Re: starship-design: Fuel costs

[Steve VanDevender <stevev@darkwing.uoregon.edu>]

Philip Bakelaar writes:
 > At 04:35 PM 8/26/96 -0500, Kelly Starks x7066 MS 10-39 wrote:
 > >To get to 1/3rd C thou an Explorer Class only needs 25,000,000 tons or
 > >about 16.5 trillion dollars worth.  A meer dozen federal budget years!
 > >~~~~8(
 > >
 > >Then again, we should be able to get a substantial bulk discount.
 > >
 > >Kelly
 > 
 > My question is: at what % of the speed of light does aging slow down?
 >  (I believe this slowing of aging is still theoretical, so if it is,
 >   answer my question theoretically! :D)
 > 
 > Ben

It's not theoretical, and it doesn't magically appear above some certain
speed; the effect is present, but difficult to measure, at low speeds.

If an object is moving relative to you with a speed v (as a fraction of
c, the speed of light), then a clock attached to it runs at the rate
sqrt(1 - v^2) relative to your clock.  This effect is quite small for
speeds in our normal experience -- moving at 60 mph, your clock runs 1
part in 2.5e14 slower than a clock at rest on the road.  At about 1/7 c,
your clock will run about 1% slower than a clock on Earth.

This effect has been observed experimentally many times, such as in
slower decay half-lives for rapidly moving subatomic particles and in
atomic clocks flown around in airplanes (at around 300 mph, the clocks
slow by one part in 1e13 due to the aircraft's velocity).