"Gravitinos" --Will They Unlock the Mystery of Dark Matter in the Universe?
- Interesting post from The Daily Galaxy
(Madness takes its toll. Please have exact change)
Sent: 1/23/2013 6:12:23 P.M. Eastern Standard Time
Subj: The Daily Galaxy: News from Planet Earth & Beyond
_The Daily Galaxy: News from Planet Earth & Beyond_
_"Gravitinos" --Will They Unlock the Mystery of Dark Matter in the
Posted: 23 Jan 2013 08:38 AM PST
Astrophysicists have known for the last 80 years that most of the universe
consists of an unknown, _dark matter_
(http://en.wikipedia.org/wiki/Dark_matter) . The solution to the mystery may now be just around the corner. "We
are looking for a new member of our particle zoo in order to explain dark
matter. We know that it is a very exotic beast. And we have found a
plausible explanation," reports Are Raklev, an associate professor in particle
physics in the _University of Oslo_
(University%20of%20Oslo)&t=h) 's Department of Physics --the university's leading theorist
in astroparticle physics. Raklev has launched a model that explains what
dark matter may consist of and how one can discover the invisible particles
experimentally.Even though dark matter is invisible, astrophysicists know
it exists. Without this dark matter it is impossible to explain how the
visible things in the universe hang together. An 80 year fight The world
famous, Swiss physicist _Fritz Zwicky_ (http://en.wikipedia.org/wiki/Fritz_Zwicky)
was speculating on what dark matter might be as early as the 1930s.
Astrophysicists have calculated that 80 per cent of all the mass in the universe
is dark, invisible matter. Thanks to gravity this dark matter clumps
together as ordinary matter. Dark matter can explain why stars move like they
do. Dark matter may also explain the rotation speed of galaxies.
"Even though we can calculate how much dark matter there is in the
universe, we still know little about what dark matter is. The particles in dark
matter must either have a lot of mass, or there must be very many of them.
_Neutrinos_ (http://en.wikipedia.org/wiki/Neutrino) meet all the requirements
of dark matter. But there is one big difficulty. They have far too little
mass." Raklev is now trying to prove that dark matter consists of
gravitinos. This is a particle that has been unfairly treated for years. Gravitinos
are the _supersymmetric partner_
(http://en.wikipedia.org/wiki/Superpartner) of gravitons.
Or, to be even more precise: "The gravitino is the hypothetical,
supersymmetric partner of the hypothetical particle graviton, so it is also
impossible to predict a more hypothetical particle than this," laughs Raklev
(below), who writes on his web pages that he is looking for dark material both
under his sofa and other places.
In order to dig deeper into why Raklev believes dark matter consists of
gravitinos, and have any chance at all of understanding the theory behind
gravitinos, Apollon has to take a couple of steps back: Step 1: Supersymmetry
Physicists want to find out whether or not nature is supersymmetric.
Supersymmetry means that there is a symmetry between matter and forces. For each
type of electron and quark there is a corresponding heavy, supersymmetric
partner. The supersymmetric particles were created in the instant after the
_Big Bang_ (http://en.wikipedia.org/wiki/Big_Bang) . If some of them have
survived to today, they may be what dark matter is made of.
The supersymmetric partner of the gravitino is, as Apollon said, the
graviton. "A graviton is the particle we believe mediates gravitational force,
just like a photon, the light particle, mediates electromagnetic force.
While gravitons do not weigh anything at all, gravitinos may weigh a great
deal. If nature is supersymmetric and gravitons exist, then gravitinos also
exist. And vice versa. This is pure mathematics." But there is a small but.
Physicists cannot demonstrate the relationship between gravitons and
gravitinos before they have managed to unify all the forces of nature.
Step 2: The forces of nature One of the biggest things physicists long to
do is to unify all the forces of nature in a single theory. In the middle
of the last century physicists discovered that electricity and magnetism
were part of the same force of nature. This force has since been called
electromagnetism. Two of the other forces of nature are the strong nuclear force
and the weak nuclear force. The weak nuclear force can be seen in, among
things, radioactivity. The strong nuclear force is ten billion times as
strong and binds together neutrons and protons.
In the 1970s, electromagnetism was unified with the strong and _weak
nuclear forces_ (http://en.wikipedia.org/wiki/Weak_interaction) in what
physicists call the standard model. The fourth force of nature is gravity. Even
though it is unbelievably painful to fall down stairs, gravity is the weakest
of the _four forces of nature_
(http://en.wikipedia.org/wiki/Fundamental_interaction) . The problem is that physicists have not yet been able to unify
gravity with the three other forces of nature.
The day physicists gain a unified understanding of all four forces of
nature, they will gain a unique understanding of the world. This will make it
possible to describe all imaginable interactions between all possible
particles in nature. Physicists call this the ToE Theory (_Theory of Everything_
(http://en.wikipedia.org/wiki/Theory_of_everything) ). In order to unify
gravitational force with the other three forces of nature we have to understand
gravity as quantum theory. This means we need a theory in which the
particle graviton is included in the atomic nucleus.
Researchers are now looking for signs of both supersymmetry and the ToE
Theory. Discovering the graviton would be an enormous step in this direction.
Reveals dark matter As the reader may have understood, it is very
difficult to research dark matter. This is because dark matter has no
electromagnetic relationships to terrestrial particles at all.
One example of dark matter is the aforementioned neutrino. Unfortunately,
neutrinos make up only an imperceptibly tiny part of dark matter. Even
though it has not been possible to observe dark matter, several billion
neutrinos race through your body every second. However, their speed is somewhat
limited. The particles move just as slowly as the speed the solar system
moves around the galaxy.
In other words, a mere 400 kilometres a second. "When there are no
electromagnetic relationships with visible particles, the particles can pass right
through us without any measuring instruments detecting them. This is where
supersymmetry comes in. If supersymmetry is right, physicists can explain
why there is dark matter in the universe. That is what is fun about my
job," laughs Raklev. He is now asserting that dark matter mostly consists of
"Supersymmetry simplifies everything. If the ToE Theory exists, in other
words if it is possible to unify the four forces of nature, gravitinos must
exist." The gravitinos were formed right after the Big Bang. "A short time
after the Big Bang we had a soup of particles that collided. Gluons, which
are the force bearing particles in the strong nuclear force, collided with
other gluons and emitted gravitinos. Many gravitinos were formed after the
Big Bang, while the universe was still plasma. So we have an explanation of
why gravitinos exist."
Physicists have up to now viewed gravitinos as a problem. They have
believed that the theory of supersymmetry does not work because there are too
many gravitinos. "Physicists have therefore strived to eliminate gravitinos
from their models. We, on the other hand, have found a new explanation that
unifies the supersymmetry model with dark matter that consists of
gravitinos. If dark matter is not stable, but just very long lived, it is possible to
explain how dark matter consists of gravitinos."
In the old models dark matter was always everlasting. This meant that
gravitinos were a bothersome part of the supersymmetry model. In Raklev's new
model, their life span is no longer endless. Nonetheless, the average life
span of gravitinos is very long and actually longer than the life span of
the universe. However, there is a big difference between an unending life
span and a life span of more than 15 billion years. With limited a life span,
gravitinos must be converted into other particles. It is precisely this
conversion effect that can be measured. And the conversion explains the model.
"We believe that almost all dark matter is gravitinos. The explanation
lies in very hard mathematics. We are developing special models that calculate
the consequences of these theories and we predict how the particles can be
observed in experiments." The measurements are underway Researchers are
now trying to test this experimentally and explain why these new particles
have not yet been seen in the CERN experiments in Geneva in Switzerland.
"On the other hand, it should theoretically possible to observe them from
a space probe." The simplest way of observing gravitinos could be studying
what happens if two particles collide out in the universe and are converted
into other particles such as photons or antimatter. Even though the
collisions occur very rarely, there is still so much dark matter in the universe
that a significant number of photons should be able to be produced.
The big problem is that gravitinos do not collide. "At least it happens so
rarely that we could never hope to observe it." Nonetheless there is hope.
"Luckily for us, gravitinos are not one hundred per cent stable. They are
converted into something else at some point. We can predict what the signal
looks like after gravitinos have been converted. The conversion will send
out a small electromagnetic wave. This is also called a gamma ray."
NASA's Fermi-LAT space probe is currently measuring gamma rays. A number
of research groups are now analysing the data. "So far we have only seen
noise. But one of the research groups claim they have observed a small,
suspicious surplus of gamma rays from the centre of our galaxy. Their
observations may fit our models," says Raklev.
The Daily Galaxy via University of Oslo Related articles
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Known Galactic Collision_
ilosphy-fromplatoto.html) _"We May be Living in a Massive
Computer-Generated Universe" --Physicists Say Its Reality Can Now Be Tested_
on the Threshold of Unraveling the Biggest Mystery in Modern Physics"
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_From the X Files: "A Meteroite That Crashed to Earth this December
Contains Proof that We are All Aliens"_
Posted: 23 Jan 2013 07:53 AM PST
Sri Lankan-born British mathematician, _Chandra Wickramasinghe_
(http://en.wikipedia.org/wiki/Chandra_Wickramasinghe) , discovered that a two-inch
wide meteorite that crash landed in a fireball in central Sri Lanka in
December was pitted with tiny fossils of algae, similar to the kind found in
seaweed. Wickramasinghe, currently Director of the 'Cardiff Centre for
Astrobiology', was a student and collaborator of _Fred Hoyle_
(http://en.wikipedia.org/wiki/Fred_Hoyle) . Their joint work on the infrared spectra of
interstellar grains led to developing the hypothesis of panspermia that proposes that
cosmic dust in the _interstellar medium_
(http://en.wikipedia.org/wiki/Interstellar_medium) and in comets is partly organic, and that _life on Earth_
(http://en.wikipedia.org/wiki/Organism) was 'seeded' from
space.Wickramasinghe believes the discovery proves we are not alone in the universe: “
These finds are crushing evidence that human life started outside Earth.”
The rock was one of several fragments of a meteorite which crash landed in
a spectacular fireball and were still smoking when villagers living near
the city of _Polonnaruwa_ (http://whc.unesco.org/en/list/201) picked them
up. The fossils, discovered when the rocks were examined under a powerful
scanning electron microscope in a British laboratory, are similar to
micro-organisms found in fossils from the dinosaur age 55 million years ago.
Skeptics say the rock had probably become contaminated with algae fossils from
But Wickramasinghe replies that “The algae organisms are similar to ones
found in Earth fossils, but the rock also has other organisms we have not
“We are all aliens – we share a _cosmic ancestry_
(http://en.wikipedia.org/wiki/Cosmic_ancestry) , Wickramasinghe says. "Each time a new planetary
system forms, a few surviving microbes find their way into comets. These then
multiply and seed other planets. These latest finds are just more evidence
to point to the overwhelming fact that life on Earth began on other worlds.
The Daily Galaxy via www.dailymail.co.uk/
Image credit top of page: S Molau and P Jenniskens NASA Ames Research
Center Related articles
_Alien Biochemistries --Astrobiologists Anticipate Discovering Non-Carbon
Life Forms (Weekend Feature)_
(http://www.dailygalaxy.com/my_weblog/2012/11/from-the-x-files-the-search-for-alien-microbes-on-earth.html) _From the X Files: "The Search for Alien
Microbes on Earth"_
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