If I’m reading that paper correctly, it is talking about information content. That’s a distinct issue from simulating the universe which requires processing in a subset. It might be possible for someone to write down a complete mathematical description of the universe (i.e. initial conditions and then a time parameter from that point describing its subsequent evolution) but that doesn’t mean one can actually compute useful things about it.
If I’m reading that paper correctly, it is talking about information content. That’s a distinct issue from simulating the universe which requires processing in a subset. It might be possible for someone to write down a complete mathematical description of the universe (i.e. initial conditions and then a time parameter from that point describing its subsequent evolution) but that doesn’t mean one can actually compute useful things about it.