Probability of crossing a point?

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Discussion Overview

The discussion revolves around the probability of a spider meeting an ant within a square box, where the ant remains stationary at the center and the spider moves randomly. The scope includes conceptual definitions of probability in geometric contexts and the implications of movement models.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that if the spider and ant are treated as geometric points, the probability of them meeting is 0, but if they occupy measurable space, the probability is 1 in a finite area with no time limit.
  • Another participant questions the clarity of the problem, raising issues about the number of possible directions and distances the spider can take, and the starting point and path shape of the spider's movement.
  • A later reply agrees with the need for more definition, emphasizing that if the spider moves in a straight line, it may not meet the ant if they are not in the same plane.
  • One participant interprets the spider's random movement as akin to Brownian motion in a finite space, suggesting that without this interpretation, the question lacks coherence.

Areas of Agreement / Disagreement

Participants express disagreement regarding the definitions and assumptions of the problem. There is no consensus on how to model the movement of the spider or the implications for probability.

Contextual Notes

The discussion highlights limitations in defining the problem, including assumptions about movement, the nature of the points involved, and the conditions under which the probability is evaluated.

moonman239
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Let's say there is a spider and an ant in a square box. The ant stays in the center of the box. The spider walks a random distance, in a random direction. What are the chances that he will meet the ant?
 
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If you're talking about two geometric points representing the spider and the ant, the probability is 0. If one or both are modeled to occupy a measurable space, the probability is 1 given a finite space and no time limit.
 
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The problem doesn't sound well-defined. How many possible directions are there for the spider to walk in? How many possible distances? (If you want to keep things simple, pick a finite number.) Where does the spider start? What is the shape of the path that the spider walks in? I can't agree with SW VandeCarr because, if the spider crawls in a straight line along the inside of the box, it's going to stay in one plane, and if the ant isn't in that plane, the spider can walk forever and never meet the ant.
 
moonman239 said:
Let's say there is a spider and an ant in a square box. The ant stays in the center of the box. The spider walks a random distance, in a random direction. What are the chances that he will meet the ant?

honestrosewater said:
The problem doesn't sound well-defined. How many possible directions are there for the spider to walk in? How many possible distances? (If you want to keep things simple, pick a finite number.) Where does the spider start? What is the shape of the path that the spider walks in? I can't agree with SW VandeCarr because, if the spider crawls in a straight line along the inside of the box, it's going to stay in one plane, and if the ant isn't in that plane, the spider can walk forever and never meet the ant.

I understood that by saying the spider walks in a random direction for a random distance, the OP was attempting to describe Brownian type motion in a finite space with no time limit. Otherwise the question makes no sense.
 

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