Re: starship-design: Fuel costs

["Kevin \"Tex\" Houston" <hous0042@maroon.tc.umn.edu>]

Philip Bakelaar wrote:
> 
> 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
Ben,

Your aging *Never* slows down, no matter how fast you travel.  You will
always
experience one day at a time, and will never have more days than you are
allotted.
While this might not be exactly the question you were asking, it is
nonetheless
one way to interpret your question.  Your question seemed to imply that
while 
your "mind" might experience a month, your "body" might only experience
one day.

This, of course, never happens.  That is to say, your clock will never
slow down.
it is all the other clocks in the universe that speed up.  If you ask
nicely,
I'm sure Steve will be happy to pose some relativity puzzles for you. 
}8^)>

Here's one to get you started... It's quite old, and I'm sure many of
our
members will recognize it.  I trust they will keep to themselves until
those
younger members of this list have had a chance to ponder the
possiblities.

Assume for the moment, that this "clock-slowing" process is real.  (I
can assure
you that it is, but even if that isn't enough for you, just accept it
for the 
moment as a hypothetical) and that as you approach the speed of light,
your
local time slows down. (relative to the rest of the universe of course)

Now consider the plight of two twins:  Twin A (whom I'll call Kelly ;)
stays at 
home (due to a severe lack of antimatter) Twin B (named Kevin) Sails
away on
a maser-powered sail-ship.  The flight distance is 11.9 light-years, and 
Kevin accelerates the whole way until turn-around, and then deccelerates
at the
same rate into the target system.  After some amount of time (let's say
ten years), Kevin gets back into his maser-sail driven ship, and heads
back.  Accelerating at a
constant rate until turn around whereupon he deccelerates again until
coming 
to a rest in our own solar system.

How long does the flight take?  Consider that Kevin left on the twin's
40th birthday.
According to Kevin's clock, the trip takes about 20 years (5 years
there, 5 years back,
and ten years in the system),  But according to Kelly's clock, the trip
takes 
something closer to 45 years.  13 years there, 13 years back, and ten
years 
in the system.  Now this seems normal, considering that as you move
closer to the 
speed of light your time slows down.  But just who is doing the moving
here?

According to Einstein, there is no privileged point of reference, it is
just as
accurate to say that Kelly (and the rest of the universe) moved while
Kevin 
and his magical sail-ship stayed at rest.  So why is Kelly the doddering
old
fool in the nursing home, (at 85 yrs) while Kevin, (at 60) isn't even
ready to
collect social security?

Big hint: the problem is not with Einstein, nor with the ages of the men
as I've 
stated them.

Kevin
(snickering silently to himself)