title: Cosmic Rays: what is the probability they will affect a program?
body: <p>Once again I was in a design review, and encountered the claim that the probability of a particular scenario was "less than the risk of cosmic rays" affecting the program, and it occurred to me that I didn't have the faintest idea what that probability is.</p>
  
  <blockquote>
    <p>"Since 2<sup>-128</sup> is 1 out of 340282366920938463463374607431768211456, I think we're justified in taking our chances here, even if these computations are off by a factor of a few billion...  We're way more at risk for cosmic rays to screw us up, I believe."</p>
  </blockquote>
  
  <p>Is this programmer correct?
  What is the probability of a cosmic ray hitting a computer and affecting the execution of the program?</p>