This sounds absurd only because we have a hard time really understanding the consequences of dealing with a vast search space. Yes, 128^140 is the space of all possible tweets (in ascii), but just because we're able to count them (sorta) and assign a number to each message doesn't actually give us any power over them. After all, the omega number [1] is just another number too.

[1] http://plus.maths.org/content/omega-and-why-maths-has-no-toe...