DANGER: Mass-Independent Drive Is Perpetual Motion Machine

A thread of 2 messages, 19 April 1990 to 22 April 1990, in the order they were sent.

#1235 DANGER: Mass-Independent Drive Is Perpetual Motion Machine

Bart Massey · 19 April 1990

> ...the way an MT manuver drive works is counterintuitive (ie only volume is
> important, not mass).  In any drive that depends on mass, this won't work
> well...

Aiigh.  I don't know my Traveller well enough to comment very authoritatively,
but if the above statement is true, a Traveller perpetual motion machine
(i.e. an infinite energy source) exists.  Proof:

Take a body with finite volume V and mass m.  Let the energy required by the
maneuver drive to move the body a distance h against a gravitational field
of constant g be E(V,g,h) .  For a practical drive, there must exist a V,g,h
such that E(V,g,h) is finite.  Choose such a triple.  Note that the energy
gained in moving the body downward from a height h in the field by
conventional means (i.e. dropping the body :-) is mgh .

Thus, one can construct an engine whose energy consumption per cycle is
E(V,g,h) - mgh .  A perpetual motion machine can be constructed if there
exists an m such that E(V,g,h) - mgh < 0, i.e. m > E(V,g,h)/gh .  But for
fixed V,g,h the RHS of this inequality is constant, and we can make m
arbitrarily large -- Q.E.D.

Note that the energy yielded by such a machine increases with increasing m
for any given V.  Thus, one apparently wants an extremely dense object to
act as a piston in this machine...  Note also that such a machine could
apparently fairly easily realize a Doomsday device for the entire Traveller
universe (proof left to the reader), and thus had probably better not exist...

					Bart Massey
					..[email removed]
					..[email removed]

#1246 Re: DANGER: Mass-Independent Drive...

William Dow Rieder · 22 April 1990 · reply to #1235

Bart Massey writes:
>> ...the way an MT manuver drive works is counterintuitive (ie only volume is
>> important, not mass).  In any drive that depends on mass, this won't work
>> well...

>Aiigh.  I don't know my Traveller well enough to comment very authoritatively,
>but if the above statement is true, a Traveller perpetual motion machine
>(i.e. an infinite energy source) exists.

Yup, it sure does. However, you don't need mass-independence to get energy;
All the is required is that the drive is reactionless.  I worked through
the equations,
and it turns out that any drive that violates Newton's 3rd law
(action/reaction) will
*automatically* violate conservation of energy. Here's why:
(anyone who doesn't want the gory details, skip the rest)

	Say we have a ship that masses 1500 tons, and requires 280 MW to accelerate
at 1g.  After T seconds of accelleration in one direction, the energy
expended will be
2.8e8*T joules, and the kinetic energy of the ship will be 1/2 MV^2
= 0.5 * 1.5e6*(9.8*T)^2 = ~7.2e7 * T^2 joules. This means energy in is
linear in T,
while energy of the ship is quadratic in T; so only at one value of T
will they be equal,
and by choosing sufficiently large T ( in this case more than about 4
seconds) the ship
has more KE than energy put in.
	My perpetual motion machine design is 2 sets of reverse linear accellerators
on an airless world, about 1000 km apart.  The ship runs on batteries, and it
accellerates to ~4 km/sec then cruises through the hoops, decellerating
magnetically,
and in the process generating electrical energy, which is stored. After
the ship is
stopped, it recharges its batteries with a fraction of the energy it
just generated and
heads back towards the other set of hoops. Result: Lots of free electric power.
(HLG Inc., Patent Pending)
	Of course, the energy-producing Megacorps either squelch this or have
a monopoly on it, so you still have to pay for power :-)
	I always have had fun figuring this sort of stuff out to bug the GM with,
especially since he is a physicist :-)  He is smart tho and usually says
"OK, if you're
so bright, figure out why everyone isn't doing it..."

					W. Dow Rieder

 	When the only tool you have is a hammer, all your problems
start to look like nails...