The US political system being what it is, there are plenty of possibilities for a tie vote this evening. Fortunately, Randall Munroe of XKCD fame has taken a look at what will go down if the worst happens.

It's worth pointing out that he's not concerning himself with an electoral college tie. As he explains:

There's probably about a 1 in 500 chance of one of those this year, and the consequences are thoroughly explored. I mean both candidates getting the same number of votes in a swing state. How unlikely is it? For that matter, what if there's a tie in every close battleground state?

Good question! And he really manages to get to the bottom of it in his What If post, taking into account all kinds of issues. Eventually, though, it boils down to this:

The probability that every battleground state is exactly tied is roughly equal to the probability that, when one of the Florida electors reaches into the hat to draw a name, he or she is struck by a falling cocaine bale, the hat is hurled away within the next few seconds by a tornado, and the elector is obliterated minutes later by a meteorite impact.

So, probably not too much to worry about, then! [What If?]