|
05/25/1999
Dark But Not Empty
Many editorials and articles decry the lack of knowledge of
fundamental aspects of science on the part of the American
public. A big question is how to get children interested in
science at an early age. I can clearly recall the night, at about
age 4 or 5, when I first became curious about the nature of
things. It was in Denver, where I was born, that Clarence
McComas, an older boy, had an iron rod of some kind and the
stars were shining brightly. In those days the daylight skies were
bluer and the night skies blacker in Denver than I''ve seen
anywhere in later life. Sadly, Denver today is immersed in smog
just like any other big city. At any rate, Clarence, probably a
teenager and certainly wise beyond my comprehension, said that
he would show me something that would really surprise me and
it did! He took the rod and struck it forcefully on a rock, a
shower of sparks resulted which I can see in my mind to this day.
I can''t truthfully say that I also looked up at the sky and
wondered where all those stars came from but I do remember the
sky that night. Later, after moving to Mechanicsburg, PA, my
interest in stars and space was really spurred by listening to the
adventures of Buck Rogers, Wilma and Dr. Huer in the 25th
Century on the radio. Although I chose to become a chemist, I
have continued a keen interest in anything astronomical. Last
week I was delighted to attend a lecture given by Tony Tyson, a
renowned astronomer employed by Lucent Technologies Bell
Labs in Murray Hill, NJ. It may seem strange that Lucent still
employs an astronomer, but Bell Labs has a long history of
involvement in cosmic matters. In 1932 Karl Jansky, identified a
hissing noise associated with transatlantic radio circuits as
originating from the center of our own Milky Way galaxy, the
beginning of radio astronomy. In 1965, Arno Penzias and Robert
Wilson discovered the cosmic background microwave radiation
that confirmed the Big Bang as the origin of our universe. They
received the Nobel Prize in 1978 for this discovery.
Back to Tony Tyson, who has followed in this grand tradition by
being in the forefront of those trying to explain how things
evolved after the Big Bang and what stuff our universe is made
of. Some years ago, astronomers and physicists began to
question how the galaxies, such as our own Milky Way, came
into being but, more to the point of this article, how do they hang
together? It turns out that if you add up all the weights of the
stars in the galaxies, there''s not enough gravity to hold the
galaxies together. Our sun, and our little planet with it, should be
flying off into space instead of swirling around the center of the
Milky Way. For years now, scientists have been postulating the
existence of dark matter to provide the missing weight and the
gravity to hold us in line. One logical suggestion has been that
we just can''t see this dark stuff out there because it consists of
planets like earth or dead stars that don''t shine, or maybe just
huge numbers of "rocks" like asteroids or football-size objects
that we could never see with any kind of telescopes. But,
according to Tyson, it turns out that this explanation has been
ruled out, along with most of the other suggestions that have
been made.
Tyson says that of all the matter in the universe, at least 90% is
dark matter and that dark matter is definitely not like the matter
of which we and our earth and stars are made. Nobody knows
what this dark matter is but only a measly 10% or less of our
universe is the "stuff" we know and love. But this doesn''t stop
the theorists from speculating. As Tyson pointed out, theorists
have families to feed too! Without knowing its identity, they
nevertheless ran models on supercomputers which started with
the Big Bang and seeing what happens to the dark matter. Don''t
ask me how they did it! The result was that the dark stuff didn''t
just spread out uniformly but clumped together in stringy globs.
To me the pictures looked like if you took and pulled apart
cotton candy and sort of put it back loosely together again.
Well, you might say, "So what?" You''ve got these pretty
calculations about something you can''t see and you don''t even
know what it is. Ah, here''s the beauty and nub of Tyson''s talk.
He was about to show us how to "see" the dark matter. To do it
he took us back to Einstein, my boyhood idol right up there with
Indian Bob Johnson of the Philadelphia Athletics and Johnny
VanderMeer of the Cincinnati Reds. Among Einstein''s
overwhelming contributions to mankind''s understanding of
nature was the prediction that a ray of light passing a massive
object would be bent. This was confirmed early in this century
when the position of a star was recorded on film both during an
eclipse of the sun and some months later when the sun wasn''t
there. The star wasn''t in the same place! Why? The bending of
the light by the sun made it look like the star was somewhere it
wasn''t!
Tyson carried us further. If you have a really big object, like a
whole galaxy, not just a piddly sun, and there is another object,
like another really distant cluster of galaxies, directly behind the
big object something really bizarre happens. You not only can
see the distant cluster but you can see more than one of it! Tyson
showed a picture from the Hubble telescope with at least 4
images which, at first glance, looked like pieces of a circle (fuzzy
arcs) around some center. But if you looked closely, you saw
that each of these arcs contained the same number of little bright
spots (galaxies) and thus were images of the same cluster of
galaxies billions of light years behind some other, closer galaxy
or galaxies. We already know that this (these) closer object(s) is
(are) at least 90% dark matter. Now the piece de resistance. By
using sophisticated computer programming, and scanning
different areas of the sky, Tyson and his colleagues could
calculate how much dark matter was needed to get the amount of
light bending they observed. He showed us a contour map of the
dark matter, which looked a lot like the radar maps we see on our
weather forecasts. And the dark matter map looks surprisingly
like the calculated maps of the theorists feeding their families!
So, we were privileged to be able to actually "see" the dark
matter.
When asked what the best guess is for the identity of the dark
matter, Tyson said it is not neutrinos, the tiny little things that
stars like our sun give off by the zillions. You may have seen
recent articles in the papers about some findings that indicate
neutrinos have mass. Because of the huge number of neutrinos
flying around through the universe it was thought that they could
be the dark matter. Not so, apparently. As you''ve been reading
this article, thousands or millions or billions of neutrinos have
passed through you without your even knowing.
The most likely candidate for dark matter now is, of all things,
something known as a WIMP. The term WIMP stands for
Weakly Interactive Massive Particles. In other words, a particle
that definitely has mass but just doesn''t interact with other
things. As with the neutrinos, there may be some WIMPs
floating around in your room even as we speak. The idea of
something being around that you are totally unaware of isn''t
really that incomprehensible. Aside from the neutrinos that just
passed through you, we''ve all had X-rays pass through us and
we''re surrounded by scads of radio waves and TV signals that
we''re unaware of until we turn on our radios or TVs. In the case
of WIMPs there''s one problem. No one has ever seen a WIMP
and the amount of energy required to make one is believed to be
huge! Theorists are hoping the accelerators can be built with the
necessary energies sometime in the future. You might ask, "If
the energy is so great, where did these WIMPs come from?" The
answer proposed is the Big Bang, which had no scarcity of
energy!
Tyson also noted in his lecture that, although we don''t have to
worry about it now, the Andromeda galaxy is headed straight for
the Milky Way, attracted by our own dark matter. Talk about
your Armageddon! He also said that it is pretty definite that,
even with the dark matter, our universe will not slow down and
someday begin to collapse back to another Big Bang. In fact,
there is in addition to dark matter, dark energy that is just being
realized and, if anything, our universe is actually expanding
faster now than it was yesterday. This dark energy may be
Einstein''s cosmological constant, which he suggested but later
withdrew, thinking it to be his biggest mistake! Even his
mistakes were superb! If you hear anything about WIMPs being
discovered, please let me know and I''ll share it with our readers
in a future column.
Allen F. Bortrum
Next article...Tuesday, June 1st
|
