28th November 2006 - 01:12 AM
Here's a paradox - if gravity propagates/travels at the speed of light, but light can't escape a black hole, then how can gravity go somehow faster than light and still "escape" in order to pull more light in?
If gravity warps a fabric of
space that light travels through
then the modes of travel are different and don't need have the same delays just as a shockwave travelling through a pipe doesn't travel at the same speed as water inside it.
If gravity was a repulsive force pushing inward from outside, then no problem would exist, as you could still have "crushing" gravitational forces present from outside a black hole.
Now consider this:
If you were close to the event horizon (as seen by a distant observer) of a black hole, the event horizon would be moving outward, past you at light speed and you'd need to travel at light speed away from it, just to maintain a constant distance from it (again, as witnessed by a distant observer).
So how can you be moving away from an object at light speed, yet have it appear to someone at a distance as if you were stationary? (Truly they couldn't see you anyway as if you were travelling at light speed, you'd be light and and not yet witnessed, but we're working with hypotheticals here)
Well, consider if two black holes were to "look" at each other - both expanding localling at light speed. Would the relative size of one black hole to the other change? Not directly, and each could see the other as occupying a similar volume of space as itself (each being its own "observer" and expanding outward, the other would). Depending on the time or distance between them, each would witness the other as progressively smaller, the further back in time, or equivalently, the further away in space they were from each other, and of course over time, they'd expand and merge .... just like a mysterious gravitational force. (Space could expand in a similar manner, and diffuse into mass, though it would seem it couldn't expand at the same rate - tidal forces would seem to require this flow or diffusion have a gradient/differential in space)
So what would the force experienced standing on the surface of the Earth be, if this expansion caused the gravitational force? It would seem a differential pressure between the expansion of space, primarily outward from the Earth ... so you're being accelerated upward by an expanding mass beneath you. In this case all forces might be unifiable as a single repulsive force and relative observations made from different scales of expansion could make these appear as attractive in comparison - so the entire universe could be expanding, along with everything inside it, and "gravity" makes space appear warped because not all objects diffuse at the same rate.
If you were inside a perfectly spherical shell of mass, you'd experience no gravitational force toward the surface - you could on one hand see this as a delicate and concidental balancing of 1/d^2 attractive forces, or you could see it as a symmetrical expansion outward by mass as it expands uniformly outward (of course keeping it from buckling inward would be tricky).
Here's a graphic of Conway's Game of Life. Each cell follows simple rules when updating. (There a Java simulator there)
If you watch the cells over time, you'll find chaotic centers of action, very analogous to mass and little "gliders" that move at a constant rate through space, very similar to light. Depending upon the update rules, the chaotic centers can grow and shift around. (It's been shown that Conway's Game of Life is yet another system capable of "universal computation", and that's just in 2 dimensions)
Here's another couple examples of simple automata systems, but in 3 dimensions:
Now imagine if the bottom, spherical example was a black hole expanding at light speed and that distant objects appear small, not directly because of any parallax effect, but because what you see of a distant star is both diffused over a large space (low intensity) and actually was smaller at the time ... you aren't seeing what's "there" now but instead what you're seeing a diffused energy "here" from a prior compressed state of "then". So does the moon look larger when you get near it because you're seeing it from a less diffused and more spacially expanded state, or is that just Euclidean geometry and vanishing points, or are they part of the same thing?
Consider that local time would likely appear to be slower in an expanded/diffused state versus a compressed state, so variations in differential rates of expansion in some areas of space could make internal times appear different as internal changes would occur slower in a diffused state.
Also, light would appear frozen in time, because having a maximum forward rate of motion, leaves no additional cycles available for lateral expansion, whereas a larger chaotic mass would tend to retain spherical traits and expand slower but equally in all directions.
Disclaimer: You can ignore most all my mumbo-jumbo and hand waving, but I still don't see how you can both have black holes, where light can't escape and gravity travelling at light speed, (Hawking Radiation does seem quite possible though) and I also don't believe relativity looks closely enough at relative scales
of distances, instead of just relative locations or motions - an "observer" needs references to compare things with, and if space does expand, then relative measurements made from an expanded scale would seem to cancel out much of the expansion and leave differential rates of expansion as being observed as likely close to a warping of space, over time. If the evolution of a system over time is closely correlated to an expanding diffusion of interactions (the nice thing about this is that mass doesn't need to be self contained or have internal binding forces, as variable rates of expansion can give the appearance of this), then having two systems varying in their rate of diffusion could affect how rates of times, velocities and distances are perceived/interpreted.