Can I use "lest" in the following sentence?

I am not a native English speaker/writer, but I am working on a technical thesis written in English. To me, for some unknown reason, it feels natural to write the following:

However, the simplicity of the theory implies that it is not possible in reality, lest someone would surely have already done it.

Googling for the definition of lest seems to imply that this is not a correct usage.

So, can I use lest like I do, and if not, do any of you also feel there is any merit to my spontaneous feeling that it actually is ok to use it here? The first answer of this post (Is this usage of "lest" possible?) seems to support my case, but i am not sure.

Solution 1:

Two things.

1. Lest is always followed by the subjunctive mood. ODO's example is

   he spent whole days in his room, wearing headphones lest he disturb anyone

   Your example doesn't do this, nor can it.

2. Lest is a conjunction and means "to avoid the risk of" (ODO), and generally that phrase can be slotted in, adjusting the verb from the subjunctive mood:

   he spent whole days in his room, wearing headphones to avoid the risk of disturbing anyone

   Your example doesn't seem to be able to have this phrase inserted.

I think that what your sentence is intended to mean is

However, the simplicity of the theory implies that it is not possible in reality, or else someone would surely have already done it.

Another way of putting that would be to use otherwise. You are stating how that theory is proved (that is, it's supportive corroboration); you're not stating how a risk might be avoided (a negative result).

The confusion might be because ODO's example could also use otherwise:

he spent whole days in his room wearing headphones, otherwise he might have disturbed someone

However, this doesn't mean that otherwise and lest are generally interchangeable. To determine which to use, substitute either to avoid the risk of or or else.

Solution 2:

I don't think it's correct. Lest tends to mean "for fear that," as in Centaurus's example:

He doesn't dare leave the hotel [for fear that] he should be recognized.

That doesn't really work in your sentence:

However, the simplicity of the theory implies that it is not possible in reality, [for fear that] someone would surely have already done it.

The use of "unless" seems out of place as well.

However, the simplicity of the theory implies that, in reality, it is not possible unless someone has already done it.

The last part of the sentence, "... it is not possible unless someone has already done it," implies that it is only possible if someone has already done it, which very well may be true. But I don't think that's the intended meaning of the sentence.

I think the word you're searching for is otherwise:

However, the simplicity of the theory implies that it is not possible in reality; otherwise [if it were possible], someone would surely have already done it.