5 change "diffusing" to "moving", add [algorithms] tag

# When can a freely diffusingmoving sphere escape from a 'cage' defined by a set of impassible coordinates?

To ask this question in a (hopefully) more direct way:

Please imagine that I take a freely diffusing moving ball in 3-space and create a 'cage' around it by defining a set of impassible coordinates, $S_c$ (i.e. points in 3-space that no part of the diffusing ball is allowed to overlap). These points reside within the volume, $V_{cage}$, of some larger sphere, where $V_{cage}$ >> $V_{ball}$. Provided the set of impassible coordinates, $S_c$, is there a computationally efficient and/or nice way to determine if the ball can ever escape the cage?

Earlier version of question:

In Pachinko one shoots a small metal ball into a forest of pins, then gravity then pulls it downwards so that it will either fall into a pocket (where you win a prize) or the sink at the bottom of the machine. The spacing and distribution of the pins will help to insure that one only wins certain prizes with low probability.

Now imagine that we have a more general game where:

(1) - The ball is simply diffusing in 3-space (like a molecule undergoing Brownian motion). I.e. there is no fixed downward trajectory due to gravity.

(2) - You win a prize if the ball diffuses over a particular coordinate, just like one of the pockets in regular pachinko.

(3) - We generalize he pins as a set of impassible coordinates.

(4) - We define a 'sink' as an always accessible coordinate.

(5) - We define a starting coordinate for the sphere.

Given access the 3-space coordinates for (2), (3), (4), & (5), what's the most efficient way to find whether the game is 'winnable', or if the ball will fall into the 'sink' with a probability of unity? How can we find the minimum set from (3) that prevents the ball from reaching the pocket?

4 Changed the title, and wrote a simpler problem description; edited body

# When can a freelydiffusing sphere diffusetoescapefrom a targetwhennotallowedtopassover'cage'definedby a set of impassible coordinates?

To ask this question in a (hopefully) more direct way:

Please imagine that I take a freely diffusing ball in 3-space and create a 'cage' around it by defining a set of impassible coordinates, $S_c$ (i.e. points in 3-space that no part of the diffusing ball is allowed to overlap). These points reside within the volume, $V_{cage}$, of some larger sphere, where $V_{cage}$ >> $V_{ball}$. Provided the set of impassible coordinates, $S_c$, is there a computationally efficient and/or nice way to determine if the ball can ever escape the cage?

Earlier version of question:

In Pachinko one shoots a small metal ball into a forest of pins, then gravity then pulls it downwards so that it will either fall into a pocket (where you win a prize) or the sink at the bottom of the machine. The spacing and distribution of the pins will help to insure that one only wins certain prizes with low probability.

Now imagine that we have a more general game where:

(1) - The ball is simply diffusing in 3-space (like a molecule undergoing Brownian motion). I.e. there is no fixed downward trajectory due to gravity.

(2) - You win a prize if the ball diffuses over a particular coordinate, just like one of the pockets in regular pachinko.

(3) - We generalize he pins as a set of impassible coordinates.

(4) - We define a 'sink' as an always accessible coordinate.

(5) - We define a starting coordinate for the sphere.

Given access the 3-space coordinates for (2), (3), (4), & (5), what's the most efficient way to find whether the game is 'winnable', or if the ball will fall into the 'sink' with a probability of unity? How can we find the minimum set from (3) that prevents the ball from reaching the pocket?

3 added 90 characters in body

In Pachinko one shoots a small metal ball into a forest of pins, then gravity then pulls it downwards so that it will either fall into a pocket (where you win a prize) or the sink at the bottom of the machine. The spacing and distribution of the pins will help to insure that one only wins certain prizes with low probability.

Now imagine that we have a more general game where:

(1) - The ball is simply diffusing in 3-space (like a molecule undergoing Brownian motion). I.e. there is no fixed downward trajectory due to gravity.

(2) - You win a prize if the ball diffuses over a particular coordinate, just like one of the pockets in regular pachinko.

(3) - We generalize he pins as a set of impassible coordinates.

(4) - We define a 'sink' as an always accessible coordinate.

(5) - We define a starting coordinate for the sphere.

Given access the 3-space coordinates for (2), (3), (4), & (5), what's the most efficient way to find whether the game is 'winnable', or if the ball will fall into the 'sink' with a probability of unity? How can we find the minimum set from (3) that prevents the ball from reaching the pocket?

2 Adding a note that we have a defined starting coordinate for the sphere
1