?

Log in

No account? Create an account
SF Dumbness - The Mad Schemes of Dr. Tectonic [entries|archive|friends|userinfo]
Beemer

[ userinfo | livejournal userinfo ]
[ archive | journal archive ]

SF Dumbness [Aug. 23rd, 2007|09:28 pm]
Beemer
I am annoyed at the book I'm reading right now because it's being dumb.

It's a sci-fi mystery and I had the big secret figured out by about halfway through. Not that that's a bad thing, but the characters should have figured it out by now, too, because it's not a huge leap of the imagination, and certain connections would probably be much more obvious in person.

Also, it's science fiction set at least six thousand years in the future, except that it's mostly set in about 1990.

But it's the physics puzzle that's really bugging me. Okay, so they have flying cars, right? They way they work is they have antigravity pods that create an envelope around the vehicle that cancels 9/10 (standard setting) of the its weight, making it easy to fly around with minimal thrust and lift. "The envelope is no larger than necessary to ensure that the entire aircraft, wings, tail assembly, whatever, is enclosed. If you could see it, it would resemble a tube."

So the protagonists take off to fly somewhere and discover that the control cables to the antigravity pods on their vehicle have been disconnected and the pods set to 100%. Oh no! They start to ascend uncontrollably, and are going to suffocate and/or freeze to death in the stratosphere in fairly short order.

(I'll pause here if you want to think about it.)

Now, it seems to me that there's a pretty obvious solution to this problem. The reason they're rising is that everything inside the antigravity envelope weighs less than the surrounding air (i.e., nothing) and so buoyancy is pushing them upward. All they have to do is dangle something vaguely heavy outside the envelope and it will drag them back downward. It doesn't even have to be all that heavy. Assuming the vehicle is about the size of a car, that's what, 2 meters by 2 meters by 5 meters? Be generous and call it 30 cubic meters for the volume of the envelope. At sea level, that'd be 36 kg, or about 80 pounds. At 4 kilometers altitude (mentioned in the book) it's only a little more than half that. A pretty straightforward fix, not that hard to pull off.

But that's not what they do. Instead, they have one of the characters climb outside the vehicle, dangling within the zero-g envelope by a makeshift tether, to reconnect one of the control cables from underneath the skimmer. (The other pod is inaccessible, so they have to dangle nose-down as they drift downward and ditch in the ocean.) And yeah, it's dramatic, and kind of cleverly counterintuitive, but it just seems way too complex and risky (and time-consuming!) when there's a much simpler solution.

I would even have bought it if someone had suggested the simple solution and then discarded it as unworkable for one reason or another, but I think the author just didn't bother to think it through. Isn't that the whole point of science fiction, to think through the implications?
LinkReply

Comments:
[User Picture]From: goobermunch
2007-08-24 05:09 am (UTC)
Uhm, if they've got someone being all dangly, wouldn't they have ended up outside the envelope?

So wouldn't the damned car started to sink already?

--G
(Reply) (Thread)
[User Picture]From: dr_tectonic
2007-08-24 05:26 am (UTC)
No, they were intentionally staying close enough to be inside it. There were some dramatic moments with wind and getting blown partially out and almost losing grip on the tether, but it was mostly about staying inside the zero-g zone.
(Reply) (Parent) (Thread)
[User Picture]From: dpolicar
2007-08-24 05:32 am (UTC)
Wait, wait, wait.

If they intend to accelerate or decelerate at any significant clip under normal operating conditions, doesn't the thing have to have more than enough thrust to overcome buoyancy?

I'm willing to believe they can't land, since that would require some spiffy flying, but they should be more than capable of staying near the earth's surface.

Or does this antigrav dingus also eliminate inertia?

Or has the author forgotten the difference between weight and mass?
(Reply) (Thread)
[User Picture]From: dr_tectonic
2007-08-24 05:52 am (UTC)
If they intend to accelerate or decelerate at any significant clip under normal operating conditions, doesn't the thing have to have more than enough thrust to overcome buoyancy?

Yeah, it really ought to.

I think the author has forgotten the difference between "dramatic" and "plausible".
(Reply) (Parent) (Thread)
From: (Anonymous)
2007-08-24 06:36 am (UTC)
So the situation was weighty, but ultimately mass-less?
(Reply) (Parent) (Thread)
[User Picture]From: bryree
2007-08-24 06:37 am (UTC)
Sorry, that was me earlier.
(Reply) (Parent) (Thread)
[User Picture]From: madbodger
2007-08-24 04:58 pm (UTC)
Yeah, that's an author failure. I was reading an anecdote by an editor who found errors
in two authors' submissions. She contacted both of them. The (new, unpublished)
author was argumentative and insisted the readers would never notice (they would,
it was a major error). The other author got back to her that afternoon, apologising
for the delay, which was due to the reference book he needed being checked out of
the local library, so he rode his bike into town to check it at that library. And his
error was a minor one anyway. The second author was joe_haldeman.

(Reply) (Parent) (Thread)