Quantum fluctuations are like the in-laws of the universe. They're always showing up uninvited, making a mess, and stealing your snacks. But seriously, a quantum fluctuation is a random and temporary change in the probability of a quantum state. Like when you're trying to decide between pizza and salad for lunch, but the universe is like "nah, you know what? Just go with the pizza. Deal with it."
Or, to get a bit more scientific, it's when the vacuum energy of the quantum field fluctuates, causing a temporary and random variation in the probability of particle creation. Yeah, because that's not a thing that happens every day.
But don't worry, these fluctuations are usually short-lived and don't have any real-world consequences... until they create a black hole that consumes your socks.
Want to learn more about the existential crisis that is quantum fluctuations?
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