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Dark matter or just unobservable?

  1. Dec 24, 2008 #1
    I’m new to these forums and indeed physics as a practice. Although physics has always interested me, it has only been later in life that I have started to invest time in it and started a degree course in my spare time. I do have a propensity for coming at things from odd directions and so please don’t get too annoyed at a maybe silly question.

    I like many, am interested in the question of dark mater and energy. However, none of the theories seem to completely explain the observed. WIMPs have been favourite for some time, but appear to have been hypothesised because the known candidate, Neutrinos, do not have the necessary mass.

    However, what I have been unable to find (and am hoping you can point me in the direction of) is a theory based on dimensional particle abstraction (my term).

    We understand from string theory the concept of multiple dimensions containing branes etc. If one thinks of a two dimension being, existing in a 2d universe, then any object travelling in the plane of a third dimension would not be directly observable by the 2d being. The object may be seen to affect the 2d universe and this effect could indeed be measured. We have all seen the demonstration of warping of space/time using a stretched rubber sheet and ball. If we consider a being existing on a 2d universe represented by the sheet, then that being will observe the effect the ball has on his universe (stretching), but will have no concept of the ball, it’s shape or how to measure it.

    We assume that after the big bang, all matter expanded into a three dimensional universe plus space/time. This is assumed because it is observable; the background radiation from the event can be directly measured. However, if the big bang spewed out matter and energy in 5+ dimensions, we may only have observed the tip of an iceberg. All particles at their most elemental may move between these dimensions, existing and ‘not existing’ in an observable manner. Might not matter itself work in the similar way? Any particle existing or moving purely in say a 5th dimension would still have mass and therefore affect and be affected by gravity, but would not necessarily interact with matter existing in a 3d universe and would be invisible. However, it would still coalesce with observable matter due to gravitational attraction.

    I’m sure this has already been debunked, but would still like to see any literature concerning it. Was there a theory and if so, does anyone know the name?

    Sorry for what might be a really naive question.

  2. jcsd
  3. Jan 3, 2009 #2


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    Welcome to PhysicsForums, Jonjo!

    If I remember correctly, Kaluza & Klein introduced a 5 dimensional theory as early as 1919. There have been lots of studies of higher dimensional solutions, and in fact these are on-going and an active area of research. However, such theories have severe constraints because we have a lot of experimental requirements (i.e. they must otherwise lead to identical predictions for the "tip" we actually see). Unfortunately, that rules out most.

    To get anywhere with such a theory, you need to come up with an experimentally testable prediction that separates it from standard 4-D. Or solve some thorny outstanding theoretical problem. There are a number of theories that postulate "rolled up" dimensions, and you often see 10-D or 11-D as candidates. But despite having a lot of potential, these theories (string, LQG, etc.) have yet to produce anything very convincing. But work proceeds. :)
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