" He thought that we didn't know what the hell was going on with accretion disks but that a few powerful people in the field created the impression that we did and that there was no dissent because it was so difficult to get established in the field." ... seems to be an epidemic of this stuff in academia tbh.
This seems like a great resource for referencing the various definitions. I've tried my hand at developing an intuitive understanding: https://spacechimplives.substack.com/p/observers-and-entropy. TLDR - it's an artifact of the model we're using. In the thermodynamic definition, the energy accounted for in the terms of our model is information. The energy that's not is entropic energy. Hence why it's not "useable" energy, and the process isn't reversible.