I have a similar point that I like to make: Imagine two wireless devices that want to communicate. You can have them transmit omnidirectionally, but now you h

I have a similar point that I like to make: Imagine two wireless devices that want to communicate. You can have them transmit omnidirectionally, but now you have two problems: (a) you transmit radio power in all directions, including useless ones, which wastes energy/battery life, and (b) you create interference in that frequency range, limiting the number of such devices you can cram into an area. If your devices can transmit their signals more directionally, at just each other rather than everywhere, you can fix both problems: your devices would require less power and produce less interference, making the world a much more gadget-friendly place. Well, radio waves being what they are, they have a tendency to spread out as they travel instead of following a straight line. When waves bend around corners, it's called "diffraction", and when waves bend in empty space, it's called "divergence". Even a laser beam doesn't remain perfectly straight forever -- it "decollimates" over a long enough distance. The best way to keep radio waves from spreading out, and thus to obtain the full benefits of directionality, is to use a wave guide. A wave guide is a device that forces the wave to flow down the center of the guide, usually in a straight line. It works because, as the wave approaches a section of the guide, it produces tiny electrical eddy currents in the sides of the guide, and these eddy currents repel the wave and force it to the center of the guide. As the wave passes by and leaves, the eddy currents are re-absorbed by the wave, ideally leaving the wave with 100% of its original energy content. (In reality, unless the guide is superconducting, the eddy currents will experience resistive losses, thus converting some tiny bit of the wave's energy to wasted heat. But this tiny resistive loss is still much, much tinier than all the wasted wave energy that would've gone flying off in useless directions if the guide hadn't been there.) If they're so great, why haven't wave guides taken the world by storm? Because their cheap, flexible cousins are already ubiquitous: we call them "wires".