h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

as we see only the vibgyor of the spectrum what if we cant see the ultra-violet or the infra-red? but it is still there x-rays and long and short wave lengths and the whole universe is filled with so many invisible to our eyes energy forms if some things exist in those invisible to naked eye energy field we would not be able to see that either

tangental to that idea...
A while ago I thought up an idea that if one could travel fast enough the red shift, or blue shift for that matter, would cause the traveler to become invisible to someone they're traveling towards or away from. The only problem with this is that, even if one could achieve that speed, the observer must be on the path of the traveler and if they steped to the side far enough the traveler would become visible(assuming that they were still close enough to be spotted). Also the effect would not work, regardless of speed, if the observer is looking perpendicular to the path, the traveler would apear to pop into and out of existance very quickly...