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Can we say the ability of computers to make decisions is based on a quantum property? I refer to the PN junction in semiconductors, is the phenomena related to PN junction a quantum property?

Why I asked that, I wanted to know if the finest element able to make a decision is necessarily at quantum level. In example can we make a choice mechanically?

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    $\begingroup$ We had mechanical calculators before electronic computers. And Charles Babbage designed his mechanical Analytical Engine in the early 1800s, long before quantum theory. $\endgroup$
    – PM 2Ring
    Commented Aug 27, 2023 at 7:58
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    $\begingroup$ However, rigid solids can't be explained using pure classical physics. You need quantum mechanics to explain stable, rigid, solid-state materials. $\endgroup$
    – PM 2Ring
    Commented Aug 27, 2023 at 8:00
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    $\begingroup$ You may also find this of interest: en.wikipedia.org/wiki/Billiard-ball_computer & en.wikipedia.org/wiki/Galton_board $\endgroup$
    – PM 2Ring
    Commented Aug 27, 2023 at 8:16
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    $\begingroup$ It is unclear what you mean by "the ability of computers to make decisions". $\endgroup$
    – ACuriousMind ♦
    Commented Aug 27, 2023 at 8:34
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    $\begingroup$ Voting to reopen. It is perfectly clear what "the ability of computers to make decisions" means. Digital computers make decisions by applying Boolean logic, as implemented in their logic circuits and controlled by their programs. $\endgroup$
    – gandalf61
    Commented Aug 27, 2023 at 10:33

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It is but it's not probabilistic if that's what you mean. We understand semiconductors because of quantum theory but this doesn't mean that whatever happens in the junctions is equivalent to a measurement of a quantum property (that needs amplitude calculation and therefore probability).

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  • $\begingroup$ yeah yeah, I wanted to know if we could build a mechanical computer. I cannot figure out how to make a decision without resorting to a quantum property. So in other words do we have to resort to quantum mechanics to make choice possible? $\endgroup$
    – CoffeDeveloper
    Commented Aug 27, 2023 at 7:43
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    $\begingroup$ I agree with this answer. OTOH, transistor density on computer chips cannot get much higher without running into problems due to quantum uncertainty, see physics.stackexchange.com/q/77886/123208 $\endgroup$
    – PM 2Ring
    Commented Aug 27, 2023 at 7:53
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Can we say the ability of computers to make decisions is based on a quantum property ?

No. A digital computer is an implementation of logic circuits which embody Boolean logic, a mathematical model which is completely deterministic - the output of each operation is entirely determined by its inputs. Even the pseudo-random numbers provided in many programming languages are actually calculated by a deterministic algorithm.

The only exception to this is if you have a computer that uses a hardware random number generator which generates "true" random numbers from some environmental process. Only in this case can you say that the output of the computer is intentionally based on a quantum property. In all other cases, if the output of the computer is not deterministic then it is because the computer is malfunctioning. Indeed, a lot of the difficulty of designing chips with a very high density of components lies in avoiding any quantum effects that would make the output of the chip non-deterministic.

The occurrence of PN junctions in semiconductor transistors etc. is not an essential part of digital computer design. As has been pointed out in the comments, both mechanical and electronic digital computers were being designed and built long before semiconductor devices were available.

(Note that for the purposes of this answer I am excluding quantum computers, since the quantum gates on which they are built are more akin to analogue devices than digital devices.)

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  • $\begingroup$ Can you give an example of how a mechanical computer can “make a decision” in the way the op asks? $\endgroup$
    – Jagerber48
    Commented Aug 27, 2023 at 13:16
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    $\begingroup$ Any conditional instruction (e.g. "jump if zero") is an example of "making a decision". Mechanical computers can certainly handle conditional instructions. $\endgroup$
    – gandalf61
    Commented Aug 27, 2023 at 15:10

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