How would they get their food?
I don’t think they would need food.
I’d envision an advanced planet as:
- an outer layer that is black in the visible spectrum and radiating in the infrared that collects solar energy and radiates waste heat,
- a middle layer consisting of the information processing that does the “thinking” for the planet and is the planetary intelligence.
- a lower layer consisting of robotics and other mobile and material/energy processing systems that maintain the upper layers.
Such planets probably send probes or photon bursts to each other to communicate across interstellar distances. Since the AI systems are essentially immortal, the lengthy wait for return probes and messages is not a problem.
Why, from grocery stores. Ask any shitlib.
Why would aliens need to grow their own food when they could visit here and bring the stuff home—humans make such great hors d’oeuvres.
;-)