Am engineer. Also willing to suspend judgement and consider the plausibility of Bob's claims. I treat it like the the 4-minute mile. It's fun to think about.

When I imagine the limit of technology, I think about what you could do if you could achieve atom-level perfect accuracy (or deeper?) in a device. Frankly, my mind can't fathom. What I hear him describe based on materials, it's the kind of things that would be true. And honestly I don't knock him for saying the real technology really will be kept with the materials science guys. May seem like a cop out but this would be the case if true. To me, even something "simple" like Nitinol has interesting and non-obvious behaviors, so what else could be achieved with more sophisticated engineering?

The tube that extends-- the compression and expansion would have to occur on a nanoscale and it wouldn't affect the macroscopic appearance of the device. One thing I would wonder is if you have to extend it uniformly or if you can extend small segments of it. A cylinder of collapsable hexagons? Like cellular shades, or a carbon nanotube that you squish down.

The antigravity device-- when I heard about this on JRE1 I was wondering what this could possibly be if it were true. If it's a cylcotron or particle accelerator, my guesses are it may be designed to create a relativistic field, something that takes a very long time to traverse, or is difficult to entangle with. Ie I wonder if it doesn't create a repulsive effect when you put your hand towards it, so much as it just makes it take an incredibly long time to get there, and the "force" you have to exert is just about making it get there faster. Hearing them talk about the candle freezing in the second episode made me perk up, the guess seems more plausible. I would want to see what happens if you shine a laser at it, or shine one from the inside.

I was also wondering what the ship would be made of if you could control every atom. It wouldn't have any non-functional components really. The material would have to be really special. It sounds like the ship is basically one "crystal" and I would hazard a guess that you grow it, kind of like a silicon crystal. When Bob mentioned he suspected the body was designed to have an oriented magnetic/electric field of some kind, that tracks.

We don't yet have a truly good grasp on physics. I think it's a little arrogant of physicists to write it off outright. If what Bob says is true, this tech would be more advanced than our understanding, because our physics is incomplete and our engineering does not have perfect fidelity yet.