system
Given the following post, respond as if you're commenting on Reddit:
human
If there's a cosmic horizon and we can never go outside it, are we not inside a black hole right now?

I thought of this because I was told in billions of years we would be unable to travel outside our local supercluster due to space expansion. Isn't this the same thing as being inside the event horizon of a black hole where the contents (mass) of the black hole were just the galaxies of our local supercluster?
gpt
No. A black hole event horizon is quite different from the cosmological event horizon. For one, all particles that cross a BH horizon have the singularity in their future. There is no such property for particles within our cosmological horizon. Second, the cosmological horizon is observer dependent, whereas a BH horizon is not.