Ok please comment on this one. Let's suppose for our thought experiment you the reader were suddenly promoted to god-like status. You decided to take the our universe and remove all matter, but bearing in mind that all known laws of physics will still apply as they do now. You then create two earth-like planets; that is to say they are exactly the same size in volume and density. With your newly obtained god-like hands, you place these two planets 10 light seconds apart, or even 1000 light-years apart, it doesn't matter. Let's just say 10 light seconds since we are impatient here. You are able to then release your hold on these planets in such a delicate manner that you cause no angular movement in any direction. They are in all sense of the word "motionless". Question: What would happen? Would the two planets remain "motionless" for 10 seconds as the gravity waves from each planet propagate outward and eventually reach each other (as in General Relativity)? OK so after you've answered that question consider this: Same conditions. You are still god-like and remove all matter from the universe and create two planets again. This time, however, you place them so that the surfaces are touching. I realize there would be distortions to the shapes of the planets, but we can discard that for now. You then, with your god-like arms and hands, begin moving them away from each other at a significant speed, perhaps at 10,000 miles an hour or so. As you move these planets apart you occasionally check the gravitational attraction, and, according to Newton, you see the attraction is inversly proportional to the square of the distance, but it is there. You eventually move the two planets a distance that is let's say 1 light year away, or even 1000 light years away. You then stop the seperation and they become for all practical purposes, "motionless". You again take a gravity attraction reading. Then what? Would they instantly start moving towards each other? They are already "aware" that the other exists and the attration is inversly proportional to the square of the distance. But, they have been moving further and further away and the delay of the speed at which gravity can transmit it's information is becoming greater and greater. At some point (and I dare say even right away), the two planets and the gravity information is becoming more and more "outdate". One planet recieves gravity information from the other at a delay, and so it "thinks" it is actually closer. This would explain (perhaps) how galaxies can hold together. The gravity information the outer stars are receiving is "old" and the starts "think" they are closer to the center of the galaxy, and feel a gravity force that is closer to the center than it actually is (assuming the galaxy expanded (as is the whole universe) from some much closer collection in the center). So let's take that a step further, the whole universe is expanding and so "old" gravity information from all matter that was once much closer is still being transmitted (just like we see "old" light from distant galaxies (or even background radiation). Thus holding it together at a much greater rate than can be calculated from the known matter of the universe (thus the need for "dark matter"). This might also explain the pioneer probe being closer to the sun than expected. It is recieving gravity information at a delay, even though it is further away, it still feels the sun's gravity from a time in the past, when it was closer to the sun. Thoughts?