Here's another one of those posts where I want to find out what you think about things - especially since this particular question is an important one for all of Urban Planescape.
Since I can't have two poll questions, though, I'll have to add a second one here:
Do you think that technology should be affected by planar traits and proximity to the Spire, in a similar way to magic?
I say everything is annulled by the Spire's presence if you get close enough. That blankness you see when you look over the edge of Sigil? That's the Spire "balancing" all light, darkness, space, thought, entropy, and time out of existence.
In the 1e Manual of the Planes, ordinary chemical reactions - not just gunpowder, but normal fires and even digestion - stopped working within 100 miles of the Spire. "Neither man nor god can come closer to the center."
That is interesting. If biochemical reactions stop, then the spire itself would be at absolute zero from total lack of heat energy. It almost makes an argument to add techy stuff to magic-psionics transparency.
As for Magic vs Tech... I get the feeling that, once again, magical forces and electronic miniaturization would have a certain amount of interference between each other. IE, creating a Palm Pilot with any sort of magic installed on it would be hell (figuratively speaking) because the constant ionization of the electrons would scramble the magical fields and vice versa.
Ok, that's general, everyday hardware covered......But how do you then explain stuff like software? I mean, it would be better *not* to write code around a Wish spell, or a varient of it......right?.........http://www.asstr.org/~JR_Parz/MasterPCUniverse.htm.........case in point. Or probably just a cautionary tale about what is precisely the wrong kind of mass-market software to go and develop....take your pick.
If you go by the pure physics, then it would probably be cold, but if you go with the fantasy side, it would be neither warm nor cold. There was a forum post recently linking to some articles on the plane of vacuum. It had some good lines about "nothing" being a different kind of "something" rather than the lack of "something". Same thing with cold being something rather than the lack of heat.
If biochecmical reactions do not function, then there is no need to breathe. Then again, your cells couldn't convert sugar into energy. There has to be some sort of barrier or limitation on what works and what doesn't. Why doesn't gunpowder work but muscles can "burn" fuel?
Then there's the ever-absolute: "cuz" 
Well, that's an easy question to answer and most people will probably pick what I did. I definitely belief that technology should be affected by planar traits, although those traits should be different from what is described in MotP. It's just too cool if computers are twice as efficient on Mechanus and you can't ever start your car engine on the Gray Waste. 
I second Kaelyn's MotP1E reference. That book has a great little set of tables on what alternate Primes would be like, and it can easily be adapted to describe the UPS planes.
Those traits should definitely be different from the MotP. While their rules for such things are fast and simple (if only I could say that for all of their rules!), I'd almost like to see 2e style planar effects come back.
...and I now officially want a 1e MotP.
So, if the Spire affects technology, should there be tech levels that are annulled in order? Sometyhing like the progress levels of d20 Modern... though these seem too general for this purpose?
d20F PLs are a bit awkward for the purposes of something like this, especially when technology doesn't have to do all the work on its own.
Levels based on something like complexity would probably work, I think. A limit on enchantments/enhancements could easily be done this way, too, with item complexity limiting magic.
I imagine, as a base case, middle-ages/renaissance tech (possibly up to basic clockwork) would probably be zero complexity (and have a special exception to not be anulled by the Spire).
As a side note to this discussion - there are worlds and settings where magic and technology both exist. (Shadowrun) It's something to consider, that it *is* possible - and that both sciences, the arcane and the technological, may find their own 'niches'. After all - mages are *expensive* to train and hire. But you can hand any mook a gun. On the other hand, it's not just *any* mook that can read your opponent's mind. In order to balance the two though you may need to weaken magic, or strengthen technology...
The other side to that is the party hacker working at an electric doorlock for ten minutes before the mage gets sick of it and casts knock.
In a sense, though, they already balance - magic has a significant opportunity cost associated with it, and has flexibility problems. It's not just any mook that can read an opponents mind, but I'll bet that opponent has more ammunition than the mage has spell slots. Similarly, the desired effect will probably help you decide between fireball or RDX - especially since the former won't make a mess of the geography.
The two will probably tend to naturally carve out their own niches (except, I suppose, for a technomagic profession - but that's different) without needing to be particularly strengthened or weakened.
If necessary, technology can also be articifially 'weakened' by lowering the levels attached to things, giving greater scope for nifty engineering to add enhancements (perhaps like adding metamagic onto spells).
I imagine, as a base case, middle-ages/renaissance tech (possibly up to basic clockwork) would probably be zero complexity (and have a special exception to not be anulled by the Spire).
Oookayyyyyy....Then the question has to be asked, what is to stop a bunch of people with....issues (when it comes to the Spire's power-canceling properties at least) from going to the Outlands with sledgehammers or the like, and just *going to town* on the thing?
Take a sledghammer to the Spire?
Or to the tech there?
The tech there, if I read this right, would be the tech you would see in a standard DnD game. Medieval and Renaissance. I mean, keep in mind, the *Romans* had running water systems, indoor plumbing, and a hydraulic vending machine. (Don't laugh - seriously - they did. It sold holy water at one of the temples in Egypt.)
So - taking a sledgehammer to tech there would be just like taking a sledgehammer to tech in a regular PS game: Lots of kabooms and little tink-tink sounds as pieces hit the floor.
Taking a sledgehammer to the Spire - I don't think would really... *change* anything. It's sorta a big giant mountian. Even in Modern PS, the same way it is in standard PS.
The tech there, if I read this right, would be the tech you would see in a standard DnD game. Medieval and Renaissance. I mean, keep in mind, the *Romans* had running water systems, indoor plumbing, and a hydraulic vending machine. (Don't laugh - seriously - they did. It sold holy water at one of the temples in Egypt.)
So - taking a sledgehammer to tech there would be just like taking a sledgehammer to tech in a regular PS game: Lots of kabooms and little tink-tink sounds as pieces hit the floor.
Taking a sledgehammer to the Spire - I don't think would really... *change* anything. It's sorta a big giant mountian. Even in Modern PS.
Ah, yeah. Taking a couple hundred sledgehammers straight to the actual Spire itself was more or less what I meant- if almost nothing else works there, and you, for whatever insane reason, actually want to get rid of the thing- physically, permanently AFAYK....then yeah, that would be it.
Well. There's no one stopping people from trying that in a *regular* planescape game either. So it's just as much a question for regular planescape as it is for Modern PS. If you wouldn't consider it a problem in regular planescape there's no reason to consider it a problem in modern either.
As for what's stopping you: rilmani, belief as a whole helping to maintain the existance of a Spire and its purpose in the planes, lack of high tech and higher magic, and the general idea that trying to 'knock over an infinately tall mountian' is about the same as trying to 'dig your way into Sigil from the underside'.
There's the idea - not completely canonical anymore, but we're not talking canon - that mortals or gods can't even reach the Spire itself - it stops their biochemical processes - it balances them out of existence - I'm experimenting with dashes.
There's also the line from the Torment novelization that the Spire is not just infinitely high but infinitely far away, which makes a certain amount of aesthetic sense. You can get "closer" to it, but there's always an endless journey still to go.
Another idea is that, in the modern "urban" planes, someone or something already smashed the Spire. It's crumbled, an infinite heap of stone sprawled across the Land. Then the question becomes does the magic/technology-deadening effect actually come from the Spire, or was the Spire just a side-effect of it? Maybe the circles are still arranged around the "center" of the Land as usual, with or without the Spire's presence.
So - taking a sledgehammer to tech there would be just like taking a sledgehammer to tech in a regular PS game: Lots of kabooms and little tink-tink sounds as pieces hit the floor.
You read it right. Bows and stuff should work, maybe (if you're lucky) wind-up pocketwatches, brass cannon and flintlock pistols, but nothing much more advanced than that.
The thought of having a plane that stretches infinitely into the middle of itself is rather special. It'd be interesting to note what happens walking back away from the Spire, or going past it at a distance near enough to invoke that infinite distance.
I'm suddenly struck by an urge to go read up on physics and how phsyics reacts to a deep gravity well...
On the otherhand - belief may impact this. Much like in the Hinterlands no mater how for out you go yer always one day away out.
Have fun! If you'd like to make the results human-readable, then it'd probably make a good read.
Which always makes me wonder if it's one of those rules that always takes effect - so that, if you walk out for two hours, you're still a day out.
The idea that the Spire is infinitly far away is interesting to say the least. The image of there being a Hinterlands both "outside" and "inside", with a zone of relativly "normal" existence surrounding the "inner" Hinterlands.
Um, before we start on the whole "infinitely far away from everywhere" bit, what about the Athar? I mean, aren't they stuck at the base of the Spire? Kinda difficult when it's always infinitely far away from you.
The Athar could have been granted the knowledge of special portals that lead to the Spire. This brings the question of - why are the Rilmani sponsoring them so? Furthermore, how do portals work that close to the Spire when powers are powerless? Perhaps there's something to the chant that Rilmani can use magic at the Spire...
Another idea is that, in the modern "urban" planes, someone or something already smashed the Spire. It's crumbled, an infinite heap of stone sprawled across the Land. Then the question becomes does the magic/technology-deadening effect actually come from the Spire, or was the Spire just a side-effect of it? Maybe the circles are still arranged around the "center" of the Land as usual, with or without the Spire's presence.
*claps* Nice one.
It depends on what you mean by "base." The base of the Spire is simply the circle of dead magic; the Athar don't have to be physically leaning against the Spire to be within the radius of the null-divinity effect.
OK, this is a bump....
Also, Eco-Mono, I've gotten to wondering if your example would actually apply to desktop PC's specifically, thus: /forums/viewtopic.php?p=6439#6439
As I read Eco-Mono's comment, it was for the miniaturisation of devices - which is almost exactly like something I had in mind anyway.
Consider some piece of technology a PC might like to make. Let them do extra work to miniaturise it, since it makes the device more complex; if you want a wristwatch computer, for example, then the size difference has to come from somewhere (either it's less powerful, or more complex). Too much magic, or having tech that's a bit too tricky, means that your magic widget is likely to fail... somehow. How disatrously it does could be interesting...
That way, it's fairly simple to limit either the magical or technological elements of a particular device - more complicated gadgetry can't handle higher powered magic.
Instead of a hard limit, I'd suggest something more like a cost multiplier for different items, based on their PL. The more complex an item is, the more difficult (and therefore more expensive) it is to enchant.
Might even justify a discount on lower PL items.
Speaking from my own opinion that the Spire is a stormdrain for the extra Magic floating around in the multivers, I feel that this natural magnetism for powerful forces would adversely affect anything relying too heavily on precision in where the electrons are going; while it doesn't suck UP electricity, it does pull it aside a bit from where it's supposed to be going. So, miniaturization at the microchip level would stop working as one gets closer, and the closest circle of influence would probably mess with things slightly less complex than that. However, something like gunpowder would still work at the base of the Spire.
As for Magic vs Tech... I get the feeling that, once again, magical forces and electronic miniaturization would have a certain amount of interference between each other. IE, creating a Palm Pilot with any sort of magic installed on it would be hell (figuratively speaking) because the constant ionization of the electrons would scramble the magical fields and vice versa.