Inertialessness (the Lensman & Arilou sort), top speed, and spinning

[johndallman]

Originally Posted by whswhs

(The way Smith defined it, the ship would "stop" dead in space every time it hit a molecule, but that can't be reconciled with the description in the books, so presumably there's some minimal size below which gas and dust just gets shoved aside.)

... except where that's inconvenient. The "Primary beams" armament that comes along in the course of the series handles the problem that you can't hurt an inertialess ship with an energy weapon because the pressure of the beam pushes it away. Primaries do this by being so brief that the gas and dust of space provide sufficient support. Which I remember thinking didn't make sense at age 13 or so.

[whswhs]

Originally Posted by vicky_molokh

Okay, acceleration is infinite. Also, I realise that SC is made of pure handwavium. OTOH, Doc is one of the old-school hard-ish fellas, right? How did he arrive at the numbers? From school days, I'm vaguely (mis) remembering that drag is 'roughly proportional to the square, or, later, to cube of speed'*; I'm not even sure what sort of unit a dragness of a medium would be measured in.

Really? That's basic fluid mechanics.You're looking at a version of terminal velocity calculation. Drag force is a function of the product of velocity, radius (for a sphere), and viscosity; and the MKSA unit of viscosity is the Pa s. Usually, though, you'll see the cgs poise or centipoise.

I would not be surprised if Smith could assume a viscosity for his interstellar medium as a function of its density, and go on from there.

Bill Stoddard

[whswhs]

Originally Posted by malloyd

Within the framework of real physics, it's undefined. Actually I'm pretty sure that having no momentum and energy content also means you can build a thermodynamics argument it has no information content, and "something is here" is information, so going inertialess means you cease to exist.

When Smith wrote those books the relationship between information, entropy, and energy was not generally understood, even though it's implicit in Maxwell's Demon.

Bill Stoddard

[vicky_molokh]

Originally Posted by whswhs

Really? That's basic fluid mechanics.You're looking at a version of terminal velocity calculation.

Sorry, as I said, memory's very fuzzy when it comes to those lessons. Looking over the wiki, there seems to be many factors, exceptions and paradoxes involved.

[Fred Brackin]

Originally Posted by johndallman

Well, no. "Doc" Smith was a practitioner of "Make it sound really cool"; his spiritual descendant is George Lucas.

He might have done arithmetic to pick a suitable speed for plot purposes, but since he never says how far apart anywhere is, I doubt it.

There are hard numbers for average speed under inertialess flight in Gray Lensman. Cruise is 60 parsecs per hour and max is 90 pc/hour suibject to local variation in the density of the interstellar medum. Kinnison explains this himself.

[whswhs]

Originally Posted by Fred Brackin

There are hard numbers for average speed under inertialess flight in Gray Lensman. Cruise is 60 parsecs per hour and max is 90 pc/hour suibject to local variation in the density of the interstellar medum. Kinnison explains this himself.

Which is fairly neatly calculated: It comes to just under 200 light-years per hour or a bit under 5000 light-years per day, which will get you across the galaxy in a bit under a month.

It also explains why they hesitated to travel to Lundmark's Nebula. Apparently it's around 30 million light-years away, which would take 6000 days to reach at intragalactic speeds. The intergalactic medium has to have been vastly less dense. Though if that's the case, I wonder if it would have been possible to cross the Milky Way faster by cruising up into intergalactic space, flying from end to end, and then cruising back down into the galaxy. . . .

Bill Stoddard

[johndallman]

Originally Posted by Fred Brackin

There are hard numbers for average speed under inertialess flight in Gray Lensman. Cruise is 60 parsecs per hour and max is 90 pc/hour suibject to local variation in the density of the interstellar medum. Kinnison explains this himself.

Indeed, but all that shows us is that Smith knew appropriate units and had a reasonable idea of the size of the galaxy. It doesn't demonstrate that he was doing calculations on the density of the medium.

[Bruno]

Originally Posted by whswhs

Though if that's the case, I wonder if it would have been possible to cross the Milky Way faster by cruising up into intergalactic space, flying from end to end, and then cruising back down into the galaxy. . .

Sure, seems reasonable. Although out of curiosity, at what point was the disk-like shape of our galaxy and our place in it well established?

[Whyte]

Originally Posted by Bruno

Sure, seems reasonable. Although out of curiosity, at what point was the disk-like shape of our galaxy and our place in it well established?

From Wikipedia (http://en.wikipedia.org/wiki/Galaxy#...tion_history):

"The first attempt to describe the shape of the Milky Way and the position of the Sun in it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center.[25] Using a refined approach, Kapteyn in 1920 arrived at the picture of a small (diameter about 15 kiloparsecs) ellipsoid galaxy with the Sun close to the center. A different method by Harlow Shapley based on the cataloguing of globular clusters led to a radically different picture: a flat disk with diameter approximately 70 kiloparsecs and the Sun far from the center.[24] Both analyses failed to take into account the absorption of light by interstellar dust present in the galactic plane, but after Robert Julius Trumpler quantified this effect in 1930 by studying open clusters, the present picture of our host galaxy, the Milky Way, emerged.[26]"

Spiral structure is from the neutral hydrogen 21cm measurements from 1950s onwards.

Distance of the Sun from the Galactic Center is not that easy to determine, but the widely accepted value is 8.2 +- 0.5 kpc, which is close to what you can get by adjusting Shapley's work with Trumpler's extinction.

[Fred Brackin]

Originally Posted by johndallman

Indeed, but all that shows us is that Smith knew appropriate units and had a reasonable idea of the size of the galaxy. .

Which puts him well ahead of George Lucas to whom you compared him..