Not sure if this belongs in GQ or CS – mods, move if you think appropriate. I’m watching an episode of Stargate: SG-1 where they’ve opened a wormhole to a planet that’s being sucked in by a nearby black hole. At one point Carter notices here dog tags drifting towards the Stargate and shouts, “Close the iris!” A tech says, “That’s an outgoing wormhole, Captain! Nothing can get in!” She replies, “Nothing but the gravity from the black hole! Close the iris!” Which staves off certain disaster (for the moment).
Wait a minute. What’s the thinking here? Why is gravity any different? If it’s possible to create a “one-way” wormhole, through which physical matter and energy can pass in only one direction — then why should fundamental forces, such as gravity, be able to pass through in both directions?
The one-way travel restriction is a safety precaution that was built into the stargates by the Ancients. I haven’t heard what the reason was, but offhand I can think of two good ones: to ensure that people don’t collide within the wormhole (which would probably be bad), and to prevent things like hostile aliens or toxic gases from travelling back through the wormhole and ending up on your planet.
Essentially, it’s an arbitrary limitation, not a scientific one. Radio waves can travel in either direction, as Balthisar has already mentioned. It appears that graviton particles can travel in either direction too. Probably, the Ancients never thought about this sort of problem.