Hector Plasmic's Light Cone

By Hector Plasmic

Bzzzt. Elsewhere is the term cosmologists use for "outside the universe's lightcone." Nothing outside the light cone can ever interract with us, Rick. It's irrelevant. Any speculations about what's outside the lightcone (Elsewhere) are irrelevant as they cannot be tested, confirmed or disproven. That sinking in yet?

Here's a picture to help you get it:

   ^                  \      the      /
   |                   \   universe  /
   |                    \(lightcone)/
   |        Elsewhere    \         /    Elsewhere
   |                      \       /
   t                       \     /
   i                        \   /
   m                         \ /
   e                      big bang

                Elsewhere           Elsewhere

Will another picture help, Rick?

                            |     ^
               \            |     |<--------allowed for massive body
                \           |     |     ^
                 \          |    |     /<-----allowed for light
                  \         |    |    /
    lightcone----->\--------+---+--->/        ^<----not allowed
                    \       |   |   /       /
                     \      |  |   /      /
                      \     |  |  /     /
                       \    | |  /    /
                        \   | | /   /
                         \  || /  /
                          \ ||/ /
           event-------->   +-------------------------->
                           /             space
Special relativity is what states that nothing outside the lightcone can interract with anything inside the lightcone, Rick. "This means that the path of any object through space and time must be represented by a line that lies within the light cone at each event on it." General relativity's predictions (when quantum mechanics are added in; remember that GR is a "classical" theory) are even more profound; space-time can be curved to form a space-time without edge or boundary (as in a 4-D hypersphere, old bean). Guess what big bang/big crunch describes?

How about some definitions? After all, we want to help penetrate that drunken stupor of yours.

event:               A point in space-time, specified by its time and
                     place [Hec's note:  gee, Rick, looks like an
                     event requires time and space, just like I told
                     you, eh?].

space-time:          The four-dimensional space whose points are events.

lightcone:           A surface in space-time that marks out the possible
                     directions for light rays passing through a given

general relativity:  Einstein's theory based on the idea that the laws
                     of science should be the same for all observers, no
                     matter how they are moving.  It explains the force
                     of gravity in terms of the curvature of a
                     four-dimensional space-time.

  (Definitions and diagram #2 from _A Brief History of Time_, Hawking,
   Bantam, 1988, reproduced (sorta) without permission, but I'm sure
   Mr. Hawking wouldn't mind an attempt to educate the ignorant.)
RV>Obvously you can prove this.... Prove it, then I'll believe you.

So, now that you have your evidence, complete with references, you believe me, right? How nice! Now sober up and stop contemplating your navel.