It's been a long while since I've written anything, but I'll touch more on what I've been up to in another piece. Today I want to make a correction and add some clarification on my recent column, The Would-be Travelers, in UFO Magazine Vol. 24, No. 5 #158. Special thanks go out to Kirk Shorting. for bringing this to my attention and offering his input.
In my column, I said the following:
Presumably, any extra terrestrials out there come from very far off places. Let's say there is a planet 40 light years away that is inhabited by an advanced civilization capable of traveling near the speed of light. It would take them over 40 years to get from their planet to Earth. Assuming that their lifespans are similar to our own, they would spend half of their existence aboard a ship. The vast distances and limitation on speed would seem to make such long distance travel impractical for the purpose of simply visiting, and is one of the main reasons the idea of alien visitation isn't taken too seriously. After all, Earth is just one in trillions of planets that help make up our galaxy, and one that orbits a rather ordinary star, to boot.This is not entirely correct, as I had not touched on the travel time relative to the traveler, as a result of time dilation -- and I hadn't noted a particular speed other than "near the speed of light" which can be interpreted differently, have numerous outcomes, and was therefore vague. I did this to kind of keep things simple for those less familiar with this type of subject, but at the same I don't want to give misleading information. So, let's start again with a more solid number, though, I will still simplify the results to ease this along.
A planet 40 light-years from Earth would take a little over 40 years to reach while traveling very close to that of light (ignoring acceleration and deceleration times), but only from the perspective of those of us on Earth. For the travelers themselves, the trip would be shorter because of the effects of dilation. How much shorter depends on how close to the speed of light they were traveling. At 50% the speed of light, the effects of time dilation are significantly less than at 90%, where, 1 year of travel as recognized by the ship's clock, would be equivalent to roughly 2 years back on Earth (though it's probably closer to 2.25 years). So, with that in mind, astronauts traveling to a destination 40 light-years away at 90% the speed of light might experience half that time (and some change when you account for acceleration and deceleration). Once you start getting to 90% the speed of light and above, the increase of dilation becomes extremely dramatic.
This happens because the closer one travels to the speed of light, the more time appears to slow down for the traveler. The clock on board the traveling vessel will show less time having passed in contrast to the clocks located at the ships point of origin. The faster a ship travels, the greater the dilation. If 90+ % the speed of light were achievable, the passing of time as perceived by passengers would be a fraction of that compared to how much time has passed at home.
So, while this type of travel might seem practical from the point of view of the traveler, it's important to remember that time still moves the same as always for the observers back on Earth. Which means that while the crew of our ship might have only aged 20something years at 90% the speed of light during their journey, people back home will have still aged 40something years. If that ship were to immediately return home at the same speed, you can double those numbers.
I've been rounding off and using approximations in the above examples, for ease of understanding (and because I'm nowhere near a physicist), but you begin to see some of the reasons why travel at near-light speeds becomes impractical, unless that trip is intended to be one-way only, and you don't mind the possibility of your destination not existing any more.
More about what I've been up to, later!