system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40k] How is the Emperor of Mankind still alive? I know he's sustained through sacrifices and the Golden Throne but what are the scientific/psionic principals behind his longevity? Nanomachines? Mental Upload to a computer?

I've seen images of the God Emperor of Mankind. At the risk of being submitted to inquisition, he's basically a skeleton or perhaps a mummy. There's nothing there to keep alive anymore.


How do we know he's even doing anything and the Golden Throne isn't just sustaining the Astronomican beacon by itself at this point through the energy dumped into it by the sacrificed psykers?


So what part of him is being kept alive? How? Is it nano-regeneration? Some kind of virtual reality his mind is uploaded and stored in? Straight up magic?
gpt
Even before he was interred onto the Golden Throne, the Emperor was straight-up immortal. He had been alive for something in the neighborhood of 35,000 years before his altercation with Horus. So the potential and some of the groundwork for serious biological longevity was already present in his body before the mechanical assistance got involved.

The Golden Throne is absolutely a tool of psychic power. It's attached to a webway portal, and its only other occupant was another powerful psyker who got burnt out from exposure. So whatever is going on, in one way or another it's tied into super-strong psychic bullshit. The distinction between that and magic is academic. 

We know the Emperor is alive because his will holds closed that demon portal that the Golden Throne is built on top of. If no one's powering it, then demons invade Terra (as they did during the Horus Heresy). The Golden Throne cannot do this itself, it is a conduit for the psychic power of the one who sits within it.