I made no claim that those are the only two possibilities. But, for what it's worth, here are the options I actually see. First, "legitimate" ones where someone read what I wrote, thought it was bad, and voted it down on that ground:

• Perhaps I made a dumb mistake, or someone thought I did. (Not at all unlikely; I make mistakes, and so do other people, and downvoting something for being wrong is not uncommon behaviour on LW. Further, this is a discussion involving fiddly reasoning that it's easy to get wrong, making it more likely that I've done something dumb and more likely that someone else wrongly thinks I have.)
• Perhaps I was (or someone thought I was) pointlessly rude, or something of the kind. (I can't see any reason why anyone would think that in this instance, though.)
• Perhaps there is (or someone thinks there is) some other thing badly wrong with my comment. (I can't think what.)

Then there are the options where the downvote was not on the basis of (actual or perceived) problems with the comment itself:

• Perhaps someone downvoted it purely by mistake -- finger-slip or whatever. That's always possible, but I've seen no sign that this happens with non-negligible frequency on LW. (It happens fairly often on Hacker News, but their UI design puts the upvote and downvote arrows very close together and provides no way to correct accidental votes.)
• Perhaps someone downvoted it purely at random. Also always possible, but it seems like a very odd thing to do and I've not encountered any evidence that that's a thing that happens here. (Though perhaps I shouldn't expect to have; it might be very hard to spot.)
• Perhaps someone downvoted it for the sake of downvoting me: they dislike other things I've written, or have a personal grudge against me, or something. (I have had this happen multiple times before, often shortly after an exchange of comments with Eugine/Azathoth/Ra; in at least one case and I think more than one, a moderator has confirmed that Eugine/Azathoth/Ra has been downvoting substantial numbers of my comments in fairly rapid succession; Eugine/Azathoth/Ra has been observed behaving in a similar way towards other people, and has actually had three identities kicked of LW for such behaviour already. So the prior for this is not small. And, as it happens, I have recently been disagreeing elsewhere on LW with someone who shows signs of being the latest incarnation of Eugine/Azathoth/Ra.)
  • Of course it's possible that this is the explanation but it isn't Eugine/Azathoth/Ra. But I don't know of any good evidence that there's anyone else engaging in such behaviour, and in particular I haven't noticed any obvious signs of anyone else doing it to me.
• Perhaps someone downvoted it because they don't like the topic: they think LW shouldn't be discussing such things. (Unlikely in this case; this is a very typical LW topic, and I don't see other comments in the discussion getting mysterious downvotes.)
• Perhaps there was some other kind of reason that I haven't thought of. (Always possible but, well, I haven't thought of any plausible candidates.)

So. It looks to me like there are lots of low-probability explanations, plus "someone thinks I made a dumb mistake", plus "Eugine/Azathoth/Ra wanted to downvote something I wrote", both of which are things that have happened fairly often and good candidates for what's happened here. And if someone thinks I made a dumb mistake, it seems like explaining what would be a good idea (whether the mistake is mine or theirs). Hence my comment.

(This feels like about two orders of magnitude more analysis than this trivial situation warrants, but no matter.)

But a large, unknown number could easily be some sort of infinity.

Let's look at it another way. Say I choose some unknown number as you described. Any reason I couldn't be enlightened by "well, if you had chosen number+1, you could have saved the universe"?

I definitely am lacking in my mathematical knowledge so if there's a way to deal with un-measured numbers I'd appreciate if someone could enlighten me.