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Topic: Cosmic string


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In the News (Fri 24 May 19)

  
  Cosmic string - Wikipedia, the free encyclopedia
Cosmic strings are hypothesized to form when different regions of spacetime undergo phase changes, resulting in domain boundaries between the two regions when they meet.
Cosmic strings would form a network of loops in the early universe, and their gravity could have been responsible for the original clumping of matter into galactic superclusters.
Cosmic strings were once thought to be an explanation of the large scale structure of the universe, but all what is known today through galaxy surveys and precision measurements of the cosmic microwave background fits an evolution out of random, gaussian fluctations.
en.wikipedia.org /wiki/Cosmic_string   (584 words)

  
 String theory - Wikipedia, the free encyclopedia
String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects (strings) rather than the zero-dimensional points (particles) that are the basis of the Standard Model of particle physics.
Since string theory may not be tested in the foreseeable future, some scientists have asked if it even deserves to be called a scientific theory: it is not yet a falsifiable theory in the sense of Popper.
Originally discussed in the 1980s, cosmic strings are a different type of object than the entities of superstring theories.
en.wikipedia.org /wiki/String_theory   (2656 words)

  
 A Science Odyssey: People and Discoveries: Cosmic string theory introduced   (Site not responding. Last check: 2007-10-22)
Also, the cosmic background radiation discovered in 1965, considered a virtual echo of the big bang, was completely uniform throughout the sky, ruling out the notion that irregularities in the initial bang could account for the distribution of matter.Why then is the universe so inconsistent, with some places jammed with matter and others apparently empty?
It is thought that strings oscillate near the speed of light and give off gravitational waves (predicted by Einstein's theory of general relativity), ripples in space-time.
Strings could be a form of dark matter which attracted matter to cohere.
www.pbs.org /wgbh/aso/databank/entries/dp76st.html   (433 words)

  
 Cosmic (super)strings and LIGO
Cosmic strings were also appealing because their cosmological evolution (at least the gross features) turned out to be quite simple.
In this regime, the energy density of the string network becomes a small constant fraction of the radiation or matter density, and the statistical properties of the system, such as the correlation lengths of long strings and average sizes of loops, scale with the cosmic time.
The formation of cusps on cosmic string loops and long strings is generic, and their gravitational waveforms simple and robust [3].
www.phys.lsu.edu /mog/mog25/node12.html   (858 words)

  
 Alternate View Column AV-19
Cosmic strings are now of great interest because they may be the "seeds" that caused the formation of galaxies.
Both strings and monopoles are imperfections in space itself that may have occurred in the initial phases of the Big Bang, when normal space was precipitated from the energy saturated Higgs space of the primeval universe.
When we consider that a hypothetical cosmic string that may have caused the formation of our galaxy would have a length of thousands of light years, it becomes clear that a single such cosmic string could indeed be the dark matter responsible for a large part of the mass of our galaxy.
www.npl.washington.edu /AV/altvw19.html   (1905 words)

  
 Luboš Motl's reference frame: Astronomers prove string theory?
The gravitational field of a cosmic string in 3+1 dimensions is simple - the spacetime is flat everywhere except for the locus of the string, but it has a deficit angle, much like a usual cone (multiplied by two more flat dimensions along the stringy worldsheet).
This fits the estimate for the tension that you expect from some GUT cosmic strings or the fundamental strings in string theory themselves - in the nearly old-fashioned models where the string scale is close to the GUT scale.
String theory obviously offers several explanations - from the ordinary ones (cosmic strings from spontaneously broken gauge group) to the super-exciting ones, namely the fundamental superstrings grown to a macroscopic size.
motls.blogspot.com /2004/12/astronomers-prove-string-theory.html   (3270 words)

  
 Superconducting Cosmic Strings   (Site not responding. Last check: 2007-10-22)
As imagined by physicists, cosmic strings are exceedingly narrow filaments of primordial material, strands of a trapped, unconverted phase left over from the early moments of cosmic history.
A cosmic string forms when, for purely topological reasons, the orientation of the arrows cannot be adjusted so as to keep the Higgs field in the minimum energy state at all places.
To an observer, the presence of a cosmic string would be betrayed by its effect on the trajectory of passing light rays, which are deflected by an amount equal to the deficit angle.
www.iafe.uba.ar /relatividad/gangui/SCS.html   (6427 words)

  
 [No title]
Below are two movies of the phase space of particles falling into the wake of a cosmic string.
The baryonic matter temperature in K of a cosmic string wake: Z_init = 100, linear scale ~ 0.0002 Mpc
Since the velocity imparted to the fluid by the gravitational force is not greater than the sound speed, an outward moving shock is created, depleting the core of the wake of baryonic matter and creating high a temperature and pressure at the core of the wake.
camelot.mssm.edu /~ats/string.html   (1028 words)

  
 Alternate View Column AV-24
Cosmic string should not be a new notion for regular readers of this column because I discussed them in a fairly recent Alternate View column published in the April, 1987 issue of Analog.
Cosmic strings are hypothetical remnants of the Big Bang which have been described by popularizers as "cracks in space" or as "strings of pure energy".
Cosmic strings are predicted to be infinitesimally small in cross section but very long, perhaps forming closed loops a few hundred thousand light years long that encircle entire galaxies.
www.npl.washington.edu /AV/altvw24.html   (2008 words)

  
 Cosmic String Simulations
Therefore, one of the aims of performing numerical simulations of the evolution of cosmic string networks is to subsequently use the resulting information as an input to build (relatively) simpler analytic models that reproduce (in an averaged sense) the crucial properties of these objects.
Understanding string evolution during the matter epoch from a few thousand years through to the present day is important for predicting their potential role in galaxy formation.
The evolution of a cosmic string network during the transiton from the radiation-dominated to the matter dominated epochs.
www.damtp.cam.ac.uk /user/gr/public/cs_evol.html   (1635 words)

  
 Backstitching Time with Cosmic String, Alaska Science Forum   (Site not responding. Last check: 2007-10-22)
Princeton physicist J. Richard Gott contemplated the effects of cosmic strings on spacetime, and decided they'd be prodigious.
The pure energy of a cosmic string translates into a mass equivalence of 40 million billion tons an inch.
He played with the equations of general relativity, he tuned the cosmic strings, and he finally found a warp so severe it produced a potential time machine.
www.gi.alaska.edu /ScienceForum/ASF10/1089.html   (662 words)

  
 Two cheers for string theory | Cosmic Variance   (Site not responding. Last check: 2007-10-22)
String theory, with all of its difficulties, is by far the most promising route to one of the most long-lasting and ambitious goals of natural science: a complete understanding of the microscopic laws of nature.
String theorists, arrogant as they are, ignored all of that and claimed that all of chemistry was an application of string theory.
If string theorists continue to develop a really outdated theory at one hand and arrogantly claim that are doing (they believe that in their infinite ignorance) the most important, the most powerful, the most fundamental theory at the other, then they would feel comfortable with the mocking of their colleagues.
cosmicvariance.com /2005/07/21/two-cheers-for-string-theory   (15208 words)

  
 ADASS 2003 Conference Proceedings
If the defects were generated at the GUT energy, the cosmic string can be observed as an origin of gravitation lensing (Vilenkin 1984) and its detection can be an observational confirmation of the standard theory.
Features of a string lens event are characterized as non-distorted equal-brightness double images which are aligned in the direction of the string network.
Since the detection rate of the GL candidates by a cosmic string is expected to be very small, a survey of large amount of data is crucial and development of the automatic detection system is required.
adass.org /adass/proceedings/adass03/P1-9   (1351 words)

  
 Cosmic F- and D-strings | The String Coffee Table
A “macroscopic” fundamental string is a string with large occupation numbers for certain string modes.
Everybody agrees that the classical dynamics of a cosmic string (a huge linear defect of some sort) is to a good approximation described by a Nambu-Goto/Polyakov action (whichever).
Of course this is an exact solution to the free string equations of motion but the question is whether this behaves as a macroscopic string.
golem.ph.utexas.edu /string/archives/000271.html   (1217 words)

  
 Quasar   (Site not responding. Last check: 2007-10-22)
Small perturbations causing the string end to oscillate (random oscillation of the direction of a flicker is a good analogy) imply that the beam of energy can meet the Earth at each period of oscillation and cause a sequence of pulses.
The shape of the pulse is predicted to reflect only the time development of the direction of the cosmic string rather than the actual intensity distribution of the pulse and this should nake it possible to distinguish between TGD based and other explanations for the bursts.
The value of Omega had better to be rather small since the oscillations in the direction of the cosmic string leading to fluctuations in the intensity of beam must be of the order of Omega and too large fluctuations are not expected (cosmic string is quite a heavy object!).
www.physics.helsinki.fi /~matpitka/quasar.html   (1696 words)

  
 Science & Technology at Scientific American.com: String Revival -- [ COSMOLOGY ] -- Are cosmic strings behind ...
In particular, cosmic strings, which fell out of favor in the late 1990s, are making a comeback thanks to observations that may have actually detected them.
Cosmic strings are hypothetical one-dimensional defects in the fabric of space-time.
The moving cosmic string would have acted as an additional gravitational lens, affecting both quasar images simultaneously.
www.sciam.com /article.cfm?chanID=sa004&articleID=0008306C-3A8A-11E7-B78C83414B7F0000   (551 words)

  
 String Evolution
The evolution of cosmic string network is the relatively complicated result of only three rather simple and fundamental processes: cosmological expansion, intercommuting and loop production, and radiation.
In fact the network dynamics is such that the string density will eventually stabilize at an exactly constant level relative to the rest of the radiation and matter energy density in the universe.
Thus the string evolution is described as `scaling' or scale-invariant, that is, the properties of the network look the same at any particular time t if they are scaled (or multiplied) by the change in the time.
www.damtp.cam.ac.uk /user/gr/public/cs_interact.html   (794 words)

  
 Cosmic String Lenses   (Site not responding. Last check: 2007-10-22)
Below are a series of simulated pictures showing the effects of cosmic string lensing on high redshift galaxies in the Hubble Deep Field.
These pictures were created from 450 nm, 606 nm, and 814 nm channels of the Hubble Deep Field, where the redshifts of all objects were determined photometrically (data for this work was gracously provided by Marcin Sawicki).
Galaxies were binned by redshift at intervals of dz = 0.5, and the images were lensed using the methods outlined in "Observing Long Cosmic Strings Through Gravitational Lensing".
theory2.phys.cwru.edu /~delaix/cosmic.html   (191 words)

  
 Luboš Motl's reference frame: WMAP and cosmic strings
Quantoken asked what's new with the observed cosmic strings - his or her personal theory is that CSL-1 "was really just bird shit causing the original telescope to record a slightly distorted image".
The article first of all confirms that there are no cosmic strings seen in the microwave background whose tension would exceed a certain bound and whose velocity is smaller than 0.7c or so.
They observe the discontinuity of the microwave background temperature near the cosmic string with *2 sigma* significance which may or may not be a sign of the cosmic string.
motls.blogspot.com /2005/03/wmap-and-cosmic-strings.html   (2100 words)

  
 Formation of Black Holes from Collapsed Cosmic String Loops (ResearchIndex)   (Site not responding. Last check: 2007-10-22)
Abstract: The fraction of cosmic string loops which collapse to form fl holes is estimated using a set of realistic loops generated by loop fragmentation.
The smallest radius sphere into which each cosmic string loop may fit is obtained by monitoring the loop through one period of oscillation.
For a loop with invariant length L which contracts to within a sphere of radius R, the minimum mass-per-unit length ¯ min necessary for the cosmic string loop to form a fl hole according to the hoop...
citeseer.ist.psu.edu /caldwell95formation.html   (272 words)

  
 Is it a cosmic string we're seeing?
String theory suggests that our universe may be a three-dimensional island, or "brane", and that the big bang was the result of a collision between our universe and another 3D brane.
The collision would have given rise to one-dimensional cosmic strings, and finding such a string would strengthen the theory and support the idea that extra dimensions exist.
If a string is producing the twin galaxy images, the edges of the images should be extremely sharp, but our turbulent atmosphere prevents telescopes on Earth from detecting this.
www.eurekalert.org /pub_releases/2005-07/ns-iia072705.php   (629 words)

  
 What is a 'cosmic string'?   (Site not responding. Last check: 2007-10-22)
Super strings are what physicists consider the 'end of the line' in describing the structure of both particles and fields in nature.
String theory is the current theory which looks like it might be able to describe, in one consistent language, how all of the particles and fields we know about, work, and blend together to form the physical world and all of its laws and 'symmetries'.
They are called Cosmic Strings, but they have nothing to do with Super Strings.
www.astronomycafe.net /qadir/ask/a11828.html   (237 words)

  
 a search for traces of cosmic string didnt find much - Physics Help and Math Help - Physics Forums   (Site not responding. Last check: 2007-10-22)
However, if this edge is real and produced by a cosmic string, it would have to move at velocity $\ga$ 0.94c.
Maybe it isn't a cosmic string, but the evidence seems to be there to suggest something is going on.
The cosmic string scenario predicted they would arise from GUT phase transitions, and be abundant.
www.physicsforums.com /showthread.php?threadid=66368   (1353 words)

  
 Gravitational effect of the quantum vacuum outside a cosmic string   (Site not responding. Last check: 2007-10-22)
The conical geometry of a static cylindrically symmetric cosmic string gives a non-vanishing contribution to the vacuum expectation value of the energy-momentum tensor of a quantum field.
The strongly curved interior of the string is modelled by a homogeneous fluid with vanishing tangential and radial stress.
The integrated effect of vacuum polarization in this region is assumed to be accounted for by a singular layer with a traceless energy-momentum surface density at the surface of the string.
www.nr.no /~soleng/papers/strings-abs/CQG_9_1231_1992.html   (133 words)

  
 Citebase - Limits on Black Hole Formation from Cosmic String Loops   (Site not responding. Last check: 2007-10-22)
In theories with standard cosmic strings, it is known that a small fraction of string loops may collapse to form fl holes, which puts various constraints on such models.
The fraction of cosmic string loops which collapse to form fl holes is estimated using a set of realistic loops generated by loop fragmentation.
Observational restrictions on a population of primordial fl holes are used to restrict f, the fraction of cosmic string loops which collapse to form fl holes, and μ, the cosmic string m...
citebase.eprints.org /cgi-bin/citations?archiveID=oai:arXiv.org:astro-ph/9707146   (1249 words)

  
 Near-field expansion of the metric due to a cosmic string   (Site not responding. Last check: 2007-10-22)
Near-field expansion of the metric due to a cosmic string
By erecting a co-ordinate system tailored to the geometry of a cosmic string and examining the properties of the near gravitational field, it is possible to distinguish two types of gravitational waves supported by a general string metric.
The first type, travelling waves, are completely decoupled from the curvature of the world sheet, whereas the second type, which I choose to call curvature waves, are generated in response to any non-trivial geometric structure on the string.
anziamj.austms.org.au /V41/part2/Anderson.html   (128 words)

  
 The Official String Theory Web Site   (Site not responding. Last check: 2007-10-22)
Personal safety issues aside, when fl holes are tied up in strings, they get even more interesting.
Now playing in the String Theatre: a Real Audio physics colloquium by Prof.
Discuss string theory and the legacy of Albert Einstein in our community forum.
superstringtheory.com   (153 words)

  
 Wired 11.08: The Super Power IssueA User's Guide to Time Travel
All it takes is a grasp of theoretical physics, control of the space-time continuum, and maybe a ball of cosmic string.
Many scientists believe the big bang that created the universe left behind cosmic strings - thin, infinitely long filaments of compressed matter.
Use the ship's gravity to shape the string into a rectangle roughly 54,000 light-years long and.01 light-years wide.
www.wired.com /wired/archive/11.08/pwr_timetravel.html   (1103 words)

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