Communist
22nd March 2010, 02:39
Dark Matters
Sometimes pursuit of a great discovery
is its own reward (http://www.scientificamerican.com/article.cfm?id=dark-matters)
By Lawrence M. Krauss
Scientific American Magazine
April 2010
Even as scientists and politicians from around the world
debated in December how to deal with a practical problem
of profound importance-global climate change-another
international group of physicists was waiting with bated
breath for a more esoteric development. In both cases,
at the conclusion of events, the participants were left
salivating and unsatisfied.
The Cryogenic Dark Matter Search (http://en.wikipedia.org/wiki/Cryogenic_Dark_Matter_Search) (CDMS (http://cdms.berkeley.edu/)) experiment,
located in the deep Soudan mine in Minnesota, is
designed to directly detect new elementary particles
that might make up the dark matter known to dominate our
galaxy. In early December rumors started circulating
that the CDMS experiment might actually have seen a
signal.
To appreciate the significance of such an event, one
needs to recognize that scientists have spent the past
40 years building a magnificent theoretical house of
cards that could have toppled with the slightest whiff
of inconsistent data. In the 1970s evidence began to
accumulate from observations of our galaxy's rotation
that there was perhaps 10 times as much invisible as
visible material out there. Although mundane
explanations for such material-from snowballs to planets
to cold gas-at first seemed possible, gradually it
became clear that none of these could fit the bill.
Meanwhile independent calculations of the abundance of
light elements expected to be produced in the first
minutes after the big bang implied that the universe
simply lacked enough protons and neutrons to account for
this dark matter if the predictions were to agree with
observations.
Similarly independent computer calculations about the
formation of galaxies as the universe expanded suggested
that only some new kind of material, which did not
interact as normal matter does, could collapse early
enough to lead to the structures we see.
The past 50 years of particle physics has also driven us
to realize that for what we see to make sense, a host of
new elementary particles quite likely exists. If so,
theorists have determined that the earliest moments of
the fiery big bang could have produced these particles
in precisely the abundance to account for dark matter,
and their interactions with normal matter would have
been weak enough to make them invisible to telescopes
today.
Egged on by the suggestion that such new dark matter
particles in our galactic halo might be directly
detectable, a brave set of experimentalists began to
devise techniques to observe them with detectors deep
underground, far from the reach of most cosmic rays that
would overwhelm such acute sensors.
When we first proposed those experiments more than 25
years ago, I had expected that within a decade we would
have the answer. But technologies at the forefront take
time to build and develop, and nature rarely reveals its
secrets willingly.
So after a generation of anticipation, when the physics
community heard rumors that the CDMS experiment had
detected something, we tuned in to the online
announcement as if it were a Beatles reunion concert. It
is an unreal feeling, if you are a theorist like me, to
imagine that nature might actually obey the delicate
theories and fanciful ideas you develop at your desk
late at night on scraps of paper or at a computer
screen.
The actual announcement was disappointing, however: just
two pulses were detected over almost a year, and they
might have been caused by dark matter. Unfortunately,
there was also about a 25 percent chance that the events
were instead caused by background radioactivity. I admit
to feeling let down at the time, but months later it is
easier to regain perspective. Within a year bigger
detectors will turn on, and they may yet confirm the
present hints to be real signals. Moreover, the
hypothesized particles might yet be detected if
collisions can create them at CERN's Large Hadron
Collider.
If these experiments pan out, the result won't yield a
better toaster or solve the problems of climate change.
But it will provide remarkable vindication of the power
of human imagination, combined with rigorous logic and
technological know-how, to uncover hidden worlds that
even half a century ago could not have been conceived.
And if not, we will all just have to work harder to
solve the mystery of dark matter. New challenges bring
new inspiration, which isn't such a bad thing, either.
.
Sometimes pursuit of a great discovery
is its own reward (http://www.scientificamerican.com/article.cfm?id=dark-matters)
By Lawrence M. Krauss
Scientific American Magazine
April 2010
Even as scientists and politicians from around the world
debated in December how to deal with a practical problem
of profound importance-global climate change-another
international group of physicists was waiting with bated
breath for a more esoteric development. In both cases,
at the conclusion of events, the participants were left
salivating and unsatisfied.
The Cryogenic Dark Matter Search (http://en.wikipedia.org/wiki/Cryogenic_Dark_Matter_Search) (CDMS (http://cdms.berkeley.edu/)) experiment,
located in the deep Soudan mine in Minnesota, is
designed to directly detect new elementary particles
that might make up the dark matter known to dominate our
galaxy. In early December rumors started circulating
that the CDMS experiment might actually have seen a
signal.
To appreciate the significance of such an event, one
needs to recognize that scientists have spent the past
40 years building a magnificent theoretical house of
cards that could have toppled with the slightest whiff
of inconsistent data. In the 1970s evidence began to
accumulate from observations of our galaxy's rotation
that there was perhaps 10 times as much invisible as
visible material out there. Although mundane
explanations for such material-from snowballs to planets
to cold gas-at first seemed possible, gradually it
became clear that none of these could fit the bill.
Meanwhile independent calculations of the abundance of
light elements expected to be produced in the first
minutes after the big bang implied that the universe
simply lacked enough protons and neutrons to account for
this dark matter if the predictions were to agree with
observations.
Similarly independent computer calculations about the
formation of galaxies as the universe expanded suggested
that only some new kind of material, which did not
interact as normal matter does, could collapse early
enough to lead to the structures we see.
The past 50 years of particle physics has also driven us
to realize that for what we see to make sense, a host of
new elementary particles quite likely exists. If so,
theorists have determined that the earliest moments of
the fiery big bang could have produced these particles
in precisely the abundance to account for dark matter,
and their interactions with normal matter would have
been weak enough to make them invisible to telescopes
today.
Egged on by the suggestion that such new dark matter
particles in our galactic halo might be directly
detectable, a brave set of experimentalists began to
devise techniques to observe them with detectors deep
underground, far from the reach of most cosmic rays that
would overwhelm such acute sensors.
When we first proposed those experiments more than 25
years ago, I had expected that within a decade we would
have the answer. But technologies at the forefront take
time to build and develop, and nature rarely reveals its
secrets willingly.
So after a generation of anticipation, when the physics
community heard rumors that the CDMS experiment had
detected something, we tuned in to the online
announcement as if it were a Beatles reunion concert. It
is an unreal feeling, if you are a theorist like me, to
imagine that nature might actually obey the delicate
theories and fanciful ideas you develop at your desk
late at night on scraps of paper or at a computer
screen.
The actual announcement was disappointing, however: just
two pulses were detected over almost a year, and they
might have been caused by dark matter. Unfortunately,
there was also about a 25 percent chance that the events
were instead caused by background radioactivity. I admit
to feeling let down at the time, but months later it is
easier to regain perspective. Within a year bigger
detectors will turn on, and they may yet confirm the
present hints to be real signals. Moreover, the
hypothesized particles might yet be detected if
collisions can create them at CERN's Large Hadron
Collider.
If these experiments pan out, the result won't yield a
better toaster or solve the problems of climate change.
But it will provide remarkable vindication of the power
of human imagination, combined with rigorous logic and
technological know-how, to uncover hidden worlds that
even half a century ago could not have been conceived.
And if not, we will all just have to work harder to
solve the mystery of dark matter. New challenges bring
new inspiration, which isn't such a bad thing, either.
.