Alright, I'm just gonna get a little technical here, ignore this if you hate technicallity
The Minecraft world actually isn't infinite, although it may say it is. After... about 3 million blocks, maybe more, you'll reach the world border. If SOMEHOW you manage to get through (probably Ender Pearls), you'll find that all blocks are broken. Well, not literally, but you'll fall right through. So, really, the world isn't infinite.
Then again, the Minecraft world defys most of science because if it was a real planet then you'd probably be very dead if you tried to explore. Mainly because you'd be crushed by gravity if ya went past the equator.
Please note that I'm going off of information from one of Game Theories' videos (yes, the Youtube Channel) so-
Caption this Meme
