Expanding universe question

[gavwvin]

I may be grossly oversimplifying this but I have always wondered:

Lets say the edge of the universe is expanding at the speed of light, and the Earth resides at an arbitrary point, lets say half-way to the edge an is therefore moving pretty fast. Stuff on the other side of the universe could have a relative velocity of greater than c to the Earth, hence from our point of view measuring it's recessional velocity it could appear to be beyond the speed of light. Or perhaps since we're receding faster than light the light will never reach us, implying theres a lot of the universe that cannot and will never be seen.

As I say thats probably an over-reduction of the situation, not allowing for relativistic weirdness, but I have always wondered about it. Can anyone set me straight?

[wstevenbrown]

I don't know about "setting you straight," but I can put in my two cents, Relativists sometimes call the observable universe the Light Cone of the observer. It looks like a Feynman diagram in the sense that time is on one axis, and space on the other. Anything outside the cone is not observable (some say, doesn't exist). This is only what you have already stated, with pretty analytic geometry dressing. To go a bit further with the gedankenexperiment, tho, if objects on the edge of your light cone are receding at (ok, near) c, their mass has been increased to an arbitrary degree, and consequently, their gravity-- so as they recede, they pull everything else with them, continuing the "expansion". Relativists would say, though, that the approach to c is asymptotic (you can't get there from here), and that the combination of doppler redshift and gravitational redshift causes the amount of energy received from progressively larger distances to drop off proportionally (there's a lot of discussion over the proportions). Stuff doesn't go over the edge, it just browns out. There! Once again, didn't enlighten anything. Really good for those sleepless nights, tho--'round and 'round... Regards--Steve