Thoughts I had during a boring afternoon in work: If you can
manipulate gravity, does that automatically give you an inertia-less
drive? I'm kind of imagining creating a gravity well in front of your
spaceship and falling into it, but wouldn't that be like pulling
yourself along by your shoelaces?

Obviously you could still use it to stick yourself to the floor and
avoid the disadvantages of freefall, stop smashing your passengers at
high acceleration, deflect space debris, or create very small black
holes in your enemies' stomachs :)

: caitmackenzie@googlemail.com
: Thoughts I had during a boring afternoon in work: If you can
: manipulate gravity, does that automatically give you an inertia-less
: drive?

No. Because, theoretically, momentum is still a conserved quantity,
even if you can sling gravity/gravitons/whatnot around.


Wayne Throop throopw@sheol.org http://sheol.org/throopw

:: caitmackenzie@googlemail.com
:: Thoughts I had during a boring afternoon in work: If you can
:: manipulate gravity, does that automatically give you an inertia-less
:: drive?

: throopw@sheol.org (Wayne Throop)
: No. Because, theoretically, momentum is still a conserved quantity,
: even if you can sling gravity/gravitons/whatnot around.

Oops, sorry. I read that as "reaction-less" by mistake.
But still... no. Your *spacecraft* will still have inertia.
You may be able to keep the interior in freefall (or 1g transverse
to your direction of acceleration like in all the TV shows) under large
accelerations, but I don't think that's quite the same thing. And you'd
still want seatbelts, if Star Trek is any indication.

Now, if you could manipulate the Higgs field, maybe....
but even then, it'd seem likely that momentum would be conserved,
so you'd still need some sort of reaction mass.


Wayne Throop throopw@sheol.org http://sheol.org/throopw

Here, Wayne Throop <throopw@sheol.org> wrote:
>
> Now, if you could manipulate the Higgs field, maybe....
> but even then, it'd seem likely that momentum would be conserved,
> so you'd still need some sort of reaction mass.

Science-fictional artificial gravity is frequently ambiguous, if
not actually hostile, about conversation of energy and momentum. When
Spaceman Spiff sails into an open airlock and does that neat flip,
hitting the floor feet-first as he enters the ship's AG field, do the
engines register a quick power drain? Does the ship shift fractionally
upwards as Spiff falls twelve inches? So hard to tell, and I usually
figure the author hasn't thought about it.

[* As opposed to spin-gee, which is not science fictional even though
it's common in SF and has never been used in real-life space
travel[**]. Got it? Good.]

[** That's true, right? We've had plenty of spin-stabilized
spacecraft, but we've never spun a spacecraft for the purpose of
keeping a human against the floor. Never launched a big enough
spacecraft for that, I guess.]

--Z

--
"And Aholibamah bare Jeush, and Jaalam, and Korah: these were the borogoves..."
*
Bush's biggest lie is his claim that it's okay to disagree with him. As soon as
you *actually* disagree with him, he sadly explains that you're undermining
America, that you're giving comfort to the enemy. That you need to be silent.

caitmackenzie@googlemail.com wrote:

> Thoughts I had during a boring afternoon in work: If you can
> manipulate gravity, does that automatically give you an inertia-less
> drive? I'm kind of imagining creating a gravity well in front of your
> spaceship and falling into it, but wouldn't that be like pulling
> yourself along by your shoelaces?

Yep, that's why the idea can't work. If you have to bring it along with
you, then you're "holding" it, so Newton's third law applies and any
force it applies to you via gravitation will result in an equal and
opposite force on it from you, for the purposes of holding it still.

The only way to get around this is to "let go" of the gravity well, but
that potentially creates other problems. Presumably this would result
in a constant displacement (in otherwise empty space) per "drop," so you
in effect have some sort of impulse drive. Then, of course, the
question becomes how you're creating the gravity well and what
properties it has. Presumably, regardless of how you're doing it, the
gravity wells you're creating have some amount of inherent energy that
you're supplying, some of which is imparted to the ship, and some
momentum, which is resulting in Newton's third law resulting in thrust.
So it's basically a normal reaction drive; you're just using exotic
particles for the thrust.

--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
Maybe soul mates exist / After all
-- Des'ree

On Feb 6, 1:46 pm, thro...@sheol.org (Wayne Throop) wrote:
> :: caitmacken...@googlemail.com
> :: Thoughts I had during a boring afternoon in work: If you can
> :: manipulate gravity, does that automatically give you an inertia-less
> :: drive?
>
> : thro...@sheol.org (Wayne Throop)
> : No.  Because, theoretically, momentum is still a conserved quantity,
> : even if you can sling gravity/gravitons/whatnot around.
>
> Oops, sorry.  I read that as "reaction-less" by mistake.
> But still... no.  Your *spacecraft* will still have inertia.
> You may be able to keep the interior in freefall (or 1g transverse
> to your direction of acceleration like in all the TV shows) under large
> accelerations, but I don't think that's quite the same thing.  And you'd
> still want seatbelts, if Star Trek is any indication.
>
> Now, if you could manipulate the Higgs field, maybe....
> but even then, it'd seem likely that momentum would be conserved,
> so you'd still need some sort of reaction mass.

I'm reminded of HG Wells' 'First Men in the Moon' - the spaceship
there
relied (iirc) on an Unobtanium called Cavorite, which 'sheilded
gravity'.
You covered the spacecraft in it, then opened a window facing the
moon,
and the ship fell towards the moon, since it was sheilded from earth's
gravity.

pt

On Feb 6, 6:46 pm, thro...@sheol.org (Wayne Throop) wrote:
> :: caitmacken...@googlemail.com
> :: Thoughts I had during a boring afternoon in work: If you can
> :: manipulate gravity, does that automatically give you an inertia-less
> :: drive?
>
> : thro...@sheol.org (Wayne Throop)
> : No. Because, theoretically, momentum is still a conserved quantity,
> : even if you can sling gravity/gravitons/whatnot around.
>
> Oops, sorry. I read that as "reaction-less" by mistake.
> But still... no. Your *spacecraft* will still have inertia.
> You may be able to keep the interior in freefall (or 1g transverse
> to your direction of acceleration like in all the TV shows) under large
> accelerations, but I don't think that's quite the same thing. And you'd
> still want seatbelts, if Star Trek is any indication.
>
> Now, if you could manipulate the Higgs field, maybe....
> but even then, it'd seem likely that momentum would be conserved,
> so you'd still need some sort of reaction mass.
>
> Wayne Throop thro...@sheol.org http://sheol.org/throopw

Oh, whoops, I actually meant reactionless! That shows how brain-dead I
was after work!