of crap by today''s standards",
according to David Wilkinson, who''s worked on both MAP and
COBE. COBE had no telescopes and could only resolve a region
of the sky 14 times as large as the moon''s apparent size. MAP
has telescopes and state-of-the-art detection equipment that
wasn''t available when COBE was built. COBE was in a low
earth orbit while MAP will be placed a million miles out, at a
point where the sun''s and earth''s gravity are the same. This will
reduce the background microwave noise from the earth.
MAP''s increased resolution (35 times better than COBE''s) should
result in a much more detailed map of the temperatures in the
cosmic microwave radiation over the complete sky. Hopefully,
this map will show the patterns of those sound waves in the
primordial soup. Although I find it hard to believe, one of the
mission scientists, Charles Bennett, is quoted as saying that the
early universe is relatively easy to describe. He says freshman
physics and a knowledge of the properties of sound waves in
different mediums is enough to model the hoped-for results from
MAP. The frozen patterns in the microwave background would
then permit a calculation of the amount of matter in the universe.
That number would immediately answer the question of whether
our ultimate fate is a fiery crunch or a frigid expansion forever.
The data could also answer the other profound questions posed
above. One question is really a weird one. This concerns the
possibility that if the universe is of a certain type, light that
starts out into space will follow a curved path. The ridiculous
conclusion is that what we think is another distant galaxy may
actually be our own Milky Way as it was billions of years ago. Or
if the light made two circuits, there could even be another view
of us a few billion years before that!
If you''d like more detail on MAP, log on to the NASA Web site
nasa.gov. Incidentally, the Discover article cited a November
launch date; the NASA site now says April. Perhaps you would
like to detect some of the cosmic background yourself. Actually,
if you''re of my vintage, before the advent of cable TV, you''ve
already done so. With an antenna, part of the "snow" on your
screen means you''ve picked up some of those 13 billion year old
cosmic microwave photons.
Allen F. Bortrum
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