(Not sure if this is the right place to ask this question.)

Let's say I get a computer to calculate 1+1. It should give 2, obviously. Will it always give 2? Is there any possible combination of circumstances that could cause a computer to, after finishing its calculations, give a number other than 2?

To illustrate what I'm thinking of, for humans the answer is "no" because if they're (e.g.) sufficiently drunk, they might get it wrong.


An algorithm may be infallible. Any physical computer can make an error e.g. if it is hit by a stray cosmic ray, a bolt of lightning or a large axe.

  • $\begingroup$ Do these events actually lead to the computer finishing its calculations (as given in the question)? Presumably if one takes an axe to a computer, it would simply not give an output. $\endgroup$ – Allure Sep 9 at 21:19
  • $\begingroup$ @Allure The large axe example was not completely serious. But anything that affects voltage levels within the computer (e.g. cosmic ray or lightning strike) could switch a 1 and a 0 and cause an incorrect result. The simple answer is that physical computers, like any other physical system, cannot be 100% reliable. $\endgroup$ – gandalf61 Sep 10 at 7:48

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