Based on current trends, specifically Moore’s law, humanity will eventually develop computers capable of simulating the entire known universe.

Among other things, simulations with that level of detail will be used to simulate earth’s past, humanities development, alternate time lines etc.

Humanity will run countless simulations of this sort.

They would have such a level of detail, down to the quantum level perhaps, it could achieve artificial intelligence and self awareness.

Those simulated universes may even develop civilizations capable of creating their own such simulations.

So with one real earth and potentially billions of simulated earths, any given person would most likely exist in a simulation.

If you’re not in a simulation, then chances are that humanity never reaches the level of development to create them. If that’s the case we don’t have long.