I would be interested to know if the size of the neuron is important in some way. In other words, can we make really tiny neurons like tranzistors in computer chips and create a small (in size) brain with 1 quadrillion nano-scale neurons with incredible intelligence?

I think your assertion is spot on, that’s exactly the case. It would be interesting (or scary) to see what kind of insects we would have in a 50% oxygen atmosphere, although that would be really dangerous as giant fires would also arise.

This reminds me of the square cube law, which is an essentail element of the structure of life, similar to what has been described so far. Something that wouldn’t scale as described by power laws would be the size of a cell – the size of the cell itself would remain the same, a bigger animal simply having more cells instead of “bigger” cells.

The idea of using plasma sounds exciting, although I haven’t heard anything yet on this and it’s 2021. We may be quite some time away from it. Another option would be to create an accelerator in outer space and despite that sounding really futuristic and expensive, we might compensate with clever ideas such that we don’t have to use as much material as here on Earth.

We could discover supersymmetric particles and use the theory together with the experimental results and astronomical observations and check if the dark matter could actually be in the form of an LSP = Lightest Supersymmetric Particles. Personally, I take this strongly under consideration as a potential candidate for dark matter.

Collider energy is directly proportional to its size, therefore collider size is the limiting factor. For exciting developments we would need to build it in space.

I would say that thought experiments are definitely underappreciated, and teaching others as well. It’s important to expose yourself to other opinions and questions and that’s what usually happens during teaching.