Is my computer Turing Complete?

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The question of whether something is Turing Complete or not usually pertains to computer languages rather than computers or other things like human brains. However, it might make some sense to try to ask this same question about computers.

If we do, then what we might be asking is whether your computer can do anything that a Turing Machine can do. Can your computer answer any question that a Turing Machine can answer? Can your computer calculate any number that can be computed by some Turing Machine?

Well, if your computer can run a program that was written in a language that is Turing Complete, then I guess your computer is Turing Complete as well. Most computer languages are Turing Complete, and these include Fortran, Cobol, C, etc.

Another way to answer this question is to ask if you can run a simulation of a Turing Machine on your computer. If you can, then the answer is yes, your computer is Turing Complete.

If you had downloaded the Excel file from the Home Page of this website, and if you had built and run some Turing Machines using it, then your computer is Turing Complete.

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HEY! WAIT A MINUTE!

A computer is Turing Complete if it can simulate a Turing Machine, so my computer is Turing Complete? But, a Turing Machine uses an infinitely long tape, so how can my computer simulate an infinitely long tape?

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You know what! You're right!

There is no computer on earth that has an infinite amount of memory. Therefore, there is no computer on earth that can simulate a Turing Machine that uses more tape than the amount of memory in the computer. Therefore, I guess your computer is not a Turing Machine. So, I guess I must have lied to you earlier.

If you had downloaded the Excel file from the Home Page of this website, and if you had built a Turing Machine on it that required more tape than the number of columns in the Excel file, then, when you ran your Turing Machine, it would at some point in time stop and display an error message telling you that the Excel file is not large enough for your Turing Machine.

The number of columns that an Excel file can have is really very large, so it probably should be able to handle almost any Turing Machine that you build. If you do happen to build a Turing Machine that really requires more tape than the Excel file can handle, then you might try it again if Microsoft ever upgrades the Excel file to have more columns. Then, when you try it at that time, it might work. Or, maybe it won't, if you really require that much tape.

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So, if we can just ignore that minor detail of requiring an infinitely long tape, then I guess your computer can still be thought of as a Turing Machine. That's probably what people mean when they say that "Your computer is a Turing Machine."