Jellyfishes are much simpler than mammals. And modern medicine can effectively bring people back from the dead in some cases when the damage is not too extensive and doctors can act fast enough. But even if you could repair severe damage to any dead human being to make them alive again, the lost information in the brain caused by dying would mean they wouldn't effectively be the same person - we already have some cases like that when people survive significant brain trauma.
Isn't there a type of medusa that can "rebirth" itself and essentially live forever? Why can't we?
Jellyfishes are much simpler than mammals. And modern medicine can effectively bring people back from the dead in some cases when the damage is not too extensive and doctors can act fast enough. But even if you could repair severe damage to any dead human being to make them alive again, the lost information in the brain caused by dying would mean they wouldn't effectively be the same person - we already have some cases like that when people survive significant brain trauma.