I wouldn’t dream of trying (nor would I be able) to explain string theory — for a popular treatment of that, see Brian Greene’s The Fabric of the Cosmos (Knopf, 2004). But I do know that ideas like string theory and supersymmetry arose to help us unify the world of quantum mechanics and that of general relativity. Extreme energies can unite electromagnetism and the weak force (think radioactive decay). The next generation of particle accelerators may unify both with the strong force (atomic nuclei bonding). But where will we get the energies needed to explore the unification of the quantum world with gravity?
The answer may come from outside the galaxy. Researchers at Northeastern University and the University of California, Irvine think that deep space neutrinos colliding with protons can release energies that test string theory. The notion is being examined in the AMANDA project, a neutrino detector at the South Pole. Although few high-energy neutrinos have been detected so far, the researchers believe a next-generation detector called IceCube, now being built, could help them compare ‘down’ neutrinos (coming in from above) and ‘up’ neutrinos (passing through the Earth and coming up from below).
“String theory and other possibilities can distort the relative numbers of ‘down’ and ‘up’ neutrinos,” said Jonathan Feng (UC-Irvine). “For example, extra dimensions may cause neutrinos to create microscopic black holes, which instantly evaporate and create spectacular showers of particles in the Earth’s atmosphere and in the Antarctic ice cap. This increases the number of ‘down’ neutrinos detected. At the same time, the creation of black holes causes ‘up’ neutrinos to be caught in the Earth’s crust, reducing the number of ‘up’ neutrinos. The relative ‘up’ and ‘down’ rates provide evidence for distortions in neutrino properties that are predicted by new theories.”
Centauri Dreams‘ take: Are we on the edge of the first experimental verification of at least some aspects of string theory? The potential seems clear, but using extragalactic sources as cosmic accelerators may reveal as many surprises as confirmations. What is germane to interstellar studies is that string theory posits extra dimensions via its exquisite mathematics, and promises to tell us much about the nature of expanding spacetime. But thus far even the most elegant of its predictions have proven untestable.
Is string theory a case of art masquerading as mathematics, what an old professor of mine used to call a ‘rabbit hole’ for the unwary, or a description of underlying physical realities? The sooner we start finding out, the better, as the amount of intellectual capital being expended on strings and the theories that bind them is breathtaking. The paper is Anchordoqui, Goldberg and Feng, “Particle Physics on Ice: Constraints on Neutrino Interactions Far above the Weak Scale,” in Physical Review Letters 96, 021101 (2006). An abstract is here.
Cosmic Strings via their Strong Gravitational Lensing Effect: I. Predictions for High Resolution Imaging Surveys
Authors: Maria Alice Gasparini, Phil Marshall, Tommaso Treu, Eric Morganson, Florian Dubath
(Submitted on 29 Oct 2007 (v1), last revised 21 Dec 2007 (this version, v2))
Abstract: We use current theoretical estimates for the density of long cosmic strings to predict the number of strong gravitational lensing events in astronomical imaging surveys as a function of angular resolution and survey area. We show that angular resolution is the most important factor, and that interesting limits on the dimensionless string tension Gmu/c^2 can be obtained by existing and planned surveys. At the resolution of the Hubble Space Telescope (0.14″), it is sufficient to survey of order a few square degrees — well within reach of the current HST archive — to probe the regime Gmu/c^2 ~ 10^{-7}. If lensing by cosmic strings is not detected, such a survey would improve the limit on the string tension by a factor of two over that available from the cosmic microwave background. Future high resolution imaging surveys, covering a few hundred square degrees or more, either from space in the optical or from large-format radio telescopes on the ground, would be able to further lower this limit to Gmu/c^2 less than 10^{-8}.
Comments: 7 pages, 3 figures, accepted for publication in MNRAS following in-press correction
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0710.5544v2 [astro-ph]
Submission history
From: Phil Marshall [view email]
[v1] Mon, 29 Oct 2007 22:18:37 GMT (42kb)
[v2] Fri, 21 Dec 2007 22:15:04 GMT (30kb)
http://arxiv.org/abs/0710.5544
Cosmic strings in a test tube?
Ultracold helium could be an analogue of the early universe
http://physicsworld.com/cws/article/news/32344
Scientists propose test of string theory based on neutral hydrogen absorption
Contact:
James E. Kloeppel
Physical Sciences Editor
1-217-244-1073 kloeppel@uiuc.edu
January 28, 2008
CHAMPAIGN, Ill. — Ancient light absorbed by neutral hydrogen atoms could be
used to test certain predictions of string theory, say cosmologists at the
University of Illinois. Making the measurements, however, would require a
gigantic array of radio telescopes to be built on Earth, in space or on the
moon.
String theory – a theory whose fundamental building blocks are tiny
one-dimensional filaments called strings – is the leading contender for a
“theory of everything.” Such a theory would unify all four fundamental forces of
nature (the strong and weak nuclear forces, electromagnetism, and gravity). But
finding ways to test string theory has been difficult.
Now, cosmologists at the U. of I. say absorption features in the 21-centimeter
spectrum of neutral hydrogen atoms could be used for such a test.
“High-redshift, 21-centimeter observations provide a rare observational window
in which to test string theory, constrain its parameters and show whether or not
it makes sense to embed a type of inflation – called brane inflation – into
string theory,” said Benjamin Wandelt, a professor of physics and of astronomy
at the U. of I.
“If we embed brane inflation into string theory, a network of cosmic strings is
predicted to form,” Wandelt said. “We can test this prediction by looking for
the impact this cosmic string network would have on the density of neutral
hydrogen in the universe.”
Wandelt and graduate student Rishi Khatri describe their proposed test in a
paper accepted for publication in the journal Physical Review Letters.
About 400,000 years after the Big Bang, the universe consisted of a thick shell
of neutral hydrogen atoms (each composed of a single proton orbited by a single
electron) illuminated by what became known as the cosmic microwave background.
Because neutral hydrogen atoms readily absorb electromagnetic radiation with a
wavelength of 21 centimeters, the cosmic microwave background carries a
signature of density perturbations in the hydrogen shell, which should be
observable today, Wandelt said.
Cosmic strings are filaments of infinite length. Their composition can be
loosely compared to the boundaries of ice crystals in frozen water.
When water in a bowl begins to freeze, ice crystals will grow at different
points in the bowl, with random orientations. When the ice crystals meet, they
usually will not be aligned to one another. The boundary between two such
misaligned crystals is called a discontinuity or a defect.
Cosmic strings are defects in space. A network of strings is predicted by string
theory (and also by other supersymmetric theories known as Grand Unified
Theories, which aspire to unify all known forces of nature except gravity) to
have been produced in the early universe, but has not been detected so far.
Cosmic strings produce characteristic fluctuations in the gas density through
which they move, a signature of which will be imprinted on the 21-centimeter
radiation.
The cosmic string network predicted to occur with brane inflation could be
tested by looking for the corresponding fluctuations in the 21-centimeter
radiation.
Like the cosmic microwave background, the cosmological 21-centimeter radiation
has been stretched as the universe has expanded. Today, this relic radiation has
a wavelength closer to 21 meters, putting it in the long-wavelength radio
portion of the electromagnetic spectrum.
To precisely measure perturbations in the spectra would require an array of
radio telescopes with a collective area of more than 1,000 square kilometers.
Such an array could be built using current technology, Wandelt said, but would
be prohibitively expensive.
If such an enormous array were eventually constructed, measurements of
perturbations in the density of neutral hydrogen atoms could also reveal the
value of string tension, a fundamental parameter in string theory, Wandelt said.
“And that would tell us about the energy scale at which quantum gravity begins
to become important.”
Funding was provided by the Alexander von Humboldt Foundation.
To reach Benjamin Wandelt, call 1-217-333-9374; e-mail: bwandelt@uiuc.edu.
March 13, 2009
Cause Identified of Surges in Antimatter Sweeping Through Space
Scientists have seen surges in antimatter particles sweeping through space, and some believe the cause could be collapsing cosmic strings. As opposed to Ming the Merciless.
Note that cosmic strings are entirely different strings from string theory – blame any confusion on the fact that there are far more cool things happening in space than we have words for.
Full article here:
http://www.dailygalaxy.com/my_weblog/2009/03/collapsing-cosm.html
A review of Brian Greene’s new book, The Hidden Universe:
http://www.bookforum.com/inprint/017_05/7029