Consider it this way: Imagine there were three pool balls, suspended above Earth’s north pole, not in orbit, but stacked vertically directly above the pole and touching. Now, since they’re not orbiting, they’ll immediately begin to fall, right? So which ball falls fastest? Which falls slowest? The answer is completely intuitive-- the ball nearest the earth falls fastest, because it’s more affected by the gravity. The ball furthest from the Earth falls slowest, because the gravity affects it least. The same thing is happening with tides: the lowest ball represents the water nearest the moon, the ball in the center is the Earth, and the highest ball represents the water on the opposite side of the moon. Is that clearer?
Part of my head just exploded. Can you help me out here, please?
Consider two slow-moving electrons interacting weakly by exchanging a Z-boson. Suppose for the sake of discussion the electrons are very far away from each other. Well, by conservation of energy there is much less than 1 GeV of energy available, and yet in order to interact weakly, they have to exchange a 90 GeV Z boson! How could they possibly interact weakly and not violate energy conservation? The answer is given by the energy-time uncertainty principle. There are a number of ways of looking at this, but basically (without getting into interpretive issues that would derail this thread) the energy can be violated as long as it is given back after a very short time. This is the same principle that allows quantum tunneling (where faster-then-light travel is likewise a feature). What this means is that if the weak interaction is to take place, the W-boson can’t just mosey along slowly between the two electrons – it has to “tunnel” between the two electrons in a time short enough to not violate the above uncertainty principle. The minimum time for this tunneling is independent of the separation between the electrons! This means that for electrons sufficiently separated, the W-boson has to travel faster than light if it is to tunnel between them.
Now, can we exploit this fact to communicate faster than light? No. Suppose you had one electron on one side of the universe and another on the other side, and you decide to wiggle your electron to try to send 1’s and 0’s to the other side of the universe. Well, the quantum tunneling will be random, and the person on the other side of the universe will see a random string of 1’s and 0’s, and won’t be able to tell which are from quantum randomness and which are from the intended signal. The other issue as that when you wiggle the electron, the changes you make to the wave function get propagated to the other side of the universe at the speed of light. So even though the tunneling is faster-than-light, any intended signal has to wait for the changes in the wave function to make it to the other side of the universe. In other words, the random faster-then-light tunneling to the other end of the universe will be dependent on the state of the electron years ago, rather than what you are trying to signal at the current moment. So no information can be sent faster than light. An analogy might be if you had a gun that fired bullets faster than light, but when you pull the trigger you have to wait a while before the gun actually fires.