by Dale Bryant
I just calculated something out and the result is rather bleak.... The nearest star to Earth is Proxima Centauri (one of three stars in the Alpha Centauri system). Proxima is 4.3 light-years away. There are 5.8 trillion miles in one light-year (or 5.8 thousand billion, if you prefer), so we're dealing with about 25 trillion miles. That's bad enough. Let's say we decide to send an astronaut to Proxima Centauri in the fastest rocket at the fastest manned-flight speed we've been able to attain (that would be the Saturn V booster for the Apollo missions - a top speed of 26,000MPH).
Now even if we could send that astronaut at the speed of light (roughly 186,282 miles per second), it would take him or her 4.3 years to complete the trip as measured by an observer on Earth (because of time-dilation, only a few days will have passed as judged by the astronaut - but that's another story).
Here's the sad part; at 26,000MPH, which is 0.000037% the speed of light, the trip would take 116,000 years - one-way! The duration would be about the same for the astronaut. The effects of time-dilation at such low speeds are negligible so we can dismiss them here. The nearest star with a known planetary system is in the 15 light-year range. So, if we have cosmic relatives somewhere out there, the chances of meeting up with them are about nil. These distances and times involved are the main reason most astronomers don't believe we're being visited by extraterrestrials. They do believe they exist but not that we're being visited by them on a regular basis. The situation isn't much better with radio communications. Even though radio waves travel at the speed of light, a one-way transmission to those hypothetical beings will take 15 years - telepathy would prove much more economical! Another plausible answer would be travel through worm-holes to beat the clock, but that is, at this point, pure speculation.