system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When astrophysicists say it's possible we are "living in a simulation," what do they mean?
gpt
The idea is that given enough time an advanced civilization would have the technology to create a simulation so real that the participants would think it was real.  Since we live in a huge universe there is a good possibility that one such civilization exists.  If a simulation is possible then it seems likely that we are living in one.  There is, of course, no evidence that points to this being true.