Time travel into the past is—I’m sorry—impossible. Time travel into the future, well; I’ll tell you tomorrow. Kidding! Okay, consider this: there are a thousand pyramids in Egypt, but zero intact mummies. Yes looters la la la but also focused gravity wave rectifiers. Sandstone is hardly an ideal material, though easier to stack than neutronium, it takes a heckload of rock to brute force spacetime into submission. Take away the limestone tuning layer, however, and they lose focus. The payload could end up anywhere. Or anywhen—as long as the transmitter is bigger than the threshold size, range is essentially unlimited. Building a bigger one just allows a bigger cargo chamber. The receiver, on the other hand, doesn’t have to be very big at all; you just gotta make sure it’s big enough to fit the contents, and didn’t we make a mess learning that one. Anyway, it’s next door, come see.