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##

Space Travel

The velocity addition law 11.11 implies that no object
can be accelerated to speeds greater than the speed of light. At first
glance this seems to put a damper on the prospects for
space travel beyond our solar
system. The nearest star to our Sun is four light years away, and to get
to a potentially more interesting star, say one with planets, you
would have to travel hundreds of light years. A light year is the unit
of distance corresponding to the distance light travels in a year. It is a
terribly long distance, about 10^{12}kilometers. More importantly, the speed limit imposed by Special
Relativity forbids us from getting anywhere in less time
than it would take light to get there, so that trips to even nearby
stars would take many years, and perhaps even hundreds of years. If
this were true it
would make travel between the stars undesirable at best for
a species whose life span is only about one hundred years. Luckily, what Special Relativity takes away with one hand, it
gives back with the other.
A trip to the nearest star would take
approximately four years for a spaceship traveling at 99% of
the speed of light. However, this is the time as measure by observers
stationary with respect to the Earth and the star (we assume that the
relative motion between them is nowhere near light speed). According
to the time dilation effect, the time required for the same journey
would be shorter to those on the spaceship. For example, if the
spaceship is moving at 0.99*c*,
the time dilation factor is seven, so that to the
astronauts, the journey takes only 4/7 of a year,
or about seven months. If the spaceship were able to reach 0.999*c*,
the time dilation factor would be twenty, and the trip would take only
about one month. Space travel, and the colonization of space are
therefore possible despite the relativistic speed limit. The only
downside is that the taxpayers on Earth who funded the mission would
still have to wait at least eight years before the astronauts
returned, even though the astronauts themselves would have only aged
two months.

** Next:** The Twin Paradox
**Up:** Other Implications of Special
** Previous:** E = mc
*modtech@theory.uwinnipeg.ca *

1999-09-29