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Testing string theory soon, with Cosmic Microwave Background?

  1. Feb 11, 2007 #1
    Has anyone heard of this proposed test of string theory's extra dimensions? What do you think? Within the realm of reason? Doable within the next decade?




    ...physicists at the University of Wisconsin-Madison have devised an approach that may help unlock the hidden shapes of alternate dimensions of the universe. A new study demonstrates that the shapes of extra dimensions can be "seen" by deciphering their influence on cosmic energy released by the violent birth of the universe 13 billion years ago. The method, published today (Feb. 2) in Physical Review Letters, provides evidence that physicists can use experimental data to discern the nature of these elusive dimensions ...

    ...Our minds are accustomed to only three spatial dimensions and lack a frame of reference for the other six, says UW-Madison physicist Gary Shiu, who led the new study. ...The new Wisconsin work may provide a long-sought foundation for measuring this previously immeasurable aspect of string theory.

    ....Shiu says the many-dimensional shapes are far too small to see or measure through any usual means of observation, which makes testing this crucial aspect of string theory very difficult. "You can theorize anything, but you have to be able to show it with experiments," he says. "Now the problem is, how do we test it?" He and graduate student Bret Underwood turned to the sky for inspiration. Their approach is based on the idea that the six tiny dimensions had their strongest influence on the universe when it itself was a tiny speck of highly compressed matter and energy — that is, in the instant just after the big bang.

    "Our idea was to go back in time and see what happened back then," says Shiu. "Of course, we couldn't really go back in time."

    Lacking the requisite time machine, they used the next-best thing: a map of cosmic energy released from the big bang. The energy, captured by satellites such as NASA's Wilkinson Microwave Anisotropy Probe (WMAP), has persisted virtually unchanged for the last 13 billion years, making the energy map basically "a snapshot of the baby universe," Shiu says. The WMAP experiment is the successor to NASA's Cosmic Background Explorer (COBE) project, which garnered the 2006 Nobel Prize in physics.

    Just as a shadow can give an idea of the shape of an object, the pattern of cosmic energy in the sky can give an indication of the shape of the other six dimensions present, Shiu explains.

    To learn how to read telltale signs of the six-dimensional geometry from the cosmic map, they worked backward. Starting with two different types of mathematically simple geometries, called warped throats, they calculated the predicted energy map that would be seen in the universe described by each shape. When they compared the two maps, they found small but significant differences between them.

    Their results show that specific patterns of cosmic energy can hold clues to the geometry of the six-dimensional shape — the first type of observable data to demonstrate such promise, says Tye.

    Though the current data are not precise enough to compare their findings to our universe, upcoming experiments such as the European Space Agency's Planck satellite should have the sensitivity to detect subtle variations between different geometries, Shiu says.

    "Our results with simple, well-understood shapes give proof of concept that the geometry of hidden dimensions can be deciphered from the pattern of cosmic energy," he says. "This provides a rare opportunity in which string theory can be tested."
  2. jcsd
  3. Feb 12, 2007 #2


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    One of the most fundamental predictions of string theory is that a certain amount of energy should 'leak' into the hypothetical extra dimensions. In years past, there was similar hope that extra dimensions could be detected via this 'leak' effect in sufficiently powerful particle accelerators. However, no evidence of any 'missing' energy has surfaced in experiments to date. There remains some hope the LHC will be powerful enough to detect the effect.

    This approach is more appealing in that it relies upon the most powerful acclerator possible - the big bang. Unfortunately, current CMB resolutions are not yet sufficiently sensitive to detect any such 'leak' effect either. Perhaps the Planck satellite will be sufficiently sensitive to yield some answers. I doubt either the LHC or the Planck mission will resolve the issue to anyone's satisfaction, but, you never know.
  4. Feb 12, 2007 #3
    Wouldn't the leak out of our brane into another be compensated by the same amount of leak from other branes into ours?
  5. Feb 14, 2007 #4


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    Perhaps, but if the 'missing' energy is instantly returned to where it 'leaked' from, the 'leak' hypothesis is untestable.
  6. Feb 20, 2007 #5
    hi chronos,

    i got a big kick out of your 2 signatures. LOL. the one thing about string theory that just begs to be answered - what are strings made of ? the very notion of a string is something comprised of many points.

    according to string theory, matter is composed of various strings vibrating in certain ways. it seems to be that these strings, if they exist, can not possibly be the ultimate answer.
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