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(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.

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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.

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  • $\begingroup$ 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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