Okay, you've probably heard of this thought experiment. If a tree falls alone in the woods, and no one's there to see it, will it make a sound? If you say "yes", it means you believe in objective reality - you think the world exist regardless of people and other observers and their observings. If you say "no", you think the world is an illusion - a mere dream - and deny the objectivity of the world. If you say "I don't know", you're taking the easy way, since there's indeed no way to know for sure if there's a sound if no one's there to listen. But there's a fourth stand, one that tackles the very premise of the thought experiment.
What if the tree never falls?
You go to the woods, the tree is standing, and the next time you go there, the tree has fallen down to the ground. But who's saying it fell at all? If it's possible that a tree makes a sound when falling without observers, and if it's possible that a tree makes no sound when falling without observers, couldn't it be possible that the tree is standing at one moment in time, and down the next?
What I'm referring to here is the so-called simulation theory. Simulation theory suggests that the universe we live in is a simulation, not unlike the video game universes that humans have simulated by programming them. Because if we can create simulated universes, it's perfectly plausible that we are living in one ourselves.
In video games, there's no point updating the entire universe every fraction of a second - it would take too much CPU capacity, memory, etc. - the game updates only the things the player is looking at from his point of view. And therefore, if the simulation theory is real and we are living in a simulation and you're not present at tree-falling event, the tree never falls. The processor, getting ready to generate the woods for your visit, updates the status of the tree next time you go to visit it from "standing" to "fallen down", generating the view accordingly.
I don't know about you, but for me, believing in this theory changes everything - opening up a bunch of new possibilities about life.