What is probability per unit time

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Discussion Overview

The discussion revolves around the concept of probability per unit time, particularly in the context of electron collisions as described in Aschroft and Mermin. Participants explore the implications of the average time between collisions (τ) and how it relates to the probability of collisions occurring over infinitesimal time intervals.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant expresses confusion about the concept of probability per unit time, particularly how the probability of collision relates to the average time τ.
  • Another participant suggests that the probability of no collision after time t can be represented by the equation e-t/τ, drawing a parallel to the concept of half-life.
  • A later reply emphasizes the distinction between the probability of collision and the probability of no collision, seeking clarification on how this interpretation arises from the initial statement.
  • One participant encourages further research and calculation to derive the relevant equations related to the probability of no collision.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus, as there are differing interpretations of the probability concepts discussed, particularly regarding the distinction between collision and no collision probabilities.

Contextual Notes

The discussion highlights potential limitations in understanding the definitions and implications of average time τ and its relationship to collision probabilities, as well as the mathematical steps involved in deriving related equations.

mcodesmart
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I am reading Aschroft and Mermin and I came across the probability per unit time

I have trouble understanding the concept as it is. But they do try to explain.

They say that the probability that an electron will experience a collision in an ifinetismal time, dt, is just dt/τ.

From this i gather, that if the time dt is close to 0, the probabitly will be small. If the time dt is equal to τ, then the probability that an electron will collide is 1.

But in the next sentence, they say that τ is an average time that a collision will occur, meaning that the probability that it will occur at time τ cannot be 1, because if it is an average time, then, collision will occur sometimes longer that τ and sometimes shorter that time τ. All this has got me confused and I need some clarification.
 
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hi mcodesmart! :smile:
mcodesmart said:
They say that the probability that an electron will experience a collision in an ifinetismal time, dt, is just dt/τ.

From this i gather, that if the time dt is close to 0, the probabitly will be small. If the time dt is equal to τ, then the probability that an electron will collide is 1 …

this is like half-life

the probability of no collision after time t will be e-t/τ :wink:
 
I see.. it is not the probability of collision but the probability of NO collision..

Can you please explain how you get that from the statement that I provided in the OP..
 
(just got up :zzz:)
mcodesmart said:
I see.. it is not the probability of collision but the probability of NO collision..

Can you please explain how you get that from the statement that I provided in the OP..

oh come on

you do a bit of research and calculation, and see if you can get that equation! :wink:
 

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