Thinking With Portals

[Hanuman]

So my DM allowed a custom 2-way bag of holding, this allows my character who currently runs a lab on a different plane to store items within a mutual space and because of his role in the party they can leave objects in the bag and pull them out later to find they have been magically upgraded with all sorts of prototype inventiony things.

Here's the question though, how does gravity effect the object coming out of a bag of holding that has a fixed reference point on 2 planes?

Does the gravity of the object on the one entrance cease as soon as it enters the bag, and then once it leaves the bag it becomes heavy on that end?

If this is so, would the bag be gravitationally biased to any weight sticking out of it as if it were attached to the bag? Or would an object have no relevance to the portals direction?

If on a stool you had a bag of holding, and let's say you put a regulation adventurer's 10' pole into one 5' deep, would the pole itself calculate both the weight outside and inside of the bag and hold reference points? Like is the bag of holding's nondimensional space fixed in axis?
So in the above scenario would it stay balanced, or would the bag flip off the stool because the weight on the inside is not factored on the outside, or would it suspend the staff as fixed in mid air without weight because the inside of the bag is carrying the load?


Anyone know the physics of this?

[Cog]

Anyone know the physics of this?
There is no single physical explanation of this.

Any process that produced such portals would probably involved massively curved space, and as Einstein's work tells us, curvature of space is equivalent to gravity. The portal itself would likely have some sort of gravity of its own, or it might be so crafted as to try to keep that gravity out of the portal's own area; if you're assuming the latter, then that same crafting could be excused to produce whatever variant you're looking for.

Essentially, it's so arbitrary a setup that the best answer is an arbitrary one as well. Choose something you like and stick with it.

[sonofzeal]

If the inside lacks gravity, then the situation would act somewhat like drawing a wood pole with density equal to water, out of a pool. It would feel light at first, and gain weight as you drew it up out of the water. It would not balance vertically, but would fall away from it more slowly. Assuming the bag is static while drawing, everything should go fairly traditionally. If the bag turns in any way while the pole is within its mouth, the pole would turn accordingly.

[Yorrin]

Thinking as a DM here I'd try to eliminate the problem altogether. The most obvious way is requiring the bag to be closed on at least one end of the portal at all times, and so gravity is based on whichever end is open. As long as you're not trying to put anything into the bag that's larger than the bag (eg that 10ft pole you just mentioned) this avoids the problem altogether.

[DeAnno]

A simple solution is that mass inside the bag is unaffected by gravity and any mass outside is affected as normal (for whichever side it's on).

But I'm sad because I thought this would be a thread about using Gates to make a Closed-Timelike-Curve computer :smallfrown:

[Hanuman]

Hm, with this data I think I'll bid to build a machine to coat the walls on the inside of the bag, then eject legs from the bag of holding. I'll base the original concept on the Sorting Beast http://www.wizards.com/default.asp?x=dnd/cw/20070226a&dcmp=ILC-RSSDND

The legs could weigh a sizable amount to topple the bag upright, then from there it could act like a spider. The main girth of the machine could be on the inside of the bag.

This way the sorting beast could double as a bag of holding, and would work similarly to a mechanical Ozodrin.

Thoughts?

[NichG]

Physically, I'd say you should treat the interior of the bag as a topologically connected space. So there'd be fairly significant tidal forces at the bag mouth, but nothing is a sharp distinction between things.

So for example, lets say you hold the bag upside-down with the mouth open. Inside the bag would normally be a zero-G environment. Now what happens is that when you open the bag this way, everything on the inside feels gravity as if the opening of the bag were a source. That means, everything on the inside suddenly falls towards the door at, say, 9.8 m/s^2. Pretty awful.

Correspondingly, if the other side of the bag were some heavy gravity environment, opening the bag mouth would create a massive suction of things towards it on the other end. Pretty abusable.

What happens to the bag itself? Well, momentum should be conserved, which means that as things fall towards the bag, the bag also should be pulled towards them. However, momentum conservation with portals is a really tricky subject, because you can have rotations and such applied to vectors going through a portal. So what happens actually depends on the misorientation of the bag.

If the bag opening is oriented perfectly on a line with the gravitational source on the other side, it should experience no force when pulling something through (because momentum is being conserved by the planet or whatever on the far side of the bag being pulled forward). If the bag is rotated slightly, then it should experience a force along the vector difference between those forces so that momentum is conserved.

What that probably means is that the bag is rigidly locked to orient its two portals most of the time, since those forces will be huge (just the forces of the two planets pulling at eachother through the bag opening...). Trying to rotate it would be like trying to rotate something containing a very rapidly spinning gyroscope - it feels like it fights you somehow.

Actually, thats pretty awful if the two mouths of the portal are on planets with different rates of rotation. It means the portal mouth appears to be constantly spinning with a rate equal to the differential of the planetary rotations. While that's not so bad (thankfully its the angular frequency and not the velocity!), it's another weird effect. I guess that one is probably exactly as noticeable as Focault's pendulum, so its pretty subtle.

The other thing (and this is already taken care of by the way gravity should work through the mouth, but I figured I'd explicitly mention it) is that if one opening is deeper in a gravitational well than the other, the bag's portal is more or less one way if you don't fly. Going through it would be like dropping down a pit in one direction, and climbing up against gravity the other way.

So explicitly, if you have a 10ft pole half in the bag and half out of the bag, the pole and the bag drop to the ground like normal objects (freefall is like zero-G, so you don't observe anything inside the bag either). Once the pair are on the ground, the pole comes to rest against the 'lower' surface of the portal and exerts about half its weight against it.

Now, that said, if you apply all this in game, it's going to introduce a lot of weird issues that turn the bag from a neat toy where a wizard can have an extraplanar lab to a weapon of mass destruction.

[RedWarrior0]

Congratulations. You have killed all the catgirls. All of them.

Now that they're out of the way, what happens when you put one end inside the other? What about turning both inside out at the same time?

[NichG]

Honestly I've just been thinking of these as ring gates with a useless flap of leather on one side, so turning them inside out shouldn't do anything physically interesting. If you treat it as a more traditional BoH you can get into serious trouble. For instance, it has bad cosmological implications if you run with 'inverting a BoH dumps the contents', since the 'contents' are the universe, including the other end of the portal!

Passing the portal through itself requires a grasp of 4D geometry I'm pretty sure. Lets see if we can do the 2D/3D analogue.

The portal mouths are a pair of finite lines on the 2D sheet that is the universe. Imagine that the lines lead up into a strip of paper that goes over the sheet, connecting them.

To pass one through another, you'd turn one of the lines edge on and pass it up into the strip. What this means is, the exit to that portal exists in the portal neck. It's a loop that doesn't go anywhere, because it has nowhere to go. You've just made an extradimensional pocket. You can keep looping it to make complicated internal spaces, but you can't actually 'tie a knot' through the universe. You'd need a second pair of gates for that I think.

[Hanuman]

Ok, for the full system overview, I'll break it down to 2 parts with colorful images to help:

http://img560.imageshack.us/img560/2789/bag1w.jpg
The current setup simplified, lab space has a ring gate, opens to ND space and the back into party space. More of the exact workings will be explained below in the modification plans:


http://img231.imageshack.us/img231/6716/bag2a.jpg

Now to explain:

Lab Space
There's actually a system already built, it has 2 timer devices (light green) that automatically feed or retrieve items from the bag, anything in the bag falls out onto the tray, anything in the feeder goes into the bag. This is set automatically at time intervals to make it more automatic as the creator has a lot of stuff he's working on constantly and it's better for projects to just be delivered and sent back without altering his schedule.

The portal from the lab is a ring gate with a mechanical iris, it's fixed but could be moved easily enough.


ND SPACE
This is where the modifications are happening.
First of all, the tinkerer being a modron (think warforged) is going to climb inside the bag and construct a hull (orange) around the entire inside of the bag, this will protect the bag from puncture on the inside in case of sharp objects.

Second, the RED pads represent compartment walls (the ceiling and floor are also all compartments, these are lockers for the items to be stored, labeled and locked. To deal with the lock a large robotic arm with a mechanical power unlocker has been fitted and must unlock a compartment before it can be accessed.

The black pad represents the sorting beast's new body, which is fixed into the hull of the ND space.

The green pad represents a miniature examination table for items as the sorting beast is a sorting, collecting, labeling and identification machine.

The sorting beast has 20 legs total, 8 powerful legs used to walk and 12 less powerful legs used to rapidly take in goods from the ground and do fine work.

Many more articulating limbs exist on the inside of the machine to rapidly access compartments, provide labeling, to hold and sort and to move items around the ND space.

Party
The bag would open and 8 spider-like legs would be visible, the rest of the legs would be hidden from view except when it needs to use them.


Thoughts? Any problems?

[FelixG]

The simplest answer is that the bag od holding is always effected by standard gravity. This ceases the problem of trying to recalculate the bag of holdings weight every time it is opened...and I am not quite sure where you would be opening it that is heavier gravity as, as far as I know, there is no actual rules for changed gravity.

[Hanuman]

The simplest answer is that the bag od holding is always effected by standard gravity. This ceases the problem of trying to recalculate the bag of holdings weight every time it is opened...and I am not quite sure where you would be opening it that is heavier gravity as, as far as I know, there is no actual rules for changed gravity.
Well here's a question...

The legs are directly connected to a hull which is aprox 500lbs in weight (give or take 300), let's say the bag is 60lbs and the legs weigh 20lbs.

Q: Would the bag negate the weight of the material inside the bag that was directly connected to the legs outside the bag?

If the gravity remained constant as soon as the legs tried to bear the weight it would be crushed, or it would be incapable of dragging the weight inside the bag.

If the gravity on the inside of the bag is negated to the physics outside the bag, you could have a 500lb weight on the inside of the bag connected to the bag and hold it up by that.

If you connect to the weight on the inside through the handle making the weight just as heavy, the legs could have clasps on the outside, only lifting or pulling the outside of the bag while allowing the hull to be carried by the ND space boundaries instead of the legs. If this is the case I could probably rig up a fold out cage around the bag to carry it.

In terms of strengthening the bag (which is now a construct worth aprox 20-30k), what method do you suggest? I think there's spells to improve item hardness but I can't quite remember.

[Coidzor]

Is the bag open on the other side when they're trying to retrieve an item from it?

If no, then see regular bags of holding.

[Hanuman]

Is the bag open on the other side when they're trying to retrieve an item from it?

If no, then see regular bags of holding.
Well, I had some questions that are generally not answered by that, and have read the description text.