wormhole problematics

Image: Corvin Zahn, physics education group (Kraus), Theoretische Astrophysik Tübingen, Space Time Travel (http://www.spacetimetravel.org/)
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1. Would require negative energy density
   * don't know yet why this requirement, 
   * but it is done via Riemann tensor in spacetimetravel.org
   * also mentioned in Motion Mountain - adventures in Physics
     by Christoph Schiller
    * nature asserts limits on energy, mass and length-to-mass ratio: 
      * energy cannot be negative
      * mass cannot be negative
      * limits on Length to mass ratio
2. Would require an infinite horizon
   * I don't know if this refers to the Minkowsky space plane
     that is involved with spherical topology
   * or whether this refers to the gravitational horizon, 
     as in event horizon, the Schwarzchild limit.
   * a general horizon equation is derived from the principle 
     of maximum force in Schiller, p. 445 eq. (238), III ch. 6.
3. Would require enormous radial tension 
   * radial tension, if i'm not mistaken is known in english
    (wikipedia) as radial stress which refers to the pressure
    on matter such as iron rings around a barrel. 
   * weirdly, it is measured in (unit mass x unit Area) per 
     unit length - don't know why yet.
   * requirement is said to be for the material of the wormhole. BUT !
     * why would we need a material per se, is not the wormhole 
     a matter of bending space, or connecting space, or otherwise
     acting on the space topology? Why would a material be needed,
     other than for gravitational mass requirements?
     * unless the radial tension refers to that to which objects transiting
       via the wormhole are subjected. But isn't the idea of wormholing
       to remove amount of time in transit? ie, with a wormhole, 
       there should be no transit! that's the whole point.
       the displacement through the wormhole should be indistinguishable
       from "local" displacement.
4. Question on the behavior of light in or through the wormhole
   * namely the inability of light exterior to the wormhole 
     to interact with its interior , or vice versa.