# Re: starship-design: FTL and Special Relativity

```Steve VanDevender wrote:

> Both of these are in direct contradiction to experimental observation;
> moving objects _do_ show slower rates of time lapse and mass neither
> increases or decreases with velocity.

Found in a FAQ.
----------------------Cut-----------------------------------------------
There is sometimes confusion surrounding the subject of mass in
relativity. This is because there are two separate uses of the term.
Sometimes people
say "mass" when they mean "relativistic mass", mr but at other times
they say "mass" when they mean "invariant mass", m0. These two meanings
are
not the same. The invariant mass of a particle is independent of its
velocity v, whereas relativistic mass increases with velocity and tends
to infinity as
the velocity approaches the speed of light c. They can be defined as
follows.

mr = E/c^2
m0 = sqrt(E^2/c^4 - p^2/c^2)

Where E is energy, p is momentum and c is the speed of light in vacuum.
The velocity dependent relation between the two is.

mr = m0 /sqrt(1 - v^2/c^2)
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You must have both time increase and mass decrease proven or the theory
is wrong.
Energy to increase a object becomes infinity as the mass becomes
infinity.

Ben.
------------------
"We do not inherit our time on this planet from our parents...
We borrow it from our children."
"Where a calculator like the ENIAC is equipped with 18,000 vacuum tubes
and
weighs 30 tons, computers in the future may have only 1,000 vacuum
tubes
and weigh only 1 1/2 tons."  Popular Mechanics, March 1949
```