[TML] "Dies the Fire"

[shadow at shadowgard.com]

On 11 Dec 2007 at 0:20, Richard Aiken wrote:

> On Dec 10, 2007 11:16 PM,  <shadow at shadowgard.com> wrote:

> What about Jerry's points about renewing/circulating the atmosphere?
> Having it spill into the sun without a barrier wall around the core
> (call this the Spindle?).  Hmmm.  Is the solar gravity weaker than
> "all those millions of kilometers of rock" due to the inverse square
> law?  Or will the hole have to get bigger to let it work without a
> barrier wall (and thus that loooooong shadow zone).

I'm told it'll take care of itself. I don't recall the explanation 
(if any was offered)

> And what about Jerry's point about the Sun moving toward the disk?
> Ah!  Wait one.  The disk is pulling on it equally from all sides, so
> the forces cancel out.  Right?

They cancel out, but they also don't act to keep it centered, so 
there's need for something to keep it from wandering off center. 

> > > > Given that there *isn't* any such thing as orbital velocity (not
> > > > until you are dozens of AU out, anyway) and that escape velocity is
> > > > in the thousands of km/sec range, you could have some really high TL
> > > > societies that never got to a fraction of the disk before dying out.
> 
> Jerry was saying all those millions of kilometers of rock are also
> millions of kilometers away.  Inverse square law again?  So how bad is
> the rim/core gravity anyway?

You add up the invers square contributions from all those atoms and 
you get a significant force.

For a flat plane, the gravity depends on the density and the 
thickness. The density of the material is the same either way whether 
you are on the surface or the edge.

So if (say) 8000 miles thickness gives 1 g, then at the center of the 
outer edge (whether we can treat it as a plane) where the thickness 
is over 400,000 miles... 

Try something over 50,000 g.
 
> Hmmm.  Thinking about it, now.  Would the core surface gravity be
> higher that the rim surface gravity?  At the core, the disk material
> is curving in and around you, rather than back and away.  Or would the
> effects cancel out?  Would there be a horizontal component?


Not sure. I'm not good at even simplre calculus.

> > The sun doesn't have to worry about friction, nor about density waves
> > going thru it.
> 
> Friction?  I don't know.  Isn't there a gas corona around it that
> stretches out rather far?  Normally this would have no effect.  But
> Suns don't normally bob up and down, either.  Wouldn't moving like it
> does mean it would be trailing loose gas along behind, so it would be
> constantly moving through a tenuous atmosphere of it's own making?
> Not that this would probably have much effect on a human time scale.
> But I'd say it's peak apparent height would get steadily lower on a
> geological time scale.

It's small enough that we can hide it in the same handwaves that keep 
the sun from wandering off center.

> I'm not sure what density waves are.  But I know the Sun has solar
> storms and hot spots and such.  So it's not a solid body.  So the
> constant up-and-down should have internal pressure effects over time.

What I mean is that if the rate of flow of air thru the hole changes, 
that'll take a while to propogate, and does so as a zone of higher or 
lower density moving thru the column.

> BTW, since the Sun is only 1/640th of the mass of the disk, I assume
> that's why we're saying the Sun is bobbing up and down, rather than
> the disk doing it.

Yeah, and my figures for that may be off by a lot since I've seen a 
figure almost a hundred times smaller mentioned in a site I checked 
for more info. (ie something like 1:50,000 rather than 1:640)

> > You don't get an airflow due to the different altitudes. That's
> > because the presure varies with altitude the same way on both ends of
> > the tunnel.
> 
> Okay.  But the outside air between the two ends of this real-world
> tunnel is free to travel outside the tunnel.  The air can't freely
> travel between the ends of a tunnel through the disk.  Doesn't that
> make a difference?

Nope. The pressure at the bottom of two columns of air of the same 
composition in the same gravirty field depends only on their height. 

So if there's no flow between the two sides of a hole that extends 
the same distance from the zg plane in each direction, there won't be 
any between the ends of any other hole even if the depth is different 
the two sides.

That's because air can flow between those two holes on the *same* 
side of the disk.

The pressure in the hole varies with altitude the same way it does in 
the outside world. So the height of the exit point doesn't matter.
 
> > What would get a flow going would be if the pressure at a given
> > altitude above the zero-gee plane on side A was different from that
> > at the same altitude above side B.
> 
> Never mind the above then.  I guess.
 
> > There are other processes that'll tend to make water accumulate
> > unless it's really hot down there.
> 
> So - given a geological time scale - there won't be any "air holes" by
> the time sentience can naturally evolve.  At best, you'd get amazingly
> circular, below-sea-level lakes.  Unless there were some active agency
> to pump the holes clear.  Or it's hot enough to keep the water
> vaporized.

depends on a lot of things. But it's more likely than not.
 
> A microgravity ecology in the center of the hole?  One using heat
> released from the rocks as a power source instead of light?  Like the
> weird life at ocean geothermal vents?

The pressure at that depth is going to be such that I'm not sure 
organic life can exist above the bacteria level (and I only say that 
because we've found bacteria in rock formations miles below the 
surface).

> > > Hey!  I just thought of a design reason for having big holes.
> > > Incoming debris - comets, asteroids, etc - can't be destroyed without
> > > the pieces continuing on to impact the disk anyway.  So if there isn't
> > > enough time for robotic tugs to steer such debris away from the disk
> > > entirely, big holes exist to allow a chance at passing safely
> > > *through* it.
> 
> Since you made no comment on this bit, I assume the holes are a good idea?

The shock wave from anything sizable going thru would be as bad as 
the object hitting.

The system has to be *really* empty because anything coming close to 
impacting will get up to insane velocities. 

Then again, given the sheer amount of material it takes to *build* an 
Alderson Disk, the builders probably cleared out several *sectors* of 
all matter bigger than gas and dust particles.


--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com