Posted on 05/20/2003 9:56:23 AM PDT by RightWhale
Florida Physicist Says Dark Matter, Extra Dimensions Related And Possibly Detectable
the universe is the "twilight zone"
Gainesville -May 19, 2003
A team of scientists that includes a University of Florida physicist has suggested that two of the biggest mysteries in particle physics and astrophysics -- the existence of extra time and space dimensions and the composition of an invisible cosmic substance called dark matter -- may be connected.
"For the most part, these two questions have been treated separately in the past, and for the first time we're making a direct link," said Konstantin Matchev, a UF assistant professor of physics. "We're suggesting that the dark matter may be due to extra dimensions."
If correct, the scientists' theory may lead to the discovery of the first concrete evidence of dark matter, an invisible substance that may comprise as much as 30 percent of the universe. Dark matter has never yet been directly or indirectly observed.
Matchev co-authored a paper on the subject that has been widely cited by other scientists since appearing in the journal Physics Review Letters in November. The other authors are Hsin-Chia Cheng and Jonathan Feng, physicists at Harvard University and the University of California at Irvine, respectively.
Scientists have long inferred dark matter is present based on a discrepancy between galaxies' rotational speed and the amount of visible stars within them. In a nutshell, there are not enough stars or visible objects to account for the speed, which means the galaxies must also contain the invisible dark matter. Its composition is unknown.
Extra dimensions are predicted by the superstring theory, which offers a unified description of all of the fundamental particles and forces in nature, including gravity. While this widely accepted theory predicts at least 10 dimensions, however, no one has ever found more than one dimension in time and three in space.
According to one alternative theory, these additional dimensions might be curled up into a ball so small -- significantly smaller than atoms -- that they are difficult or impossible to observe. Matchev said his team believes these dimensions may give rise to heavier versions of known particles, the lightest of which could constitute the elusive dark-matter particle. "This phenomenon of extra dimensions provides a completely new dark-matter candidate," Matchev said. "We named it Kaluza-Klein dark matter, after the two physicists who first proposed theories with extra dimensions in the early 1920s."
Most important is that Kaluza-Klein dark matter may be detected using a variety of current and future experiments, Matchev said. In addition to dedicated underground searches designed specifically to look for dark-matter particles, Kaluza-Klein particles may give distinct, albeit indirect, signals in numerous other experiments, he said.
For example, an ongoing experiment on the South Pole designed to detect elementary particles called neutrinos -- as well as an antimatter detector set to be placed aboard the International Space Station -- could be used to find these heavier particles. The South Pole device, known as the Antarctic Muon Neutrino Detector Array, or AMANDA, is designed to detect particles with no electrical charge and no mass created in massive cosmic events such as supernovas.
But this "neutrino telescope" also may pick up telltale high-energy neutrinos necessarily created when dark-matter particles collide where they are most concentrated, at the gravitational centers of stars and planets. The detection of these types of neutrinos from these areas would provide indirect evidence of dark matter, Matchev said. "Most of the stuff produced by dark-matter particle collisions is probably absorbed in the dense cores of the sun or the Earth, but the neutrinos, being so weakly interacting, escape and may reach our detectors," Matchev said. "So what we're looking for are unusual sources of neutrinos near gravitational centers."
Matchev said scientists also have a separate shot at detecting dark matter in a future antimatter detector, the Alpha Magnetic Spectrometer, slated to reach the International Space Station in 2005. The detector may pick up positrons, the antiparticles of electrons, similarly created when the dark-matter particles collide. "If we see more positrons than we expect, then we know there is something going on," Matchev said. "What is more, the positron signal is rather unique for Kaluza-Klein dark matter and may thus provide the first evidence of extra dimensions."
Yet another experimental apparatus, the Gamma Ray Large Area Space Telescope, is slated for satellite launch in 2006. This telescope could discover very high-energy photons
Okay now, are they changing their minds again, or are they just out of the loop?
Keep it clean!
Or rather, "Whatza Matter".
Be careful with that. If you drop it, we'll never find it again...
That's the truth. It's so small we might not even find it in the first place.
I'll think about that tomorrow.
Given the computation power required to do this given lightspeed delay of gravitional effects simulating the motion of galactic bodies, I believe that this calculation is done assuming instantaneous gravitational effects!! Someone correct me if I am wrong.
Well, whaddya know!
Dark matter arising from extra spatial dimensions could be detected with existing or future experiments, according to the 18 November print issue of PRL. If an additional dimension were hidden in the right way, heavier replicas of the known particles might traverse space and account for the mysterious "dark" component of the Universe's mass. Detecting the unique particles would potentially confirm the existence of extra dimensions and solve at least part of the dark matter riddle.
Researchers think that 30% of the Universe's mass is made up of unknown particles that are invisible to telescopes but have gravitational effects on galaxies. Potential culprits called weakly-interacting massive particles (WIMPs) come from proposed extensions to the standard model of particle physics, such as supersymmetry and extra-dimensional theories. To verify the theories, searches for some of these particles look to space, because particle accelerators are too weak to produce them. But the big bang should have produced every particle. "Maybe the Universe made them for us and they're floating around out there and are dark matter," says Jonathan Feng of the University of California at Irvine. "Now the [difficulty] is you have to find them."
Kaluza-Klein particles are named for the two theorists who first proposed that extra dimensions could be "curled up" to a size too small for us to notice them. In the simplest case, these particles would be much like those of the standard model, but would move through four spatial dimensions instead of three. Their momentum along the fourth dimension would appear as additional mass in three dimensions, so we would observe heavy photons or heavy electrons, for example. The smaller the extra dimension, the greater the mass.
Now Feng and his colleagues have found that Kaluza-Klein particles would heat up or ionize a block of material such as germanium at rates comparable to other dark matter candidate particles. They could also annihilate each other in space, creating showers of ordinary particles. The researchers calculated that Kaluza-Klein dark matter would generate a unique, sharp positron signal, distinguishing it from the neutralinos of supersymmetry. Because dark matter feels the gravitational force, it would be drawn toward the sun's large mass and lead to an excess of neutrino and muon showers from the sun's direction. The AMANDA neutrino detector, buried within the Antarctic ice, or the Alpha-Magnetic Spectrometer (AMS), an antimatter detector scheduled to fly on the International Space Station in late 2005, could hunt out these signals.
"Kaluza-Klein dark matter is definitely worth looking for with AMS," says Kate Scholberg of the Massachusetts Institute of Technology in Cambridge, who works on the detector project. "The indirect signature would be quite dramatic for some of the possible parameters they discuss." She adds that detecting and distinguishing Kaluza-Klein and supersymmetric dark matter would depend strongly on how nature actually behaves, but coming up empty wouldn't rule them out, just constrain their possible characteristics.
--JR Minkel
Kaluza-Klein Dark Matter
Hsin-Chia Cheng, Jonathan L. Feng, and Konstantin T. Matchev
Phys. Rev. Lett. 89, 211301
(issue of 18 November 2002)
PDF file of the original letter is linked at the above page but is available only to subscribers or for a fee.
And, of course, as Heisenberg showed: There are things that are unknowable.
I've given this dark matter/extra dimensions/time conundrum quite a bit of thought, research and pondering.
It seems to me that 'time' (as in the cause/effect, before/after human construct) only exists inside the head of the observer. We manufacture time and causality as a survival instinct synonymous with 'self-awareness'.
The greater universe certainly doesn't follow our construct, thus the 'dark matter' is everything that is not the 'present'. It has both mass and quantum energy, but is impenetrable to us in our relative 'time-space'.
In 'non-time' space, imagine a small 'cube' of space. 'Now' there is nothing in it, it is space. Before, maybe there was stuff in it. Maybe there will be stuff in it later. All those 'potentialities' of no stuff/stuff in it carry weight and energy because they all exist at once. Our tiny 'conscious 'now-filter'' only shows us a time-slice of those potentialities (the energy of probability) and then fills in the rest of the story like our minds fill in the rest of a sliver moon.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.