[Paleopsych] Economist: Cosmology: A braney theory

[Lynn D. Johnson, Ph.D.]

     Here is a nice illustration of the anthropic principle I thought 
you might enjoy.


Premise Checker wrote:

>    Oct 6th 2005
>
>    An explanation for the anthropic principle comes a little closer
>
>    DID God have a choice? Or, to put the matter less theologically, does
>    the universe have to be the way that it is? The answer to this
>    question, posed by Einstein among others, remains elusive. But it is
>    important, not least because a universe with laws only slightly
>    different from those actually observed would be one in which life--and
>    therefore human life--could never have come into existence.
>
>    That observation, known as the anthropic principle, disturbs many
>    physicists because they cannot see any fundamental reason why things
>    could not be different. In particular, they cannot see why space has
>    to have three dimensions. But a paper due to be published this month
>    in Physical Review Letters by Andreas Karch of the University of
>    Washington and Lisa Randall of Harvard University suggests that the
>    laws of physics may, indeed, be biased towards three-dimensions.
>    Curiously, though, they have a similar bias towards seven-dimensions.
>
>    The idea that there may be more dimensions than the familiar ones of
>    length, breadth and height (and also, to be strictly accurate, the
>    fourth dimension of time) is a consequence of attempts to solve an old
>    problem in physics. Ever since Einstein developed his theories of
>    space, time and gravity, physicists have sought a "theory of
>    everything" that would unite those theories with quantum
>    mechanics--the part of physics that describes electromagnetism and the
>    forces that hold atomic nuclei together. Such a theory would, it is
>    hoped, describe how the universe developed from the Big Bang. It would
>    explain why there appears to be more matter than anti-matter. It would
>    even indicate the nature of the dark energy and dark matter that lurk
>    at the edge of perception.
>
>    To date, the best candidates for a theory of everything are various
>    versions of a branch of mathematics called string theory.
>    Unfortunately for common sense, these theories require the universe to
>    have ten or even 11 dimensions rather than the familiar three of space
>    and one of time. To get round this anomaly, some physicists propose
>    that the familiar dimensions are "unfurled", while the other six or
>    seven are rolled up so tightly that they cannot be seen, even with the
>    most powerful instruments available. For an everyday analogy, think of
>    a thread of cotton. This appears one-dimensional for most purposes.
>    Only under a magnifying glass are the other two dimensions
>    perceptible.
>
>    A second interpretation of multidimensionality, however, is that the
>    extra dimensions are not always rolled up, but that even when they are
>    not humans cannot readily observe them because they are not free to
>    move in them. In this version, the space inhabited by humans is a
>    three-dimensional "surface" embedded in a higher dimensional
>    landscape. The particles of which people are composed, and the
>    non-gravitational forces acting on them, are strictly confined to this
>    surface--called a brane (short for membrane)--and, as such, have no
>    direct knowledge of the higher dimensional space around them. Only
>    gravity is free to pervade all parts of the universe, which is one of
>    the reasons why it obeys a different set of rules from the other
>    forces.
>
>    It is this second interpretation that is invoked by Dr Karch and Dr
>    Randall. They assume that, initially, the universe was filled with
>    equal numbers of branes and anti-branes (the antimatter equivalent of
>    a brane). These branes and anti-branes could take any number of up to
>    ten different dimensions. Dr Karch and Dr Randall then demonstrated,
>    mathematically, that a universe filled with equal numbers of branes
>    and anti-branes will naturally come to be dominated by 3-branes and
>    7-branes because these are the least likely to run into their
>    anti-brane counterparts and thus be annihilated.
>
>    This result is interesting for two reasons. It is the first piece of
>    work to show that branes alone can explain the existence of hidden
>    dimensions. They do not have to be rolled up to be inaccessible. It is
>    also the first to suggest an underlying preference in the laws of
>    physics for certain sorts of universe, and thus perhaps provide a
>    solution to the anthropic principle. Yet it is not a total solution.
>    Other realities, whether three- or seven-dimensional, could be hidden
>    elsewhere in the landscape. And life in seven-dimensional space would
>    look very different from life on Earth--if, indeed, it existed at all.
>    That is because the force of gravity would diminish far more quickly
>    with distance than it does in this world. As a result,
>    seven-dimensional space could not have planets in stable orbits around
>    stars. Like dark matter and dark energy, therefore, the anthropic
>    principle is still grinning from the sidelines, taunting physicists to
>    explain it.
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